Figs. 2942 and 2943 represent a similar former for the step irons of
freight cars. In Fig. 2942 the piece is thrown in place ready to be
bent, its ends being fair with the lines J K on the bending levers E F.
In Fig. 2943 the levers are shown closed and the work C therefore bent
to shape. The bed plates A are mounted on a suitable frame to raise them
to a convenient height for the blacksmith.
FORGING A STABLE-FORK.--In the manufactories where stable and hay forks
are made, the whole process of forging is done under the trip hammer,
and is conducted as follows:--
[Illustration: Fig. 2944.]
[Illustration: Fig. 2945.]
[Illustration: Fig. 2946.]
[Illustration: Fig. 2947.]
[Illustration: Fig. 2948.]
To forge a four-tined fork, such as in Fig. 2944, a blank piece of steel
is employed, its dimensions being 5-3/4 inches long, 7-3/4 inches wide,
and 1/2 inch thick. The first operation is to swage down one end, as at
A in Fig. 2945. A split is then cut down as at B in Fig. 2946. The split
is then opened out as in Fig. 2947, and is fullered and drawn out at C.
Two more splits are then made at D D, and the ends are bent open as in
Fig. 2948, when the four tines E E and F F are drawn out and shaped out.
The stem, A, Fig. 2945, is then finished for the handle.
[Illustration: Fig. 2949.]
The following example of forging under the hammer is derived from _The
Engineer_, of London, England. Fig. 2950 shows the piece to be forged.
A block of iron, Fig. 2951, is drawn out as in the figure, the
dimensions of A and B being considerably above the finished ones. A
forked tool T, Fig. 2952, may be used to nick the two grooves shown in
Fig. 2953, which marks the locations for the hub and forms a starting
guide for the two fullering tools shown in Fig. 2954, one of which is
held by the blacksmith and the other by the helper. After this fullering
the forging will appear as in Fig. 2955. The ends E, F may then be drawn
out, having the shape as in Fig. 2956. To shape the curve between the
side of the hub and the body of the stem, grooves are formed as in Figs.
2957 and 2958, Y and B being top and bottom half-round fullers, and
these two grooves are subsequently made into one by means of larger
half-round fullers, as in Fig. 2959. The object of making two small
fullered grooves and then making them into one is to prevent the
fullering from spreading the body of the stem by lessening the strain
due to using a large fuller at once. The piece now appears as in Fig.
2960.
[Illustration: Fig. 2950.]
[Illustration: Fig. 2951.]
[Illustration: Fig. 2952.]
[Illustration: Fig. 2953.]
[Illustration: Fig. 2954.]
[Illustration: Fig. 2955.]
[Illustration: Fig. 2956.]
[Illustration: Fig. 2957.]
[Illustration: Fig. 2958.]
[Illustration: Fig. 2959.]
[Illustration: Fig. 2960.]
The next operation is to cut or punch away the metal between the ends of
the hub and the body of the piece, which is accomplished as follows:
[Illustration: Fig. 2961.]
A top and bottom die and block are made to contain the work, as in Fig.
2961, A and B being the work ends. Through these dies are two holes for
two punches which are driven through together as marked; the dies are
held fair, one with the other, by four holes in the lower and four pins
in the upper one, a section and top view of the dies being shown in Fig.
2962.
The piece is at this stage roughed out to shape all over, and may be
finished between the pair of finishing dies shown in Fig. 2963, which
also represents a plan and sectional view, _a_, _b_, _c_, _d_ being the
holes to receive guide pins in the upper die.
An excellent example of forgings in Siemens Martin steel is given in
the following figures, being the rope sockets for the Brooklyn Bridge.
[Illustration: Fig. 2962.]
[Illustration: Fig. 2963.]
[Illustration: Fig. 2964.]
[Illustration: Fig. 2965.]
Fig. 2964 represents two views of the forgings, and it will be readily
perceived that they are very difficult to make on account of the taper
hole, which is shown in dotted lines. The first operation was to take a
bar of steel 6-1/2 inches square and punch a hole, as at A Fig. 2965.
[Illustration: Fig. 2966.]
[Illustration: Fig. 2967.]
[Illustration: Fig. 2968.]
Next the piece was fullered at B, C by the fuller A, Fig. 2966, and cut
partly off as at D. The fullering at B was then extended by a spreading
fuller, shaped as at B, and the end E was drawn out. Then the piece was
cut off at D. Next the spreading fuller was applied to C, and the
forging appeared as in Fig. 2967. The end F was then drawn out, and the
appearance was as in Fig. 2968.
[Illustration: Fig. 2969.]
The next operation was to enlarge the hole A, Fig. 2965, by drawing
taper mandrels through it, the mandrels being about 7 in. long, having
1/2-in. tapes on them, and being successively larger. With the last of
these mandrels in the hole the hub was drawn out to length and diameter,
leaving the forging roughly shaped, but having the form shown in Fig.
2969.
[Illustration: Fig. 2970.]
To finish the hole the forging was then placed in a block such as shown
at G, in Fig. 2970, a finishing punch being shown at H in the figure.
[Illustration: Fig. 2971.]
The next operation was to let the steam hammer down upon the face of the
punch and bring up the wings E F parallel, but not more than parallel,
as then the mandrel could not be got out; the forging then appearing as
in Fig. 2971.
The next process was to put in a bar mandrel such as shown in Fig. 2972
at I, the pieces J, K fitting on their sides to the mandrel and being
curved outside to the circular and taper shape of the hole. The wings E
F may then be closed on the mandrel to their proper width and the whole
hub end being trimmed by hand, all the previous work having been done
under the steam hammer. The hub being finished the key M may be taken
out and the washer L taken off, when I can be pulled out, leaving J K to
be taken out separately. A pair of tongs are then put through the
finished hub end, while the wings are punched and trimmed under the
steam hammer, and subsequently finished by hand.
[Illustration: Fig. 2972.]
[Illustration: Fig. 2973.]
[Illustration: Fig. 2974.]
The forging of wrought-iron wheels for locomotives is an excellent
example. The spokes are first forged in two pieces, as 1 and 2 in Fig.
2973, and then welded to form the complete spoke. Piece 1 is first
forged in dies under the steam hammer to the form shown in Fig. 2974,
the dimensions being correct when the faces of the dies meet. The stud C
D is then drawn out to the required length and dimensions.
[Illustration: Fig. 2975.]
[Illustration: Fig. 2976.]
[Illustration: Fig. 2977.]
[Illustration: Fig. 2978.]
The upper half of the spoke is first blocked out under dies to the shape
shown in Fig. 2975, and the block B spread so as to form a section of
the wheel rim, as shown in Fig. 2976, in which D is a die, L a movable
piece wedged up by the wedges W W, and removable to enable the
extraction of the forging, and F is an end view of the fuller, the use
of which is necessary to cause the metal to spread sufficiently in the
direction of the dotted lines. The corners of the rim are then cut off,
as shown in Fig. 2973, and the rim is bent in a block having its top
face of the necessary curve, as in Fig. 2977, A being the block, and B a
piece movable, to allow the extraction of the work, and fastened in
place by the key or keys C. The two pieces are then welded together,
their lengths, &c., being gauged by a sheet-iron template, formed as in
Fig. 2978. The welding is usually performed with sledge-hammers, but as
soon as the pieces will hold well together, the drawing down is done
under a steam hammer.
[Illustration: Fig. 2979.]
The spokes thus forged are then put together, as in Fig. 2979, B
representing a wrought-iron band, encircling the rim of the wheel and
closed upon the same by the bolt and nut at N.
[Illustration: Fig. 2980.]
Two washers are then forged, to be placed and welded in as at W W, in
Fig. 2980.
The welding together of the spokes and of the washers to the spokes
proceeds simultaneously. The washers are heated to come to a welding
heat at the same time as the wheel hub is at a welding heat, and the two
are welded together under a steam hammer. During the heating of the
wheel hub, however, the band B, Fig. 2979, is tightened up with the
screw to bring the spokes into closer contact when heated to the welding
point.
[Illustration: Fig. 2981.]
[Illustration: Fig. 2982.]
The seams between the spokes at the circumference of the hub are welded
with bars as shown in Fig. 2981, in which R R are two bars of iron which
are operated by hand as rams. The wedge shape of the washers on their
inside faces performs important duty in spreading the metal as well as
simply compressing it, giving a much more sound weld than a flat washer
or plain dish would.
The rim of the wheel is welded up as follows:
In Fig. 2982 are shown four spokes of the rim as they appear after the
hub is welded. Into the [V] spaces, as _a_, _b_, _c_, _d_; wedges of
metal, of the form shown at E, are welded, after which the surplus metal
of E is cut away, and the rim is solid as at F. In this process,
however, it is necessary to weld all the pieces on one side of the
wheel, as at _a_ _b_, &c., except one, which must be left unwelded until
all the pieces save one on the other side are welded, and the wheel must
be allowed to become quite cool before these last two pieces are welded.
Otherwise the strain induced by the contraction of the wheel rim while
cooling will often cause the rim to break with a report as loud as that
of a rifle. In those cases in which this breakage does not occur the
wheel will be very apt to break at some part of the rim, when subjected
to heavy shocks or jars.
The Figs. 2983 to 2999 (which are taken from _Mechanics_), illustrate
the method employed to forge the rudder frame of the steamship
_Pilgrim_.
[Illustration: Fig. 2983.]
A side elevation of the rudder frame is shown in Fig. 2983.
The forging is made in eight separate pieces, which are so united as to
make three pieces. These three pieces are finally joined by five welds.
The whole length being 29 feet 11-3/4 inches, and the weight 6,500
pounds.
[Illustration: Fig. 2984.]
[Illustration: Fig. 2985.]
[Illustration: Fig. 2986.]
[Illustration: Fig. 2987.]
[Illustration: Fig. 2988.]
[Illustration: Fig. 2989.]
The work is commenced by piling and welding on the porter-bar at the
point in the shaft marked A. The stubs B and C having been previously
prepared, the pile on the porter-bar is heated and welded up and drawn,
shown in Fig. 2984, and scarfed as shown in Fig. 2985; the piece, shown
in Fig. 2986, is then laid in the scarf and welded; then the part from B
to A is finished to size, the finished forging of the post being shown
in Fig. 2984. The surplus stock to the right of B, Fig. 2984, is worked
down into the post E, and the distance from B to F is thus made correct
without loss of stock or time. The curve at D, Fig. 2983, was worked
down somewhere near, and then another pile and weld carries the job to
G. Here the same operations as at first are repeated, and the arm C is
welded in. There is left a good lump of stock in front of C, and by
another pile and weld enough is added to make the job to I, as shown in
Fig. 2987. Holes are then punched at J and L, and the piece of stock M
cut entirely out. A cut is made to L with a hack opening out the piece N
from the shaft. A taper punch, with a 3-inch point and a 4-inch head, is
then driven at L; to throw the piece N out into the position shown at
N^{1}, Fig. 2983; N^{1} is then finished, and the post from L to J
brought to forging size; then, by the ordinary process of piling,
welding and drawing, the shaft is finished from I to O. Next the
porter-bar is cut off, so as to leave stock enough to make the lower
part of the shaft, as shown in Fig. 2988. A hole was punched at Q, and
the stubs drawn out, as shown in Fig. 2989, which gives the post
complete.
[Illustration: Fig. 2990.]
The pieces S and T, and the tiller V, having been forged, as shown in
Fig. 2991, the upper member of the frame is started on the porter-bar at
W, Fig. 2983, and filed, welded and drawn to make the job as far as
X^{1}. Wooden templates, such as in Fig. 2992, are provided for the
pieces of the frame, the first extending from W to X^{1} and X, and the
second including the part from X^{1} to X^{2} and X^{3}. After W, X^{1}
has been drawn out with lumps left where the tiller and the arm S are to
be joined, the scarf is made for the tiller and that is welded in, and
the job finished to piece S. The scarf for S is then made, and S welded
in. This makes the upper member of the frame. The lower member is made
in the same way, starting at X^{3}. These two members are shown complete
in Fig. 2993. The post, Fig. 2989, was sent to the machine shop, and was
turned, planed, bored, and slotted, as shown in Fig. 2990. The frame was
now ready to be pieced up, by welds at W, X, X^{1}, X^{2}, and X^{3},
Fig. 2983.
[Illustration: Fig. 2991.]
[Illustration: Fig. 2992.]
[Illustration: Fig. 2993.]
[Illustration: Fig. 2994.]
[Illustration: Fig. 2995.]
[Illustration: Fig. 2996.]
[Illustration: Fig. 2997.]
[Illustration: Fig. 2998.]
[Illustration: Fig. 2999.]
The several sections are now ready to be welded together for the
complete frame, these welds being made as follows: The ends are upset as
in Fig. 2994 to receive on each side a [V]-piece such as in Fig. 2995,
which is heated on a porter-bar, and is of a more acute wedge than the
ends to be welded, so that when laid in as in Fig. 2996 it will touch at
the bottom first, and thus allow the air and whatever dirt there may be
on the surfaces to squeeze out as the welding proceeds. The method of
heating the frame for these welds is as follows: The [V]-block (which
has the grain of the iron running in the same direction as that of the
frame) being heated in the blacksmith's forge, the frame is clamped
together and counterbalanced by means of weights, so that it may be laid
over a fire pot, constructed as in Fig. 2997. This fire pot is lined
with brick, and has its blast supplied through a piece of flexible tube.
