HAND DRILLING AND BORING TOOLS.--The tools used for piercing holes in
wood are generally termed boring tools, while those for metal are termed
drilling tools when they cut the hole from the solid metal, and boring
tools when they are used to enlarge an existing hole. Wood-boring tools
must have their cutting edges so shaped that they sever the fibre of the
wood before dislodging it, or otherwise the cutting edges wedge
themselves in the fibre. This is accomplished, in cutting across the
grain of the wood, in two ways: first, by severing the fibre around the
walls of the hole and in a line parallel to the axial line of the boring
tool, and removing it afterwards with a second cutting edge at a right
angle to the axis of the boring tool; or else by employing a cutting
edge that is curved in its length so as to begin to cut at the centre
and operate on the walls of the hole, gradually enlarging it, as in the
case of Good's auger bit (to be hereafter described), the action being
to cut off successive layers from the end of the grain or fibre of the
wood. Tools for very small holes or holes not above one-quarter inch in
diameter usually operate on this second principle, as do also some of
the larger tools, such as the nail bit or spoon bit and the German bit.
[Illustration: Fig. 1757.]
[Illustration: Fig. 1758.]
The simplest form of wood-piercing tool is the awl or bradawl, shown in
Figs. 1757 and 1758, its cutting end being tapered to a wedge shape
whose width is sometimes made parallel with the stem and at others
spread, as at C D in figure. It is obvious that when the end is spread
the stem affords less assistance as a guide to pierce the hole straight.
It is obvious that the action of an awl is that of wedging and tearing
rather than of cutting, especially when it is operating endways of the
grain.
Thus in Fig. 1758 is shown an awl operating, on the right, across the
grain, and, on the left, endwise of the same. In the former position it
breaks the grain endwise, while in the latter it wedges it apart. Awls
are used for holes up to about three-sixteenths of an inch in diameter.
[Illustration: Fig. 1759.]
Fig. 1759 represents the gimlet bit having a spiral flute at F and a
spiral projection at S S, which, acting on the principle of a screw,
pulls the bit forward and into its cut. These bits are used in sizes
from 1/16 inch to 1/2 inch. The edge of the spiral flute or groove here
does the cutting, producing a conical hole and cutting off successive
layers of the fibre until the full diameter of hole is produced. The
upper part of the fluted end is reduced in diameter so as to avoid its
rubbing against the walls of the hole and producing friction, which
would make the tool hard to drive.
[Illustration: Fig. 1760.]
[Illustration: Fig. 1761.]
Figs. 1760 and 1761 represent the German bit, which is used for holes
from 1/16 inch to 3/8 inch in diameter. This, as well as all other bits
or augers, have a tapered square by which they are driven with a brace,
the notch shown at N being to receive the spring catch of the brace that
holds them in place. The cutting edges at A and B are produced by
cutting away the metal behind them.
[Illustration: Fig. 1762.]
[Illustration: Fig. 1763.]
Fig. 1762 represents the nail bit, which is used for boring across the
grain of the wood. Its cutting edge severs the fibre around the walls of
the hole, leaving a centre core uncut, which therefore remains in the
hole unless the hole is pierced entirely through the material. If used
to bore endways or parallel with the direction of the fibre or grain of
the wood it wedges itself therein.
The groove of the nail bit extends to the point, as shown by the dotted
line in the figure. Nail bits are used in sizes from 1/16 to 3/8 inch.
Fig. 1763 represents the spoon bit whose groove extends close to the
point, as shown by the dotted line C.
[Illustration: Fig. 1764.]
Fig. 1764 represents the pod or nose bit, whose cutting edge extends
half way across its end and therefore cuts off successive layers of the
fibres, which peculiarly adapts it for boring endways of the grain,
making a straight and smooth hole. It is made in sizes up to as large as
four inches, and is largely used for the bores of wooden pipes and
pumps, producing holes of great length, sometimes passing entirely
through the length of the log.
[Illustration: Fig. 1765.]
