Drill Bits, Countersinks, Reamers & Counter-bores
Last updated on Tuesday, September 09, 2014 05:40:01 PM Eastern US Time Zone

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Drill Bits, Left-hand Drill Bits, Long Boy, Silver & Deming, Metric, Tapered Shank, Drill Bit Gages,
Sharpeners, Center Drill Bits, Stepped Drill Bits, Circle Cutter, Countersinks, Reamers, Floating Reamer Holder,
Taper-pin Reamers, Counter-bores, Engraving Bits, Combo Drill-Tap Bits, Diamond Wheels, Wood bits, Masonry Bits

Drilling a hole through metal is one of the most basic machining tasks.
However, there are many variables associated with successful execution thus requiring careful consideration of: the
material to be drilled, setup, bit design, bit material, sharpness, length, RPM, feed rate, chip removal, heat, & lubrication.

Also see, drill presses, how to drill a hole & how to drill the center of a rod.
Decimal Equivalents of Fractions   Decimal Equivalents of # Drills   Decimal Equivalents of Letter Drills

Inch to mm Conversion   mm to Inch Conversion   Metric & Inch Equivalents
Guide for Cutting Speeds & Feeds for Drills  
Machinist Calculator

Drill Bits

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


Set of HSS micro-drill bits (import) numbered 61 to 80.
In general, the smaller the drill bit, the higher the required RPM. Clear the chips frequently.


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

Polished (bright finish): Polished drills do not have a coating which helps increase chip flow in soft materials.
For use in aluminum, wood, & plastic. Titanium Nitride (TiN) gold color: Multi-purpose coating that increases tool
life & performance. Hardness & heat resistance allows running at higher speeds & feeds (25% higher than uncoated).
Black Oxide surface treatment: Retains lubricants to aid in wear resistance & chip flow. Do not use in non-ferrous materials.

Left-hand Drill Bits

Left-hand HSS drill bit set, 135° split-point design, used to drill a hole in a broken screw or bolt to extract it.
Sizes: ¼", 15/64", 7/32", 13/64", 3/16", 11/64", 5/32", 9/64", ⅛", 7/64", 3/32", 5/64", & 1/16".


Left-hand split-point ¼" cobalt steel drill bit. Run drill in reverse.


Drill extraction set that has left-handed, split-tip cobalt drills for hard materials (USA).

Long Boy Drill Bits

Eight-inch, black oxide, HSS long boy drill bit set ⅛" x ½" x 1/64" (import). The drill bit stand is by Huot (USA).

Silver & Deming

Set of 8, 9/16" to 1" by 1/16" Silver & Deming HSS drill bits with ½" shanks (USA) in a Huot drill bit index.
Clamped parts & low RPM with the proper cutting fluid are required for successful large bit hole drilling.


Set of 33, ½" to 1" by 1/64" Silver & Deming HSS drill bits with ½" shanks (import) in a Huot drill storage stand.


Set of eight, 1-1/16" through 1½" by 1/16" Silver & Deming HSS drill bits with ½" shanks (import).
The chisel edges (
bit geometries) for these bits are large thus causing chatter & wandering when drilling metal.
Pre-drill the hole with a bit slightly larger than the chisel edge. Then, just the cutting lip will smoothly drill the hole.
Use low RPM & adequate amounts of the appropriate cutting oil.


The stand uses ¼-28 x 2¼" bolts, with tube spacers, threaded into the upper plate. Bolt heads act as feet.


1½" mounted drill bit in RF-25 mill.


1.5" drilled hole through a ¼" steel plate.


Stands afford high-density storage for drill bits, transfer punch, & transfer screw sets.

Tapered Shank

Long drill bits having MT2 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.

Metric Drill Bits

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


Set of
51, 1mm to 6mm by 0.1mm, jobber-length, TiN coated HSS metric drill bits in a steel index (China).


Set of 50, 1mm to 5.9mm by 0.1mm, jobber-length, HSS metric drill bits in a Huot index (mixed manufacture).


Set of 41, 6mm to 10mm by 0.1mm, jobber-length, HSS metric drill bits in a Huot index.


Micro-drill bit set (carbide). Size marked on the plastic collar which also acts as a depth stop for setup repeatability.

Drill Bit Gages

Fractional, numbered, & metric drill bit gages.


Metric drill bit gage 1mm to 13mm by ½mm made out of ¼" aluminum plate. A ¼" hole is on the far right end.

Sharpeners

Low-cost, all metal drill bit sharpener that uses a bench grinder.
Dress the grinder wheel before use. Grinding attachment manual.


The Drill Doctor 750X uses a 180 grit diamond wheel to sharpen drill bits (manual).
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.


Split-ring design drill bit stop collars securely clamp OD. Sizes: ⅛", 3/16", ¼", 5/16", ⅜", 7/16", & ½".