The anvil is of cast iron, shaped as in Fig. 2998, and placed on the
other side of the frame and opposite to the fire pot or portable forge,
as shown in Fig. 2997, so that the frame, when the heat is ready, may be
turned over upon the blocks on which it rests, and the part to be welded
will come upon the anvil. After one side is welded the anvil and the
portable forge change places, and the second side of the weld is made.
In the following figures (which are taken from _Mechanics_) is
illustrated the method employed to build up the shaft shown in Fig.
3001, which was for the steamer _Pilgrim_. Forgings of such large
dimensions are built up of pieces or slabs, called blooms, which are
themselves forged from scrap iron, which is piled as in Fig. 3000. For
the forging in question this scrap iron consisted of old horseshoes,
boiler-plate clippings, boiler rivets and old bolts, and the first step
in the manufacture is to form this scrap into piles ready for the
furnace.
[Illustration: Fig. 3000.]
[Illustration: Fig. 3001.]
[Illustration: Fig. 3002.]
[Illustration: Fig. 3003.]
These piles are made upon pieces of pine board 1/2 inch thick by 16
inches long by 10 inches wide. On these the scrap is piled about 14
inches high, each pile weighing about 270 pounds. After piling, the
scrap goes into the furnace and is raised to a welding heat, the board
retaining its form as a glowing coal almost to the last. The pile of
scrap is heated so nearly to melting as to stick together enough so that
it can be picked up in a long pair of tongs with peculiarly-shaped jaws,
and, as these tongs are suspended by a chain from an overhead traveller
running on an iron track, the bloom is easily transferred to the anvil
of the steam hammer, where, after one or two blows, a small porter-bar
with a crank end, such as shown in Fig. 3003, is welded on, and the pile
is rapidly drawn out into a square bar. When completed the porter-bar is
cut off, and the bar is laid aside to cool. The pile of scrap has now
become a "bloom," such as shown in Fig. 3002, and has been reduced in
weight from 270 lbs. to 240 lbs. The bloom is about 30 inches by 5
inches by 5 inches in dimensions, and has rounded, ragged ends, and a
surface full of lines marking welding of the individual pieces, and at
the ends looking as though the scrap had united by melting rather than
by any welding process.
[Illustration: Fig. 3004.]
These blooms are then taken to the large steam hammer and furnace by
which the shaft is to be built up. The porter-bar, although merely a
tool whereby to handle the mass, forms practically a base wherefrom to
build up the shaft. The construction of the furnace is shown in Fig.
3004, the heat, after passing the work being used for the steam boiler
that supplies steam to the steam hammer.
The porter-bar is held by a crane, the chain being placed in such
position in the length of the porter-bar as to balance it. On the end of
the porter-bar is a clamp, having arms by which the bar may be turned in
the furnace and when under the hammer.
Fig. 3005 represents the bar in position in the furnace, the aperture
through which it was admitted having been closed up by bricks luted with
clay, one brick only being left loose, so that it may be removed to
examine the heat of the bar. The end of the bar is flattened somewhat,
and a slab is laid upon it as in Fig. 3006, the appearance after the
first weld being shown in Fig. 3007. It is then turned upside down, and
blooms are piled upon it as in Fig. 3008. After these are welded the end
is shaped up round and to size. The extreme end is again flattened, or
"broken down," as it is termed, and first a slab, and after reheating,
blooms are added, as already explained; when these are welded and forged
enough to consolidate the mass the mass is rounded up again, thus
increasing the length of finished shaft. The end is again broken down
and a slab added, and so on, the shaft thus being forged continuously
from one end, and being composed of alternating slabs and blooms.
To forge this shaft 118,000 lbs. of blooms, 185 tons of coal, and 360
days of labor were required, the time occupied being 34 working days.
The slabs are simply forged pieces of larger dimensions than the blooms,
and more thoroughly worked, the difference between slabs and blooms
being that there is more waste with the blooms than with slabs, because
the blooms heat quicker than the forged part of the crank.
Between both the slabs and the blooms there are placed rectangular
pieces to hold them apart, and let the furnace heat pass between them,
the arrangement of these pieces being shown in Figs. 3009 and 3010.
Figs. 3011 to 3024 (which are taken from _Mechanics_), represent the
method employed to forge the crank shaft of the United States steamship
Alert.
[Illustration: Fig. 3005.]
[Illustration: Fig. 3006.]
[Illustration: Fig. 3007.]
[Illustration: Fig. 3008.]
[Illustration: Fig. 3009.]
[Illustration: Fig. 3010.]
[Illustration: Fig. 3025.]
[Illustration: Fig. 3026.]
[Illustration: Fig. 3027.]
[Illustration: _VOL. II._ =FORGING UNDER THE HAMMER.= _PLATE XVII._
Fig. 3011.
Fig. 3012.
Fig. 3013.
Fig. 3014.
Fig. 3015.
Fig. 3016.
Fig. 3017.
Fig. 3018.
Fig. 3019.
Fig. 3020.
Fig. 3021.
Fig. 3022.
Fig. 3023.
Fig. 3024.]
Fig. 3011 represents the crank shaft, and Fig. 3012 an end sectional
view, showing how the throws were built up. The first operation was to
forge the saddles shown in Fig. 3013, these being the pieces that are
shown between the cap and the wrist.
These saddles were made in halves, each half appearing as in Fig. 3014.
From a pile and weld of blooms on the porter-bar, enough to make the two
halves, one half was cut off. The other half was then drawn down on the
porter-bar, and the first half was then piled on the latter, as shown in
Fig. 3015. The square cross bar goes clear across and projects about an
inch at each side. The back pieces were short bits. The square cross bar
makes the saddle less liable to split in welding it on to the square
shaft. Two "caps" were also made before the forging of the shaft itself
began. These are shown in Fig. 3016, and their position in the finished
work is shown in Fig. 3012.
The shaft itself was piled, welded, and drawn on the porter-bar in the
usual manner, until the location of a crank was reached. Then a part of
the work some distance from the new end was squared, as shown in Fig.
3017, and on this square the saddle was piled to heat and weld, as shown
in Fig. 3018. As will be seen, the saddle rested upon the outer lines of
the angle. The first blow was struck square on the top of the saddle,
and after three or four blows the job presented the appearance shown in
Fig. 3019. The piece was now turned so as to lie as shown in Fig. 3020,
and worked with blows on the sides to the shape shown in Fig. 3021. This
opened the top of the juncture of the saddle and squared the shaft down
to the point where the weld was good. The piece was then turned back to
the position shown in Fig. 3019, and worked with blows which again
closed the angle on top, and made the weld good all through. The piece
was then returned to the furnace, and at the next heat the saddle was
squared up and finished, and the cap was piled on top of the saddle, as
shown in Fig. 3022. The cap was welded on at the next heat, and two
cheeks, like that shown in Fig. 3023, were laid upon one flat of the
crank and pinned with 1-5/8-inch round pins. One of these pins is shown
in the figure. Bits of iron were put under these cheek pieces in the
usual manner. As the cheeks were very much smaller in section than the
crank body, it was necessary to turn them over away from the fire, or
else the cheeks would be burned before the crank body was hot enough to
weld. To prevent the cheeks from falling off in the furnace the pins
were put in as described before heating. After two cheek pieces had been
welded on one side, two more were added on the opposite side, and then
the crank was finished, as shown in Fig. 3024.
As will be seen by inspection of Fig. 3012, the weld between the cap and
the saddle comes about the middle of the wrist, and the cheek pieces
support the cap sideways. By means of the piles and welds described, the
grain of the iron was so disposed as to offer the most resistance to
working strains. This method was devised by Mr. Farrell Dorrity, of the
Morgan Iron Works.
FORGING LARGE CRANK SHAFTS.[45]--The following paper describes the
method of forging marine crank shafts adopted at the Lancefield Forge,
Glasgow. It will be better understood if a short account is first given
of the ordinary methods in use for the same purpose.
[45] From a paper read at the Glasgow meeting of the Institution of
Mechanical Engineers, by W. L. E. MacLean.
"_First Method._--The most common method is technically termed by the
forgeman, 'finishing the piece before him.' He begins with a staff or
stave, as shown in Fig. 3025, suspended by a chain from the crane, and
made round for the convenience of manipulating under the steam hammer;
this stave is used over and over again for many forgings, as it is
merely the "porter" to carry the piece and enable it to be worked. The
forging is begun by two or three slabs being placed on the stave as at S
S S, and then inserted in the furnace. These slabs are flat blocks made
up of pieces of scrap iron, which have been piled and heated, and then
welded together. After being brought to a welding heat in the furnace,
the slabs are withdrawn, placed under the steam hammer, and beaten down
solid. The piece is then turned upside down, and two or three similar
slabs placed on the opposite side, as shown at S S. When sufficient iron
has been thus added to form the collar of the shaft (assuming it is to
have a collar), it is rounded under the hammer, as at C, Fig. 3026, and
the body of the shaft next to the collar is roughly formed, as at D.
More slabs, S S S, are added to bring out the body, and afterwards the
crank itself is proceeded with, on the same plan. The piece will begin
to assume the appearance of A, Fig. 3026. Then more slabs are welded on
the top, as at S S S, till the depth of the crank is obtained, after
which the forgeman proceeds to finish the collar and body of the shaft,
as shown. The collar on being finished is cut all round, as shown at C
D, Fig. 3027, so that it may be more easily detached from the stave when
the shaft is completed, leaving only sufficient connection to carry it
till then. The forgeman then cuts the gable of the crank as at E G, and
rounds up the body and neck as at B N, Fig. 3027.
"This, it will be observed, is a speedy process, and would invariably be
adopted if it were not attended with a very serious drawback; it is very
hazardous to the solidity of the forging. For it will be easily
understood that not above a third of the crank itself can be thus
formed, because the iron at the neck N would not carry a greater mass;
if the whole mass of the crank, or even the half of it, was formed
before the body and neck of the shaft were finished, a proper heat could
not be taken on the body and neck for finishing, without the neck giving
way or rupturing. Indeed, as it is, the undue proportion often causes
the shaft to be strained at this part, where most strength should be, so
that it is rendered weak, and a flaw is developed which by-and-by causes
it to be removed from the steamer as dangerous and useless, if indeed it
does not break outright; so that the forgeman, if he adopts this method,
must be very careful to proportion the amount of iron he has massed in
the furnace to the size of the body he is finishing, otherwise the
weakening above mentioned will take place. All marine engineers will
easily recognise this defect, which frequently occurs, but the cause of
which is probably not well understood. Such a flaw will present a
similar appearance to that shown at F, Fig. 3033, taken from an actual
example.
[Illustration: Fig. 3028.]
[Illustration: Fig. 3029.]
"This difficulty of proportioning the part of the crank first forged to
the size of the neck, will be still better understood by the appearance
of it in the furnace, as shown in Fig. 3028. Having reached this stage,
with one end of the shaft completed, as also that portion of the crank
itself which of necessity was completed before the collar was cut, in
order that the neck might be finished, no more iron can be added on the
top edge, as it is up to the full depth already; it must therefore be
added on the flat, as in Fig. 3029, where the piece is shown on its flat
side in the furnace, the finished portion being outside the furnace
door. A number of slabs S S S are then placed side by side to bring out
the width of the crank further; these being welded down, the piece is
turned upside down, and the process repeated on the other side.
Afterwards other slabs are similarly placed on both sides, as shown in
Fig. 3030, of which one is the flat, and the other is the edge view of
the crank at this stage; and this is continued until sufficient iron
has been massed to allow of the other gable of the crank being cut down,
as at A, Fig. 3031, and sufficient also to allow of the other part of
the body B being rounded and prepared for further piecing out.
[Illustration: Fig. 3030.]
[Illustration: Fig. 3031.]
[Illustration: Fig. 3032.]
"Now it will be observed that the first gable finished has the slabs all
welded on the edge of the crank, and the hammering has all been on the
edge; hence the subsequent hammering on the flat has a tendency to open
up the weldings, if they have not been thoroughly made. A section taken
at A B, Figs. 3028 and 3029, will show as in Fig. 3032, on the left, the
weldings being across the web of the crank; the circle indicates the
section which the crank pin would present if cut through there. But when
the slabs are placed on the flat afterwards, some of the joinings of the
ends of the slabs, or "scarf ends," are certain to fall within the crank
pin, as seen in Figs. 3028 and 3029; therefore the section through C D,
Fig. 3030, will show somewhat like Fig. 3032 on the right, and the crank
pin necessarily includes some of these flaws. The flaw thus produced,
called 'a scarf end in the pin,' is readily recognizable by all marine
engineers; at F, Fig. 3033, is a sketch from an actual occurrence.
"When the second gable is cut, and the other end is rounded, there is
only the other collar to be put on (if a double-collared shaft), and the
forging is completed.
[Illustration: Fig. 3033.]
This method is so speedy, compared with any other, that it is often
resorted to even at the risk of making a bad forging; and too many
broken shafts testify to the fact. Besides, it may be observed that in
making a double crank shaft, while the one crank may be made in this
way, the other must; for, the first crank, A, Fig. 3033, being
completed, and the body, B, between the two cranks, also completed, the
second crank, C, must of necessity be pieced off this body, even at the
risk of the neck N being strained. This may account for the many
instances in which one of the cranks of a double crank shaft gives way,
rendering the shaft useless; and also for the plan, now almost
universal, of making the two cranks separately and coupling them
together; a further object being, no doubt, to have the means of
replacing a defective half, if need be, without losing the whole shaft.
