Drill and sharpening fixture

A single point drill particularly adapted to producing small diameter deep holes utilizing a peck feed cycle routine. The preferred embodiment features a limited flute length with a depth approximately 1/3 the drill diameter and a dual point edge consisting of a shallow cutting angle and a steep relief angle. A negative rake angle runs along this edge functioning as a knife edge that will cut on opposite rotation, countering the unbalanced forces inherent in a single point tool. A sharpening fixture consisting of 2 parallel slates secured with a T-headed bolt and an anti-rotation pin. The lower plate features a central groove to locate the drill, the upper plate having a short land that facilitates orienting and clamping the drill flute. The forward end of the fixture mimics the drill point allowing the drill to be sharpened on a grinder table or by hand with a suitable abrasive stone or file.

BACKGROUND OF INVENTION 
The current invention relates to improvements in drills and especially 
drills for producing small diameter holes, and in particular drills 
capable of producing deep holes on the order of 50-200.times. the drill 
diameter. 
Producing holes by drilling in sizes below 1/16 to the depths indicated has 
been all but unobtainable using conventional drills and equipment. In the 
case of difficult materials such as 300 series stainless steels, drilling 
beyond 10.times. the drill diameter has been unachievable in these small 
sizes. 
In addition, maintaining small size drills in share cutting condition 
requires very sophisticated and expensive resharpening equipment. Because 
of the great expense involved in the resharpening of small drills, it is 
common practice to simply discard dull drill bits. 
OBJECTS OF THE INVENTION 
It is therefore an object of the current invention to provide a drill that 
can be produced in sizes at least as small as 0.005" capable of drilling 
50.times. its diameter in readily drillable materials. And it is an object 
to produce a drill at least as small as 0.015" capable of drilling to 
depths of 50.times. the drill diameter in difficult to drill materials 
such as 316 stainless steel. Still another objective is to provide a drill 
that will produce accurate holes closely sized to the drill size. Yet 
still another object is to provide a drill that will drill straight holes. 
It is still another object to provide a long wearing point. Again yet 
another object is to provide a drill capable of performing to the 
aforementioned depths on conventional machine shop equipment without the 
need of special equipment or attachments. 
It is still another object to provide a drill that can be resharpened 
without the need of specialized resharpening equipment. It is another 
object to provide a drill that can be economically mass produced. 
Another object is to provide a fixture for facilitating resharpening of the 
drills using common shop grinding equipment. Again, another objective is 
to provide a fixture that can accomodate a range of drill diameters for 
resharpening. Futher objects and advantages will he seen from the text and 
drawings that follow. 
SUMMARY OF INVENTION 
The current invention consists of a drill constructed from suitable cutting 
material (H.S.S. or carbide) and consists of a straight diameter 
throughout its length and terminates in a single point cutting edge. The 
cutting edge is created by the flute which is approximately 1/3 the drill 
diameter. This flute is preferably of a uniform dimension but may be 
tapered. The length of the flute is limited (from 4-20.times. the drill 
diameter) depending on the material to be drilled. Additionally the flute 
ends in a radius or an angle for strength. In one embodiment the point 
consists of a single compound angle resembling a boring bar. In another 
embodiment the point consists of a dual compound angle ground to the 
centerline. The lesser angle being the drilling portion is inclined to 
create a conical point. The oppossing relief angle has the addition of a 
negative rake angle creating a "knife-edge" counter cutting surface. 
The sharpening fixture consists of two halves of rectangular stock, secured 
by a T-head central screw in conjunction with an antirotation pin. An 
axial groove in the rectangular member and a cross hole in the screw 
facilitates the central positioning of the drill in the fixture. A raised 
land on the forward portion of the upper member clamps and orients the 
drill. Set screws or a rear raised land control the attitude of upper 
clamping member insuring positive clamping. The forward portion of the 
fixture mimics the drill geometry. A longitudinal bevel facilitates 
grinding the negative rake angle. The flat base and the horizontal 
fixturing of the drill enables regrinding to the centerline. 