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

Center Drill Bits


Different center drill bit (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.

CENTER DRILL BIT SIZES
  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
4½ .3750 9.53 .1406 3.57 .4063 10.32 2.500 64
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

Stepped Drill Bits

Unibit stepped drill bits are excellent for thin materials. See Unibit packaging information.

Metric Stepped Drill Bit Set

Metric sized five piece step drill bit set having HSS split-point with cobalt coating, two flutes, & tri-flat shank (China).
 Metric sizes: 1 Pc, 10mm shank step bit, 13 steps from 6mm to 35mm x 6, 8, 10, 13, 16, 18, 20, 22, 25, 28, 30, 32, 35mm;
1 Pc, 8mm shank step bit, 10 steps from 4mm to 22mm x 2mm; 1 Pc, 8mm shank step bit, 7 steps from 6mm to 18mm x 2mm;
1 Pc, 6mm shank step bit, 9 steps from 4 mm to 12mm x 1mm; 1 Pc, 6mm shank step bit, 5 steps from 4mm to 12mm x 2mm.


Lightweight aluminum storage case included.



The angled shape of each step can be used to chamfer the hole's sharp edge.



Circle Cutter

Adjustable, large hole cutter that uses a HSS tool bit (USA).
½" shank & replaceable ¼" pilot drill bit.
Cuts sheet metal, brass, copper, aluminum, plastic, wood & composition materials.
It has an inches scale that adjusts for diameters from 1¾" to 7⅞". 500 RPM maximum.
General No. 55 circle cutter instructions.

Countersinks

A Weldon zero-flute 82° countersink set (USA). The one center/rear countersink is 100° & is used for
flat-head screws when fastening 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 these
excellent countersinks have, so far, not required any maintenance even after heavy use in mild steel.
The (above) USA manufactured countersinks are superior to the (below) import counterparts.


60°, 82°, & 90° zero-flute countersink sets. These imports are barely worth their low cost.
M.A. Ford, KEO, & Weldon are excellent countersinks.

60° 82° 90° ZERO-FLUTE COUNTERSINK SPECIFICATIONS
SIZE DIAMETER CUTTING RANGE (in) SHANK DIAMETER (in)
0 1/16 ~ 15/64 0.0625 ~ 0.2344 ¼
1 5/32 ~ 13/32 0.1563 ~ 0.4063 ¼
2 3/16 ~ 17/32 0.1875 ~ 0.5313 ¼
3 5/16 ~ 25/32 0.3125 ~ 0.7813 ½
4  9/16 ~ 1-3/32 0.5625 ~ 1.0938 ½



Morse 1" x 82° countersink.


Piloted countersinks (10-24 thread) with 0.001" increment adjustment micro-stop cage adapters.
Sizes: #40 (3/32"pilot), #30 (⅛" pilot), #21 (5/32" pilot), #10 (3/16" pilot) all 100º.


A ¾" (19mm), five-flute reamer/countersink handy for lathe work (General 196). 5⅛" (130mm) overall length.


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    25.40
 
Fract.
(in)
Decimal
(in)
Wire No. Metric
(mm)
Fract.
(in)
Decimal
(in)
Letter Metric
(mm)
Fract.
(in)
Decimal
(in)
Letter Metric
(mm)

Reamers

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


A set of 14, over & under sized (±0.001") decimal HSS chucking reamers (import).
These reamers are
±0.001" of the standard fractional sizes: ⅛", 3/16", ¼", 5/16", ⅜", 7/16", ½".

NOMINAL SIZE PLUS 0.0010" MINUS 0.0010"
0.1250" 0.1260" 0.1240"
0.1875" 0.1885" 0.1865"
0.2500" 0.2510" 0.2490"
0.3125" 0.3135" 0.3115"
0.3750" 0.3760" 0.3740"
0.4375" 0.4385" 0.4365"
0.5000" 0.5010" 0.4990"

Drilled holes are for clearance. Precision holes are either bored, reamed or ground. The hole should be ~1/64"
smaller than the reamer. Chamfer the hole before reaming. Liberally 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 can increase the hole size.
Chucking reamers have long shafts that allow some flexing to follow the hole.


Eleven, adjustable, precision hand reamers (India) for holes from 15/32" to
or .468'' to 1.5".
Adjusting
the nuts expands the reamer to the smallest size of the next larger sized tool.
Setting to a precise size is tedious even with a micrometer; reamed test holes, recommended.
I clamp the shank's square end into the bench vise & adjust using two, open-end wrenches.


The two nuts move & press the six blades along & against slants in the bottom of the six grooves.
 