"At Lancefield, when a double crank shaft is to be made, the after
crank, A, is first made by the method afterwards described, so as to
insure that this crank, through which, as being next the propeller, all
the power of the engine passes, is perfectly sound; and in piecing the
other crank off the body, it is worked with slabs on the flat instead of
on the edge, as afterwards described.
"The writer's own opinion is that the crank is the most important part
of the shaft, and, therefore, at all costs, should be made first.
Others, no doubt, may take the same view, and, to avoid the risks just
mentioned, may adopt the process described in the second method.
[Illustration: Fig. 3034.]
[Illustration: Fig. 3035.]
"_Second Method._--This method builds the middle first, and is called
"turning the shaft end for end." The shaft is begun from a stave, by the
addition of slabs, as shown in Figs. 3034 and 3035; Fig. 3034 shows it
with iron added in slabs, till a butt is formed, as at B, to form the
nucleus of the crank; slabs S S S are then piled on it to bring the
crank up to the height.
[Illustration: Fig. 3036.]
"These are beaten down and welded, and more are added, as at S S S, Fig.
3035, till the full height of the crank is reached. Should the web (or
edgeway of the crank) be thick, two slabs are frequently used to make up
the breadth, placed edge to edge, as shown in Fig. 3035 on the right
hand of the figure; the widths of these slabs are limited by that at
which the shinglers can conveniently work and turn them under the steam
hammer. The crank, however, is completed without any "side slabs," for
the beating down of the slabs on the edge will broaden out the mass, and
give sufficient material to forge out the crank to the proper height by
hammering on the flat. The crank is afterwards cut at the off gable at
G, Fig. 3036, the body B pieced out and rounded, the collar welded on,
and then a small stave S is drawn upon the end, to enable the forgeman
to handle the piece when he "turns it end for end" to complete the other
end of the shaft.
[Illustration: Fig. 3037.]
"This method, though better than the last, is also objectionable; for
though there is not equal risk of 'scarf ends' in the pin, yet the
weldings are all on the edge, as in the lower view, in Fig. 3036, where
the section of the crank pin is shown by the dotted circle; and the
cheeks of the crank, O O, are thus liable to give way if a heavy strain
comes on the crank when at work. The defects arising from this cause are
shown in Fig. 3037, and will be readily recognised by all engineers.
"_Third Method._--Considerations such as these have led to the adoption
of the third or Lancefield method.
[Illustration: Figs. 3038 and 3039.]
"Fig. 3038 shows the piece begun from the stave in the usual way, with
the slabs all welded, however, on the flat, till a basis is formed for
the building up of the crank. A portion A is roughly rounded to form the
one end of the shaft, and the butt of the crank will present the
appearance of a slightly elongated square, as shown at B, Fig. 3039. The
workman then "scarfs" or hollows it down at one edge all along the side,
as indicated in the end view by the dotted line from C to D; it will
then present the appearance shown by the end view, Fig. 3040, being
somewhat bulged outward at the points E and F. Three long thin slabs,
Fig. 3042, shaped for the purpose, are then placed on the hollowed part,
the piece lying flat in the furnace. These slabs are tapered a little
the broad way, not on the length, and little pieces of iron are
interposed between them, to keep the surfaces apart, and allow the flame
free access between them. The object of making them thin is that they
may be all equally heated, which is not so readily achieved when the
slabs are thick; and the object of the tapering is to allow the slag to
flow out freely when the uppermost slab is struck by the steam hammer.
The surfaces thus get solidly welded.
[Illustration: Figs. 3040 and 3041.]
[Illustration: Fig. 3042.]
"Fig. 3041 represents the slabs thus placed in elevation, and the figure
on the right, in section. The slabs are forged long enough to go right
across the whole width of the crank, excepting about 6 inches; this
margin is necessary to allow of the lengthening out of the slabs to the
whole width under the process of forging. After these slabs are
perfectly welded, the piece is turned upside down, and the process is
repeated on the other side, as shown in Fig. 3042. When welded down the
mass has increased in depth as well. Another scarfing takes place on the
first side, and then another on the second side, as shown in the figure,
and so on, till the full size is obtained; and it will be seen, as in
the right-hand view in Fig. 3042, that by this process of "scarfing"
equally from, both sides, the iron from the very middle of the body of
the shaft is drawn up quite to the crank pin. The location of the pin is
indicated by A A, and it will be seen that by no possibility can there
be a "scarf end" in the crank pin, as the slabs in all cases go right
across the crank, and also that the cheeks of the cranks have no edge
weldings crossing them, as in the previous cases; for the tail of a slab
may be at R, Fig. 3042, while the other end may be at S. The fibre is
also developed by the continuous drawing up of the iron consequent upon
the repeated flat scarfings across the whole width of the crank. When
the crank has been thus massed sufficiently large, it is cut at the
gable, with sufficient material left to piece out the other body of the
shaft. This is now done, the coupling welded on, and a small stave drawn
on the end to enable the forgeman to manipulate it, when it is turned
end for end, to complete the other end.
"These proceedings occupy longer time than either of the other two
methods, and consequently costs a little more; but the advantage is well
worth all the difference, as greater confidence can be entertained that
the forging is every way satisfactory. In brief, by making the crank
first, is avoided the liability to weakness at the neck, characteristic
of the forgeman's making the shaft before him, as in the first method;
by the repeated 'side scarfing' is avoided the liability to fracture
across the cheeks, consequent upon the edge weldings of both first and
second methods; while by having the slabs the whole length of the width
of the crank, any 'scarf end' in the length way of the crank pin is
impossible (such as may occur in the first method); and the welding of
the mass of the crank being wholly on the flat must tend to form a more
solid forging than if hammered otherwise. Thus, if the forging is well
heated and properly hammered, the system promises to insure that no weak
part will be found in the shaft after it is finished and put to work.
The writer believes, from the success which has already followed in
every case the adoption of this method, that it will eventually be found
that almost more depends on the mode in which a crank shaft forging is
constructed than on the material of which it is made.
"This leads him to some observations regarding the material for such
shafts. It is of course well known that in the early days of
engineering, before the time when steam navigation had received a great
impetus by the invention of the screw propeller, the connecting rods,
cranks, shafts, &c., of land engines were all formed of cast iron;
except, indeed, where the connecting rods were made of wood, strapped
with plates of wrought iron, as frequently was the case with pumping,
winding and blowing engines. In fact, all the parts that could be made
of cast iron were so made, and the piston rods, bolts, keys, straps, and
other smaller parts were alone made of malleable iron, the smaller
pieces being made from rolled bars direct, as at present, and the larger
made of similar bars, but placed side by side and bound together or
'fagoted,' as they were called, from their resemblance to a bundle of
fagots. These bars, thus fagoted, were either brought to a welding heat
in a smith's hearth and welded under the sledge-hammers of the men
called 'strikers,' or hammermen; or else heated in a furnace, and welded
under the tilt hammer worked by a steam engine. By-and-by it was found
necessary to adopt the stronger material, wrought iron, for parts
hitherto confined to cast iron, because the latter was found too
deficient in cohesion to stand the strains due to the power of
high-pressure steam, which was now almost universally superseding the
use of low-pressure steam in the condensing engine. The system of
fagoting, however, was still carried out, even far into the history of
marine engineering; but when the rapid increase in the dimensions of
engines, both stationary and marine, called forth the steam hammer, and
so rendered the forging of heavy masses comparatively easy, the system
of fagoting fell into disuse, for the following reason: In making up a
fagot, say, of 18 inches or 20 inches square, it was found, that in the
furnace the outside bars would reach a welding heat much sooner than
those in the middle; consequently on welding this fagot under the steam
hammer, though the blow might reach to the centre, yet the interior
would not be welded, while the surface was; hence the shaft or other
forging would not be welded throughout, and it was no uncommon thing for
a shaft to break and expose the internal bars quite loose and separate
from each other.
"When it was seen that malleable was so much superior to cast iron, and
that the system of fagoting was so imperfect, the adoption of 'scrap
iron,' which was then composed principally of parings of boiler plates,
pieces of cuttings from smiths' shops, old bolts, horseshoes, angle
iron, &c., became general. These being piled together in suitable
pieces, and in a pile of suitable size, for the convenience of working,
were brought to a welding heat, and beaten out into a slab, or
oblong-shaped piece, ready for the forgeman; who would build two or
three together, adding more when required, and so bring out his piece to
a sufficient size to enable him to shape his forging out of it. Then it
was that engineers, seeing what an increase of strength they obtained by
these means, invariably specified on their drawings (as many of them
still do), 'These forgings are to be made of carefully selected scrap
iron, free from flaws and defects.'
"To meet the requirements of their customers, therefore, forge-masters
had now nothing to do but to select and use the best available scrap
iron; but the universal adoption of iron hulls in place of wooden ones,
conjoined with the rapid and unprecedented increase in steam navigation,
soon introduced a class of scrap iron which did not possess the
qualifications of good scrap, and also called for a very much greater
supply of forgings than could be obtained in superior scrap iron. The
consequence was that shafts of scrap iron, when turned and finished,
became liable to exhibit streaks and seams, not due alone to imperfect
welding in the forging, but likewise to the laminations and
imperfections of the original scrap iron, which the process of piling
and shingling into the slab was not sufficient to obliterate. So
constantly does this yet occur that it causes a strong temptation to
make such forgings of new iron puddled direct from the pig and then
shingled into slabs or blooms, under the idea that these streaks and
seams will thus be avoided, and that the iron will be improved almost to
the condition of scrap iron, while being forged under the steam hammer.
This, however, is found not to be the case. The forging is certainly
free from the streaks of the scrap iron, but this is obtained at the
expense of strength; for the material is too raw; it wants cohesion, and
has not had the proper kind or amount of working to bring it to the
condition of superior wrought iron. This method is still further
tempting, inasmuch as it is far cheaper than the other; the material
costs less than scrap iron, and, as it welds at a lower temperature, a
forging can be much more quickly and easily made. Still, for whatever
class of machinery it may be fitted, it should certainly be renewed in
every case for a crank shaft or propeller shaft.
"From these considerations it has been the custom at Lancefield, in the
preparation of the iron for crank shafts, to improve upon the ordinary
condition of the scrap iron in the following manner: The pile is made up
of carefully cleaned and selected scrap; it is brought to a welding
heat, and then hammered under the steam hammer. But instead of being
beaten into a flat slab for the forgeman, it is beaten into a square
billet, which is afterwards rolled in the rolling-mill into a flat bar,
as if for 'best best' merchant iron. By this additional heating,
hammering and rolling, all the different qualities of the scrap iron
composing the pile are merged into one homogeneous material, having the
fibre given to it that was lost in the separated portions of the scrap
iron; and this, when cut up into proper lengths, and again piled and
shingled into the slab, results in a material possessing somewhat the
closeness and density of steel, while retaining all the toughness and
tenacity of superior malleable iron. The improved method of constructing
the forging, previously detailed, is worthy the use of this superior
material; and both having been adopted at Lancefield with results which
have commended themselves so unmistakably to many engineers, that they
now not only specify the material, but stipulate for the mode of
manufacture, it is thought the system has only to be more widely known
in order to be universally adopted. It is certain to give greater
confidence in the endurance of such important parts of the machinery,
although this confidence may have to be obtained by a small increase in
the cost, due to the extra workmanship both on the material and on the
forging.
"When we take into consideration the vastly accelerated speed of the
marine engine in late years, and the many disastrous effects which
follow the breaking of a shaft at sea--also that the tendency of the age
is still towards much higher pressures, and further lengthening of
stroke it is not surprising that improvement in such an important part
as the crank shaft should be eagerly sought after; but it has hitherto
been sought in the direction of the material alone. Cast steel has been
advocated, and brought to some extent into use; but its expense renders
such shafts costly out of all proportion to the other parts of the
engine; while, in the event of their heating when at work (a very
frequent casualty), and having the water-hose directed upon the crank
pin or journals, it cannot be expected that the material will behave any
better, or even so well, as tough wrought iron. What is termed puddled
steel is liable to the same objection, and probably, from its mode of
manufacture, in a still greater degree. The so-called mild steel is no
doubt proving itself a superior material, and yielding good results when
rolled into ship or boiler plates. But thus prepared it is more costly
than 'rolled scrap bar;' and if not rolled, but cast into an ingot, then
it possesses some of the crystalline characteristics of steel, with all
the disadvantages attending its manipulation into a forging.
"For extra large crank shafts, the fear of unsoundness, arising from the
ordinary mode of forging, has led some engineers to consider the
propriety of building the shafts and cranks in separate pieces. This,
with engineers generally, has not hitherto been looked upon with favor;
as the fewer the pieces the more rigid the shaft. Moreover, the
increased weight necessitated by this separate building is viewed as a
disadvantage, even although it were not attended with greater cost, as
undoubtedly it is.
"The material and mode of manufacture advocated in this paper may tend
to dissipate some of these apprehensions. They will not obviate
defective construction in the engines themselves, or faulty proportion
of their parts, or neglectful supervision of their working, but they
will reduce to a minimum the risk of breakage in such untoward
circumstances. If any objection be taken on the score of extra size, the
enterprise which a quarter of a century ago engaged in the making of the
unusually large shafts necessary for the 'Great Eastern' may still be
trusted to meet the advancing requirements of the present day."
