Improvements in Appliances for Holding and Guiding Twist Drills During Grinding.
Year: 1887

page_text: Date of Application, 23rd Dec., 1887
Complete Left, 5th Mar., 1888
Complete Accepted, 6th Apr., 1888
PROVISIONAL SPECIFICATION.
Improvements in Appliances for Holding and Guiding Twist Drills
During Grinding.
I WALTER JAMES GRIFFITHS of 22 Annandale Road Greenwich in the County of
Kent, Engineer, do hereby declare the nature of this invention to be as follows:-
The appliance I propose using for holding and guiding twist drills during grinding,
while it will enable drills of various sizes to be ground to the proper form for
working, can be made and sold for considerably less than those at present to be
obtained.
It consists of the following parts 1st a base plate on which is cast a vertical socket.
2nd a casting having in it a horizontal cylindrical socket and supported by a pivot
that fits the vertical socket before mentioned. 3rd a chuck for holding the drill that
is to be ground, the forward part of the outside casing of this chuck is cylindrical and
fits into the above horizontal socket: the chuck is constructed with three wedge
shaped pieces which enter from the after end and approach each other as they go
forward, these wedges are constructed with projecting pieces at their after ends so
arranged that when a certain one of them is moved forward it moves equally the other
two by means of its projecting end pushing against the other projecting ends, and in
consequence drills of various sizes can be fixed central. As it is necessary to give
considerable taper to these wedges in order that they may hold drills differing
considerably in size I prefer not to depend on friction alone for holding them and
place a screw parallel with the outside of the wedge which as before explained
pushes in the other two, and a nut on this screw holds the three wedges from moving
back.
Now a twist drill can be ground so that it drills properly if during the grinding of
each of its sides the drill is turned about its axis through an angle of 90° and at the
same time the inclination of its axis to the grinding surface is altered by about 10°
and the drill drawn back endways from the grinding surface a small amount, and in
treating drills of different sizes the first two movements do not require to be altered
but the third, viz., the drawing back action requires its amount to be proportioned to
the diameter of the drill.
To get the above motions I construct a cam fixed about the middle of the length of

page_text: the outside casing of the chuck, the shape of the cam being such that when the chuck
is turned through an angle of 90° (turning in the horizontal socket) and the cam kept
in contact with a fixed guide bar, the inclination of the axis of the chuck, and the
drill which it holds are altered the 10°, the vertical pivot allowing freedom for this
movement. The drawing back movement I regulate by means of a second cam, this
cam resembles a helical surface given to the forward side of the other cam and is held in
contact with the end of a screw which passes through a mut fixed in a slot in the pieco
in which is the horizontal socket, this helical surface has at its greatest radial distance
from the axis of the chuck a suitable pitch for giving the drawback necessary for the
largest twist drill that the chuck will hold and the pitch is gradually reduced as the
radial distance is diminished until it becomes 0 just outside the cylindrical end of
the chuck the drawing back motion can consequently be made more or less
according to the position in which the nut of the screw is fixed in the slot, and by a
scale marked on the side of the slot the nut can be set to the position to give the
movement suitable for the size of drill that is about to be ground. The screw
passing through the nut also serves another purpose for by turning it the chuck is
allowed to approach the grinding surface and continue the grinding as the drill is cut
away.
In grinding one side of the drill the chuck is turned through 90° but on the
opposite side of the axis the cams are made exactly the same and those parts are
brought into contact with the guide bar and screw respectively for grinding the other
side of the drill the fixed guide bar is attached by two screws to the base plate
carrying the vertical socket one of the screw holes being slotted so that its position
may be changed if necessary to suit drills that differ in the inclination of their cutting
edges to the axis.
When inserting a drill into the chuck a templet made of sheet metal is used to
enable the point to be fixed the proper distance beyond the end of the chuck. The
grinding I prefer to do on the side of an emery-wheel or what is better on a cup-
wheel the appliance as above described can be used with nearly any emery-wheel
grinder all that is required for adjustment in fixing it is to make the axis of the
vertical pivot coincide with the grinding surface although a deviation of small amount
does not matter.
In conclusion I may mention that the socket described as horizontal may
advantageously have a slight dip so as to be at about 85° with the vertical as the
grinding of the cutting edges of the drill will then commence with about the proper
angle of relief" namely about 5º.
1000