Fig. 1765 represents the auger bit, which is provided with a conical
screw S which pulls it forward into the wood. Its two wings W have
cutting edges at D, D, which, being in advance of the cutting edges A,
B, sever the fibre of the wood, which is afterwards cut off in layers
whose thickness is equal to the pitch of the thread upon its cone S. The
sides of the wings W obviously steady the auger in the hole, as do also
the tops T of the twist. This tool is more suitable for boring across
the grain than lengthways of it, because when boring lengthways the
wings W obviously wedge themselves between the fibres of the wood.
[Illustration: Fig. 1766.]
This is obviated in Cook's auger bit, shown in Fig. 1766, in which the
cutting edge is curved, so that whether used either across or with the
grain the cutting edge produces a dished seat and cuts the fibre endways
while removing the material in a spiral layer. The curve of the cutting
edge is such that near the corners it lies more nearly parallel to the
stem of the auger than at any other part, which tends to smooth the
walls of the hole. This tool while very serviceable for cross grain is
especially advantageous for the end grain of the wood.
[Illustration: Fig. 1767.]
[Illustration: Fig. 1768.]
In the smaller sizes of auger bits the twist of the spiral is made
coarser, as in Fig. 1767, which is necessary to provide sufficient
strength to the tool. For the larger sizes the width of the top of the
flute (T, Fig. 1765), or the land, as it is termed, is made narrow, as
in Fig. 1768, for holes not requiring to be very exact in their
straightness, while for holes requiring to be straight and smooth they
are made wider, as at D, in Fig. 1769, and the wings A, B in the figure
extend farther up the flutes so as to steady the tool in the walls of
the hole and make them smoother. It is obvious that the conical screw
requires to force or wedge itself into the wood, which in thin work is
apt to split the wood, especially when it is provided with a double
thread as it usually is (the top of one thread meeting the cutting edge
A in Fig. 1765, while the top of the other thread meets cutting edge B).
[Illustration: Fig. 1769.]
[Illustration: Fig. 1770.]
In boring end-grain wood, or in other words lengthways of the grain of
the wood, the thread is very apt to strip or pull out of the wood and
clog the screw of the auger; especially is this the case in hard woods.
This may be to a great extent avoided by cutting a spiral flute or
groove along the thread, as in Fig. 1770, which enables the screw to cut
its way into the wood on first starting, acts to obviate the stripping
and affords an easy means of cleaning. The groove also enables the screw
to cut its way through knots and enables the auger to bore straight.
In boring holes that are parallel with the grain or fibre of the wood,
much more pressure is required to keep the auger up to its cut and to
prevent the thread cut by the auger point from pulling or stripping out
of the wood, in which case it clogs the thread of the auger point and is
very difficult to clean it out, especially in the case of hard woods.
[Illustration: Fig. 1771.]
[Illustration: Fig. 1772.]
Furthermore, after the thread has once stripped it is quite difficult to
force the auger to start its cut again. To obviate these difficulties,
the screw is fluted as shown. It is obvious also that this flute by
imparting a certain amount of cutting action, and thereby lessening the
wedging action of the screw, enables it to bore, without splitting it,
thinner work than the ordinary auger. But it will split very thin work
nevertheless; hence for such work as well as for holes in any kind of
wood, when the hole does not require to be more than about twice as deep
as that diameter, the centre bit shown in Figs. 1771 and 1772 is
employed, being an excellent tool either for boring with the grain or
across it. The centre B is triangular and therefore cuts its way into
the work, and the spur or wing A extends lower than the cutting edge C,
which on account of its angle cuts very keenly.
[Illustration: Fig. 1773.]
Fig. 1773 represents the twist drill which is used by the wood-worker
for drilling iron, its end being squared to fit the carpenter's brace.
[Illustration: Fig. 1774.]
[Illustration: Fig. 1775.]
Fig. 1774 represents an extension bit, being adjustable for diameter by
reason of having its cutting edge upon a piece that can be moved endways
in the holder or stem. This piece is ruled with lines on its face so
that it may be set to the required size. Its upper edge is serrated with
notches into which a dish screw or worm meshes, so that by revolving the
worm the bit piece is moved farther out on the spur or wing side or end,
it being obvious that the spur must meet the walls of the hole. A better
form of extension bit for the end grain of wood is shown in Fig. 1775,
the cutting edge being a curve to adapt it to severing the fibre in
end-grained wood, as was explained with reference to Good's auger bit.