Fig. 3043 represents a foot-power hammer or Oliver. The hammer is upon a
shaft in bearings, and is held in the position shown by an open coiled
spring. On the shaft is a chain pulley, the other end of the chain being
connected through a leather strap to the treadle. Means are provided to
adjust the height to which the hammer will lift to bring the hammer face
fair with the work and to give the required degree of tension to the
spring.
Fig. 3044 represents a Standish's foot-power hammer, in which the hammer
and the anvil are provided with dovetail seats for receiving dies,
swages, &c. The force of the blow is regulated by the height to which
the hammer is raised, which may be adjusted by the nuts beneath the
spiral springs. The handle on the hammer is for pulling the hammer down
by hand when adjusting the lower die fair with the upper one.
What are known as power hammers are those driven by belt and pulley;
while those known as trip hammers have their helve lifted through the
medium of revolving lugs or cams. Steam hammers are those in which the
hammer is lifted by a piston in a steam cylinder; while in hydraulic
hammers, the hammer is moved by water pressure.
Fig. 3045 represents a Justice's power hammer, in which the hammer is
guided in a slideway and is operated by leather straps attached to the
ends of a spring, at the crown of which is attached a connecting rod
driven by a crank disk. The stroke is altered by means of placing the
crank pin in the required position in the slot in the crank disk. By
means of gibs the hammer may be set to match the dies. The pulley is
provided with a friction clutch operated by the treadle, shown.
Fig. 3046 represents a Bradley's Cushioned Hammer, in which motion is
obtained by a belt passing over a pulley on a crank shaft, whose
connecting rod R is capable of adjustment for length, so as to govern
the distance to which the hammer shall fall, which obviously varies with
different sizes of work. The hammer is lifted through the medium of a
rubber cushion A, seated in a casting to one end of which is connected
the rod R, while the other end is pivoted. The lever to which the hammer
is affixed is raised against the compression of the rubber cushion B,
and at the top of its stroke also meets the rubber cushion C; hence
these two cushions accelerate its motion after the crank has passed its
highest point of revolution. The cushion D prevents the rebound of the
hammer after the blow is struck; hence as a result of these cushions,
heavy or light blows may be struck with great rapidity and regularity.
The weight W is on a lever that actuates a break upon the wheel shown at
the side, so as to enable the stopping of the hammer quickly. The
machine is put in motion by pressing the foot upon the treadle T, which
operates a belt tightener, the belt running loose when the treadle is
released.
[Illustration: Fig. 3043.]
[Illustration: Fig. 3044.]
[Illustration: Fig. 3045.]
[Illustration: Fig. 3046.]
The hammer lever or helve is adjustable for height by means of the screw
G and hand-wheel H, which raise or lower the bearings in which the helve
journals are carried. This is necessary, because as the helve moves in
the arc of a circle the faces of the upper and lower die, or of the
hammer and the anvil, as the case may be, can only come fair at one
particular point in the path of the hammer; hence in proportion as the
blow terminates (by meeting the work surface) farther from the anvil
face, the pivot or journal of the helve must be raised, so that the
journal will be horizontally level (or as nearly so as possible) with
the hammer face at the moment the blow is delivered.
By giving motion to the helve through the medium of cushions, a direct
mechanical connection, and the destructive concussion that would
accompany the same, is avoided; hence a high speed may be obtained
without the frequent breakage that would otherwise ensue.
[Illustration: Fig. 3047.]
Fig. 3047 represents Corr's power hammer, the construction being as
follows: The semi-elliptic springs, shown on top and bottom of the beam,
serve to balance the stroke, so that the hammer may run from 350 to 450
strokes per minute, with safety to the machinery. The hammer is adapted
to almost any form or kind of forging. Large dies may be inserted for
various kinds of forming and welding, such as making plough-shares and
other articles, which require that the operation be commenced with a
light tap, and increased to a heavy blow at the will of the operator.
The whole structure is mounted on a substantial iron bed V, 18 inches
deep, 22 inches wide and 5-1/2 feet long. Attached to this bed V are two
circular arms L; between them is pivoted near their top, at K, an
oscillating frame H, having a longitudinal opening, in which is attached
two semi-elliptic springs G G, and two plates I, with trunnions
projecting laterally through the oscillating frame at K; the hammer beam
F is inserted between the springs G G, and the trunnion plates I, which
are bolted firmly to beam F at I; the ends of the trunnions and outsides
of the oscillating frame H rest evenly against the inside of the
circular arms L; at K a shaft is passed through the trunnions and beam
F, and made rigid in them with its ends resting in boxing at K. Caps are
provided to cover the ends of the boxing and shaft with set-screws
projecting against the ends of the shaft, which secures it against end
play.
By these mechanical arrangements the beam F and oscillator H are
securely attached independently, vibrating on one common centre,
allowing no side play of the hammer E, admitting F to the free action of
the springs G G; in the lower end of the oscillating frame at N is a
lateral opening 10 inches vertically by 6 inches longitudinally and 4
inches laterally, with flanges projecting longitudinally one inch into
this opening from both sides. This makes the opening two inches smaller
on the outside than the internal cavity; the rear and front internal
walls are provided with steel plates, 4 by 10 inches, 1/4 thick, resting
against the inner ends of four set-screws, not shown, provided to adjust
these plates to or from the sliding box at N, to compensate for wear and
prevent lost motion. These plates and flanges form slides and guides
between which a loose box and eccentric is provided with shaft
projecting laterally through boxing at N, which project upwards from an
adjustable frame immediately under the oscillator H; this permanently
locates the eccentric and shaft in the lateral opening in the oscillator
H, at N. The adjustable frame mentioned rests on suitable bearings on
the inside of the circular arms L, and is fastened down by four bolts
passing through suitable slots in the adjustable frame, entering the
bearings on the arms L. This frame is adjusted back or forth by
set-screws S S; this adjustment is for the purpose of giving a greater
or less distance between the anvil and hammer at D, as may be desired
for large or small work, long or short dies, &c.
The anvil B, weighing about 500 lbs., sits down in the bed at R and
rests on circular bearings (between R and B), which radiate to the
centre of the top of the anvil at D, and is held rigidly in any position
longitudinally desired by set-screws Q Q, with their inner ends resting
on shoulders on the sides of the anvil B, which projects down about ten
inches; between this lower projection and the internal wall of the bed
is sufficient space to admit of any adjustment desired. This lateral
adjustment is accomplished by set-screws R, passing through the sides of
the bed V, with their inner ends resting against the anvil which holds
it rigid at any lateral adjustment. By this arrangement the anvil is
accommodated to all and any class of work or shape of dies.
The anvil is constructed in two parts. Four inches of the top C may be
taken off, leaving a suitable place to insert large dies for various
purposes, such as dies for welding plough-shares and dies for forging
journals on large shafts. A counter-shaft, provided with suitable
pulleys, is attached on the rear end of the bed; this shaft is kept
constantly in speed and power by the vertical belt in the direction
indicated by the arrow; the other end of the shaft is provided with a
flanged pulley, corresponding to a flanged pulley M, on the eccentric
shaft; around these pulleys is placed a loose belt, as shown; in contact
with this is a press pulley T, adjustably attached by two arms to the
projecting end of the treadle P at O. If the foot be placed on the
treadle at U and it be pressed down, the break on the opposite side
breaks contact with the balance wheel (not shown); the press pulley will
at the same time tighten the loose belt on the flanged pulleys. This
gives motion to the pulley M, in the direction indicated by the arrow.
Its motion is increased by a heavier pressure until it attains the same
speed as the other flanged pulley; this would be the full speed, which
may be diminished to any speed desired by lessening the pressure on the
loose belt. By this means motion and power is given to the eccentric,
which carries back and forth the lower end of the oscillating frame H;
this gives vertical motion to the springs G G, and this imparts
corresponding motion to the beam F. These springs accomplish a threefold
object:
1st. They carry the hammer E up and down.
2nd. They cushion the hammer at the returning points and give off that
power which was stored in them while cushioning.
3rd. By the power exerted in the machinery they follow up and impart
still greater force to the blow.
It is found by this arrangement of eccentric loose box and oscillator
that when the machinery is moved in the direction indicated by the
arrow, that the downward stroke is one-sixth quicker than the up stroke;
this is a natural result, for the down stroke is performed while the
eccentric is revolving above the centre of its shaft and nearest the
fulcrum of the operator H. With the present arrangement the downward
stroke is performed with 5/12 of the revolution and the up stroke is
performed with 7/12; the difference is 2/12, which equals one-sixth. The
up stroke is performed while the eccentric is revolving below the centre
of its shaft and in that part farthest from the fulcrum of the
oscillator H, so if the machinery were reversed the quick stroke would
be up and the slow stroke would be down.
[Illustration: Fig. 3048.]
In Fig. 3048 is shown a Kingsley's trip hammer. The main bed or
foundation plate A carries the bed plate or frame B, at one end of which
are the pillar blocks C, which afford journal bearing to the casting
carrying the hammer shaft E, being fastened thereto by the clamp D.
These journals are the centre of motion of the hammer helve E.
At the other end of the bed plate B, are the pillar blocks F, affording
journal bearing to the cam and fly-wheel shaft, _a´´_ is the tripping
cam, which is provided with two toes or cam arms, which meet the
tripping piece _b´´_, and this gives the hammer two strokes in a
revolution of the fly-wheel shaft or cam shaft G. The stroke of the
hammer may be altered by means of the set-screws _c´´_, which move the
pillar blocks F, so that the cam toes _a´´_ have contact with the
tripping piece _b´´_ through more or less of the revolution of _a´´_;
the pillar blocks F being retained in their adjusted position by means
of the set-screws shown below them in the bed piece B.
By the following means provision is made whereby the face of the hammer
may be set out of parallel with that of the anvil block or lower die
_d´_.
[Illustration: Fig. 3049.]
Fig. 3049 is a sectional view through the pillar blocks C, and casting
and clamp D. The pillar blocks C C are carried in a semicircular frame
_a´_, hence by unscrewing the bolts _b´_ and screwing up the pillar
block on the other side, the journals are thrown out of parallel, and
the plane of motion of the hammershaft is altered so that the face of
the upper die does not meet that of the anvil die fair to an amount
which may be varied at will by operating the screws _b´_. The object of
this is to enable the forging taper (as in sword blades) with common
dies, and thus to save the making of special dies for each degree of
taper required.
Similar provision is made in the anvil block which is easier to set,
providing the degree of taper is within the limit of its range, of
movement, otherwise the hammer also may be set.
Fig. 3050 represents a drop hammer, and Fig. 3051 is a sectional view of
the lifting mechanism.
This machine consists of a base or anvil, a hammer which moves up and
down between two uprights, and a lifting device, which is secured to the
top of the uprights.
A board secured to the hammer passes up between two friction rolls,
which revolve in opposite directions. When the two rolls are moved
towards each other, the friction on the board causes the hammer to rise;
and when again separated the hammer will fall. The _back_ roll is keyed
to a shaft, on each end of which is a driving-pulley; and thus by the
use of two pulleys on the same shaft, equal wear comes on the bearings
in which it revolves. The _front_ roll turns freely on its shaft, and is
driven by the back roll being geared to it. To secure to the gears both
strength and durability, they are made with wide faces, are geared at
both ends, and the teeth are of peculiar shape.
The bearings to the shaft, on which the front roll revolves freely, are
eccentric to the roll, and a partial revolution of the shaft moves the
_front_ towards the _back_ roll, pinching the board. To an arm which is
secured to the front shaft is fastened the upright rod, the _upward_
movement of which _opens_ the rolls, and whose downward movement closes
the same; the weight of the rod being sufficient to cause the hammer to
rise. This arrangement, simple and yet substantial, dispenses with the
two eccentric-armed bushings, and the spreading of the upright rod at
the top to reach both bushings, which caused so much trouble in the old
way. In place of the dog which is usually used to hold up the hammer,
(which is limited in adjustment to holes located at fixed distances in
one of the uprights, necessitating not only the removal of the dog to
another hole, and connecting and disconnecting the same to the treadle,
but also the most accurate adjustment of the collar on the upright rod
to the dog holding the hammer), we use a pair of clamps, located on the
lifter, under the rolls. These clamps, holding the hammer centrally,
prevent the side blow against the upright, the inevitable result of the
contact of hammer and dog, when the former is only held on one side, as
it must be, by the use of the dog. The opening of the clamps by the
foot-treadle allows the hammer to fall; and the clamps are so made that
the hammer will ascend freely, whether the foot is on the treadle or
not, and if the foot is off the treadle, will hold up the hammer at any
point where it may be arrested in its upward movement. It will be
readily seen that the only adjustment required is that of the collar on
the upright rod, to any height of blow desired.
[Illustration: Fig. 3050.]
This machine has two treadles, one connected to the clamps, and the
other to a lever which operates the upright rod.
[Illustration: Fig. 3051.]
To obtain repeated blows with one motion of the foot, place the foot
upon the treadle connected to the clamps. If variable blows are wanted,
place the foot upon the _other_ treadle, and the hammer will follow the
motion of the foot. This extra treadle is a late improvement, and is not
shown in the cut. The operation required to obtain automatically any
number of blows of the same height is described as follows:--
[Illustration: Fig. 3052.]
