Convenient as the circular saw is when fitted as an adjunct to the
lathe, its use is confined to pieces which are rectilineal. Curved
lines cannot be cut by its means, and as it must frequently happen
that portions of the proposed work are composed of arcs of various
dimensions, it becomes necessary to provide the means of cutting them
out. We may remark here, that although the circular saw, and that of
which we are about to speak may be fitted to mount on the ordinary
lathe bed; it is better for many reasons to have a separate stand,
made like that of the lathe, but smaller, and fitted with crank,
treadle, and flywheel, to serve for the various purposes of sawing,
grinding, or polishing; the latter operations especially soiling and
tending to damage the lathe. The above description of the methods of
mounting circular saws will answer for a separate stand, as will the
following details of saws for curvilinear work. In respect of the
latter we have to provide for the perpendicular motion of the blade,
which is necessarily thin and narrow, and also for stretching the
blade so as effectually to prevent it from bending or buckling--guides
are not required in general, as the work is moved about by hand in all
directions according to the intricacies of pattern to be traced. For
plain circular pieces, however, a very simple expedient is sometimes
used, which will be described in its proper place, when treating
of Bergeron's _scie mecanique_. The guides for parallel motion are
various, and a selection may be made from the following Fig. 191.
No. 1 is the arrangement used by Professor Willis, and detailed in
Holtzapffel's work. A, A are wooden springs, one above, the other
below the platform B. C is a guide pulley, D an eccentric. The catgut
band which gives motion to the saw may be passed round this, or
affixed to a metal ring as in the eccentric of a steam engine--or
may be attached to a ring slipped over the pin of a crank disc, as
shown at E. This pin being adjustable, permits the traverse of the
saw to be regulated, which gives it perhaps an advantage over the
first method. In the above the motion of the saw is not truly in a
right line, but the deviation in so short a traverse is unimportant.
The reader may, perhaps, imagine wooden springs a somewhat primitive
expedient, but this is by no means the case, as they will retain their
elasticity longer than metal ones when they are subjected to the
rapid vibration which they are called upon to undergo. No. 2 is the
parallel guide, used by Mr. Lund, and also described by Holtzapffel;
the metal springs, however, shown by the latter being here replaced
by india-rubber, which is now formed into springs of various sizes and
powers suitable for our present and many similar purposes. A, A, and
D, here form guide pulleys, the saw, E, being suspended from the first
by the two catgut bands, on the ends of which are the india-rubber
springs, F, F. The lower end of the saw is attached to another catgut
band which passes over the pulley, D, and thence to the eccentric
or crank disc as before. The platform is at B, B. Number 3 is an
arrangement similar to the beam of Newcomen's engines. The arc at
the end of the oscillating rod, and from the furthest point of which
the saw is suspended, forms the guide for parallelism. Underneath
the platform the pulley and eccentric may be used as before, and the
saw is raised by the spring attached to the arc as shown. It will be
evident on inspection that this arrangement is similar in principal to
the last, as the arc forms part of a large wheel of which the centre
is the point of oscillation. Watt's parallel motion, represented
in the next diagram, is also suitable, the saw being attached to
the centre of the short link--the springs being so contrived as to
act upon the ends of the longer bars. With regard to the means of
producing the necessary rapidity of movement, the above-described
eccentric or crank disc can hardly be surpassed. In the saw patented
lately by Mr. Cunningham, the disc is attached to the mandrel like a
chuck, and the crank pin is connected to the oscillating rods that
carry the saw by an intervening rod or link.
[Illustration: FIG. 191. N^o 1.]
[Illustration: No. 2.]
[Illustration: No. 3.]
[Illustration: No. 4.]
[Illustration: FIG. 192.]