PRIOR ART 
Deep holes produced by the drilling process has been accomplished by gun 
drilling. This is accomplished on specialized machines with special drills 
that may be single or double pointed and which characteristically have a 
thru the tool coolant port. Additionally they have a substantial flute 
length. Gun drills however are not available much below 1/16". 
In addition to gun drills, half round drills (FIG. X,Y,Z) bear a strong 
resemblence to the current invention and they are available in small 
sizes. These drills differ in that they have a concave flute 99. The flute 
length is longer 101 and it is ground to the centerline, whereas the flute 
on the current invention is shorter in length, ground straight across, and 
ground to about 1/3 the diameter. In addition the point geometry is 
different, half round drills employ the helical point 100 of a 
conventional twist drill. 
While 1/2 round drills are well known in the art their use is restricted to 
readily drillable materials such as wood, brass, etc. They are not 
utilized for drilling difficult materials such as 316 SS. 
Much of the prior art regarding the drilling of small holes has not been 
very forthcoming as to drill geometry, method of drilling, pointing and 
resharpening of the tool. 
In 1887 Sawyer discloses a method for manufacturing drills (U.S. Pat. No. 
361,452 using an acid bath to dissolve away a reactive metal from an 
electrodeposited wire to expose a point. He does not illustrate a geometry 
of this tool stating only "The tip may be given any special shape by means 
of filing". This is by no means obvious, and would be considered an 
incredible feat even today--considering he suggests this be done to a wire 
possibly less than 0.001" in diameter! 
Latour (Pat. No. 2,968,200) and Mieville (Pat. No. 3,029,644) both disclose 
drills for drilling small size holes. Both being primarily directed 
towards a synethic body for holding and driving the tool. Neither divulge 
the geometry of the drill point, flute construction or overall tool 
extension. In addition Mieville's tool is supposedly capable of drilling 
extremely hard metal while the tool is purportedly constructed of an 
elastic steel wire. He does not divulge what extremely hard materials his 
tool will drill, but it is well known a cutting tool will not cut a 
material harder than itself. Additionally, producing drills in this 
fashion has to increase the cost of the tool. 
Pat. No. 3,824,026 discloses a point geometry similiar to one of the 
embodiments of the present invention. This geometry is for a double edged 
tool with inverted oppositely disposed cutting edges however. 
The patent to Kashwagi and Kasutani (Pat. No. 4,395,169) divulges a 
similiar dual edge single point tool geometry in a V groove fluted gun 
drill of their design as well as illustrating a similiar prior art 
geometry. 
Saxon et al (Pat. No. 4,536,108) disclose a microdrill with a larger shank 
diameter somewhat similiar to one of the embodiments disclosed in the 
current invention. 
The teachings of Frank (Pat. No. 3,029,664) while not for a drill divulges 
a peck feed drill cycle method utilized by the current invention for 
drilling small holes. 
The patent to English (Pat. No. 3,121,983) discloses a fixture very 
similiar to the current invention except it was designed for twist type 
drills and has a different clamping arrangement as well as lacking an 
unrelieved clamping land, which orients the flute and secures the drill. 
The patent to Wolf (Pat. No. 4,566,227) also disclose a similiar type of 
fixture for sharpening drills on a grinder table having a different means 
of securing the drill. 
The current invention overcomes the limitations of the prior art and offers 
additional advantages as will be seen.

DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, in which the simplest embodiment of this invention is 
shown, the drill consists of a solid cylindrical length of suitable 
cutting material (high speed steel or carbide) generally indicated at 1. 
The tool may be coated with titanium nitride, Ovshinsky, or other coatings 
to enhance tool life and/or performance. A flute or chip pocket is 
indicated at 2. In this embodiment the flute generally runs from 
10-15.times. the drill diameter regardless of the length of the drill. The 
chip pocket terminates in an angular shoulder or radius 3 to retain 
strength The flute 2 is ground approximately 371/2% of the drills' 
diameter creating a substantial pocket that chips readily fill (A FIG. 2). 