Pressure upon the treadle opens the clamps and allows the hammer to
fall; just before the dies come together, the trip at the bottom which
holds up the upright rod is released, and allows the rod to drop; this
closes the rolls, causing the hammer to ascend. The hammer continues to
rise until it strikes the collar on the upright rod, and, lifting the
rod, opens the rolls, removing the pressure upon the board, and allows
the trip at the bottom to go under to hold the rod up, and the hammer
remains suspended, provided the foot is off the treadle. So long as
pressure is kept on the treadle, the blows of the hammer will be
continuous; but upon removal of the pressure, the hammer will assume its
original position.
[Illustration: Fig. 3053.]
[Illustration: Fig. 3054.]
[Illustration: Fig. 3055.]
To procure variable blows, the operation is as follows:--
Pressure upon the treadle connected to the lever which operates the
upright rod communicates itself to the treadle that opens the clamps,
and the hammer falls; a locking device (not shown in cut) keeps this
treadle down, and on completion of the variable blows wanted, removal of
the foot from the treadle disconnects the locking device, and the hammer
goes up to its original position, and is there held by the clamps.
When the work is such that the operator requires an assistant, variable
blows may be obtained by the use of the hand lever by this assistant.
A gentle pressure upon the treadle will allow the hammer to go down
slowly, but it will stop and remain suspended at any point as soon as
the pressure is removed. The hammer can also be arrested at any point on
its way up, by bringing into action the hand lever, so that the next
blow can be given from a state of rest at a less height than the collar
is set for. The clamps in holding up the hammer keep the board from
touching either roll, and prevent the same from being worn uneven when
not in use.
The back roll is made adjustable to different thicknesses of lifting
board, as are also the clamps.
[Illustration: Fig. 3056.]
Figures from 3052 to 3056 represent a steam hammer. The head A is set at
an angle in the frame. The anvil or die C is oblong, as is also the
anvil die D. The object of this arrangement is to enable the workman,
after drawing out his work across the short way of the die, to turn it
and finish it lengthwise without being inconvenienced by the frame. By
this means skew and [T]-shaped dies can be dispensed with, and the full
service of the ram utilised. The latter is moved between the guides E E,
and held in place by the steel plate F, bolted through the frame B. The
valve G is a plain cylinder of cast iron, enlarged at each end to work
in the cylindrical seats H H, in which the ports I I are placed. Steam
is admitted through the valve J, and circulates round the valve G,
between the seats. The exhaust chamber K is below the cylinder, which
therefore drains condensed steam into it at each stroke through the
lower steam port. The exhaust above the piston passes down through the
interior of the valve, as shown by the arrow on the drawing. The valve
stem L is connected with the valves in the exhaust chamber. No stuffing
box is therefore required, there being only atmospheric pressure on each
side of it. This combination enables the valve to be so perfectly
balanced that it will drop by its own weight while under steam.
[Illustration: Fig. 3057.]
[Illustration: Fig. 3058.]
The automatic motion is obtained by an inclined plane M upon the ram A,
which actuates the rocker N, the outer arm of which is connected by a
link to the valve stem, and thus gives motion to the valve. The valve is
caused to rise in the up-stroke by means of the rocker N and its
connections, through the inclined plane. The steam is thus admitted to
the top, which drives down the piston, while the valve and its
connections follow by gravity, thus reducing considerably the friction
and wear upon the valves. In very quick work the fall of the valves may
be accelerated by the aid of a spring; or it may be retarded in heavy
work by friction springs, so as to obtain a heavier blow by a fuller
admission of steam. For general work, however, the arrangement shown is
perfectly effective, and as the rocker N is hung upon the adjustment
lever P, any required variation can be obtained by the movement of the
lever. Single blows can be struck with any degree of force, or a rapid
succession of constant or variable strokes may be given.
The anvil O rests upon a separate foundation, in order to reduce the
effect of concussion upon the frame. The drawing illustrates the
arrangement. The bed is long, extending beyond the hammer on each side
so as to give plenty of area, and the ends are left open for convenient
access in case the anvil should settle and require re-adjustment.
Other forms of hammers having the same general principles of
construction are as follows:--
Fig. 3057 represents a double frame hammer, the weight of the hammer
being supplemented by steam pressure. The spiral springs shown beneath
the cylinder are to prevent the hammer from striking the cylinder and
causing breakage from careless handling by the operator. The valve gear
is arranged for operation either automatically or by hand.
Fig. 3058 represents a double frame steam drop hammer for stamping work
out in formers or dies. The frames are bolted to the anvil base and the
ram for the top die is guided by vertical slides on the inner face of
the frame. Shoes are provided, whereby the wear of the ram and of the
slides may be taken up, and the upper die kept properly matched with the
lower one.
[Illustration: Fig. 3059.]
[Illustration: Fig. 3060.]
[Illustration: Fig. 3061.]
[Illustration: Fig. 3062.]
[Illustration: Fig. 3063.]
Fig. 3059 represents a double frame steam drop hammer for locomotive and
car axles and truck bars. The frame is spread at the base to admit wide
work, and the upper surface of the base is provided with rollers
supported by springs, these rollers supporting the work. The same may be
operated automatically or by hand.
The hydraulic forging press at the Edgemore Iron Works of Wilmington,
Delaware, consists of a piston operating in a cylinder, and having at
its lower end a head guided by four cylindrical columns that secure the
base plate, or anvil, as it may be termed, to the cylinder. To the
above-mentioned head is secured the upper die, the lower one being
secured to the base plate.
Fig. 3060 represents a female die, and Fig. 3061 plan of another female
die, and Fig. 3062 plan of male die used in connection with the press to
forge the eye bars for the Brooklyn Bridge, five pieces each an inch
thick being welded to the bar and pressed into shape at one operation.
[Illustration: Fig. 3064.]
[Illustration: Fig. 3065.]
[Illustration: Fig. 3066.]
Figures from 3063 to 3066 represent a locomotive driving wheel ready to
have its hub welded by hydraulic pressure. The spokes having been forged
are held together by a band or hoop, as shown. The thickness of the hub
or boss is made up by the rings or washers shown in the sectional view.
The dies under which the welding is done are shown in Figs. 3064 and
3066.
[Illustration: Fig. 3067.]
Thin forgings are often made by compression between two rollers, the
form of the surface of the rollers, or projections or depressions upon
the same, pressing the forging to shape.
Thus, in Fig. 3068 are shown a pair of rolls A B, P representing a piece
of work, and C D two cam pieces fast upon the roll surfaces; S is a
fixed stop.
Suppose the work to be pushed through the rolls and to rest against the
stop S, then when the cams C D meet it they will pull it through and
reduce its thickness by compression towards the workman. The rollers are
obviously rotated by gear wheels; but they are sometimes provided with a
certain amount of give or elasticity at their bearings, so that the
reduction of work diameter may be obtained by several passages of the
work through the rolls.
[Illustration: Fig. 3068.]
[Illustration: Fig. 3069.]
The shape of the cams, as C D, determines that of the work; thus in Fig.
3069 is shown a pair of rolls for forming knife blades, each cam having
sunk in it a die equal in depth to half the thickness of the knife.
If the work is very short in comparison with the circumference of the
rolls, two, three, or more cams may be arranged around the
circumference, making an equal number of forgings or impressions, as the
case may be, at each revolution of the rolls.
In Fig. 3067 is shown a nail-forging machine for producing, from strip
iron, nails similar to hand-made, at rates varying from two to three
hundred per minute, and lengths of from six to one inch, two nails being
completed at each revolution of the driving shaft of the machine. The
framing consists chiefly of a main casting, to which are fixed an upper
frame, carriages for the driving shaft, and other details. The principal
moving part is a heavy steel slide, deriving its motion from a crank pin
with adjustable throw; this slide carries two shears, two gripping dies,
and sundry indispensable appendages, to some of which it imparts motions
for guiding the nails between the stages of cutting off and finishing.
The successive operations by which each nail is perfected are as
follows:--
A piece of iron about six inches long, and of a width and thickness
respectively of the finished nail, is inserted at a red heat to the
feeder of the machine; a narrow strip is immediately cut off the lower
side of the heated iron, and by the motion of the steel slide is carried
to and pressed against a fixed die; while in this position another die
rises at right angles and presses the partially formed nail against
another fixed die. Thus the headless nail is firmly held on its four
sides, and while in this position a lever, moved by a cam, and carrying
a suitable tool, advances and forms the head, thus completing the nail.
The return motion of the steel slide releases the nail, leaving it free
to fall, but as its weight is not sufficient to insure this happening, a
"knocker off" is provided, which at the right moment forcibly ejects the
nail by way of a guiding shoot into a receptacle placed outside the
machine. It is to be noted that the tools for shearing and gripping, and
which have to be changed with each different size of nail, are made of a
special mixture of cast iron. They are thus easy of preparation and
renewal, while at the same time answering their intended purpose as well
as or better than the finest cast steel, at less than half the cost. The
whole of the machine is carried upon an open-top cast-iron water tank,
serving as a receptacle for the tongs and tools heated in withdrawing
the iron from the furnace.
[Illustration: Fig. 3070.]
Figs. 3070 and 3071 represent a machine for forging threads on rods and
screws. As forgings, the threads are beautifully clean, and for the
general work of coach screws much stronger than the cut threads. A
perspective view of the machine is given in Fig. 3070, and a vertical of
it shown in Fig. 3071. In the former figure, _a_ _b_ are the screw dies.
The rod or bolt to be threaded is placed upon the lower die _b_, and fed
forward while screwing it. The upper die is mounted on a slide _c_,
which is actuated in the downward direction by an eccentric _e_ on the
main shaft and the toggle-bar _d_, the upward motion being obtained by
an internal spiral spring _f_. The lower die _b_ is carried in a slide
_g_, and is adjusted at the proper distance from the upper die by means
of wedge _h_, and the inclined plate _i_, beneath the slide _g_. The
wedge _h_ is operated by a pedal _l_, and secured in its highest
position by a bolt _j_, received in a mortice made in the plate _i_, the
bolt being operated by a pedal _m_. In order to release the wedge and
return it to its lowest position, the bolt is raised by pressing down
the pedal _m_, whereby the wedge is free to be returned by the
counterweights _k_, in connection with pedal _l_; slide _g_, carrying
the lower die, then descends by its own gravity, and so separates the
two dies sufficiently to allow of the removal of the screw-bolt or rod
therefrom. To compensate for the wear of the dies, and admit of their
adjustment, another wedge _o_, with screw adjustment, is disposed below
the inclined plate _i_.
Fig. 3072 represents a lag screw forged by the machine.
[Illustration: Fig. 3071.]
[Illustration: Fig. 3072.]
[Illustration: Fig. 3073.]
Fig. 3073 represents a finishing machine for horseshoes. The bars of
iron are rolled with the creases (for the nail heads of the finished
shoe) in them. The blanks for the shoes are then cut to length and bent,
and the nail holes punched. The shoes then pass to a machine, Fig. 3073,
which consists of a frame A B, carrying the roll C, above the table D,
and a second roll, not shown in the cut, but being directly beneath C,
there being between these two rolls sufficient space to let the dies
(which press the shoes into shape) pass.
These dies rest upon the table D, and are carried around upon it in a
direction from left to right of the chain H, to the links of which the
dies are attached. This chain is operated by the vertical shaft J,
having a pulley for belt power at K.
As each die approaches the rollers, a shoe (cut to length, creased, and
punched as already described) is placed on it, and on reaching the rolls
the shoe is pressed into form on the die by the rolls, the bottom roll
serving as a rolling bed so as to reduce the friction that would be due
to a sliding motion on the bottom of the die. The top roll C, which
presses the shoe into the die is driven by power.
[Illustration: Fig. 3074.]
[Illustration: Fig. 3075.]
A plan view of the machine is shown in Fig. 3074, and a view showing the
shape of the dies is given in Fig. 3075.
[Illustration: Fig. 3076.]
The surface _h_ forms the frog. To give the required concavity to the
toe and sides of the shoe, the surface _i_ is made convex, and tapered
or inclined towards _h_. The tread _e_ is deepest at the heel on both
sides, and highest at the toe. It is obvious that by suitably shaping
the surfaces _h_, _i_, and _e_, any required form may be given to the
shoe. Fig. 3076 represents a shoe creased, punched, and bent ready to be
passed to the machine.
[Illustration: Fig. 3077.]
Fig. 3077 represents a circular saw for cutting off hot iron; A is the
frame of the machine, the arm B pivoted at C carrying the saw D; F is a
spring bolted to the frame and serving to hold the saw in the position
shown. The work E is gripped by the lever L, which is pushed over by
hand. The lever L is adjusted to suit different sizes of work by the
screw G, which raises or lowers the piece H, to which L is pivoted. The
saw is brought into contact with the work, and fed to it by applying the
foot to the lever or arm B at I, the screw J being made to contact with
the foot of the machine by the time the saw has passed through the work,
thus preventing the saw from moving too far forward after passing
through the work.
CHAPTER XXXIV.--WOOD-WORKING.
