Home

  

Drill Bits, Countersinks, Reamers & Counter Bores

Drilling a hole is one of the most basic machining tasks.
However, there are many variables associated with successful execution thus requiring consideration of the
material to be drilled, setup, bit design, bit quality, sharpness, length, RPM, feed rate, chip removal, heat & lubrication.
Apparently, you can't have too many drill bits.

Also, see how to drill a hole & how to drill the center of a rod.


Set of USA made fractional (1/16" to ½" by 1/64"),
numbered (1-60) & lettered (A-Z) jobber-length HSS drill bits.


Sets of USA made fractional, numbered & lettered (Cleveland Forge) stub-length HSS drill bits.
The short stub drill bits afford reduced flexing & aid use in tight areas.


Set of German made Dewalt fractional, pilot-point, jobber-length drill bits.
The shanks have three flat sides for enhanced chuck gripping.
These split-point bits work nicely on a lathe.


Set of 9/16" to 1" by 1/16" USA made Silver & Deming HSS drill bits with ½" shanks.
Clamped parts & low RPM with proper lubrication are required for larger bits.


Long drill bits having MT-2 shanks with tang (import) for use in lathe tailstock or floor drill press.
Sizes are ½", 9/16", ⅝", 11/16" & ¾".  These are black-oxide treated HSS.


Set of USA made 1mm to 13mm by 0.5mm metric, jobber-length HSS drill bits.


Set of HSS micro-drills (import) numbered 61 to 80.
In general, the smaller the drill bit, the higher the required RPM.
Clear the chips frequently.
Low-cost, all metal drill sharpener that uses a bench grinder.
Dress the grinder wheel before use.


The Drill Doctor 750X uses a 180 grit diamond wheel to sharpen drill bits.
This model affords variable grinding control over several important bit geometries
such as point angle, chisel & relief angles, split-point & amount of material removal.


Drill bit stop-collar set to control hole depth & afford repeatability.

Drilled holes are for clearance.
The resulting hole size is often larger than the drill & may not be perfectly round.
 Precision holes are either reamed or bored.


Different center drill (plain type) sizes. KEO is a quality brand name.
Left to right: #6, #5, #4½, #4, #3, #2, #1, #0. The long, 4" bit is a #2.

  Body Diameter Drill Bit Diameter Drill Bit Length Overall Length
# Inches mm Inches mm Inches mm Inches mm
0 .0938 2.39 .0312 0.79 .0380 0.97 1.125 29
1 .1250 3.18 .0468 1.19 .0468 1.19 1.250 32
2 .1875 4.76 .0781 1.98 .0781 1.98 1.875 48
3 .2500 6.35 .1093 2.78 .1093 2.78 2.000 51
4 .3125 7.94 .1250 3.18 .1250 3.18 2.125 54
5 .4375 11.11 .1875 4.76 .1875 4.76 2.750 70
6 .5000 12.70 .2187 5.56 .2187 5.56 3.000 76


Unibit stepped drill bits are excellent for thin materials.


A Weldon zero-flute 82° countersink set (USA).
The one center/rear countersink is 100°. Use this countersink for a flat-head screw that fastens thin sheet metal.
These no-chatter countersinks deburr holes very well.
They can be sharpened from inside the hole with a fine round stone or diamond file
but they have, so far, not required any maintenance even after heavy usage.

A Table of Decimal Inch Equivalencies for Fractional, Numbered, Lettered & Metric Drill Bits

Fract.
(in)		 Decimal
(in)		 Wire No. Metric
(mm)		   Fract.
(in)		 Decimal
(in)		 Wire No. Metric
(mm)		   Fract.
(in)		 Decimal
(in)		 Letter Metric
(mm)
 
