Drill Bits, Countersinks, Reamers & Counter-bores

Drill Bits, Countersinks, Reamers & Counter-bores
Last updated on Thursday, February 02, 2012 06:46:56 PM Eastern US Time Zone

Drill Bits, Long Boy, Silver & Deming, Metric, Tapered Shank, Sharpeners, Center Drills, Stepped Drills, 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.
Apparently, you can't have too many drill bits, either.

Also see, drill presses, how to drill a hole & how to drill the center of a rod.
Decimal equivalent conversion chart Additional Reference Tables

Drill Bits

Set of USA made fractional (1/16" to ˝" 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 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.

Long Boy Drill Bits

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

Silver & Deming

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

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

Set of eight, 1-1/16" through 1˝" by 1/16" Silver & Deming HSS drill bits with ˝" 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 & use plenty of the appropriate cutting oil.

The stand uses ź-28 x 2ź" bolts, with tube spacers, threaded into the upper plate. Bolt heads act as feet.

1˝" mounted drill bit in RF-25 mill.

1.5" drilled hole through a ź" steel plate.

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

Tapered Shank

Long drill bits having MT-2 shanks with tang (import) for use in lathe tailstock or floor drill press.
Sizes are ˝", 9/16", ⅝", 11/16" & ž". 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 HSS micro-drills (import) numbered 61 to 80.
In general, the smaller the drill bit, the higher the required RPM. Clear the chips frequently.

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

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

Sharpeners

Low-cost, all metal drill 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", ź", 5/16", ⅜", 7/16", & ˝".

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.

Center Drills

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

CENTER DRILL 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
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 Drills

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

Adjustable, large hole cutter that uses a HSS tool bit (USA). ˝" shank & replaceable ź" pilot drill.
Cuts sheet metal, brass, copper, aluminum, plastic, wood & composition materials.
It has an inches scale that adjusts for diameters from 1ž" 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 steel.
The (above) USA manufactured countersinks are superior to the (below) import counterparts.

60°, 82°, & 90° zero-flute countersink sets. These imports are not even 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	ź
1	5/32 ~ 13/32	0.1563 ~ 0.4063	ź
2	3/16 ~ 17/32	0.1875 ~ 0.5313	ź
3	5/16 ~ 25/32	0.3125 ~ 0.7813	˝
4	9/16 ~ 1-3/32	0.5625 ~ 1.0938	˝

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 100ş.

A ž" (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)	Letter	Metric (mm)	Fract. (in)	Decimal (in)	Letter	Metric (mm)
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

Reamers

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

Set of 14, over-under sized (ą0.001") 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.

OVER-UNDER REAMER SIZES
FRACTION	DECIMAL	OVER (+.001)	UNDER (-.001)
⅛"	.1250	.1260	.1240
3/16"	.1875	.1885	.1865
ź"	.2500	.2510	.2490
5/16"	.3125	.3135	.3115
⅜"	.3750	.3760	.3740
7/16"	.4375	.4385	.4365
˝"	.5000	.5010	.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 1˝ or .468'' to 1.5".
Adjusting the nuts expands the reamer to the smallest size of the next larger size.

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

ADJUSTABLE REAMER SET SPECIFICATIONS

# LABEL NOMINAL CENTER
SIZE (inches) FRACTIONAL SIZE RANGE (inches) DECIMAL SIZE
RANGE (inches) METRIC SIZE
RANGE (mm)

1 A ˝ 15/32 ~ 17/32 .468 ~ .530 11.88 ~ 13.46

2 B 9/16 17/32 ~ 19/32 .530 ~ .593 13.46 ~ 15.06

3 C ⅝ 19/32 ~ 21/35 .593 ~ .655 15.06 ~ 16.63

4 D 11/16 21/32 ~ 23/32 .655 ~ .718 16.63 ~ 18.23

5 E ž 23/32 ~ 25/32 .718 ~ .780 18.23 ~ 19.81

6 F 13/16 25/32 ~ 27/32 .780 ~ .842 19.81 ~ 21.39

7 G ⅞ 27/32 ~ 15/16 .842 ~ .937 21.39 ~ 23.80

8 H 1 15/16 ~ 1-1/16 .937 ~ 1.062 23.80 ~ 26.98

9 I 1⅛ 1-1/16 ~ 1-3/16 1.062 ~ 1.187 26.98 ~ 30.14

10 J 1ź 1-3/16 ~ 1-11/32 1.187 ~ 1.344 30.14 ~ 34.13

11 K 1-7/16
1-11/32 ~ 1˝
1.344 ~ 1.500 34.13 ~ 38.10

Chuck capacity is 0.17" to 0.4". This tap handle holds up to the ž" E hand reamer or ź" to ˝" 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.
ź 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, ˝ & ⅜ shanks.

Counter-bores

HSS counter-bore set (Israel): #2, #3, #4, #5, #6, #8, #10, ź", 5/16", ⅜", ˝" 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
ź"	13/32	.4062	9/32	.2812
5/16"	˝	.5000	11/32	.3438
⅜"	19/32	.5938	13/32	.4063
˝"	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", ź", 5/16". The 1" counter bore has ˝" & 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 & tap. SAE sizes: 4-40, 6-32, 8-32, 10-32, 10-24, ź-28, ź-20, 5/16-18, ⅜-16 & ˝-13.

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

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

SAE sizes: 6-32, 8-32, 10-24, 10-32, 12-24 & ź-20.

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, ź, 5/16, ⅜, 7/16 & ˝").
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: ź" 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.

Masonry Bits

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

ADJUSTABLE REAMER SET SPECIFICATIONS
#	LABEL	NOMINAL CENTER SIZE (inches)	FRACTIONAL SIZE RANGE (inches)	DECIMAL SIZE RANGE (inches)	METRIC SIZE RANGE (mm)
1	A	˝	15/32 ~ 17/32	.468 ~ .530	11.88 ~ 13.46
2	B	9/16	17/32 ~ 19/32	.530 ~ .593	13.46 ~ 15.06
3	C	⅝	19/32 ~ 21/35	.593 ~ .655	15.06 ~ 16.63
4	D	11/16	21/32 ~ 23/32	.655 ~ .718	16.63 ~ 18.23
5	E	ž	23/32 ~ 25/32	.718 ~ .780	18.23 ~ 19.81
6	F	13/16	25/32 ~ 27/32	.780 ~ .842	19.81 ~ 21.39
7	G	⅞	27/32 ~ 15/16	.842 ~ .937	21.39 ~ 23.80
8	H	1	15/16 ~ 1-1/16	.937 ~ 1.062	23.80 ~ 26.98
9	I	1⅛	1-1/16 ~ 1-3/16	1.062 ~ 1.187	26.98 ~ 30.14
10	J	1ź	1-3/16 ~ 1-11/32	1.187 ~ 1.344	30.14 ~ 34.13
11	K	1-7/16	1-11/32 ~ 1˝	1.344 ~ 1.500	34.13 ~ 38.10

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