[Illustration: Fig. 1776.]
Fig. 1776 represents a drill for stone work, whose edge is made curved
to steady it. This tool is caused to cut by hammer blows, being slightly
revolved upon its axis after each blow, hence the curved shape of its
cutting edge causes it to sink a dish-shaped recess in the work which
holds that end steady. The end of the tool is spread because the corners
are subject to rapid wear, especially when used upon hard stone, and the
sides of the drill would bend or jam in the walls of the hole in the
absence of the clearance caused by the spread. To prevent undue abrasion
water is used.
In soft stones the hammer blows must be delivered lightly or the cutting
edge will produce corrugations in the seat or bottom of the hole, and
falling into the same recesses when revolved after each blow the
chipping action is impaired and finally ceases. To prevent this the
cutting edge is sometimes curved in its length so that the indentations
cross each other as the drill is revolved, which greatly increases the
capacity of the drill, but is harder to forge and to grind.
[Illustration: Fig. 1777.]
The simplest hand-drilling device employed for metal is the fiddle bow
drill shown in Fig. 1777. It consists of an elastic bow B, having a cord
C, which passes around the reel R, at one end of which is the drill D,
and at the other a stem having a conical or centre point fitting into a
conical recess in a curved breast-plate. The operator presses against
this plate to force the drill to cut, and by moving the bow back and
forth the cord revolves the drill.
[Illustration: Fig. 1778.]
As the direction of drill revolution is reversed at each passage of the
bow, its cutting edges must be formed so as to cut when revolved in
either direction, the shape necessary to accomplish this being shown in
the enlarged side and edge views at the foot of the engraving. It is
obvious that a device of this kind is suitable for small holes only, as,
say, those having a diameter of one-eighth inch or less. But for these
sizes it is an excellent tool, since it is light and very sensitive to
the drill pressure, and the operator can regulate the amount of pressure
to suit the resistance offered to the drill, and therefore prevent the
drill from breakage by reason of excessive feed. In place of the
breast-plate the bow drill may be used with a frame, such as in Fig.
1778. the frame being gripped in a vice and having a pin or screw A. If
a pin be used, its weight may give the feed, or it may be pressed down
by the fingers, while if a screw is used it must be revolved
occasionally to put on the feed.
[Illustration: Fig. 1779.]
Fig. 1779 represents a hand-drilling device in which the cord passes
around a drum containing a coiled spring which winds up the cord, the
latter passing around the drill spindle, so that pulling the cord
revolves the spindle and the drill, the drum and spiral spring revolving
the drill backwards.
[Illustration: Fig. 1780.]
Fig. 1780 represents a drilling device in which the drill is carried in
a chuck on the end of the spindle which has right and left spiral
grooves in it, and is provided with a barrel-shaped nut, which when
operated up and down the spindle causes it to revolve back and forth.
The nut or slide carries at one hand a right-hand, and at the other a
left-hand nut fitting into the spindle grooves, and cut like a ratchet
on their faces. Between these is a sleeve, also ratchet cut, but
sufficiently short that when one nut engages, the other is released,
with the result that the drill is revolved in one continuous direction
instead of back and forth, and can therefore be shaped as an ordinary
flat drill instead of as was shown in Fig. 1777. The drill is fed to its
cut by hand pressure on the handle or knob at the top.
[Illustration: Fig. 1781.]
Fig. 1781 represents Backus' brace for driving bits, augers, &c., the
construction of the chuck being shown in Fig. 1782. The two tongues are
held at their inner ends by springs and are coned at their outer ends,
there being a corresponding cone in the threaded sleeve, so that
screwing up this sleeve firmly grips the tool shank and thus holds it
true, independent of the squared end which fits into the inner tongue
that drives it.