This leaves cutting edge 4 approximately 2/3 of the drill diameter 
creating a very strong cutting tooth. The 2/3 geometry provides better 
guidance of the drill in the hole reducing chatter and deflection until 
the full diameter of the drill enters the hole. The cutting edge typically 
is a 20.degree..times.20.degree. compound angle. This simple geometry is 
readily manufactured and can be made in sizes at least as small as 0.005". 
As the geometry is a simple single point beveled edge, without a second 
matching edge to replicate as to geometry, angle and length (as in a twist 
drill) it is of no consequence if the the original angles are not 
reproduced exactly. It will be noted therefore that the drill can be 
resharpened by anyone skilled enough to resharpen a lathe tool bit. 
Sizes as small as 1/32 can be resharpened on an off hand tool grinder. 
Smaller sizes down to 0.015 can be hand stoned. This size is best 
resharpened with the aid of the sharpening fixture that will be described 
later. 
It will also be noted that this embodiment can be converted into a left 
hand tool by regrinding the point with an oppositely angled bevel. 
The cutting edge of this embodiment is not capable of creating its own 
starting hole and requires the tool follow a combined center and 
countersink drilled hole at the very least. The geometry of this 
particular embodiment is suited to readily drillable materials such as 
brass, aluminum, wood, plastic, etc. 
In operation, drilling proceeds as follows: 
The work is first center drilled with a generous center drilled hole. The 
conical recess will act to guide the drill into the hole. The drill is 
chucked in either a chuck or preferably held in a collet. The tool 
extension is adjusted to just beyond the length of the flute. Spindle 
speed is adjusted from several hundred rpm to a few thousand rpm. In so 
much as the tool is a single point tool, it represents an unbalanced 
cutting condition. The use of higher rpm magnifies the detrimental effects 
of this condition. 
Drilling proceeds until the depth of the drill extension is reached using a 
Peck feed cycle either manually or under CNC control. Careful depth 
control is essential for the proper performance of the tool as the chin 
pocket capacity is limited. Peck depth is generally 1/2 the tool diameter 
for this embodiment. After reaching the drill extension depth, the drill 
is extended to twice the original extension. The Z datum is reestablished 
and drilling proceeds via peck cycle to this depth. While the total 
extension of the tool is increasing the effective extension remains the 
same as the tool is supported by the walls of the hole previously drilled. 
The operation is repeated numerous times until the desired depth is 
reached. Depths of 50.times. the tool diameter are readily achievable on 
vertical spindle machines. Depth penetration is limited by the tool's 
ability to overcome gravity in pulling chips out of the hole. On a 
horizontal spindle machine such as a lathe with a dead spindle, chips 
remain on the pocket and are extracted a "spoonful" at a time. Here depth 
capability can be 200.times. the drill diameter. Holes produced by this 
embodiment tend to be drill quality holes--somewhat oversize. While the 
drawings show the drilling portion as a straight uniform shaft it is 
understood that the drill can be manufacturer with a larger concentric 
shank segment (FIG. 4). The larger portion 15 of the tool is for chucking 
the tool. In sizes below 0.010" manipulating the drill becomes difficult. 
In addition, few chucks are available that can accomodate these sizes and 
it is difficult to get the drill to run true. In addition, these size 
drills are easily lost. In the case of these "micro" sizes, the drills 
would be manufactured as a set having progressively longer drill lengths. 
These drills would be used in sequence to achieve small diameter deep 
holes. It should also be understood that while the tool may be constructed 
from solid carbide or H.S.S. it is feasible to manufacture the drill as a 
carbide tipped tool whose performance would be superior to the solid 
homogenous construction of either material. The tipped tool can be 
produced in sizes at least as small as 1/32". Shown in FIGS. 8 and 9 are 
two embodiments. In FIG. 8 a concentric diameter 63 is around on the HSS 
tool 62 and a blind hole 61 is EDM in the carbide 60. The assembly is 
brazed together and centerless around. In the embodiment in FIG. 9 the 
carbide tip 73 has a concentric ground diameter 70 which may be in 
combination with a keyed portion 71. The HSS shank 72 has an EDM hole and 
a slot to accomodate the carbide tin. The assembly is brazed together and 
centerless ground. Then the flute and the point are ground into the tool. 
Tungsten carbide holds an edge many times longer than HSS, however carbide 
is very brittle and breaks easily in these small sizes. By employing 
carbide only for the cutting tip the benefit of the long wearing edge is 
obtained while the use of the HSS shank provides the benefit of the 
resiliant steel. 
Another embodiment of this drill is shown in FIG. 5. This version of the 
tool is capable of drilling difficult materials, produces more accurate 
holes and will produce straighter holes. Like the previous embodiment it 
has a body portion of straight uniform diameter indicated at 1. The chip 
pocket portion of the tool is shown at 2. It is shorter in length than the 
previous embodiment generally from 6-8.times. the drill diameter for 
increased strength and it terminated in a radius or angular shoulder 3 as 
with the previous embodiment. 
The point geometry of this embodiment differs however. It consists of a 
dual angled point. A lesser angle 5 and a greater angle 6. The lesser 
angle 5 is the cutting edge, typically a 10.degree..times.20.degree. 
compound angle. The width of this angle is from 1/3 to a maximum of 1/2 
the drill diameter. This relaxes the tolerance on grinding the cutting 
point and provides some advantage when resharpening is necessary, for if 
the width of the edge is 1/3 the diameter then only surface 5 need be 
reground instead of multiple surfaces. The angle of cutting edge 5 is 
disposed in the opposite direction of the previous embodiment. This 
represents a conical edge that has gyroscopic cutting action that helps 
keep the tool centered. The combination of the centering action and 
guidance from the body of the drill serve to produce straight accurate 
holes. The greater angle 6 is the relief angle, typically it is a 
45.degree..times.20.degree. compound angle. As the tool has one cutting 
edge and is cutting a conical cavity in the work, the surface of the 
opposing quadrant of the drill must be relieved so not to rub on the 
surface of the work. Without rubbing relief, fracturing of the opposing 
surface or breakage of the drill may occur. In the case of the previous 
embodiment the oppositely disposed cutting edge is cutting an M shaped 
profile (cavity) which creates greater clearance for the tool. Shown at 7 
is a salient feature of this embodiment, it is a negative rake angle, 
which runs along greater angle 6 typically it is a 30.degree. negative 
rake. In a conventional two flute drill the cutting teeth are mirror 
images of each other, with the opposite tooth being inverted and 
oppositely disposed to the other tooth from the centerline. The opposing 
tooth is inverted as it is as it must cut on the opposite rotation. The 
two cutting teeth balance and cancel out the cutting forces generated. 
While the single point has a stronger tooth geometry and better chip 
clearance the cutting forces are unbalanced. These forces are significant. 
While the modified point embodiment can start its own hole if done 
carefully the forces are significant enough to push the drill over to the 
opposite quadrant. Even with opposing relief 6 this surface can contact 
the opposite wall of the workpiece causing possible chipping or complete 
failure of the tool. While the design of the single flute precludes an 
opposing tooth, the negative rake 7 along relief angle 6 functions as a 
counter cutting edge--when deflected into the workpiece it will cut, 
exerting some force to counter the deflection. Even though it is on the 
opposite rotation, the negative rake functions as a knife edge that will 
cut regardless of the rotation it encounters. 
Seen at 8 is a land approximately 1/2 to 11/2 diameters in length. This 
portion of the flute is ground to the centerline of the drill making a 
more efficient cutting edge. In the previous embodiment the cutting edge 
remains above the centerline. With the tool above centerline, it means 
there is an area of the work that is not being drilled. The tool is able 
to cut because in small sizes the difference between the centerline and 
the 2/3 flute geometry may be only a few thousandths of an inch and 
because the material is soft the tool can plow through the work. In the 
case of harder materials leaving an area of the work uncut is intolerable. 