page_text: COMPLETE SPECIFICATION.
Improvements in Appliances for Holding and Guiding Twist Drills
During Grinding.
I, WALTER JAMES GRIFFITHS of 22 Annandale Road Greenwich in the County of
Kent, Engineer, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and by
the following statement :-
The appliance I use for holding and guiding twist drills during the process of
grinding, while it will enable drills of various sizes to be ground to the proper form
for working, can be made and sold for considerably less than those at present to be
obtained.
For holding drills during grinding I use a chuck of which Fig. 1, in the drawings
annexed, is a longitudinal section and Fig. 2 an end view, the chuck is constructed
with three wedges A, A, and A, and these wedges have projecting or flanged ends so
so arranged that the flange of A, overlaps those of the other two, as shown in Figs. 1
and 3, and consequently when the wedge A, is pushed forward it pushes forward the.
other two equally and drills of various sizes can be fixed central in the chuck; the
wing nut on the screw B prevents the wedges slipping back.
The forward part of the chuck is cylindrical and fits a socket C, shown in Figs. 5
and 6, which is supported by a vertical pivot D. The cast iron foundation plate F
(which may be cast with the bearings which carry the emery wheel spindle, or when
the appliance is supplied as an attachment for an existing grinder, will be simply a
plate to fasten to the bench) holds by means of the screws G G the casting E, in the
socket in the middle of which is inserted the vertical pivot D before referred to.
This casting E heing held at one end between the screws G G is supported at the
other end by the screw H by turning which and raising or lowering that end of the
casting E the drill being ground will be moved to a different part of the emery wheel,
thus enabling the operator with a very slight amount of care to prevent the grooving
of the wheel which would result from grinding many small drills on the same part of
the wheel.
Now a twist drill can be ground so that it will drill properly if during the grinding
of each of its faces the drill is turned about its axis through an angle 90° and at the
same time the inclination of its axis to the grinding surface is altered some 10° to 15°
and the drill drawn back endways a small distance. In dealing with drills of
different sizes the first two movements do not require to be altered but the third, viz.,
the drawing back action requires its amount to be proportional to the diameter of the
drill.
To enable the above movements to be given to the drill I construct on the outside
of the chuck segmental cams I, and I, Figs. 1, 2 and 4 (Fig. 4 being a front view of
the chuck) I, is an exact duplicate of 1, and each is used while grinding a single face
of the drill for giving the necessary change of inclination of the axis of the drill to the
grinding surface, the cam being kept in contact with a fixed guide bar K Fig. 6 ás
he chuck is turned in the socket C.