In another form this brace is supplied with a ratchet between the chuck
and the cranked handle, as shown in Fig. 1783, the construction of the
ratchet being shown in Fig. 1784. The ring is provided on its inner edge
with three notches, so that by pulling it back and setting it in the
required notch the ratchet will operate the chuck in either direction or
lock it for use as an ordinary brace. The ratchet enables the tool to be
used in a corner in which there would be no room to turn the crank a
full revolution. This end may, however, be better accomplished by means
of the Backus' patent angular wrench shown in Fig. 1785, which consists
of a frame carrying a ball-and-socket joint between it and the chuck, as
shown.
[Illustration: Fig. 1782.]
[Illustration: Fig. 1783.]
[Illustration: Fig. 1784.]
[Illustration: Fig. 1785.]
[Illustration: Fig. 1786.]
[Illustration: Fig. 1787.]
Figs. 1786 and 1787 represent the brace arranged to have a gear-wheel
connected or disconnected at will, the object of this addition being to
enable a quick speed to the chuck when the same is advantageous.
[Illustration: Fig. 1788.]
For drilling small holes in metal, the breast drill shown in Fig. 1788
is employed. It consists of a spindle having journal bearing in a
breast-plate at the head, and in a frame carrying a bevel gear-wheel
engaging with two gear-pinions that are fast upon the spindle, this
frame and the bevel gear-wheel being steadied by the handle shown on the
right. At the lower end of the spindle is a chuck for holding and
driving the drill, which is obviously operated by revolving the handled
crank which is fast upon the large bevel gear. The feed is put on by
pressing the body against the breast-plate.
It is obvious that but one bevel pinion would serve, but it is found
that if one only is used the spindle is apt to wear so as to run out of
true, and the bore of the gear-wheel rapidly enlarges from the strain
falling on one side only. To avoid this the spindle is driven by two
pinions, one on each side of the driving gear as in figure.
Breast-drills do not possess enough driving power to capacitate them for
drills of above about quarter inch in diameter, for which various forms
of drill cranks are employed.
[Illustration: Fig. 1789.]
Fig. 1789 represents a drill crank which receives the drill at A, and is
threaded at B to receive a feed screw C, which is pointed at D; at E is
a loose tube or sleeve that prevents the crank from rubbing in the
operator's hands when it is revolved.
[Illustration: Fig. 1790.]
To use such a drill crank a frame A, Fig. 1790, is employed, being held
in a vice and having at T a table whereon the work W may be rested. The
feed is put on by unscrewing the screw S in this figure against the
upper jaws of A; holes of about half inch and less in diameter may be
drilled with this device.
[Illustration: Fig. 1791.]
A very old but a very excellent device for hand drilling when no
drilling machine is at hand is the drilling frame shown in Fig. 1791,
which consists of two upright posts A, and two B, placed side by side
with space enough between them to receive and guide the fulcrum lever
and the lifting lever. The fulcrum lever is pivoted at C, and has an
iron plate at E, and suspends a weight at its end which serves to put on
the feed. The lifting lever is pivoted at D, and at F hooks on to the
fulcrum lever. At its other end is a rope and eye G, and it is obvious
that the effect of the weight upon the fulcrum lever is offset by any
pressure applied to G, so that by applying the operator's foot at G the
weight of drill feed may be regulated to suit the size of hole and
strength of drill being used. The work is rested on a bench, and a drill
crank or other device such as a ratchet brace may be used to drive the
drill. This drill frame is capable of drilling holes up to about two
inches in diameter, but it possesses the fault that the upper end of the
brace or drilling device moves as the drill passes into the work in an
arc H of a circle, of which the pin C is the centre. The posts A are
provided with numerous holes for the pin C, so that the fulcrum lever
may be raised or lowered at that end to suit the height of the work
above the work bench. Another objection to this device is, it takes up a
good deal of shop room.
Ratchet braces are employed to drill holes that are of too large a bore
to be drilled by tread drills, and that cannot be conveniently taken to
a drilling machine.
[Illustration: Fig. 1792.]