The whole is represented in Fig. 192, which is copied from the
inventor's circular. There is a satisfactory parallel motion, and
an india-rubber ball with a small tube attached is pressed at every
stroke to blow away the sawdust. The whole plan and details are as
good probably as can be devised, and as an addition to the lathe this
saw is invaluable. Another form of mechanical saw to work with the
foot, but without any flywheel, is figured by Bergeron, and is thence
copied into Holtzapffel's book, and would therefore have been omitted
here were it not that the price of Holtzapffel's work places it beyond
the reach of many whom it is specially qualified to instruct; and that
the former is in French and has not been translated. Therefore, as the
arrangement of saw is exceedingly good, the writer has determined to
introduce it here. Its construction is simple enough to be within the
reach of any amateur in carpentry, and the only metal work required
consists of a few iron rods screwed at the ends, such as the village
blacksmith can readily supply. The saws are precisely those sold as
turn or web-saw blades. It must be understood that the use of this
tool is not the same as that to which fret or buhl saws are applied,
but merely the cutting of boards in strips or curved pieces, such as
the felloes of small wheels, circular plates to be finished in the
lathe, as bread platters, or such other curvilinear works as the chair
or pattern maker is accustomed to cut out with the several sizes of
frame saws.
A, B, Fig. 193, is a stout bench with cross bar, C, underneath, cut
away to allow of the movement of the treadle and its rod. On the top
of the bench is a pillar, D, to support the spring bow E, by which
after depression the saw is raised to its original position. F, F, and
G, G, are guide rods (not continuous). The lower ones are fixed to the
cross bar, _c_, and under side of the bench. The upper form the sides
of a rectangular frame, H, H, of which the top and bottom bars of wood
are dovetailed at the back to slide up and down the chamfered bar
behind them, K. The frame thus allows of being raised or lowered, not
only to suit work of various thicknesses, but also to act as a stop to
prevent the saw from lifting the work as it ascends. The lower bar
is extended on one side as in the figure, and is divided into inches,
and on this graduated part is a slide with a point below, which can
be fixed by a screw. This is, as the drawing plainly shows, intended
for the guidance of the wood in cutting circular pieces. The saw is
similar to the ordinary framed saw used by chair makers, but has two
blades, and one central stretcher. The saw for curved work is narrow,
that for straight cutting is broader. Near the latter a parallel
guide is fixed, as described when treating of circular saws. This
simple contrivance, although planned so many years ago, is of great
value, and deserves to be far more generally known. To the joiner and
cabinet-maker it would form a most useful addition to the usual tools
of the workshop.
[Illustration: FIG. 193.]
Akin to the circular saw are the various revolving cutters used either
for the purpose of ornamentation or for grinding, such as circular
files for flat surfaces, in which the teeth are cut upon the face or
tool-cutters of particular sections for cutting the teeth of wheels,
in the manner already described, to which may perhaps be added milling
and embossing tools, although the action of the latter is rather that
of a revolving die by which the work is stamped or indented with the
pattern formed upon the edge of the cutter. The small grindstones and
emery laps belong also to this section, as their action results from
the abrasion of the material by means of the combined cutting power of
innumerable small points or miniature teeth formed by the particles of
emery or other material attached to the surface of the laps.
Most of the steel cutters may be made by the amateur, the metal
being turned to the required shape and the teeth cut by small files
or punches while the material is in a soft state. The little discs
are then hardened and mounted, by a central hole previously made, on
suitable spindles, the latter being either attached at one end to
the mandrel as arbor chucks, or centred at both ends and driven like
miniature circular saws. The ornamental cutters for embossing, Fig.
193B, A and B, are turned to the form of short cylinders,
and the patterns cut by punches. These and the milling tools are
mounted alike, Fig. 194. The rest is placed a short distance from the
work, and the tool revolves against it. Some pressure is necessary to
imprint the design, and this is easily obtained if the cutter wheel
is placed so as to attack the work below the axis; the rest then
becomes a fulcrum, and the shank and handle of the tool acting as the
long arm of a lever supply the required force with little exertion
on the part of the operator. In this way the milling is done on the
edges of screw heads, and the embossed patterns on soft wood boxes.
It is not easy to understand how the patterns in these cases are
produced clearly without one part cutting into and effacing another,
unless the size of the work is exactly a multiple of that of the
tool. The error is plain if the work is stopped exactly at the end
of the first turn, but in successive revolutions this error becomes
gradually obliterated, and the pattern is eventually impressed clear
and well defined. The same shank is arranged for different patterns
of wheel-cutters, as the pin which forms the central axis is readily
withdrawn and is made to suit the holes in several sets of discs.