page_text: The movement that is required to be given to the drill end ways 1 regulate by means
of the form given to the front surface of the cam plate at J, and J, these segments
being exact duplicates of each other and each used for a single face of the drill: they
come in contact with the end of the screw L, Figs. 5 and 6, this screw passes through
a nut that can be fixed higher or lower in the slot in which it is shown by means of
the set screw M and can consequently be fixed opposite the part of the cam surfaces J₁
and J. at less or greater radial distance from the axis of the chuck.
1
The cam surfaces J₁ and J, are formed so that at their greatest radial distance they
will give the drawing back required for the largest size drill that can be inserted in
the chuck and are bevelled off gradually to a plane surface at the least radial distance
at which the screw L can be fixed, consequently a longitudinal movement varying
from that necessary for the largest size drill that can be ground in the appliance
down to zero can be obtained, and by fixing the nut of the screw L according to the
scale marked on it the adjustment can at once be made. The screw L also serves
another purpose, for by turning it the chuck is allowed to approach the grinding
surface and continue the grinding as the drill is cut away.
The grinding I prefer to do on an emery wheel of the shape known as a cup wheel,
but it may also be done on the periphery or side of an ordinary emery wheel or
grindstone. Fig. 7 shows the complete appliance N being the cup wheel and the
other letters referring to the same parts as before, the base of the appliance requires
to be fixed so that the axis of the vertical pivot D shall coincide with the grinding
surface and the screws G G which hold the casting E are made sufficiently long that
by drawing back one and advancing the other the axis of the pivot D may be moved
as the wheel wears away.
In order to determine the proper form for the cams I use the following method,
suppose Figs. 8 and 9 to represent to scale the largest drill that can be inserted in the
chuck, then by taking the sections through 33, 4 and 55 and intermediate points if
necessary I draw the diagram shown in Fig. 10 in which the angle 023 is the angle
of inclination of the axis of the drill to the grinding surface when line 33 is
horizontal, 024 when line 44 is horizontal and 015 when line 55 is horizontal, the
distance between 2 and 1 being the amount that the drill must be moved back in the
direction of the axis while it is turned the 45° between 4 and 5, in Fig. S, to avoid
grinding away the front point of the drill on one side while the heel of the opposite
side is being ground. This gives a form to the drill in which the line of intersection
of the two faces, or what is commonly termed the point, is not quite straight but is full
in the middle as shown in Fig. 9. If however the so called point is required to be
perfectly straight as shown in Fig. 11, that being considered best by some engineers,
the necessary alteration of the cams can be deduced from Fig. 12 in which 063 is the
angle of inclination of the axis of the drill to the grinding surface when line 33
Fig. 8 is horizontal, 024 when line 44 and 015 when line 55 is horizontal, and the
movement then to be got from the face cam will be an advance towards the grinding
surface equal to the distance between 6. and 2 in Fig. 12 when the drill is turned
from 3 to 4 Fig. 8 and a drawing back equal to the distance between 2 and 1 Fig. 12
when turned from 4 to 5 Fig. 8. In the above manner by using more sections the
form of the cams can be completely determined.
In Fig. 5 it will be seen that the socket C is not exactly at right angles to the
vertical pivot D the reason being that by inclining it as shown the grinding surface is
brought tangential to the surface required to be given to the drill and there is less
tendancy to cause flats than if it were horizontal.
If considered desirable a spring may be used to draw the socket C towards the
fixed guide bar K and thus render it unnecessary to keep the cam, I, or I, as the case
may be, in contact with the guide bar by pressing the chuck that way.
Though the segmental cams have been described as being in duplicate, I can by
having a single pair on a plate that could be shifted around the chuck through 1800,
accomplish the grinding of both faces of the drill, but the duplicate arrangement I
consider best. I also propose fastening a leather washer to the front of the socket C

page_text: as it will assist in keeping the dust produced by grinding from getting into the socket
and causing wear.
When a drill is to be fixed in the chuck, either the emery wheel can be stopped and
the end of the drill allowed to rest against it while the wedges are pushed tight, or
the chuck may be removed from the socket C for the drill to be fixed in it, in which
case a templet or guage will have to be used for determining the correct position
for it.
In the drawings of the chuck Figs. 1 and 2 it will be seen that the wedge pieces A₁
A, and A, have a ridge along their outer edges which fitting a groove in the slots in
which they slide, prevents the wedges falling out of their places when there is no drill
in the chuck, a more economical way of managing the same thing however would be
merely to make a groove along the side of the wedges into which the end of a screw
passing through the outer casing could project.
The advantages I consider possessed by the appliance are moderate cost, capability
of being added to existing grinders, and particularly its suitability for dealing with
very small drills.
Besides being used for twist drills the appliance can be used for common drills if
they are sufficiently true in the shanks, and it can also be adapted for fluted drills.
Having now particularly described and ascertained the nature of my said Inven-
tion and in what manner the same is to be performed I declare that what I
claim is
1st. The chuck for the purpose of holding drills during the process of grinding,
substantially as hereinbefore described and illustrated in the drawings hereto
annexed.
2nd. The combination and use of segmental cams for regulating the change of
inclination of axis and longitudinal movement of drills as they are turned partly
around during the process of grinding, substantially as hereinbefore described and
illustrated in the drawings hereto annexed.