With the cutting edge on centerline all the material is being cut. This 
also contributes to the production of more accurate holes. The centerline 
land 8 is restricted in length to retain strength and it terminates in an 
angular shoulder 9, likewise to retain strength. Leaving the land on the 
long side, 1-11/2.times. the diameter is a practical consideration as it 
means that in resharpening only surfaces 5,6,7 need be restored as 
necessary. Once land 8 is gone it must be reground as well. This requires 
a surface grinder and the sharpening fixture. 
Seen at #10 is an optional slot or groove approximately 1-11/2.times. the 
drill diameter in width that is around to the centerline being located 
approximately 3 or 4 diameters from the tip. It is suited for through hole 
applications. As noted earlier the unbalanced cutting force causes tool 
deflection so that the bottom of the hole tends to be slightly smaller 
than the rest of the hole. Grinding the flat to the centerline gives it 
cutting properties allowing it to cut the bottom of the hole by extending 
the cutting flat portion of the drill beyond the exit depth of the work. 
Shown in FIGS. 5A & 7 are alternate embodiments of the modified point tool. 
The embodiment in FIG. 5A is identical to that shown in FIG. 5 except 
flute 2 is tapered as shown. This produces maximum strength in the drill 
for very difficult materials albeit at the expense of decreased peck 
depth. The embodiment in FIG. 7 is for larger sizes of the tool. Features 
1,2,3,5,8,9 are the same as the previous embodiment. Relief angle 6 is 
instead ground away 13 up to or just shy of the tool's centerline. This 
represents the half of the tool that would rub on the workpiece. Relief 
area 13 is a mirror angle to edge 5 typically 10.degree..times.20.degree. 
and relieved back for about 1/4-1/2 the tool diameter. Centerline land 8 
is about 1.times. the tool's diameter in length. In larger sizes splitting 
the centerline is easier to achieve and a tolerance of .+-.0.001" is much 
less significant in larger size drills. The advantage of this geometry is 
that it eliminates the chisel edge 12 at the center shown in the 
embodiment in FIG. 5. This cuts more efficiently and penetrates the work 
easier. A counter cutting edge 14 is ground on the periphery of the tool. 
It is typically ground at 45.degree. to the horizontal axis of the tool 
and typically 10.degree. to the longitudinal axis of the tool. The edge 11 
of flute 2 may be honed to a radius to kill any cutting action that may 
take place by the edge rubbing against the work producing oversize holes. 
In operation drilling proceeds as with the previous embodiment with peck 
depth limited to 1/3-1/4 the drill diameter. In the case of the 0.015" 
drill peck depth may be limited to 1/15 the drill diameter. 
Holes produced by the embodiments in FIGS. 5 & 7 are more accurate than the 
holes produced with the previous embodiment. Additionally, the modified 
point embodiment also produces straighter holes. In addition it will be 
noted that either embodiment is free from the breakout phenomenon 
experienced with conventional twist drills whose helical flutes tend to 
grab and pull the workpiece upward. In the same regard drilling 
intersecting holes in the workpiece also does not create a problem. 
To facilitate the resharpening of the embodiments shown in FIG. 1 and FIG. 
5 a sharpening fixture shown in FIGS. 10-15 is utilized. The fixture 
consists of two rectangular pieces 25 and 50 secured by screw member 40 
and nut 41. The through hole 42, 51, in upper and lower fixture members 
25, 50 is located on the centerline of the fixture. On the underside of 
bottom member 50 is an axial slot 52 sized to accomodate the T head of 
screw A. The T head insures cross hole 43 in screw 40 is aligned with the 
axis of the fixture, permitting the drill to pass through the screw and it 
prevents the rotation of screw 40 upon tightening or loosening of nut 41. 
An anti-rotation pin 28 can be located virtually anywhere on the fixture, 
is shown in the lower left corner of FIG. 8. The pin is pressed or 
otherwise secured in through hole 33 in one member and is a slip fit in 
the other 33a. it will be noted that the fixture can be tightened or 
loosened by simply turning a single nut, or knob 41. 