[Illustration: Fig. 193B.]
[Illustration: Fig. 194.]
[Illustration: Fig. 195.]
By the aid of the above simple tool a neat finish is readily given
to many small works in wood and metal. A modification of the beading
tools is here shown very similar to the screwing guide already
given, but made with figured instead of sharp-cutting edge. This was
communicated to the _English Mechanic_, Nov. 2, 1866. E, 195, is the
guide which is placed on the handle A, B, C, D, and fixed by screw F.
The mark _i_, on the guide, is placed against the rim, A, B, which is
graduated and numbered. Each figure, as it is brought up and placed
opposite _i_, will cut a different pattern when the guide is fixed.
The tool must be held very firmly on the rest (the bottom of the guide
G, H, being flat, is carried on the rest), the tool is advanced to
the wood. The tool must be worked very steadily; but with a little
practice, any amateur will soon use it perfectly, and produce many
very pretty patterns. It is evident that provision is here made for
placing the cutter at different angles to the work, by which means
the circles of patterns may be traced spirally and in other positions
varying from the ordinary one at right angles to the axis of the work.
The laps alluded to, which are to be mounted on spindles like the
circular saw, are composed of wood and metal of determinate forms.
First, there is the thin sheet-iron slitting wheel used by lapidaries,
and which, when charged with emery, or sand and water, forms the
nearest approach to the circular saw. It _is_, in fact, the circular
saw of the stone worker, the ordinary saw used in their trade being a
flat blade without teeth, stretched in a wooden frame and similarly
fed with sharp sand and water in lieu of being made with teeth, the
latter being replaced by the grittiness of the material. The circular
plate of iron, brass, or lead alloyed with antimony, mounted on a
spindle vertically, is used in a similar manner for grinding flat
surfaces with the aid of emery, crocus, oilstone powder, and other
substances, and the same is used edgewise for other work, as grinding
and polishing tools, the section of the lap being such as will form
the article required by reproduction of the revised plan of its own
edge. Thus a lap running horizontally with a convex edge will produce
the concave form required in beading tools, the latter, however, are
more conveniently ground on brass cones mounted like the arbor chucks
used for turning washers, rings, &c. The face of the tool or flat side
is held towards the small end of the cone, and the latter is armed
with flour emery. See Fig. 196.
[Illustration: Fig. 196.]
Before describing the eccentric and other compound chucks, a few
examples will be given of the method of turning some of those forms
in which the circle does not appear, where, in short, the boundaries
of the figures are straight lines. It seems at first sight impossible
to produce in the lathe by any simple means such solids as are formed
from squares or triangles, of which the cube or die is the most common
and most generally understood. This can, however, be accomplished,
and a number of mathematical problems may be clearly demonstrated to
the eye by such works skilfully made in the lathe. In this kind of
work it is absolutely necessary to strive after perfection. In short,
as Bergeron rightly says, the work imperfectly done is simply worth
nothing at all; but when accomplished with exactness, nothing can be
more worthy of a place in a cabinet of curiosities. The usual method
of turning a cube is by shaping it out of a perfect sphere, but as the
latter can hardly be made without a special slide rest made for the
purpose, a method of turning the cube by hand alone will be given,
the foundation of it being that which the lathe so readily produces,
namely, a cylinder. By far the most proper material for the work in
question is sound boxwood, and special care is to be taken to keep all
angles as sharp as possible, and therefore to cut clean with sharp
tools, and to avoid as far as possible the use of sand or glass paper.
Fig. 197 shows a square described in a circle. The non-mathematical
reader may be told to draw through the centre two diameters at right
angles to each other, and to complete the square, as in the figure,
by joining the extremities. The largest square that is possible to
be drawn in the circle is thus described. This square will form one
face of the cube, and the diameter of the piece of wood must be
regulated according to the proposed size of the finished work. It is
evident that this diameter is equal to the line drawn from corner
to corner called the diagonal of the square. Now, in turning a ball
or sphere, a cylinder would be turned of the exact length of A, C,
because every measurement taken on a diameter of the sphere would
be of that length. In the present case, however, the cylinder must
be of the same length as the line A, B. Turn, therefore, with great
care a cylinder of any desired size, gauging it carefully with the
callipers and squaring off the ends truly. On one end, in which the
centre point just remains visible, draw diameters and construct the
figure 197. Turn out a chuck to fit it exactly, and let the bottom
of this chuck be truly square. Take the precise length of the line
A, B, with finely pointed compasses that can be fixed with a screw,
and measure off the same, and mark it on the side of the cylinder.
When the figure is placed on the chuck, a mark must be traced round
it at this point, A, B, Fig. 198, _and this must remain to the end_.
It may be made with a hard pencil or steel scriber, and, though
distinct, must be very fine. It is at this line the wood will have
to be cut off, but in this operation keep beyond it so as not to
erase it. While the piece is in the chuck, rule lines, as E, G, from
the points C, D, E, F, 198. Bisect also the length of the cylinder
by the line, H, K, also finely drawn. Draw two more diameters, as
shown by the dotted lines bisecting the sides of the cylinder, which
is now divided round its circumference into eight equal parts. The
lines, E, G, &c., can be ruled along the edge of the rest, or, if the
latter is untrue, the cylinder may be laid on a plane surface, and
a scribing block, or gauge, Fig. 199, may be drawn across it, or,
lastly, a small steel square may be used; one part being carefully
placed on the lines at the end of the piece in succession, the other
part will lie evenly along the side, and will form a ruler by which
to work. A division plate on the lathe pulley will facilitate the
above measurements, but they can be readily made without it, and once
carefully marked, all the guides required for cutting out the cube
will be complete, and the work can be proceeded with, with confidence
and decision. Proceed, therefore, to cut off the piece at A, B, with
a parting tool, but with the precaution already named of not erasing
the line by so doing. Now prepare a chuck which will take the piece
lengthwise, Fig. 199-2, and insert it in that position to the depth
of the diameter so as to hold it securely, and the central line will
show whether it lies evenly (which is, in fact, the use of this
line). If even, a point-tool held on this line will form a mere dot
upon it; if uneven, it will make a circle as it revolves. Place the
rest across the face of the work, and, beginning at the centre, cut
carefully towards the outside until you have cut away the wood as far
as the line, A, B. You will thus complete one face of the cube, and
an inspection of the end of the piece, shown black in the sketch to
show the quantity removed, will prove that you thus produce a right
line, C, D. Take out the work, and reverse it, and operate similarly
on the opposite face; but in every case do not quite obliterate the
lines first marked as guides. You have now a piece shaped like Fig.
200, A and B, and must make a smaller chuck to hold it; you have then
to cut away in a similar manner the remaining parts of the cylindrical
portion, and the cube will be complete. To finish the sides more
neatly, lay upon the table the finest sand paper, and tack it at the
corners, and with gentle movements work down precisely to the guide
lines. This requires extreme care, for if once the piece is but in
the slightest degree tilted up, an angle will lose its sharpness, and
the beauty of the work will be marred. Hence we recommend to cut with
sharp tools, instead of trusting to the finishing process. To cut,
however, _exactly_ to the line is very delicate work, and to the less
practised hand the use of the sand paper on the faces in succession
may be the _necessary_ expedient. The main secret of sharp edges in
works of wood and metal is to finish with hard substances, as emery
stick or glass paper glued to a piece of wood, or the same nailed on
the bench, and to try always to work on the centre, leaving the edges
or angles to take care of themselves. When the reader has made a cube,
as above, that will bear delicate measurement, he will be more than
usually gratified, and will be qualified for still more difficult
work. A chuck figured by Bergeron, Fig. 201, is very convenient, as
it holds the work truly central; the jaws work simultaneously by a
right and left-handed screw as in the die chuck. It is, however,
perfectly easy to do good work without it, but the chucks should
be carefully made, turned very flat at the bottom, with side truly
perpendicular. A little extra care bestowed upon chucks will save
many disappointments, and conduce to good work. The formation of a
four-sided solid, consisting of triangles solely, in the lathe is a
work of difficulty, owing to the impossibility of fixing the work
satisfactorily in an ordinary chuck. The natural way to form such a
solid is to turn a cone A, B, Fig. 202, and on its base to mark a
triangle of the required size. It is then necessary to place the cone
in a chuck, so that the ends of one of the lines thus marked and the
apex of the cone are precisely level with the surface of the chuck, as
shown in Fig. 203. But it is evident that adequate support is not thus
obtainable. The apex of the cone cannot, in point of fact, be inside
the chuck at all, as it is necessary to cut clean to its extremity,
and even the base of the cone is imperfectly held at two points.
Hence it becomes necessary to make use of "turner's cement," and to
imbed the work fairly in it, while both are warm, to such a depth as
will hold it securely and still allow the guide lines to be seen.
The latter should be carried from the three angles of the triangle
marked on the base to the apex. On the whole, this is the easiest
method of fixing such work in the lathe; and if the piece is itself
warmed before being placed, there will be time to adjust it precisely
before the cement is cold. To do this, place the rest parallel to the
lathe bed, hold a pointed tool steadily upon it, and note whether,
as the work slowly revolves, the three points in question, viz.,
the two angles of the triangle and the top of the cone, are in one
plane. When they are so placed, the rest is turned to face the work,
and the material is carefully cut away till the gauge lines are just
reached.[14] A pyramidical solid with a square base may be similarly
turned. The following is the method of preparing the above turner's
cement:--Burgundy pitch, 2 lb.; yellow wax, 2 oz. Melt together in a
pipkin, and stir in 2 lb. of Spanish white. When the whole is well
mixed, pour it out on a marble slab and roll it into sticks. Fine
brickdust, whiteing, or any similar substance finely pulverised, will
answer equally well to add to the pitch and beeswax. This cement is
very useful, as it will hold the work firm enough to turn carefully,
and nevertheless a slight blow will loosen it. To clean it off, warm
or dip the work in hot water and wipe quickly with a piece of cloth.
The above is from the "Handbook of Turning," the author of which has
copied from Bergeron both the recipes given in his work; the one here
described is stated to be specially serviceable in cold weather. It
is perhaps rather less brittle than the first of Bergeron's, and for
this cause is the best for general use. Holtzapffel sells this at
one shilling the stick, which is of convenient size and generally of
excellent quality. Bergeron gives a method of turning pilasters or
balustrades, which is of great ingenuity, and applicable to work of
various sections. The rectangular and triangular sections illustrated
are not, indeed, strictly rectilineal figures, as the sides of the
balustrades thus formed are not flat but rounded surfaces; they are,
however, sufficiently curious, and when well turned are interesting
specimens of lathe work. Bergeron's description relates to the pole
lathe, or to work mounted between two centres with a pulley cut on
the work itself to receive the lathe cord. The ordinary method of
mounting on a foot-lathe will, of course, be much better and the whole
operation of more easy performance. Let it be required to turn a
moulded pillar or balustrade of the section Fig. 204, viz., a triangle
with slightly curved sides. A piece of wood of the requisite length
is planed up accurately to a triangular form, or, as it generally
happens that a set of such pilasters are required, a number of such
pieces are prepared which must be accurately planed to the same size,
for which purpose a gauge or template, Fig. 205, should be made
use of. Six or eight of these, if not too large, may be operated
upon at the same time; but as six pieces of two inches across each
face require a cylinder of about eight inches diameter, the number
must depend on height of centres. The larger the cylinder, however
(which, in fact, forms a chuck), the more nearly will the sides of
the finished work approach to plane surfaces, as they will form arcs
of a larger circle. Let a cylinder, then, be turned of sound wood
with a reduced part at one end so as to form a shoulder. Divide the
circumference into twice as many equal parts as there are pieces to
be turned, the divisions being equal to one of the sides of these
pieces as measured in a cross section. These divisions are to mark the
positions of the grooves or channels in which the triangular strips
are destined to lie. Half the circumference will be so cut out, the
alternate divisions being left. Thus, to turn four pieces, each two
inches wide, a cylinder of sixteen inches will be required, affording
four grooves two inches wide, and four intermediate pieces forming the
partitions between the grooves. The latter must, by means of the saw
and chisel or other tools, be made to receive the strips exactly, and
the ends of the latter being carefully squared off, are to be made
to rest against the plate C, Fig. 206, which is cut out and screwed
against the shoulder, after the above-mentioned grooves have been cut.