In Fig. 1792 is represented a self-feeding ratchet brace. A is the body
of the brace, having a taper square hole in its end to receive the
square shank of the drill. L is a lever pivoted upon A, and having a
pawl or catch B, which acts upon ratchet teeth provided upon A. When the
lever L is moved backward the pawl B being pivoted rides over the
ratchet teeth, but when L is pulled forward B engages the ratchet teeth
and rotates A and therefore the drill. At F is a screw threaded into A,
its pointed end abutting against some firm piece, so that unscrewing F
forces the drill forward and into its cut. These features are essential
to all forms of ratchet braces, but the peculiar feature of this brace
consists in its exceedingly simple self-feeding devices, the feed screw
F requiring in ordinary braces to be operated by hand when the drill
requires to be fed.
The construction and operation of the self-feeding device is as follows:
The feed screw F is provided with a feather way or spline and with a
feed collar C, operated by the pawl E. The feed-collar C has at D a
groove, into which a flange on pawl E fits, and on its side face there
is a groove receiving an annular ring on the face of lever L, these two
keeping it in place. The pawl E is a double one, and may be tripped to
operate C in opposite directions to feed or release the drill, as the
case may be, or it may be placed in hind position to throw the feed
off--all these operations being easily performed while the lever L is in
motion. Collar C is in effect a double ratchet, since its circumference
is provided with two sets of notches, one at _g_ and the other at _h_.
Each set is equally spaced around the circumference, but one set or
circle is coarser spaced than the other, while both are finer spaced
than is the ratchet operated by pawl B. Suppose, now, that the lever L
is at the end of a back stroke, and pawl E will fall into one of the
notches on side _g_ of the feed-ratchet, and when lever L is moved on
its forward stroke it will operate the feed ratchet and move it forward,
A standing still until such time as pawl B meets a tooth of the ratchet
on A. The feed screw F is provided with a left-hand thread, and the feed
ratchet has a feather projecting into the spline in the feed screw;
hence moving the feed ratchet at the beginning of the forward motion of
L and before A is operated, puts a feed on, and the amount of this feed
depends upon how much finer the notches into which pawl E falls are than
those into which B falls. The feed takes place, be it noted, at the
beginning of the lever stroke, and ceases so soon as pawl B operates A
and the drill begins to cut.
As shown in the figure, the feed collar is set for large drills (which
will stand a coarser feed than small ones), because the notches are
finer spaced at _g_ than at _h_. For small drills and finer feeds the
collar is slipped off the screw and reversed so that side _h_ will fall
under E, it being obvious that the finer the notches are spaced the more
feed is put on per stroke. The spacings are made to suit very moderate
feeds, both for large and small drills, because the operator can
increase the feed at any stroke quite independently of the spacings on
the feed ratchet. All he has to do is to give the lever handle a short
stroke and more feed is put on; if still more feed is wanted, another
short stroke may be made, and so on, the least possible amount of feed
being put on when the longest strokes are made. In any event, however,
there will be a certain amount of average feed per stroke if equal
length of strokes is taken, the spacing being made to suit such ordinary
variations of stroke as are met within every-day practice. When it is
desired to stop feeding altogether, or to release the drill entirely
from the cut, all that is necessary is to trip the feed-pawl E (without
stopping the lever motion), and it will operate the feed screw in the
opposite direction sufficiently to release the drill in a single
backward stroke of the lever. The range of feed that is obtainable with
a single feed ratchet is sufficient for all practical purposes, although
it is obvious that if any special purpose should require it, a special
feed ratchet may be made to suit either an unusually fine or coarse rate
of feed. The feed screw is not provided with either a squared head or
with the usual pin holes, because the feed ratchet is so readily
operated that these, with their accompanying wrench or pin, are
unnecessary.
[Illustration: Fig. 1793.]
[Illustration: Fig. 1794.]