  0.0098   0.25   0.1065 36     0.3480 S  
  0.0118   0.30 7/64 0.1094       0.3543   9.00
  0.0135 80     0.1100 35     0.3580 T  
  0.0138   0.35   0.1102   2.80 23/64 0.3594    
  0.0145 79     0.1110 34     0.3680 U  
1/64 0.0156       0.1130 33     0.3740   9.50
  0.0157   0.40   0.1142   2.90 3/8 0.3750    
  0.0160 78     0.1160 32     0.3770 V  
  0.0177   0.45   0.1181   3.00   0.3860 W  
  0.0180 77     0.1200 31   25/64 0.3906    
  0.0197   0.50 1/8 0.1250       0.3937   10.00
  0.0200 76     0.1285 30     0.3970 X  
  0.0210 75     0.1360 29     0.4040 Y  
  0.0217   0.55   0.1378   3.50 13/32 0.4063    
  0.0225 74     0.1405 28     0.4130 Z  
  0.0236   0.60 9/64 0.1406       0.4134   10.50
  0.0240 73     0.1440 27   27/64 0.4219    
  0.0250 72     0.1470 26     0.4331   11.00
  0.0256   0.65   0.1495 25   7/16 0.4375    
  0.0260 71     0.1520 24     0.4528   11.50
  0.0276   0.70   0.1540 23   29/64 0.4531    
  0.0280 70   5/32 0.1563     15/32 0.4688    
  0.0292 69     0.1570 22     0.4724   12.00
  0.0295   0.75   0.1575   4.00 31/64 0.4844    
  0.0310 68     0.1590 21     0.4921   12.50
1/32 0.0313       0.1610 20   1/2 0.5000    
  0.0315   0.80   0.1660 19     0.5118   13.00
  0.0320 67     0.1695 18   33/64 0.5156    
  0.0330 66   11/64 0.1719     17/32 0.5313    
  0.0335   0.85   0.1730 17     0.5315   13.50
  0.0350 65     0.1770 16   35/64 0.5469    
  0.0354   0.90   0.1772   4.50   0.5512   14.00
  0.0360 64     0.1800 15   9/16 0.5625    
  0.0370 63     0.1820 14     0.5709   14.50
  0.0374   0.95   0.1850 13   37/64 0.5781    
  0.0380 62   3/16 0.1875       0.5905   15.00
  0.0390 61     0.1890 12   19/32 0.5938    
  0.0394   1.00   0.1910 11   39/64 0.6094    
  0.0400 60     0.1935 10     0.6102   15.50
  0.0410 59     0.1960 9   5/8 0.6250    
  0.0420 58     0.1968   5.00   0.6299   16.00
  0.0430 57     0.1990 8   41/64 0.6406    
  0.0433   1.10   0.2010 7     0.6496   16.50
  0.0465 56   13/64 0.2031     21/32 0.6563    
3/64 0.0469       0.2040 6     0.6693   17.00
  0.0472   1.20   0.2055 5   43/64 0.6719    
  0.0512   1.30   0.2090 4   11/16 0.6875    
  0.0520 55     0.2130 3     0.6890   17.50
  0.0550 54     0.2165   5.50 45/64 0.7031    
  0.0551   1.40 7/32 0.2188       0.7087   18.00
  0.0591   1.50   0.2210 2   23/32 0.7188    
  0.0595 53     0.2280 1     0.7283   18.50
1/16 0.0625       0.2340 A   47/64 0.7344    
  0.0630   1.60 15/64 0.2344       0.7480   19.00
  0.0635 52     0.2362   6.00 3/4 0.7500    
  0.0669   1.70   0.2380 B   49/64 0.7656    
  0.0670 51     0.2420 C     0.7677   19.50
  0.0700 50     0.2460 D   25/32 0.7813    
  0.0709   1.80 1/4 0.2500 E     0.7874   20.00
  0.0730 49     0.2559   6.50 51/64 0.7969    
  0.0748   1.90   0.2570 F     0.8071   20.50
  0.0760 48     0.2610 G   13/16 0.8125    
5/64 0.0781     17/64 0.2656       0.8268   21.00
  0.0785 47     0.2660 H   53/64 0.8281    
  0.0787   2.00   0.2720 I   27/32 0.8438    
  0.0810 46     0.2756   7.00   0.8465   21.50
  0.0820 45     0.2770 J   55/64 0.8594    
  0.0827   2.10   0.2810 K     0.8661   22.00
  0.0860 44   9/32 0.2813     7/8 0.8750    
  0.0866   2.20   0.2900 L     0.8858   22.50
  0.0890 43     0.2950 M   57/64 0.8906    
  0.0906   2.30   0.2953   7.50   0.9055   23.00
  0.0935 42   19/64 0.2969     29/32 0.9063    
3/32 0.0938       0.3020 N   59/64 0.9219    
  0.0945   2.40 5/16 0.3125       0.9252   23.50
  0.0960 41     0.3150   8.00 15/16 0.9375    
  0.0980 40     0.3160 O     0.9449   24.00
  0.0984   2.50   0.3230 P   61/64 0.9531    
  0.0995 39   21/64 0.3281       0.9646   24.50
  0.1015 38     0.3320 Q   31/32 0.9688    
  0.1024   2.60   0.3346   8.50   0.9842   25.00
  0.1040 37     0.3390 R   63/64 0.9844    
  0.1063   2.70 11/32 0.3438     1 1.0000    
 
Fract.
(in)		 Decimal
(in)		 Wire No. Metric
(mm)		 Fract.
(in)		 Decimal
(in)		 Letter Metric
(mm)		 Fract.
(in)		 Decimal
(in)		 Letter Metric
(mm)


Fractional HSS reamer set  (import) 1/16" through ½" by 1/64" in a Huot index case.