PATTERN-MAKING.--Of the different kinds of wood serviceable to the
pattern-maker, pine is, for many reasons, usually employed. It should be
of the best quality, straight-grained, and free from knots; it is then
easy to work in any direction, possessing at the same time sufficient
strength for all but the most delicate kinds of work, and having besides
the quality of cheapness to recommend it. Care taken in its selection at
the lumber-yard will be amply repaid in the workshop. When it is
straight-grained, the marks left by the saw will show an even roughness
throughout the whole length of the plank; and the rougher the
appearance, the softer the plank. That which is sawn comparatively
smooth will be found hard and troublesome to work. If the plank has an
uneven appearance--that is to say, if it is rough in some parts and
smooth in others--the grain is crooked. Such timber is known to the
trade as cat-faced. In planing it the grain tears up, and a nice smooth
surface cannot be obtained. Before purchasing timber, it is well to note
what convenience the yard possesses for storing. Lumber on the pile,
though it be out in all weathers, does not deteriorate, but becomes
seasoned; nevertheless its value is much increased if it has an
extemporised roof to protect it from the sun and rain. But as it is not
convenient to visit the pile for every customer, quantities are usually
taken down to await sale, and for such a shelter must be provided,
otherwise it will be impossible to insure that the lumber is dry, sound,
and fit for pattern-making. It is obvious that the foregoing remarks on
the storage of lumber apply to all woods.
The superiority of pine for pattern-making is not, however, maintained
when we come to fine delicate patterns or patterns requiring great
durability. When patterns for fine work, from which a great many
castings are to be made, are required, a fine pattern wherefrom to cast
an iron pattern is improvised, because, if pine were employed, it would
not only become rapidly worn out, but would soon warp and become
useless. It is true that a pine pattern will straighten more easily than
one made of a hard wood; but its sphere of usefulness in fine patterns
is, for the above reasons, somewhat limited. Iron patterns are very
desirable on account of their durability, and because they leave the
sand easily and cleanly, and because they not only do not warp but are
also less liable than wooden ones to give way to the sand, while the
latter is being rammed around them by the moulder, a defect that is
often experienced with light patterns, especially if they are made of
pine. Iron patterns, however, are expensive things to make, and
therefore it is that mahogany is extensively employed for fine or
durable pattern work. Other woods are sometimes employed, because they
stand the rough usage of the moulding shop better and retain the sharp
corners, which, if pine be used, in time become rounded impairing the
appearance of the casting. Mahogany is not liable to warp, nor subject
to decay; and it is exceedingly durable, and is for these reasons the
most desirable of all woods employed in pattern-making, providing that
first cost is not a primary consideration. There are various kinds of
this beautiful wood: that known as South American mahogany is chiefly
used for patterns.
Next to mahogany we may rank cherry, which is a very durable wood, but
more liable to twist or warp than mahogany, and it is a little more
harsh to the tool edge. If, however, it is stored in the workshop for a
length of time before being used, reliable patterns may be made from it.
In addition to these woods, walnut, beech, and teak are sometimes
employed in pattern-making.
The one property in all timber to be specially guarded against is its
tendency to warp, bend, expand, and contract, according to the amount of
humidity in the atmosphere. Under ordinary conditions, we shall be right
in supposing a moisture to be constantly given off from all the exposed
surfaces of timber; therefore planks stored in the shop should be placed
in a rack so contrived that they do not touch one another, so that the
air may circulate between the planks, and dry all surfaces as nearly
alike as possible. If a plank newly planed be lying on the bench on its
flat side, the moisture will be given off freely from the upper surface,
but will, on the under surface, be confined between the bench and the
plank: the result being that a plank, planed straight, and left lying as
described, will be found, even in an hour, to be curved, from the
contraction of the upper surface due to its extra exposure; therefore it
is obvious that lumber newly planed should be stored on end or placed on
edge. Lumber expands and contracts with considerable force across the
grain; hence if a piece, even of a dry plank, be rigidly held and
confined at the edges, it will shrink and break in two, often with a
loud report. There is no appreciable alteration lengthwise in timber
from the above causes; and if two pieces be glued together so that the
grain of one crosses that of the other, they can never safely be relied
upon to hold. Hence they had better be screwed so that there will be a
little liberty for the operation or play of the above forces, while the
screws retain their hold. The shrinkage, expansion, and warping of
timber may perhaps be better understood by the following considerations:
The pores of wood run lengthwise, or with its grain, and hence the
moisture contained in these passes off more readily endwise or from any
surface on which the pores terminate.
THE SHRINKAGE OF TIMBER.--The direction in which timber shrinks in
seasoning or drying is shown in the following figures, which are
extracted from a lecture delivered by Dr. Anderson before the Society of
Arts in London, England. The shrinkage of timber lengthwise of the grain
is very slight, its shrinkage in a direction across or at a right angle
to the length of the grain being much greater and depending upon the
part of the log from which it is cut.
[Illustration: Fig. 2706.]
The shrinkage is greater on the outside than near the heart of the tree;
thus if a log be cut into four quarters it will shrink as in Fig. 2706,
from the full block outside to the inside or white outline; or if we cut
out a square as in figure, one corner extending to the heart, it will
shrink to the form shown in the figure. If we sever the log by the four
parallel saw cuts it will shrink as shown by the black outline, the
shrinkage of the middle piece being more clearly shown in Fig. 2707.
[Illustration: Fig. 2707.]
[Illustration: Fig. 2708.]
It is evident, therefore, that to obtain a uniform degree of shrinkage
throughout the length of a piece of timber, it should be sawn as near as
possible parallel with the grain of the log. Thus in Figs. 2708 and 2709
we have a side and an end view of a log, the saw cuts at A being from
logs that have been squared, the upper slab B being waste material, and
the planks being parallel to the squared sides of the log.
[Illustration: Fig. 2709.]
The lines from A to C on the lower half of Fig. 2709 represent planks
that are what is termed flitched, the saw cuts following the taper of
the tree, and it is plain that the shrinkage would be more uniform; thus
the outside plank is near the bark from end to end, while at the top of
the figure the outside plank is near the outside at the small end only
of the log, and would therefore shrink most at the right hand end.
Furthermore as the planks at A cross the grain of the log at its large
end, they are therefore weaker and more liable to split at that end.
BENDING TIMBER.--By bending a piece of timber to bring it as near as
possible the required shape the strength of the work is increased,
because the grain of the wood runs parallel with the shape of the work,
and, furthermore, the cutting tools act on this account to better
advantage. In bending a piece of timber it is obvious that either the
convex side must stretch, or the concave one compress, or if no
extraneous pressure is brought to bear upon the piece, both of these
actions may occur, and as the side of the piece that was nearest to the
heart of the tree is the hardest and strongest, it will stretch less if
made the convex side, or compress less if made the concave side of the
timber, but the bent piece will maintain its shape better if the heart
is the convex or outside of the curve.
The modern method of bending wood is to fasten on the outside, or convex
side of the piece, a strap that will prevent it from stretching. And it
is found that wood thus bent is stronger, stiffer, and heavier than
before it was bent, because the fibres become interwoven, and it is
found that the wood is harder to split than before.
[Illustration: Fig. 2710.]
[Illustration: Fig. 2711.]
[Illustration: Fig. 2712.]
Suppose we require to bend a piece to a half circle, and after it has
been boiled, steamed, or heated with a dry heat it is placed in an iron
strap, such as shown in Fig. 2710, having an eye at each end in which a
hook may be inserted to hold the piece in shape (after it is bent) until
it is dry again. The piece with this strap on its outside or uppermost
surface is laid on the _former_ or forming piece shown in Fig. 2711,
which has a projection at A, fitting into the recess A of the bending
block in Fig. 2712. On the outside of the piece is then placed the
strap, shown in Fig. 2713, its blocks of wood fitting to the ends of the
piece to be bent.
The winch of the bending block is provided with a rope, whose ends have
two hooks which are engaged in the eyes of the straps, shown in Fig.
2714, and by operating the winch the piece is bent to shape, as shown in
Fig. 2714. While in this position a hook is placed through the eyes of
the band that is around the bent piece of work, so that when removed
from the forming block or stand it appears as in Fig. 2715.
[Illustration: Fig. 2713.]
[Illustration: Fig. 2714.]
[Illustration: Fig. 2715.]
[Illustration: Fig. 2716.]
[Illustration: Fig. 2717.]
[Illustration: Fig. 2718.]
When, however, the piece requires to be bent to more than one sweep or
bend, the process requires to be changed somewhat. Thus, suppose the
middle is to be bent circular and the two ends left straight, and the
strap on the piece to be bent is provided with a piece, such as in Fig.
2716, the ends B engaging in eyes in the strap, and the screw A abutting
against the end of the piece to bind the strap firmly upon the ends, as
in Fig. 2717, in which the piece is shown within the strap. After it has
been bent to the former it is held there by straps and wedges, as shown
in Fig. 2718.
[Illustration: Fig. 2719.]
The next operation is to lock the curve, as shown in Fig. 2719, between
an inside and outside former by means of straps A A and wedges C, when
the ends D of the piece may be bent up to the dotted lines and locked to
the ends of the top former by straps and wedges.
The length of time a piece should be boiled or steamed for the bending
process depends upon the size of the piece and the kind of wood, hard
wood requiring longer boiling or steaming. A piece of ash, say 2 by 4
inches in cross section, would require about six hours' steaming with a
low pressure of moist or wet steam, but it would not suffer damage if it
were steamed for a day. Pieces not over half an inch thick may be bent
after steaming them about half an hour.
If the wood is steamed too much it loses its elasticity and will pucker
on the inside surface of the bend when in the former or bending block.
The period during which the piece should be held to its bent shape
before being released varies from twelve hours for thin pieces to
twenty-four hours for thick ones, and it is found that pieces which have
been bent in a strap so as to prevent the outside from stretching, will,
in drying, increase their bend or curvature, while those not confined at
their ends straighten out.
[Illustration: Fig. 2720.]
[Illustration: Fig. 2721.]
[Illustration: Fig. 2722.]
The cracks that are found in timber are termed _shakes_; thus in Fig.
2720 the black lines represent what are called heart shakes, while those
in Fig. 2721, being wider, are termed star shakes. When the shakes are
circular, as in Fig. 2722, they are called cup shakes.
Many of the tools used by the pattern-maker have been described in
connection with hand turning, hand boring tools, lathe tools, &c., and
therefore need no further reference.
PLANES.--For roughing out the work the jack plane is employed, varying
in size from 14 inches long with a cutter knife or blade 2 inches wide,
to 27 long with a blade 2-1/4 inches wide, and as its purpose is to make
a flat surface, it is preferable that it be as long as the work will
conveniently permit. The jack plane is followed by the fore plane, the
truing, or trying plane, which varies in size from about 18 inches long
with a blade 2-1/8 inches wide, to 20 inches long with a cutter or blade
2-3/8 inches wide. When the fore plane is made longer, as for planing
long joints, it is termed a jointer plane, the length being as much as
30 inches and the blade 2-5/8 inches wide.
The smoothing plane varies from about 5 inches long with a blade 1-1/2
inches wide, to 10 inches long with a blade 2-3/8 inches wide. Smoothing
planes are, as the name implies, used to simply smoothen the work
surface after it has been trued.
The angle of the plane blade to the sole of the plane is for ordinarily
soft wood 45°, but 50° or 55° may be used for very hard woods.
[Illustration: Fig. 2723.]
[Illustration: Fig. 2724.]
To break the shaving the blade is attached to what is termed a cover,
which is shown in Fig. 2723, B representing the blade and A the cover.
The cover is curved to insure that it shall bed against the blade at its
very end, and, therefore, as near to the cutting edge as a maximum
distance 1/16 inch for rough and 1/32 inch for finishing cuts. The blade
of a jack plane is most efficient when it is ground well away towards
the corners, as at A B in Fig. 2724, thus producing an edge curved in
its length.
When the blade is in position in the stock for cutting off the maximum
of stuff, its blade should project nearly 1/16 through the sole of the
stock, while the corners A B are about level with the face of the stock.
The bevelled face should stand at about an angle of 25° to the flat
face. In grinding it care should be taken to grind it as level as
possible, rounding off the corners as shown above. The grindstone should
be kept true and liberally supplied with water; the straight face should
not be ground away, nor indeed touched upon the stone, except to remove
the burr which will sometimes turn over. The pressure with which the
blade is held against the grindstone should be slight at and toward the
finishing part of the grinding process, so as not to leave a long ragged
burr on the end of the blade, as is sure to be the case if much pressure
is applied, and it will occur to a slight extent even with the greatest
of care. The blade should not be held still upon the grindstone, no
matter how true, flat, or smooth the latter may be; but it should be
moved back and forth across the width of the stone, which will not only
grind the blade bevel even and level, but will also tend to keep the
grindstone in good order.
In oilstoning a plane blade, the straight face should be held quite
level with the face of the oilstone, so that the cutting edge may not be
bevelled off. Not much application to the oilstone is necessary to the
straight face, because that face is not ground upon the grindstone, and
it only requires to have the wire edge or burr removed, leaving an
oilstone polish all along the cutting edge. The oilstoning should be
performed alternately on the flat and bevelled faces, the blade being
pressed very lightly on the oilstone toward the last part of the
operation, so as to leave as fine a wire edge as possible. The wire is
the edge or burr which bends or turns over at the extreme edge of the
tool, in consequence of that extreme edge giving way to the pressure of
the abrading tool, be it a grindstone or an oilstone. This wire edge is
reduced to a minimum by the oilstone, and is then so fine that it is
practically of but little account; to remove it, however, the plane
blade or iron may be buffed backwards and forwards on the palm of the
hand.