Figs. 1793 and 1794 represent a self-feeding ratchet brace for hand
drilling in which the feed is obtained as follows: The inside or feed
sleeve B, which screws upon the drill spindle, is fitted with a friction
or outer sleeve A, in the head of which is secured a steel chisel-shaped
pin C, the lower end of which is pointed and rests upon a hardened steel
bearing D, fixed in the head of the inner sleeve B. This sleeve, with
its bearing D, revolves upon the point of the pin C, and within the
friction sleeve A. Having thus described its construction, we will now
describe the operation of the self-feeding device. The head of the pin C
being chisel-shaped, prevents the pin and the outer sleeve A from
revolving. If the thumb or friction screw F is unscrewed, it will permit
the inner sleeve B to rotate freely upon the bearing of pin C, and
within the friction sleeve A. As the screw F is tightened, the friction
upon the inner sleeve B is increased, causing it to remain stationary,
and consequently causing the screw on the drill spindle to feed the
drill until the friction on the drill becomes greater than the friction
on the sleeve B. This then commences to rotate again within the outer
sleeve A, and continues until the chip which the drill has commenced to
cut is finished, when the same operation is repeated, thus giving a
continuous feed, capable of being instantly adjusted to feed fast or
slow as desired, by tightening or loosening the friction screw F,
thereby causing a greater or less friction upon the inside or feed
sleeve B.
[Illustration: Fig. 1795.]
To afford a fulcrum or point of resistance for the chisel-piece C, or
the pointed centre used in the common forms of ratchet brace feed
screws, various supporting arms, or stands are employed. Thus Fig.
1795[30] represents a boiler shell _a_, to which is attached an angle
frame or knee _b_, carrying the angle piece _c_ (which may be adjusted
for vertical height on _b_ by means of the bolt shown) affording a
fulcrum for the feed sleeve _d_. This sleeve is sometimes made hexagonal
on its outside to receive a wrench or to be held by the hand when
feeding, or it may have holes near its centre end to receive a small pin
or piece of wire; _e_ is a chain to pass around the boiler to secure _b_
to it, which is done by means of the device at _f_.
[30] From _The American Machinist_.
For many purposes a simple stand having an upright cylindrical bar
carrying an arm that may be set at any height and set to its required
position on the bar by a set-screw is sufficient, the base of the stand
being secured to the work by a clamp or other convenient device.
Fig. 1796 represents a flexible shaft for drilling holes inaccessible to
a drilling machine, and in situations or under conditions under which a
ratchet brace would otherwise require to be used. It consists of a shaft
so constructed as to be capable of transmitting rotary motion though the
shaft be bent to any curve or angle. A round belt driven from a line
shaft rotates the grooved pulley, and the shaft transmits the rotary
motion to bevel-wheels contained in a portable drilling frame, the
fulcrum for the feed being afforded by a drilling post after the manner
employed in ratchet drilling. The shaft is built up of several layers of
wire (as shown in the view to the left), the number of layers depending
upon the size and strength of shaft required, wound one upon the other
helically. The layers are put on in groups of three to eight wires,
parallel to each other, each successive layer containing groups of
varying numbers of wires, thus giving a different pitch to the helices
for each layer, the direction of each twist or helix being the reverse
of the one upon which it is wound. When the shaft is laid up in this
manner, the wires at each end for a short distance are brazed solidly
together, and to these solidified ends the piercers are secured for the
attachment of the pulley and tool which it is to drive.
This construction, it will be readily seen, produces a shaft which will
have considerable transverse elasticity, while it must necessarily offer
great resistance to torsional strain, the reversed helices forming a
kind of helical trussing, which effectually braces it against torsion.
The case within which it turns is simply an elastic tube of leather or
other suitable material, within which is wound a single helix of wire
fitting its inside tightly, the inside diameter of the helix being a
little greater than the outside diameter of the shaft, and wound in a
contrary direction to the outer helices of the shaft. This forms a
continuous bearing for the shaft; or at least serves as a bearing at the
points of contact between the shaft and case which are brought about in
the various bending of the whole when in use.
[Illustration: Fig. 1796.]
In order to give to the instrument all the transverse elasticity
possible, that end of the shaft carrying the pulley is made with a
feather so that it may slide endways in the pulley, while the latter is
secured to the case, the case, however, not rotating with it. It will be
readily seen that this is a necessary precaution, inasmuch as in the
varying curves given to the instrument in use a difference will occur in
the relative lengths of the shaft and tube.
It might be supposed that the friction of the shaft within the tube
would be so considerable as to militate against the success of the
apparatus; but in practice, and under test for the determination of
this, it has been found that the friction generated by running it when
bent at a right angle does not exceed that when used in a straight line
more than 15 per cent. of the latter.
In the running of it in a bent position, not only will there be friction
between the shaft and tube, but there must also be some little motion of
the layers of wire one upon another in the shaft itself; and to provide
against the wear and friction which would otherwise occur in this way,
provision is made for not only oiling the bearings at the ends, but also
for confining a small quantity of oil within the tube, by which all
motion of the wires upon one another, or the shaft upon the interior of
the tube, is made easy by its being well lubricated.
In the figure the shaft is shown complete with a wood-boring auger in
place at the shaft end. Shafts of similar but very light construction
are employed by dentists for driving their dental drills and plugging
tools, many of them having ingenious mechanical movements derived from
the rotary motion of the shaft.
[Illustration: Fig. 1797.]
In Fig. 1797 is represented a drilling device in position for drilling a
hole from the inside of a steam boiler. A represents a base piece made
with a journal stud _b_. This base piece is provided with radial arms
_a_, with threaded ends and nuts made with conical projecting ends, as
shown at _a_^{2}. One of these pieces is used at each end of the machine
when convenient, their use for centring and holding the frame being
apparent. When not convenient to use two of them, one end of the frame
is sustained as shown in the engraving, or in some other manner that may
suggest itself. The casting B is made in two pieces, and is provided
with a bearing for the pin _b_, and holds the ends of the rods C C. The
actuating shaft G carries the bevel-wheel _g_, more clearly seen in the
figure at side, which drives the drill spindle, whose ends are of
different lengths, for convenience in reaching to different distances.
The cross-head E may be slid along as required on the rods, and the
revolving frame and drill turned around to different positions.
[Illustration: Fig. 1798.]
Fig. 1798 represents a small hand drilling machine to be fastened to a
work bench. A suitable frame affords journal bearing to the upright
spindle, upon which is a bevel-gear G, which is driven by a gear upon
the same shaft as the wheel W. The spindle is threaded at S and is fed
by the hand wheel F, which is threaded upon the screw S and has journal
bearing in the cap C.
Fig. 1799 represents a hand drilling machine for fixture against a post,
the larger wheel serving as a fly-wheel and the smaller one being to
feed with.
SLOTTING MACHINE.--In the slotting machine the cutting tools are carried
in a ram or slide that operates vertically, and the work table lies
horizontal and beneath the ram.
Fig. 1800 represents a slotting machine, and Fig. 1801 is a sectional
view of the same machine.
The cone spindle shaft has a pinion which drives a spur-wheel upon an
horizontal shaft above. Upon the inside face of this spur gear is a cam
groove for operating the feed motions, at the other end of the shaft is
a Whitworth quick-return motion, such as has already been described with
reference to shaping machines. The connecting rod from the quick-return
motion attaches to the ram, which operates on a guide passing through a
way provided at the upper end of the main frame, and bolting to the
front face of the main body of the frame. The object of this arrangement
is that by adjusting the height of this guide to suit the height of the
work, the ram will be guided as close to the top of the work as the
height of the latter will permit; whereas when the guide for the ram is
fixed in position on the frame the ram passes as far through the guide
when doing this as it does when doing thick work, and is therefore less
closely guided than is necessary so far as the work is concerned.
[Illustration: Fig. 1799.]
[Illustration: Fig. 1800.]
The ram, or slotting bar as it is sometimes termed, is counterbalanced
by the weighted lever shown, so that the ram is always held up, and
there is no jump when the tool post meets the work, because the tool
motion is always taken up by the lever.
[Illustration: Fig. 1801.]