Running along the centerline on the top side of bottom member 50 is a 
rectangular U or V slot 32. This slot accomodates the drill to be 
sharpened. The fixture is made with slots having a variety of 
widths/depths for different diameter drills. Each particular slot will 
accomodate a range of drill diameters. For example a fixture with a 0.016" 
wide slot X 0.008" deep will accomodate a 1/64" diameter drill locating it 
within the U slot 32 (FIG. 14). Larger diameter drills will locate in the 
fixture by seating on the corners of the U slot 32 (FIG. 15). Each fixture 
accomodates a 0.015" range so drill sizes from 1/64"-1/16" can be 
resharpened utilizing 3 or 4 fixtures. 
On the underside of the upper member 25 of the fixture, most of the bottom 
is relieved leaving a land at the top 26, the depth of the relief and the 
width of the land is proportional to the fixtures drill size range. On the 
smallest size fixture two lands 27 separated by a longitudinal slot 31 on 
the centerline of the fixture are located at the opposite end of land 26. 
These lands are slightly higher in height than forward land 26 so that 
when clamping screw 40 is tightened the forward land assumes a downhill 
attitude. The forward land 24 clamps the flute of the drill 2 and orients 
the flute in a horizontal plane for resharpening. For larger size fixtures 
the rear lands 27 are replaced by two threaded holes 34 in upper member 25 
just rearward of screw 40. Two set screws 29 are adjusted according to the 
size of the drill being resharpened to adjust the attitude of the top 
member for optimum clamping on the drill flute. Alternatively, adjusting 
set screws 29 may be eliminated by drilling hole 33 at a slight angle, 
this results in upper member 25 having an "open mouth" bias which is 
closed onto the drill by tightening nut 41. 
The forward most portion of the fixture mimics the geometry of the drill. 
The lower member 50 would typically have 10.degree..times.20.degree. (53) 
.times.45.degree..times.20.degree. (54) angles. The secondary angles can 
be increased 10.degree..times.25.degree..times.45.degree..times.25.degree. 
for example to create increased clearance so as not to to grind the 
fixture when resharpening the drill. The forward most portion of the upper 
fixture member likewise terminates in angular surfaces typically 
10.degree..times.0.degree. or 10.degree..times.20.degree. (35) and 
45.degree..times.30.degree. (30). 
While the forward portion of the fixture mimics the modified point 
embodiment it will be noted that the previous drill can be resharpened 
with this fixture as well. One need only set the mitre gage and table 
angle to 20.degree..times.20.degree. instead of 
45.degree..times.20.degree.. 
The bottom member 50 may be longer than upper member 25 to provide 
protection to long drill bits, and the shorter length of the upper members 
allows drills to be manipulated for instalation/removal. When assembled, 
(FIG. 12) the upper and lower fixture members essentially meet at their 
forward end. Once the drill is clamped in the fixture sharpening proceeds, 
preferably with a grinder with a mitre gage and tilting table. A good 
quality belt/disc sander with 400-600 grit abrasive works well. For 
smaller sizes a jewelers loupe or other optical aid may be utilized. After 
grinding angles 5 and 6 negative rake angle 7 may be ground by tilting the 
fixture on beveled surface 55. The mitre gage is reset so that grinding 
will take place uniformly along edge 6. 
Alternatively, it is possible to sharpen a drill point by hand with nothing 
more than a stone or diamond hone. The compound angles of the fixture 
being used as a guide to resharpen surfaces 5,6,7. Since the base of 
fixture 56 is a flat rectangular surface and the drill is clamped parallel 
to this surface then centerline land 8 can be reground on a surface 
grinder. 
It should be understood that while the embodiment described is especially 
useful for small size drills the scope and spirit of the invention can 
encompass larger size drills and half round drills as well. It being 
understood the helical point would be replaced with a functional angular 
point. Chances in the clamping arrangement may be made without departing 
from the scope and spirit of the invention. For example the central 
securing T headed screw may be replaced with 4 periphial posts and 2 
screws to secure upper and lower fixture members. The invention shall not 
be considered limited except by the following claims.