Year: 1886

page_text: I, JAMES YATE JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of this Invention which Invention has
been communicated to me from abroad by John Sellers Bancroft of the City and
County of Philadelphia and State of Pennsylvania in the United States of America
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement:-
In all drills there is necessarily a certain thickness of metal left between the two
sides of the drill to hold them together, as for example, the web left between the
two spiral grooves in a twist drill, and hence the two cutting edges do not meet
and the line which connects them, formed at the intersection of the two surfaces.to
which the lips are ground, is the so-called point of the drill; the thickness of the
point is the length of this line and varies with the thickness of the metal in the
center of the drill and the amount of clearance given to the lips.*
This point offers great resistance to the progress of the drill through the work,
on account of the very obtuse angle at which the surfaces forming the point meet,
thus making the action at this line of junction rather one of scraping than of
cutting, and of course the resistance increases as the thickness of the point is
increased with the size of the drill. With large drills the thickness of this web, to
give the required strength to the lips, is so great that it has long been recognized
as necessary to reduce the point, by grinding it away so that the two flat sides of a
flat drill, or the two concave sides of a twist drill will converge more rapidly
toward the point. This grinding or pointing as it is technically termed, has, prior
to this Invention, been performed exclusively by hand without the aid of machinery
other than a revolving grinding wheel or stone. When so performed, however, it
requires great care for even the most expert workman to thin the point so that
it will be even approximately central between the two cutting edges of the drill.
In the United States Patent granted to J Sellers Bancroft, and William H Thorne,
for a machine for sharpening drills, N° 270,365, dated January 9th 1883, means are
shown and described for grinding the lips of a drill so that the two cutting edges
shall be at exactly the same angle with, and equi-distant from, the axis of the drill

page_text: and the apex of the convex point, so produced, will be exactly on this axis, but if
the metal forming the web of the drill be not central, one cutting edge will be
longer than the other, hence the two cutting edges would not work exactly alike
and the size of the hole would be uncertain. It has, therefore, been found necessary,
for accurate work, to point the drills after they have been thus sharpened.
It is the first object of this invention, therefore, to point a drill so that the axis
of rotation, from which the two cutting edges are equi-distant, and about which they
revolve at the same angle of inclination, shall be exactly in the centre of 'the above
defined point of the drill and the point itself shall be of the minimum practical
thickness.
It is a further object of this invention to hold the drill to be pointed accurately
in its true position, without depending upon exceptional skill on the part of the
operator, and to these ends the nature of this invention consists in mechanism for
chucking and clamping the drill so that each side of the point of the drill can be.
ground away or the point be reduced by forming on each side of the point a surface
inclined to a plane passing equi-distantly from and between the two cutting edges,
these surfaces being also equi-distant from the axis of the drill, and it further consists
in mechanism for automatically conforming the width of these surfaces to the
diameter of the drill to be pointed.
In the accompanying drawings which form part of this Specification Figure 1
represents an elevation of a machine constructed according to this invention with
the jaws for holding the drill removed so as to show the grinding wheel in contact
with the drill. Figure 2 is a plan showing a drill in position in the jaws. Figure 3
is an enlarged plan of the jaws for holding the drill. Figure 4 is an elevation of
part of Figure 3 showing the means for guiding the jaws. Figure 5 is an elevation
of Figure 3 showing the stops on the jaws for accurately determining the position
of the drill to be pointed. Figure 6 is a plan of the wheel-holding and guiding
mechanism, shown in position for pointing the smallest drill for which the machine
is calculated. Figure 7 is an end elevation of part of Figure 6. Figure 8 is a plan
of the parts shown in Figure 6 in position for pointing the largest drill the machine
is calculated to grind.-Figure 9 is a projection of the grinding wheel on a plane
passing through the centre of the wheel and at right angles to its path when the
wheel holding and. guiding mechanism is in the position shewn in Figure 8.
Figures 10 and 11 are side and end views respectively of a twist drill pointed by
the improved machine. Figures 12 and 13 are side and end views respectively of
a flat drill pointed by the same means. In all the figures similar letters refer to
similar parts The operation is the same whether the drill operated upon be flat or
twist.