The work is held upon a circular table capable of being revolved upon
its axis to feed the work to the cut. This table is carried upon a
compound slide having two horizontal motions, one at a right angle to
the other. The lower of these is operated by a rod running through the
centre of the machine, as seen in the sectional view in Fig. 1801. The
upper is operated through the larger of the two gear-wheels, seen at the
side of the machine in the general view of the machine in Fig. 1800. The
upper and smaller of these wheels operates a worm, which engages with
worm-teeth cut on the periphery of the circular table to rotate the
latter. Either or all of these feed motions may be put in simultaneous
action, or all may be thrown out and the feeds operated by hand.
As the tool is in many cases rigid on the ram or bar of a slotting
machine, it is preferable that the feed should occur while the tool is
at the top of its stroke and before it meets the work, so that it may
not rub on the return stroke, and thus become rapidly dulled.
Fig. 1802 represents a slotting machine in which the guideway for the
slotting bar or ram is fixed in position, and the feed motions are
entirely on the outside of the machine. In this case the worm-gear
pinion is on the side of the machine not seen in the engraving.
The cutting tools for slotting machines are carried in one of these
ways: first, bolted direct to the slotting bar or ram, in which case
they stand vertically; secondly, in a box that is bolted to the end of
the ram and standing horizontally; and thirdly, held in a tool bar, in
which case the tool may stand either horizontally or vertically.
Fig. 1803 shows a tool B secured in a hole provided in a stout bar A by
the set-screw C. The tool in this case being rigidly held the cutting
edge is apt to rub against the work during the upward stroke and become
rapidly dulled. To avoid this, various devices have been employed, but
before describing them it will be well to point out that the shape of
the tool has an important bearing upon this point.
In Fig. 1804, for example, is a tool T bolted to the box B at the end of
the slide S. W is a piece of work having the cut C taken off it. Now
suppose that A is the centre of motion or fulcrum from which the spring
of the tool takes place (and there is sure to be a little spring under a
heavy cut), then the point of the tool will spring in the direction of
the arrow E, and will cut deeper to the amount of its spring; but during
the up stroke the tool being released from pressure will not spring, and
therefore will partly or quite clear the cut according to the amount of
the spring. This desirable action may be increased by giving the face of
the tool which meets the cutting a slight degree of side rake, as shown
in Fig. 1805, in which S is the slide, T the tool, B the box, and F the
direction of the tool spring, which takes place in this case from the
pressure of the cutting in its resistance to being bent out of the
straight line.
[Illustration: Fig. 1802.]
[Illustration: Fig. 1803.]
[Illustration: Fig. 1804.]
In Fig. 1806 is a device for obviating to some extent this defect. A A
is the tool box or bar containing a tool-holding piece pivoted at C, the
tool being secured therein by the set-screw E B. A spiral spring
sustains the weight of the pivoted piece and of the tool. During the
down stroke the spiral spring holds the pivoted piece against the box or
bar A, while during the up stroke the pivoted piece allows the tool to
swing from the pivot C as denoted by the arrow D. In this case the
friction on the tool edge is that due to overcoming the resistance of
the spring only.
[Illustration: Fig. 1805.]
[Illustration: Fig. 1806.]
[Illustration: Fig. 1807.]
In round-nose tools that are slight, and which from having a maximum
length of cutting edge are very subject to spring, additional strength
may be given the tool by swelling it out at the back, as denoted by the
dotted line B in Fig. 1807.
[Illustration: Fig. 1808.]
Excessively heavy cuts may be taken by the form of tool shown in Fig.
1808, in which A is the tool, B the tool box, and C the work, the depth
of cut being from D to E, which may be made 2-1/3 inches if necessary.
The face F of the tool is ground at an angle in the direction of I, so
that the tool shall take its cut gradually, and that the whole length of
the tool cutting edge shall not strike the cut at the same instant,
which would cause a sudden strain liable to break either the tool or
some part of the machine itself. So likewise the tool will leave its cut
gradually and not with a jump. As shown in the cut, but a small part of
the cutting edge would first meet the work, exerting for an instant of
time only enough pressure and resistance to bring all the working parts
of the machine up to a bearing, and as the tool descends (as denoted by
the arrow G), the strain would increase until the whole length of tool
cutting edge was in operation. For such heavy duty as this the tool is
tempered down to a purple to give it strength.