Set of 14, over-under sized (±0.001") decimal HSS reamers (import).
Some padding was added & a tighter fitting wooden spacer was made for the index.
Most of these types of wooden cases can benefit from some sanding & gluing.

FRACTION DECIMAL OVER (+.001) UNDER (-.001)
⅛" .1250 .1260 .1240
3/16" .1875 .1885 .1865
¼" .2500 .2510 .2490
5/16" .3125 .3135 .3115
⅜" .3750 .3760 .3740
7/16" .4375 .4385 .4365
½" .5000 .5010 .4990

Drilled holes are for clearance. Precision holes are either bored or reamed.
The hole should be ~1/64" smaller than the reamer. Chamfer the hole before reaming.
Lubricate the reamer & hole with the proper cutting oil before starting.
To keep a tight tolerance, run the reamer at the lowest RPM.
When the reamer is all the way through, stop rotation & then withdraw.
Running a turning reamer in & out will increase the hole size.
Chucking reamers have long shafts that allow some flexing to follow the hole.


Taper pins & their taper-pin reamers. Sizes top to bottom: #2, #1, #0, #3/0, & #4/0.
For short pins, drill the small diameter size. For long pins, step drilling may be required;
refer to tables in Machinery's Handbook.
 
SIZE# DIAMETER - SMALL END (in.) DIAMETER - LARGE END (in.)
4/0 0.0869 0.1142
3/0 0.1029 0.1302
0 0.1287 0.1638
1 0.1447 0.1798
2 0.1605 0.2008


HSS counter-bore set (Israel): #2, #3, #4, #5, #6, #8, #10, ¼", 5/16", ⅜", ½" with fixed (solid) pilots in a Huot index case.
The pilot size is sometimes labeled on the shaft. These pilots are sized for free-fit clearance holes.
Clamp the part, use low RPM & the proper cutting fluid to avoid chatter. It is important to match the pilot hole to the pilot size.

Bolt Size Counter Bore Size (inches) Pilot Size  (inches)
#6 - .2420 - .1500
#8 19/64 .2968 11/64 .1718
#10 21/64 .3281 13/64 .2031
¼" 13/32 .4062 9/32 .2812
5/16" ½ .5000 11/32 .3438
⅜" 19/32 .5938 13/32 .4063
½" 25/32 .7813 17/32 .5313


#6, #8 & #10 counter bores that use interchangeable (3/32" shank) carbon-steel pilots.
Different combinations allow for tighter or looser fit for both the bolt cap-head & shank.
Pilot sizes shown: ⅛", 5/32", 3/16", 7/32", ¼", 5/16". The pilots were so low cost, I bought all of them.
One of the pilots had a burr that needed to be removed via precision grinding.

Bits for wood & masonry.
Brad-point wood bits (Germany) in both metric (4, 5, 6, 7, 8, 10 & 12mm) &
Imperial (⅛", 3/16", ¼", 5/16", ⅜", 7/16" & ½").
A brad point reduces bit wander as a hole is drilled.


A set of Forstner-style wood bits (import) that drill very clean, dimensionally accurate, flat-bottomed holes.
Whenever possible, use a drill press at low RPM, depth stop & clamp the piece; all of which combine to produce an accurate hole.
Sizes: ¼" to 2⅛" by ⅛". On a CD rack project, I was making ⅝" holes for standard-sized wooden dowels but they were a loose fit.
So, I put a ⅝" Forstner bit into the lathe, matched its small angle on the compound & removed a small amount, off the side.
Because of this bit's design, the mod did not change its cutting characteristics, at all. Bought a single, ⅝" bit to restore the set.
Instead of cutting the bit down, I would now use the tool post grinder set at the matching angle.


Spade-type, wood drill bits with hexagonal shanks.


 Milwaukee Brand masonry bits (USA) with brazed carbide tips. Work best with a hammer drill.
Sizes: 3/16"x3", ¼"x4", 5/16"x4", ⅜"x4", ¼"x6", ½"x6".