 

ADJUSTABLE REAMER SET SPECIFICATIONS
A ½" 15/32" ~ 17/32" 0.468" ~ 0.530" 11.88mm ~ 13.46mm
B 9/16" 17/32" ~ 19/32" 0.530" ~ 0.593" 13.46mm ~ 15.06mm
C ⅝" 19/32" ~ 21/35" 0.593" ~ 0.655" 15.06mm ~ 16.63mm
D 11/16" 21/32" ~ 23/32" 0.655" ~ 0.718" 16.63mm ~ 18.23mm
E ¾" 23/32" ~ 25/32" 0.718" ~ 0.780" 18.23mm ~ 19.81mm
F 13/16" 25/32" ~ 27/32" 0.780" ~ 0.842" 19.81mm ~ 21.39mm
G ⅞" 27/32" ~ 15/16" 0.842" ~ 0.937" 21.39mm ~ 23.80mm
H 1" 15/16" ~ 1-1/16" 0.937" ~ 1.062" 23.80mm ~ 26.98mm
I 1⅛" 1-1/16" ~ 1-3/16" 1.062" ~ 1.187" 26.98 mm~ 30.14mm
J 1¼" 1-3/16" ~ 1-11/32" 1.187" ~ 1.344" 30.14mm ~ 34.13mm
K 1-7/16" 1-11/32" ~ 1½" 1.344" ~ 1.500" 34.13mm ~ 38.10mm


Chuck capacity is 0.17" to 0.4". This tap handle holds up to the ¾" E hand reamer or ¼" to ½" tap sizes.


Maximum chuck capacity is 0.502". This larger tap handle holds up to the 1-1/16" H hand reamer.

Taper-pin Reamers

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.
 
TAPER REAMER SIZES
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


Tapered hand reamer (USA).

Floating Reamer Holder

Floating holders allow a chamber reamer to self-align with the barrel. The floating portion
of the holder has a precision-honed hole that fits chambering reamers with 7/16” shanks.
¼” shanks use an adaptor bushing. A setscrew secures the tool in the holder (Clymer).
Shown are 22 short rougher & finisher reamers, go & no-go gages, MT2,
½” &” shanks.

Counter-bores

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.

COUNTER-BORE SIZES
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


Metric counter-bore set: M3, M4, M5, M6, M8, M10, & M12. The shanks are metric sizes, too.


The #6, #8 & #10 counter bores use interchangeable (3/32" shank) carbon-steel pilots.
Different combinations allow for tighter or looser fit for the bolt. Pilot sizes: ⅛", 5/32",
 3/16", 7/32", ¼", 5/16". The 1" counter bore has ½" & 9/16" pilots with 3/16" shanks.
One of the pilots had a burr that needed to be removed via precision grinding.

A small setscrew against a tapered flat holds the pilot's stem. Detail of a 5/16" pilot.


1" counter bore (USA) with interchangeable pilots (import).


An example of three counter bores for a 10-32 cap-head bolt (left) for a tooling plate.

Engraving Bits


Solid carbide engraving tools for the CNC mill.  The end was first split in half with a diamond-wheeled
surface grinder then the tip was diamond ground to have relief behind the single-flute cutting edge.
The point was then relieved even more using a fine diamond file.


Factory sharpened half round carbide engraver bit.

Combo Drill-Tap Bits

HSS combination drill bit & tap. Imperial sizes: 4-40, 6-32, 8-32, 10-32, 10-24, ¼-28, ¼-20, 5/16-18, ⅜-16 &
½-13.


HSS combination drill bit & tap. Metric sizes: M3x.5, M4x.7, M5x.8, M6x1, M8x1.25, & M10x1.5

Each bit has integral deburr/countersink & quick-change hex shaft. The taper after the threading prevents over drilling.


Imperial sizes: 6-32, 8-32, 10-24, 10-32, 12-24 & ¼-20
.


For a 10-24, I disconnected the fine down feed & used the spring-loaded quill lever. Mill turned at 110 RPM.

Diamond Wheels

Assortment of 50, ⅛" shank diamond wheels.


Set of 20, ⅛" shank, diamond pin grinders.

Wood Bits
Bits for wood & masonry shown for comparative purposes.

Brad-point wood bits (GER) in metric (4, 5, 6, 7, 8, 10 & 12mm) & imperial (⅛, 3/16, ¼, 5/16, ⅜, 7/16 & ½").

A brad point helps to reduce bit wander as a hole is drilled. Only use in wood.


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 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. 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.


Wood Speedbors (TM). Sizes: ½", ⅝", ¾", ⅞", 1",1¼".


Spade-type, wood drill bits with hexagonal shanks.

Masonry Bits

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".

Drill Bits, Left-hand Drill Bits, Long Boy, Silver & Deming, Metric, Tapered Shank, Drill Bit Gages,
Sharpeners, Center Drill Bits, Stepped Drill Bits, Circle Cutter, Countersinks, Reamers, Floating Reamer Holder,
Taper-pin Reamers, Counter-bores, Engraving Bits, Combo Drill-Tap Bits, Diamond Wheels, Wood bits, Masonry Bits

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