A Figures 1 and 2 represents the bed of the machine. B Figure 2 Sheet 2 shows
a drill in position for pointing. The back end of the drill is carried by the sliding
back centre D which slides freely on the rod C secured in the stand A. The
centre D is retained in alignment by a feather sliding in a groove in the rod C and
is clamped by the nut S so as to steady the end of the drill B, which is held firmly
against the centre D after its longitudinal position has been fixed by the end stop n
hereafter described, when the drill is turned over to have the other side of the point
ground it is held firmly against this centre D while reclamping the cutting end.
The cutting end of the drill is clamped between the faces o and p on the jaws E
and F, the drill being first rotated by hand until its lips rest against the stops
and m on the jaws F and E respectively, in which position-it-is-retained by the
hand of the operator during the process of grinding, (see Figures 3 and 5) the
longitudinal position of the drill being determined as above mentioned by the end
stop n on the jaw E so that the drill is accurately chucked or clamped in position
radially by the clamping faces o and p, circumferentially by the stops and m, and
longitudinally by the end stop n; the corner formed by the meeting of the two
faces o and n is so located near the axis of the cylindrical part of the jaw E, that
it will always move in the same line relatively to the guiding slot in the block G
without being affected by the angle at which this block may be clamped. To

page_text: locate the reduced point of the drill between the two cutting edges so that these
edges shall be equi-distant from it and of equal length, it is essential that the
cutting edges shall be held accurately so that the outer ends of the cutting edges
shall be equi-distant from the axis about which they revolve and so that these ends
and the axis of the drill shall be in the same fixed plane and in the same position
longitudinally when either side of the point as above definod is presented to the
grinding wheel.
It will be observed that any method of grasping the body of a drill in a chuck,
or laying the drill in a groove, for the purpose of pointing, is undesirable, firstly
because these methods would be applicable to twist drills only, and secondly because
it is impossible, by such methods of holding, to be certain that the point will be
central between the two cutting edges, since any crookedness in the drill, or
irregular spacing of the flutes will vary the position of the end of the drill as it is
turned over in the chuck. It is consequently essential, for the accurate location of
the reduced point, that the drill should be held by the outer ends of the two
cutting edges, and these cutting edges, or the edges of the flutes immediately
adjoining these cutting edges, should be held against stops such as l.and m to fix
their position relatively to the grinding wheel, that is to say, the drill should be
held or chucked radially and circumferentially with reference to its cutting edges.
If the drill be thus held or chucked and the grinding wheel be brought to bear
upon the point so as to reduce it slightly and the drill be then turned half way
round, (being held against the back center D to prevent longitudinal motion, the
end stop being used only to determine- the position of the drill when first
chucked), and again grasped by the same surfaces and the grinding wheel again
brought to bear upon the reversed point without any change in the adjustment of
the wheel, it will result in the point being absolutely central between the two
cutting edges. It will be evident that instead of the back centre D the end stop n
may be used to determine the position of the drill in both chuckings, but this
requires that the back centre D shall be held against the drill by a spring or its
equivalent, to prevent side motion on the conical centre. The clamping jaws E
and F are made cylindrical on their clamping ends which are supported by the
blocks G and H as shewn in figures 3, 4 and 5, the clamping faces o and p and
stops l, m and n being formed on the upper ends of these cylinders, while the lower
ends slide in slots h and j in the guiding blocks G and H. These slots or grooves
confine the motion of the jaws in right lines laterally, while the enlarged portion of
the arms of the jaws fit in grooves a and b which prevent vertical motion of the
jaws.. These cylindrical ends of the jaws E and F, in connection with the pivot
screws c and d in the lever N, leave free the angular adjustment of the blocks G
and H; without in any manner interfering with the bearing and support of the
jaws in the blocks. The jaws E and F are moved in and out to grasp a small or
large drill by means of the lever N, pivoted at T, (Figure 2;) the short arms of
this lever are of equal length and the arms of the jaws E and F are attached thereto
by the pivot screws c and d respectively so as to vibrate freely about these screws:
When the lever N is vibrated about the centre T, the jaws E and F are simul-
taneously and equally moved to or from the centre line of the drill B.