The blade being sharpened, we may screw the cover on, adjusting it so
that its edge stands a shade below the corners of the iron, and then
screwing it tight; the blade or iron and the cover must now be placed in
the mouth of the plane stock, and adjusted in the following manner:--
The plane iron should be passed through the mouth of the stock until as
much in depth of it is seen to protrude from the bottom face of the
stock as is equal to the thickness of shaving it is intended to cut: to
estimate which, place the back end of the plane upon the bench, holding
the stock in the left hand with the thumb in the plane mouth, so as to
retain the iron and wedge in position, the wedge being turned towards
the workman. A glance down the face of the stock will be sufficient to
inform the operator how much or how little the cutting edge of the iron
protrudes from the face of the plane stock, and hence how thick his
shaving will be. When the distance is adjusted as nearly as possible,
the wedge may then be tightened by a few light hammer blows. If, after
tightening the wedge, the blade is found to protrude too much, a light
blow on the fore end on the top face of the plane will cause it to
retire; while a similar blow upon the back end will cause it to advance.
In either case the wedge should be tightened by a light blow after it is
finally adjusted.
In using a jack plane we commence each stroke by exerting a pressure
mostly on the fore part of the plane, commencing at the end and towards
the edge of the board, and taking off a shaving as long as the arms can
conveniently reach. If the board is longer than can be reached without
moving, we pass across the board, planing it all across at one standing;
then we step sufficiently forward, and carry the planing forward,
repeating this until the jack planing is completed. To try the level of
the board, the edge or corner of the plane may be employed; and if the
plane is moved back and forth on the corner or edge, it will indent and
so point out the high places.
The fore plane (or truing plane, as it is sometimes called) is made
large, so as to cover more surface, and therefore to cut more truly. It
is ground and set in the same manner as the jack plane, with the
exception that the corners of the iron or blade, for about one-eighth
inch only, should be ground to a very little below the level of the rest
of the cutting edge, the latter being made perfectly straight (or as
near so as practically attainable) and square with the edge of the iron.
If the end edge of the cover is made square with the side edge, and the
iron is ground with the cover on, the latter will form a guide whereby
to grind the iron edge true and square; but in such case the cover
should be set back so that there will be no danger of the grindstone
touching it. The oilstoning should be performed in the manner described
for the jack plane, bearing in mind that the object to be aimed at is to
be able to take as broad and fine a shaving as possible without the
corners of the plane iron digging into the work. The plane iron should
be so set that its cutting edge can only just be seen projecting evenly
through the stock. In using the fore or truing plane, it is usual, on
the back stroke, to twist the body of the plane so that it will slide
along the board on its edge, there being no contact between the cutting
edge of the plane iron and the face of the board, which is done to
preserve the cutting edge of the plane iron from abrasion by the wood:
as it is obvious that such abrasion would be much more destructive to
the edge than the cutting duty performed during the front stroke would
be, because the strain during the latter tends mainly to compress the
metal, but, during the former, the whole action tends to abrade the
cutting edge. The face of the fore plane must be kept perfectly flat on
the underside, which should be square with the sides of the plane. If
the under side be hollow, the plane iron edge will have to protrude
farther through the plane face to compensate for the hollowness of the
latter; and in that case it will be impossible to take fine shavings off
thin stuff, because the blade or iron will protrude too much, and as a
consequence there will be an unnecessary amount of labor incurred in
setting and resetting the plane iron. The reason that the under surface
should be square, that is to say, at a right angle to the sides of the
body of the plane, is because the plane is sometimes used on its side on
a shooting board.
When the under surface of the plane is worn out of true, let the iron be
wedged in the plane mouth, but let the cutting edge of the iron be well
below the surface of the plane stock. Then, with another fore plane,
freshly sharpened and set very fine, true up the surface, and be sure
the surface does not wind, which may be ascertained by the application
of a pair of winding strips, the manner of applying which will be
explained hereafter. If the mouth of a fore plane wears too wide, as it
is apt in time to do, short little shavings, tightly curled up, will
fall half in and half out of the mouth, and prevent the iron from
cutting, and will cause it to leave scores in the work, entailing a
great loss of time in removing them at every few strokes. The smoothing
plane is used for smoothing rather than truing work, and is made shorter
than the truing plane so as to be handier in using. It is sometimes
impracticable to make a surface as smooth as desirable with a truing
plane, because of the direction of the grain of the wood.
[Illustration: Fig. 2725.]
Fig. 2725 represents an ordinary compass plane, which is a necessary and
very useful tool for planing the surfaces of hollow sweeps. This tool is
sometimes made adjustable by means of a piece dovetailed in the front
end of the plane, which, by being lowered, alters the sweep and finally
converts it from a convex to a concave.
[Illustration: Fig. 2726.]
In Fig. 2726 is shown a much superior form of circular or compass plane.
Its sole consists of a flexible steel blade, whose ends are attached to
levers that are connected together by toothed segments. By means of the
large hand-screw the levers are operated, causing the sole to bend to
the required curvature, and by reason of the toothed segments the levers
move equally, and therefore give the sole a uniform curve throughout its
length.
[Illustration: Fig. 2727.]
[Illustration: Fig. 2728.]
Planes are also made with the sole and the cutting edge of the blade
made to conform to the shape of the work. Thus Fig. 2727 represents a
rabbeting plane, and Fig. 2728 a side rabbet plane. The latter is,
however, very seldom used, but is especially useful in planing hard wood
cogs fitted to iron wheels, or the teeth of wheel patterns or other
similar work. For ordinary use, it is sufficient to have two, a 3/4 and
a 1-1/4 inch, and two or three having a flat sole for flat bottom
grooves.
What is known as a core box plane has its sole at an angle of 90°, or a
right angle; the principle of its action is that in a semicircle the
angle is that of 90°.
[Illustration: Fig. 2729.]
[Illustration: Fig. 2730.]
In Fig. 2729, for example, it is seen that if a right angle be laid in a
semicircle so that its sides meet the corners of the same when revolved,
its corner will describe a true circle; hence at each plane stroke the
plane may be slightly revolved, to put on the cut, which must be very
light, as the core box plane is only suitable for finishing purposes.
For planing across the end grain of wood, what are termed block planes
are used, the angle of the blade to the sole being from 65 to 85
degrees, as shown in Fig. 2730, which represents the Stanley iron frame
block plane. In block planes the bevel that is ground to sharpen the
blade is placed in front and therefore meets the shaving instead of the
flat face as in other planes.
[Illustration: Fig. 2731.]
[Illustration: Fig. 2732.]
Fig. 2731 represents the Stanley bull-nose rabbet plane for getting
close into corners, and Fig. 2732, a block plane, in which the blade may
be set in the usual position or at one end of the stock as denoted by
the dotted lines.
[Illustration: Fig. 2733.]
[Illustration: Fig. 2734.]
For fine work planes having an iron body are much preferable to the
wooden ones, and in the improved form of planes there is provided a
screw mechanism, whereby the blade may be set much more accurately and
easily than by hammer blows, such as are necessary with ordinary
wedge-fastened blades. Thus Fig. 2733 represents Bailey's patent
adjustable planes, the handles only being of wood. The blade is secured
by a simple lever movement, and is set by means of the thumb screw shown
beneath and behind the blade. The metal stock possesses several
advantages, such as that the sole keeps true, the mouth does not wear
too large, as is the case with wooden planes. Planes are also made
having a wooden body and an iron top, the latter containing the
mechanism for locking the blade and setting it quickly. Fig. 2734
represents one of these planes.
[Illustration: Fig. 2735.]
Figs. 2735 to 2744 represent a combination plane. Fig. 2735 is a side,
and Fig. 2736 a top view of the tool as a whole.
Pieces A and B form the body of the plane, between which the bits or all
the tools are carried except the slitting knife, which is carried by A
alone.
In the figures T is a beading tool shown in position, having a bearing
or seat in both A and B so as to support it on both sides, and being
locked in position by the thumb-screw C. At G is a depth gauge which is
moved over into the hole at D, when that position is most suitable for
the kind of work in hand. Piece B is made adjustable in its distance
from A so as to accommodate different widths of bits by sliding it on
the arms M, securing it in its adjusted position by the set-screws S.
Similarly the fence F slides on arms M, and is secured in its adjusted
position by the set-screws H, thus enabling it to regulate the distance
from the edge of the board at which the bits shall operate, and also
guiding the bits true to the edge of the board or work. F is provided
with an upper pair Q, and a lower pair R of holes (as seen in Fig. 2737)
so that it may be set on the arms M at two different heights as may best
suit the nature of the work. In Fig. 2736 it is shown with arms M
passing through the lower pair of holes. The points of the set-screws H
meet the bores of both pairs of holes and therefore lock F to the arms,
whether the upper or lower holes are upon the arms. For rabbeting and
fillister work the upper holes Q are used, while using ploughs the lower
ones are brought into requisition.
[Illustration: Fig. 2736.]
[Illustration: Fig. 2737.]
[Illustration: Fig. 2738.]
[Illustration: Fig. 2739.]
[Illustration: Fig. 2740.]
At W, Fig. 2735, is a spur for cutting the end grain of the wood in
advance of the bit, as is necessary in dado and other across grain work,
the construction of the spur is seen more clearly in Fig. 2738. The
pieces A and B are provided with a recess having four arms or branches,
while the spur itself has but three, so that the spur may be set as in
Fig. 2735 and be out of action, or its screw being loosened it may be
given a half-turn, so that one of its arms will come below B as at X in
Fig. 2738. The cutting edges of the spur come exactly flush with the
outside faces of A and B, and the bits are so held in their seats that
their edges also come flush with these outside faces, which therefore
act as guide to the bit; thus Fig. 2739, shows a beading bit in
position, and Fig. 2740 a section of work finished, A and B being in
section. Fig. 2741 shows a plough in position on the work, A and B being
shown in section. It is seen that their inner edges being bevelled, will
in using a beading tool, act as a gauge regulating the thickness of
shaving taken at each plane stroke, which will equal the depth to which
the bit edge projects beyond the bevels of A and B. Similarly in
grooving or ploughing the amount to which the bits project below the
lowest edges of A and B regulates the thickness of the shaving, and as A
and B follow the bit into the work, the blade being once set requires no
further attention, the depth gauge regulating the total depth of tool
action.
[Illustration: Fig. 2741.]
[Illustration: Fig. 2742.]
[Illustration: Fig. 2743.]
[Illustration: Fig. 2744.]
This principle of the side pieces entering the work with the bits and
being adjustable to suit various widths of bits, gives to the tool a
wide range of capacity. Fig. 2742 represents the tool arranged for
slitting thin stuff into parallel slips, the piece B being removed. The
depth gauge is not shown in figure, because it would hide the slitting
knife from view, but it is obvious that it would rest on the surface of
the work and thus steady the plane. Fig. 2743 is an example of a number
of operations performed by this one tool. For tonguing, the bit shown in
Fig. 2744 is employed, the depth gauge _g_ being adjustable in the
groove by means of the slot shown.
CHISELS.--The principal kinds of chisels are the paring chisel which is
used entirely by hand, and the firmer chisel which is used with the
mallet. The difference between the two lies in the shapes of their
handles, and that the paring chisel is longest. A paring chisel worn to
half its original length will serve for a firmer chisel, because when so
worn it is long enough for the duty. A chisel should not, however, be
used alternately as a paring and a firmer chisel, because the paring
chisel requires to be kept in much better condition than the firmer
chisel does. Mortice chisels are made thicker than either the paring or
the firmer because of their being longer and requiring rougher usage. It
is necessary to have several sizes of chisels, varying in width from an
eighth of an inch to one and a half inches.
[Illustration: Fig. 2745.]
[Illustration: Fig. 2745_a_.]
[Illustration: Fig. 2746.]
Fig. 2745 represents the form of handle for a paring chisel, its total
length being 6 inches, and from A to B being 1-1/2 inches. The diameter
at C is 1-1/2 inches, the hollow below D of 3/8 of an inch radius, the
diameter at D 1 inch, and the length from B to E 1-1/2 inches. This form
affords a firm grip to the hand, the end E being applied to the
operator's shoulder. The shape of handle for a firmer chisel is shown in
Fig. 2746.
Chisels require great care both in grinding and oilstoning them, being
held very lightly upon the grindstone when finishing the grinding so as
to avoid as far as possible the formation of a long feather edge. The
flat face of the chisel should never be ground, as that would make it
rounding in its length, hence there would be nothing to guide it in
cutting straight and the value of the tool would be almost destroyed.
In oilstoning the chisel, great care is necessary in order to avoid
forming a second facet at a different angle to that at which it was
ground, because such a facet is too narrow to form any guide whereby to
move the chisel in a straight line, and the consequence is that the edge
is oilstoned rounding and cannot do good service. The whole length of
the ground facet or bevel should rest on the oilstone, but the pressure
should be directed mainly to the cutting end so that at that edge the
oilstone will entirely remove the grinding marks, which will, however,
remain at the back. If there is at hand a grindstone of sufficiently
small diameter, the chisel may be made hollow on the bevel, as shown in
Fig. 2745_a_, so that when laid on the oilstone the bevel will touch at
the back and at the end only, and this will enable the chisel to be
pressed evenly down on the stone, thus producing a very even and flat
edge, while leaving but a small area to be oilstoned.
The motion of the hands should not for the oilstoning be simply back and
forth, parallel with the oilstone length, but partly diagonal, which
will assist in keeping the chisel level. The back of the chisel should
be laid flat upon the oilstone and moved diagonally, under a light
pressure, which will remove the wire edge, which may be further removed
by lapping the chisel on the operator's hand.
[Illustration: Fig. 2747.]
Chisels for turning work in the lathe are best if made short, and to
enable the cutting edge to get up into a corner, the chisel is sometimes
given two cutting edges, as at A, in Fig. 2747, the edges forming an
angle, one to the other, of less than 90°. For finishing curves in the
lathe the chisel shown at B in the figure is employed, or for deeper
work, as in the bores of holes, handles are dispensed with, chisels
being formed as at C and D in the figure.
Gouges, like chisels, are made "firmer and paring," the distinction
being precisely the same as in the case of chisels.
When the bevel is on the outside or convex side of the gouge it is
termed an outside, while when the bevel is on the inside or concave side
it is termed an inside gouge.
[Illustration: Fig. 2748.]
Fig. 2748 represents an outside firmer gouge. The inside gouge may be
ground a little keener than the chisel, and requires great care in
grinding, because it must be held on the corner of the grindstone, which
is rarely of the desired curve. In oilstoning the concave side of a
gouge an oilstone slip is employed, the gouge being held in the left
hand and the slip in the right, the latter being supplied with clean
oil.
The convex side of an outside gouge should be made level on the face of
the oilstone, and while the gouge is moved to and fro its handle must be
revolved so as to bring all parts of the curve in contact with the
oilstone. The small amount of surface on the gouge in contact with the
grindstone makes it very liable to have a long feather edge, hence it
must be very lightly pressed to the stone, and the same remark applies
to the oilstoning in order to reduce the wire edge.
[Illustration: Fig. 2749.]
Fig. 2749 represents a gouge for lathe work, its handle being made long
enough to be held in both hands and used as described with reference to
turning with hand tools.
Another tool, very useful to the pattern-maker, is the skew chisel,
which is also described in connection with hand turning.
SAWS.--There are two principal kinds of saws, the rip saw for cutting
lengthwise of the grain of the wood, and the cross-cut saw for cutting
across the grain. In shaping these saws the end to be obtained is to
enable them to sever the fibre of the wood in advance of the effort to
remove it from the main body.
[Illustration: Fig. 2750.]
[Illustration: _VOL. II._ =THE ACTION OF SAW TEETH.= _PLATE XIII._
Fig. 2751.
Fig. 2752.
Fig. 2753.
Fig. 2754.
Fig. 2755.
Fig. 2756.]
In Fig. 2750, for example, the grain of the wood runs lengthwise and the
throat, or front face of each tooth, is hooking or hooked, so that the
cutting edge will cut through the fibres at their ends before it is
attempted to remove them from the main body of the wood. Suppose, for
example, that the saw shown in Fig. 2750 was put into a piece of timber
and a tooth pressed hard enough on the wood to leave a mark, and this
mark would appear as in Fig. 2751 at E, extending across a width equal
to the full width of the saw tooth. It would do this because the front
face or throat B and the back face A are both at a right angle to the
saw length as is denoted by the dotted lines. As the grain is supposed
in Fig. 2751 to run lengthways of the timber, clearly the fibre between
the indentation E and the saw slot is severed and would be removed as
the tooth passed farther down through the wood, the action of first
severing the fibre at its end and then removing it being carried on by
each tooth.
In Fig. 2752 is shown a cross-cut saw in action upon a piece of wood in
which the grain or fibre runs across the timber, and in this case the
teeth require to be shaped to cut on each side of the saw instead of
directly in front of it, because in that way only can the ends of the
wood fibre be severed before it is dislodged from its place.
To enable the cross-cut saw to accomplish this, one tooth cuts on one
side of the saw slot and the next tooth on the other, as at A and B in
Fig. 2751, from which it will be seen that as the grain runs lengthways
of the timber, the fibres between the lines A and B will be severed at
their ends by the extreme edges of the teeth before the thicker part of
the tooth reaches them to remove them.
The necessity for this action may be plainly perceived if we apply the
rip saw for cross-cutting and the cross-cut saw for ripping. Suppose,
for example, we place the saw shown in Fig. 2750 to cut across the grain
of the piece of timber, and as its tooth met the wood it would indent it
as at G, Fig. 2751, and as this is in line with the grain, the tooth
would wedge in the piece and the piece cut could not be dislodged
without first tearing the fibres apart at each end. Or suppose we take
the cross-cut saw and apply it for ripping (as cutting lengthways of the
grain is called) and if we indented the surface with a single tooth it
would leave a mark as at F, Fig. 2751, which is lengthways of the fibre,
so that the tooth would here again wedge between the fibres and not cut
them. The next tooth would make a mark parallel to F, but on the other
side of the saw slot or kerf as it is called, still leaving the fibre
unsevered at its ends where it should be severed first.
In order that the saw may not rub against the sides of the slot or kerf,
and thus be hard to move or drive, it is necessary that the kerf be
wider than the thickness of the saw blade, and to accomplish this the
teeth are bent sideways, each alternate tooth being bent in an opposite
direction, as shown in the front view of the teeth in Fig. 2753. This
bending is called the set of the saw, and should be sufficient to make
the kerf about two-thirds wider than the thickness of the saw blade.
While preserving the feature of severing the fibre before attempting to
dislodge it from its place, we may at the same time give the teeth of
rip saws more or less sharpness by fleaming their faces.
In Fig. 2754, for example, the throat face is filed square across or at
a right angle to the length of the saw, but the back face A is at an
angle, making the points of the teeth sharper, and therefore enabling
them to cut more freely. The result of this fleam would be that the
tooth, instead of cutting equal and level all the way across as in Fig.
2751 at E, would cut at the corner first and only across its full width
as it entered deeper into the wood; we have, in fact, placed the leading
part of the cutting edge more at the extreme point and less in front of
the tooth.
In Fig. 2755 the throat or front face of the saw is given fleam, as
shown by the line B, which is not at a right angle to the saw length,
and as a result the cutting edge is carried still more advanced at the
point and more towards the side of the tooth and we have, therefore, to
a certain extent, qualified it as a cross-cut saw.
We might give the face B so much angle as to carry the leading part of
the cutting edge to the side of the saw, thus giving it the
characteristics of a cross cut.
In Fig. 2756, both the throat face B and the back face A are given
fleam, making the points extremely sharp, and showing the leading part
of the cutting edge towards the side, the corner leading still more.
[Illustration: Fig. 2757.]
In Fig. 2757 we have two saws R and S, the latter having fleam on the
front and the former on the back face of the tooth, the amount or degree
of fleam being equal.
[Illustration: Fig. 2758.]
In Fig. 2758 we have indentations of their teeth. The teeth of S would
leave a mark as at E F, and R would leave a mark as at G H. The side cut
F being more than the side cut G, and the front cut E being at a less
angle to F than the front cut H to G, it follows that the saw S would be
the best, provided the grain of the wood ran diagonally as shown, not
only because it has more side and less front cut, but also because its
cutting edge is keener on the side, as is seen on comparing the lines P
and A in Fig. 2757.
[Illustration: Fig. 2759.]
If we give fleam to both faces we alter the indentation, as denoted in
Fig. 2759, in which E F represents the line of tooth cut when one face
has fleam, and G H the line of tooth cut when both faces are fleamed,
the shape of the actual saw cut being shown at J.
Obviously the fleam makes the points weak, but this in coarse saws may
be partially remedied by shaping the teeth as in Fig. 2760. Fleam on the
front face or throat of the tooth has the effect of preserving its set,
the pressure of the cut being as shown by the arrows in Fig. 2753.
It is evident that the finer the point of the tooth the sooner it will
become dulled, and that the harder the timber the more quickly the tooth
will become dull. So soon as this occurs the teeth refuse to cut freely,
and the extra pressure on them acts to spring them upward and to take
off the set. It is obvious that for soft wood the teeth may be given
fleam on both faces, and that the front face should have some fleam,
even for the hardest of wood, whether the back face has fleam or not.
Also, that in proportion as the grain of the wood runs more across the
saw kerf than in line with it the teeth should be filed to cut on the
side, and the hook of the front face may be lessened, while
_vice-versâ_, in proportion as the grain of the wood runs parallel with
the kerf, the tooth may have hook and fleam on the back face with a
slight fleam on the front one.
[Illustration: Fig. 2760.]
[Illustration: Fig. 2761.]
GAUGES.--Of gauges for marking on the work lines parallel to its edges
there are several kinds, a common form being represented in Fig. 2761,
in which the block that slides against the edge of the work is secured
by a set-screw.
A better method, however, is to use a key set at a right angle to the
stem, so that the head may be tightened or loosened by striking it, as
if it were a hammer, against anything that may happen to lie on the
bench, hence the gauge may be set and adjusted with one hand while the
other is holding the work, as is often necessary when marking small
work. The marking point should be a piece of steel wire fitted tightly
in the stem, the protruding part being ground or tiled to a wedge, with
the two facets slightly rounding, and whose broad faces stand at a right
angle to the stem of the gauge, the point or edge only projecting
sufficiently to produce a line clear enough to work by; otherwise it
will not be suitable for accurate work.
[Illustration: Fig. 2762.]
The mortice gauge, Fig. 2762, is similar to the above as regards the
stem and sliding piece, but it is provided with two marking points,
their distance apart being adjustable. The head screw works in brass
nuts.
[Illustration: Fig. 2763.]
For lines that are to be marked more than about ten inches from the edge
of the work a broader base is necessary to the head or block, which may
be shaped as shown in Fig. 2763.
[Illustration: Fig. 2764.]
The lines drawn upon pattern work require to be very fine, and for this
purpose the cutting scriber, Fig. 2764, is employed. The end A is
bevelled off on both sides like a skew chisel. The end B is ground to a
fine point and both ends are oilstoned. The point end is for drawing
lines with the grain, and the knife end for lines across the grain of
the wood. The wooden handle is to afford a firm grip.
[Illustration: Fig. 2765.]
In Fig. 2765 we have the cutting gauge, in which a steel cutter takes
the place of the marking point, being wedged in position. It is employed
to cut thin strips of wood, that is to say, of thicknesses up to about a
quarter of an inch. The cutter point should be tempered to a dark straw
color.
The principal forms of joints employed by the pattern-maker are as
follows:--
[Illustration: Fig. 2766.]
Fig. 2766 represents the mortice and tenon, the thickness of the tenon
being one-third that at C, which leaves a thickness at E and D equal to
that of the tenon. When the mortice is away from the end of the work the
breadth B of the tenon is made less than the breadth F of the work so as
to leave stuff at A to strengthen the mortised piece. To make this joint
the two pieces, having been planed or otherwise made to size as
required, are marked for the position and length of the mortice in one
case, and for the length of the tenon in the other; both pieces are now
gauged with a mortice gauge, both being marked alike; and then from the
face side we mark a tenon or mortice of the dimensions required.
[Illustration: Fig. 2767.]
If the stuff is broad two or more tenons and mortices may be given, as
shown in Fig. 2767.
[Illustration: Fig. 2768.]
To lock the tenon in the mortice two methods may be employed. In the
first and preferable one the mortice is tapered, as in Fig. 2768, and
the two wedges are inserted and driven home. In the second the tenon is
provided with saw cuts to receive the wedges.
[Illustration: Fig. 2769.]
A very superior method of jointing is the dovetail, shown in Fig. 2769,
which is serviceable for connecting the ends and sides of a box, or any
article in that form. The strength of the corner formed in this way is
only limited by that of the material itself; therefore it should be
preferred when available in making standard patterns, or for work too
thin to admit nails or screws; the corner formed by this joint is not
limited to 90° or a square, so called, but may form any angle. Nor is it
imperative that the sides or ends of the box or other article be
parallel. They may incline towards one another like a pyramid; a mill
hopper is a familiar example of this. If it be required to dovetail a
box together, get out four pieces for the sides and ends, to be of the
full length and width respectively of the box outside. They are to be
planed all over, not omitting the ends. The gauge, that is already set
to the thickness of the stuff, must now be run along the ends, marking a
line on both sides of each piece. Then mark and cut out the pins as on
the piece A; the dovetail openings in B are traced from the pins in A.
The pieces having been tried and found to go together are finally
brought into contact and held in their places with glue.
[Illustration: Fig. 2770.]
Fig. 2770 is a mitre joint, the only one serviceable to mouldings,
pipes, and other curved pieces. It is not a strong form of joint, and is
only used where the preceding kinds are inapplicable. It is made with
glue, the pieces having been previously sized; and as an additional
precaution, if the work will admit, nails, brads, or screws are inserted
at right angles to one another.
[Illustration: Fig. 2771.]
Fig. 2771 represents the half check joint, and it is obvious that the
thickness at A must equal that at H, and be half that at B, which will
give each half equal strength.
A gland for an engine piston rod forms a simple example of the different
ways in which a pattern may be formed. Fig. 2772 represents the drawing
for the gland.[46]
[46] From the "Pattern Maker's Assistant."