The whole are then secured by two rings, with screws. Probably the
stoutest india-rubber rings now made would answer as well as the iron
clamps in Bergeron's description. Lay the strips in their places, but
as they are flat they will not form part of the cylindrical surface,
but will lie lower, as Fig. 207, or higher, Fig. 208; the latter is
the best, and the pieces may, for this cause, be cut out a trifle
deeper than ultimately required and they may be planed down a little
to remove the angles and assimilate them to the cylindrical surface.
The whole may then be turned together so as to form a plain cylinder,
the clamping rings, Fig. 209, being shifted when requisite. The whole
is now to be formed into a balustrade, but as the proportions of the
mouldings of such a large cylinder would not suit the small pieces,
the hollows must be less deep, and the raised parts less prominent
than they would ordinarily be made. The clamps are now to be loosened,
and the pieces reinserted with another face upwards, the flange or
plate against which their ends rest forming a gauge or stop to ensure
their position, without which precaution the mouldings would not
eventually meet at the angles. In cutting a fresh side the utmost
care is requisite, for if the work on the original cylinder is cut by
the tool, it will be impossible to restore it, and the work will be
spoiled. In replacing the strips, let the finished part lie below, so
as to come first in contact with the tool, by which the angle will be
clean. Extra care is for this purpose required in cutting the last
side. It appears to the writer that another precaution should be taken
which Bergeron omits, namely, to arrange the mouldings so that certain
parts are left of the original size of the wood, in order to retain
a certain number of points of contact with the sides of the grooves,
so that the strips shall not fall deeper into them than at first. The
extremities of the strips should certainly not be left smaller than
the central portion, or the pieces will rock on the latter while in
process of being turned. The two ends, therefore, should be allowed
to retain their original triangular form, forming base and capital
of the pillar, or the pattern may be so planned that, after the
extremities have been left as supports they may be cut off when the
work is complete. Care must be taken, in working as above, to have
the cylinders so large above the estimated size that the inner apices
of the triangles do not nearly meet at the centre, else the whole
chuck would be very weak and split into triangular strips. The lathe
called a spoke-turning lathe would accomplish this kind of work in
a far more easy and speedy manner. The balustrade would have to be
made by hand as a pattern, and cast in metal, and any number could be
produced precisely similar. The lathe in question is on the following
principle:--The frame carrying the tool (a set of revolving gauges)
is made to oscillate backwards and forwards to and from the piece to
be operated on. This is accomplished by its having attached to it a
roller or rubber working against the cast-iron pattern placed parallel
to the work, and below or one side of it. The rubber and frame are
kept against the pattern by a strong steel spring. The cutters also
travel in a direction parallel to the axis of the piece. Hence any
elevated part of the pattern causes the tool to recede from the work
in a corresponding degree, and a hollow allows a nearer approach
of the tool. Thus, as the tool is carried by a screw slowly from
end to end of the work, it is made to advance and recede in exact
correspondence with the form of the pattern. An immense deal of work
is done in this way, such as balustrades, spokes of wheels, the long
handles of the American felling axes, and similar irregular forms.
[14] With the universal cutting frame this kind of work is much more
readily accomplished.
[Illustration: FIG. 198.]
[Illustration: FIG. 197.]
[Illustration: FIG. 199^2.]
[Illustration: FIG. 199.]
[Illustration: FIG. 200.]
[Illustration: FIG. 201.]
[Illustration: Fig. 203.]
[Illustration: Fig. 202.]
[Illustration: Fig. 205.]
[Illustration: Fig. 206.]
[Illustration: Fig. 209.]
[Illustration: Fig. 208.]
[Illustration: Fig. 207.]
The _principle_, indeed, is not new, as the rose engine is a similar
tool, and, so long back as Bergeron's time, pattern plates were used
giving any desired motion, endlong or otherwise, to the tool, or,
which in effect is the same, to the work to be operated on.