It is essential that the points of the drills to be ground should always come in
the same position relatively to the path of the grinding wheel, and, therefore, the
jaws E and F must move in lines parallel with the cutting edges of the drill, and
as the angles which these edges make with each other may be varied according to
the nature of the work to be performed, the guide blocks G and H are made
adjustable about the centre e as shewn in Figure 3 and their inner edges are set to
correspond with the proper graduations on the base plate to conform to the angle
of the drill lips, the bolts fand f¹, shown in dotted lines being used to clamp the
blocks in the desired position. These blocks should be adjusted so that the slots h
and j, which guide the cylindrical portion of the jaws shall be parallel to the
cutting edges of the drill B.. The centre line of these slots and j is radial to the
centre e about which the blocks G and H-rotate and the centres of the cylindrical

page_text: portion of the jaws, will, therefore, move in radial lines and hence all drills, of
whatever diameter within the range of the machine, whose cutting edges are at the
same angle as that to which the blocks G and H are set, will have their respective
points brought to exactly the same position relatively to the path of the grinding
wheel.
The grinding wheel I travels in a circular path that has for its radius the link N;
and for its centre the pivot U, the axis of which pivot is inclined as shown in
Figure 1, the line of motion of the wheel I is at a considerable angle with the axis
of the drill as indicated by the line y, y, Figure 1, so that the greatest depth of the
cut made by the wheel will be at the extreme end of the drill, this cut rapidly
decreasing in depth as it extends back from the extreme end, and hence the
supports to the cutting edges of the drill are not weakened by thinning the centre,
as is usually the case in hand grinding. The path of the cutting line of the wheel
is indicated by the line y y, in Figures 2 and 3, and it will be seen that it passes
between the line of the axis of the drill and its cutting edge.
The wheel I is secured on one end of a mandrel, which turns freely in the
bearing J and is driven by the cord pulley V secured to the opposite end, the
belt driving this pulley V passing under the fixed pulley W and also under
the tightener pulley X, carried by the weighted arm Y which is pivoted at Z.
The path of the belt is indicated by broken lines in Figure 1. The tightener
pulley accomodates the belt to the varying position of the pulley V. The vibrating
frame L is supported so as to swing freely on the pivots U and k, fastened
in a stand formed with or secured to the bed A, the axes of the pivots U
and being in the same axial line and inclined to a horizontal plane as
shewn in Figure 1 for the purpose above described. The frame K is pivoted
on the vibrating frame L by pivots g and r, which are paralled with the
pivots U and k; The other end of the frame K carries the adjustable rods 8.
to which is secured the bearing J, as shown in Figure 7. The rod s is provided
at its upper end with a screw thread which engages with the adjusting or
feed nut which regulates the height of the wheel I by sliding the rods through
its bearings in the frame K. The nut tis graduated on its circumference so
that the grinding wheel may be set to the same distance from the axis of
the drill for each side of the point, the same graduation being made to coincide
with the mark or index Z¹ on the index link R. The pivot u is secured firmly
in the bearing J so that its axis if prolonged would intersect the axis of the
grinding wheel at a right angle and pass through the point in its circumference.
where it touches or is tangent to the drill to be ground. This pivot u turns and
slides freely in the radius link M and index link R. From this combination it
follows that the point of tangency of the wheel with the drill will always move in
a fixed path determined by the length of the radius link M and the position of the
fixed pivot U. The frame K and radius link M are of equal length; the distanco
between the rods and pivot u is equal to the distance between the pivots U and
and this method of carrying the grinding wheel thus forms a parallel motion and,
as the rod s is parallel to the pivot u and in the plane of the grinding wheel, it
follows that the wheel I will remain parallel to a plane passing through the
pivots U and in all parts of its path. In figure '6, these parts are shewn in
position for pointing the smallest drill for which the machine is adapted, the
broken line y y showing the path of the pivot u and of the corresponding point of
tangency of the wheel 1 with the drill and-the-line 2. shewing the path of the
rod s; in this case it will be observed that the cut made by the wheel I will be
but little wider than the thickness of the wheel itself, as when the wheel is at the
extreme end of the drill, its centre plane is tangent to the path described by
the pivot and the cut made in the drill will be wider than the wheel only by the
amount of the versed sine of the arc through which the wheel swings while in
contact with the drill. A cam P on the inner end of the vibrating frame L is
pressed against a boss on the lever N by a spiral spring w which rotates the
lever N in the direction to close the jaws E and F and hence grips any drill held

page_text: between the jaws with a force due to the strength of the spring w. In Figure 6,
the boss is shown in contact with the cam P in the proper position for the
smallest drill the machine is calculated to grind; the, broken circle O¹ showing
the position of the boss O when the largest drill the machine is intended to grind
is clasped between the jaws; in Figure 8, the cam P is shown as moved over to
this position, thereby moving the vibrating frame L through an angle of about 15°,
the effect being to swing the axis of the grinding wheel I through the same angle
about the pivot u in a plane parallel with the path in which its grinding surface
operates, without changing the position of the pivot u which still describes the
same arc y y about the fixed centre U and consequently the point of tangency of
the wheel with the drill also moves in the same path as before; the pivot r being
shifted by the movement of the vibrating frame L, the rod s describes the path z z
about this new position, so the centre plane of the wheel is still parallel to the
plane passing through the pivots U and r and the profile of the wheel relatively to
its path at the point of the drill is represented in Figure 9 so the cut made in the
point by the wheel will now be much wider than before. By properly propor-
tioning the cam P and lever N it is possible to vary the angle of the axis of the
wheel I in a plane parallel to the path in which its grinding surface operates to
any desired extent proportioned to the size of the drill to be pointed and when
this position is once determined in the construction of the machine, the operator
has only to see that the blocks G and H are set to the angle to which the drill lips
are ground, after which the operation of clasping the drill between the jaws E
and F by means of the clamping lever N, automatically adjusts the grinding wheel
to the proper angle. The spiral spring w through the pressure of the cam P against
the lever N, tends to hold the jaws to hold the jaws E and F against the drill; the
back centre D is now moved up so as to hold the end of the drill, and the operator,
placing his hand on the radius link M moves the wheel I back and forth over the
point of the drill B, the amount of cut at each stroke being adjusted by the feed or
adjusting nut t when one side is properly pointed, the lever N is pushed back so as
to open the jaws, the drill is turned over, the lips coming against the stops and m
as before and the wheel is passed over this side of the point of the drill until the
graduation on the adjusting nut t is at the same mark as before, when the surfaces
on each side of the point will be at exactly the same distance from the axis of the
drill and consequently the chisel edge or point will be central, and the drill thus
pointed, assuming that its lips have been properly ground, will produce accurate
work.
In the foregoing description the traverse of the grinding wheel has been
described as being in a circular path of comparatively short radius, the length of
this radius is not essential, as it may be extended indefinitely, it being requisite
only that the grinding surface of the wheel should be guided in a fixed path, the
width of the path varied by adjusting the axis of the wheel in a plane parallel to
the path in which its grinding surface operates.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is,
First. In a drill Pointing Machine, a grinding wheel operating in a fixed path,
with its axis variable in a plane parallel to the path in which its grinding surface
operates, whereby the width of the path may be increased or diminished, sub-
stantially as and for the purpose herein before set forth.
Second. In a Drill Pointing Machine the combination of a grinding wheel, a
supporting frame therefore vibrating about an axis perpendicular to the axis of the
grinding wheel, drill clamping jaws, and a lever connected to said jaws and
engaging the said wheel-carrying frame, whereby the movement of the lever to
operate the clamping jaws adjusts the wheel carrying frame with relation to the
jaws and varies the width of the path of travel of the grinding wheel to correspond
to the size of the drill held by the clamping jaws.

page_text: Third. In a Drill Pointing Machine clamping jaws for holding the drill in
combination with supports which guide the clamping jaws in lines parallel to
the cutting edges of the drill, substantially as and for the purpose hereinbefore
set forth.
Fourth. The adjustable guiding blocks G and H in combination with the
clamping jaws E and F for holding the drill, whereby the movements of the
clamping jaws are made parallel to the cutting edges of the drill, substantially as
and for the purpose herein before set forth.
: