Tap and die

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Tap and die

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Not to be confused withTool and die.

Tapsanddiesarecutting toolsused to createscrew threads, which iscalledthreading. A tap is used to cut the female portion of the mating pair (e.g.,anut). A die is used to cut the male portion of the mating pair (e.g., a screw).

The process of cutting threads using a tap is calledtapping, whereas the process

using a die is calledthreading. Both tools can be used to clean up a thread,which is calledchasing.

Contents[hide]

1 History

2 Tap

o 2.1 Machine tapping

o 2.2 Tool holders for tapping operations

2.2.1 Aids for hand-tapping (simple jigs and fixtures)

2.2.2 Heads for machine tool spindles

2.2.3 Tapping stations

o 2.3 Tap drill bit sizes 3 Die

4 Lubricants

5 References

o 5.1 Bibliography

6 External links

[edit] History

While modern nuts and bolts are routinely made ofmetal, this was not the casein earlier ages, whenwoodworkingtools were employed to fashion very largewooden bolts and nuts for use inwinches,windmills,watermills, andflour

millsof theMiddle Ages; the ease of cutting and replacing wooden parts wasbalanced by the need to resist large amounts oftorque, and bear up against ever

heavier loads of weight. As the loads grew ever heavier, bigger and stronger

bolts were needed to resist breakage. Some nuts and bolts were measured bythe foot or yard. This development eventually led to a complete replacement of

wood parts with metal parts of an identical measure. When a wooden partbroke, it usually snapped, ripped, or tore. The splinters having been sanded off,the remaining parts were encased in a makeshift mold ofclay, and molten metal

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poured into the mold, so that an identical replacement could be made on the

spot.

Metalworking taps and dies were often made by their users during the 18th and

19th centuries (especially if the user was skilled in toolmaking), using suchtools aslathesandfilesfor the shaping, and thesmithyfor hardening andtempering. Thus builders of, for example, locomotives, firearms, or textile

machinery were likely to make their own taps and dies. During the 19th century

themachiningindustries evolved greatly, and the practice of buying taps and

dies from suppliers specializing in them gradually supplanted most such in-house work.Joseph Clementwas one such early vendor of taps and dies,starting in 1828.[1]With the introduction of more advancedmillingpractice in

the 1860s and 1870s, tasks such as cutting a tap's flutes with a hand file became

a thing of the past. In the early 20th century, thread-grindingpractice went

through significant evolution, further advancing the state of the art (and appliedscience) of cutting screw threads, including those of taps and dies.

During the 19th and 20th centuries,thread standardization wasevolvingsimultaneously with thetechniques of thread generation, including

taps and dies.

The largest tap and die company to exist in the United States was GreenfieldTap & Die (GTD) ofGreenfield, Massachusetts. GTD was so irreplaceably

vital to the Allied war effort from 19401945 that anti-aircraft guns were

placed around its campus in anticipation of possible Axis air attack. The GTDbrand is now a part ofWidia Products Group.

[edit] Tap

Bottoming, plug and taper taps, from top to bottom, respectively.

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Various taps.

A tap and "T" wrench

Various tap handles (wrenches).

Atapcuts a thread on the inside surface of a hole, creating a female surfacewhich functions like anut. The three taps in the image illustrate the basic typescommonly used by mostmachinists:

Bottoming tap or plug tap[2]

The tap illustrated in the top of the image has a continuous cutting edge withalmost no taperbetween 1 and 1.5 threads of taper is typical.[3]This

feature enables a bottoming tap to cut threads to the bottom of ablind hole.A bottoming tap is usually used to cut threads in a hole that has already been

partially threaded using one of the more tapered types of tap; the tapered end

("tap chamfer") of a bottoming tap is too short to successfully start into an

unthreaded hole. In the US they are commonly known as bottoming taps,but in Australia and Britain they are also known as plug taps.

Intermediate tap, second tap,[2]or plug tap[4]

The tap illustrated in the middle of the image has tapered cutting edges,which assist in aligning and starting the tap into an untapped hole. The

number of tapered threads typically ranges from 3 to 5.[3]Plug taps are themost commonly used type of tap.[citation needed]In the US they are commonly

known as plug taps, whereas in Australia and Britain they are commonly

known as second taps.Taper tap

The small tap illustrated at the bottom of the image is similar to a plug tapbut has a more pronounced taper to the cutting edges. This feature gives the

taper tap a very gradual cutting action that is less aggressive than that of theplug tap. The number of tapered threads typically ranges from 8 to 10.[3]A

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taper tap is most often used when the material to be tapped is difficult to

work (e.g., alloy steel) or the tap is of a very small diameter and thus prone

to breakage.

The above illustrated taps are generally referred to as hand taps,since they are, by design, intended to be manually operated. Duringoperation, it is necessary with a hand tap to periodically reverse

rotation to break thechipformed during the cutting process, thus

preventing an effect called "crowding" that may cause breakage.

Periodic reversing is usually not practical when power tapping isinvolved, and thus has led to the development of taps suitable forcontinuous rotation in the cutting direction.

The most common type of power driven tap is the "spiral point" plug

tap (also referred to as a "gun tap"), whose cutting edges areangularly displaced relative to the tap centerline. This feature causesthe tap to continuously break the chip and eject it into the flutes,

preventing crowding. Another version of the spiral point plug tap isthe spiralflutetap, whose flutes resemble those of atwist drill. Spiral

flute taps are widely used in high speed, automatic tappingoperations due to their ability to work well in blind holes.

Whether manual or automatic, the processing of tapping begins with

forming and slightlycountersinkinga hole (usually by drilling) with

a diameter somewhat smaller than the tap's diameter. The correcthole diameter may be determined by consulting adrill and tap size

chart, a standard reference item found in manymachine shops. If the

hole is to be drilled, the proper diameter is called thetap drill size.

In lieu of a tap drill chart, it is possible with inch sized taps to

compute the correct tap drill diameter as follows:

whereTDis the tap drill size,MDis the major diameter of thetap (e.g., inch for a "-16 tap), andNis the number of threads

per inch (16 in the case of a "-16 tap). For a "-16 tap, the

above formula would produce516as a result, which is the correct

tap drill diameter for a "-16 tap. The result produces a tap drillsize that results in an approximate 75 percent thread.

The correct tap drill diameter for metric sized taps is computed

as:

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TD =MDpitch

whereTDis the tap drill size,MDis the major diameter ofthe tap (e.g., 10 mm for a M101.5 tap), and pitch is the pitch

of the thread (1.5 mm in the case of a standard M10 tap) andso the correct drill size is 8.5 mm. This works for both fine

and coarse pitches.

With soft or average hardness materials, suchasplastic,aluminumormild steel, the common practice is touse a intermediate (plug) tap to cut the threads. If the threads

are to extend to the bottom of a blind hole, the intermediate(plug) tap will be used to cut threads until the point of the tap

reaches bottom, after which a bottoming tap will be used to

finish the hole. Frequent ejection of the chips must be madein such an operation to avoid jamming and possibly breaking

the tap. With hard materials, the machinist may start with ataper tap, whose less severe diameter transition reduces the

amount of torque required to cut the threads. If threads are to

be cut to the bottom of a blind hole, the taper tap will befollowed by an intermediate (plug) tap and then a bottomingtap to finish the operation.

[edit] Machine tapping

Tapping may either be achieved by hand tapping by using a

set of taps first tap, second tap & final (finish) tap or using amachine to do the tapping, such as a lathe,

radialdrillingmachine, bench type drill machine, pillar type

drill machine, vertical milling machines, HMCs, VMCs.Machine tapping is faster, and generally more accurate

because human error is eliminated. Final tapping is achievedwith single tap.

Although in general machine tapping is more accurate,tapping operations have traditionally been very tricky to

execute due to frequent tap breakage and inconsistent quality

of tapping.

Research has shown[citation needed]that the important reasons

causing tap breakage are as follows:

Tap-related problems:

o Wearing of tap cannot be easily quantified (use ofworn-out taps)

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o Use of tap with improper tap geometry for a particular

application.o Use of non-standard or inferior quality taps.

Clogging withchips

Tapping does not follow the pre-tap hole (misalignment) Mismatch of machine feed and tap feed may cause the tap

to break in tension or compression.

Use of improper cutting fluid or not enough fluid. No safety mechanism to limit torque below torque

breakage value of tap. Improper or zero float for use with screw machines

(recommended feed .1 slower to establish float for 40 tpior higher and .15 slower for 40 tpi or finer[5])

Improper spindle speed

In order to overcome these problems, special tool holders are

required to minimize the chances of tap breakage duringtapping. These are usually classified as conventional tool

holders and CNC tool holders.

[edit] Tool holders for tapping operations

Various tool holders may be used for tapping depending on

the requirements of the user:

[edit] Aids for hand-tapping (simple jigs and fixtures)

The biggest problem with simple hand-tapping is accurately

aligning the tap with the hole so that they are coaxialin

other words, going in straight instead of on an angle. Theoperator must get this alignment rather close to ideal in orderto (a) produce good threads and (b) avoid tap breakage. The

deeper the depth of thread, the more pronounced the effect ofthe angular error becomes. With a depth of 1 or 2 diameters,

it matters little. With depths beyond 2 diameters, the errorbecomes too pronounced to ignore. Another fact about this

alignment task is that the first thread or two that is cut

establishes the direction that the rest of the threads willfollow. In other words, you can't make corrections to the

angle once you have cut the first thread or two.

To help with this alignment task, several kinds

ofjigsandfixturescan be used to provide the correct

geometry (i.e., accurate coaxiality with the hole) withouthaving to use freehand skill to approximate it:

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Hand-tapper: A simple fixture analogous to an arbor press

in its basic shape. Its spindle is thus held accurately

perpendicular to the work. Standard taps are held in thespindle, and the operator turns the spindle manually via a

handlebar. This fixture obviates the need for the operatorto carefully and skillfully approximate perpendicularity,which even for a skilled operator can easily result in a 2

5 error. Tapping guide, or "tap and reamer aligner/holder", a

simple conical guide slipped over a tap when using a

regular tap handle. As with a hand-tapper, the basicprinciple is simply that of a jig or fixture to provide thecorrect alignment.

[edit] Heads for machine tool spindles

Tapping attachments: these may be normal (available in arange of tap sizes) or quick-change

Quick-change drilling and tapping chucks (variationsavailable for both CNC and manual-control tools)

Rigid tapping attachments (for CNC)

Generally the following features are required of tappingholders:

Twin chucking: tap is held at points of both its circularand square cross-section, holding it steady and providing

positive rotational drive. Safety clutch: The built in safety mechanism operates as

soon as the set torque limit is crossed to save the tap from

breakage. Float radial parallel: small misalignments are taken care

of by this float.

Length compensation: built in length compensation takescare of small push or pull to the spindle or feed difference.

Tapping case studies with typical examples of tapping

operations in various environments are shown on sourcemachinetoolaid.com[1]

[edit] Tapping stations

Tapping stations are worktables with a tapping headattached to the end of apantograph-style arm similar tothat of abalanced-arm lamp. The operator guides the

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tapping head to each (already-drilled) hole and quickly

taps it.

Drilling and tapping centers, whose name sounds similarto that of tapping stations, are actually light-duty,

affordablemachining centersof 2, 2.5, or 3 axes that aredesigned for a life of mainly drilling and tapping withlimited milling use.

[edit] Tap drill bit sizes

Main article:Drill and tap size chart

Imperial tap and drill bit size tableMetric tap and drill bit size

table[6][7]

Tap Fractionaldrill bit Numberdrill bit Letterdrill bit

0-80 3/64 - -

1-64 - 53 -

2-56 - 50 -

3-48 - 47 -

4-40 3/32 43 -

5-40 - 38 -

6-32 7/64 36 -

8-32 - 29 -

10-24 9/64 25 -

10-32 5/32 21 -

12-24 11/64 16 -

1/4-

2013/64 7 -

1/4-

287/32 3 -

5/16-

1817/64 - F

5/16-

24 - - I

3/8-

165/16 - -

3/8-

2421/64 - Q

7/16-

1423/64 - U

7/16-

2025/64 - -

1/2-13 27/64 - -

Tap Metricdrill Imperialdrill

3 mm

0.52.5 mm -

4 mm

0.73.3 mm -

5 mm

0.84.2 mm -

6 mm

1.05.0 mm -

7 mm 1.0 6.0 mm 15/64

8 mm

1.256.8 mm 17/64

8 mm

1.07.0 mm -

10 mm

1.58.5 mm -

10 mm

1.258.8 mm 11/32

10 mm 1.0 9.0 mm -

12 mm

1.7510.3 mm -

12 mm

1.510.5 mm 27/64

14 mm

2.012.0 mm -

14 mm

1.512.5 mm 1/2

16 mm 2.0

14.0 mm 35/64

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1/2-

2029/64 - -

9/16-

1231/64 - -

9/16-18 33/64 - -

5/8-

1117/32 - -

5/8-

1837/64 - -

3/4-

1021/32 - -

3/4-

1611/16 - -

Drill sizes are for 75% depth of thread.

16 mm

1.514.5 mm -

Drill sizes are for 75% depth of thread.

[edit] Die

File:DieHolder.jpg

Die holder

Five die sizes and types

Thediecuts a thread on a preformed cylindrical rod, which

creates a male threaded piece which functions like abolt. The

dies shown are

top left: an older split die, with top adjusting screw bottom left: a one piece die with top adjusting screw

center: a one piece die with side adjusting screw (barely

visible on the full image) right: two dies with side adjusting screws

A cylindrical blank, which is usually slightly less than the

required diameter, is machined with ataper(chamfer) at the

threaded end. This chamfer allows the die to ease onto theblank before it cuts a sufficient thread to pull itself along.[8]

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The adjusting screws allow the die to be compressed or

expanded to accommodate slight variations in size, due to

material, manufacture, or die sharpness.

Each tool is used independently, but are usually sold in pairedsets of both types, one die and three taps. Some sets may

provide a lesser number of taps. The common sets shown are

designed for hand operation, but different types such as

helical or spiral may be used in production tools such

asCNCmachining tools, which employdie headsto makelarge volumes of threaded parts.

Die nuts, also known asrethreading dies, are dies made forcleaning up damaged threads,[9]have no split for resizing and

are made from a hexagonal bar so that awrenchor shifterspanner can be used to turn them. Die nuts cannot be used tocut new threads.[10]

[edit] Lubricants

Main article:Cutting fluid

The use of a suitable lubricant is essential with most tappingand reaming operations. Recommended lubricants for some

common materials are as follows:

Carbon steel

Petroleum-based orsyntheticcutting oil.

Alloy steelPetroleum-based cutting oil mixed with a small amount (approximately

10%) ofkeroseneormineral spirits. This mixture is also suitable for usewithstainless steel.

Cast iron

No lubricant. An air blast should be used to clear chips.Aluminum

Kerosene or mineral spirits mixed with a small amount (1525%) ofpetroleum-based cutting oil.WD-40and3-In-One Oilare acceptable

substitutes in some cases.

BrassKerosene or mineral spirits.

Bronze

Kerosene or mineral spirits mixed with a small amount (1015%) ofpetroleum-based cutting oil.

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In power tapping and reaming

operations, the tool and workpiece

should be continuously flooded withlubricant.

[edit] References

1. ^Roe 1916,p. 58.2. ^

ab"Taps: Technical information".

Retrieved 2009-01-04.3. ^

abcSmid, Peter (2003-03-01).CNC

ProgrammingHandbook.ISBN9780831131586.

4. ^Degarmo, pp. 750751.5. ^Brown & Sharpe: Cam & Tool Design,

p.11-12

6. ^"US Tap and Drill Bit Size Table".BoltDepot.com. Retrieved 2006-12-03.

7. ^"Metric Tap and Drill Bit Size Table".BoltDepot.com. Retrieved 2006-12-03.

8. ^"Taps and Dies Terminology".TapDie.com. Retrieved 2006-12-03.

9. ^http://www.tpub.com/content/construction/14256/css/14256_231.htm

10. ^Keenan, Julian Paul (2005).ASVAB - TheBest Test Prep. Research & Education

Association.ISBN9780738600635.

Degarmo, E. Paul; Black, J T.;

Kohser, Ronald A. (2003).Materials

and Processes in Manufacturing(9th

ed.). Wiley.ISBN0-471-65653-4.

Roe, Joseph Wickham(1916),English and American Tool

Builders, New Haven, Connecticut,

USA: Yale UniversityPress,LCCN16-011753. Reprinted

by McGraw-Hill, New York andLondon, 1926 (LCCN27-024075);

and by Lindsay Publications, Inc.,

Bradley, IL, USA (ISBN 978-0-917914-73-7).

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Tap Drill Sizes Some explanation:

What kind of tap do I need? As explained in thescrew guide, coarse threads are much more common,

stronger, less likely to jam during installation (cross thread), and faster to install. So, if you're deciding

between coarse and fine threads for a custom hole, use a coarse thread unless you're going into sheet

metal. If you're trying to make a hole for an unidentified screw, chances are it's a coarse thread. Metric

coarse threads are in between English coarse and fine threads. Metric fine threads are finer than

English fine threads and are rarely used.

50% vs 75% tap drill sizes: 100% engagement of a male and female thread means that both threads

are fully formed and fully engaged. 50% means that only half of the thread height is engaged, and is

what you'd have if you ground off the top half of a fully formed thread. According to the machinery's

handbook, tests have shown that more than 60% thread engagement provides no significant increase in

strength. For thread engagements more than 1.5 diameters deep, 50% is usually sufficient. Most taps

drill are sized to drill a slightly larger hole than what a 100% thread could be cut into, typically 75% or50%. More commonly, holes that will create a 75% thread when tapped are used as a margin of safety,

and this is what we sell. The downside with drilling a hole that a 100% thread could be tapped into is

that it is much more difficult to tap (deeper cuts into the metal), and therefore much more likely to break

a tap. We recommend 75% tapping drills unless deep holes in steel are being made.

Clearance holes: A clearance hole is large enough for the screw to slide through without being turned.

Many tapping charts will have two types of clearance drills: tight and loose. We list the tight clearance

drills and recommend choosing whatever bit is handy and larger than the major diameter for larger

clearances--just make sure the screw head or washer is larger. Note that if several holes are being

made, the tight clearances don't leave much room for misaligned holes.

Coarse Threads - Englishtap size

(major dia. - threads / inch)screw

major dia.tap drill sizefor 75% .dia

tap drill sizefor 50% .dia

clearance drill

#0-80 0.060 3/64 (.0469) 55 (.0520) 50 (.0700)

#1-64 0.073 53 (.0595) 1/16 (.0625) 46 (.0810)

#2-56 0.086 50 (.0700) 49 (.0730) 41 (.0960)

#3-48 0.099 47 (.0785) 44 (.0860) 35 (.1100)

#4-40 0.112 43 (.0890) 41 (.0960) 30 (.1285)

#5-40 0.125 38 (.1015) 7/64 (.1094) 29 (.1360)

#6-32 0.138 36 (.1065) 32 (.1160) 25 (.1495)

#8-32 0.164 29 (.1360) 27 (.1440) 16 (.1770)

#10-24 0.190 25 (.1495) 20 (.1610) 7 (.2010)

#12-24 0.216 16 (.1770) 12 (.1890) 1 (.2280)

1/4-20 .2500 7 (.2010) 7/32 (.2188) H (.2660)

5/16-18 .3125 F (.2570) J (.2770) Q (.3320)

3/8-16 .3750 5/16 (.3125) Q (.3320) X (.3970)

7/16-14 .4375 U (.3680) 25/64 (.3906) 15/32 (.4687)

1/2-13 .5000 27/64 (.4219) 29/64 (.4531) 17/32 (.5312)

9/16-12 .5625 31/64 (.4844) 33/64 (.5156) 19/32 (.5938)

5/8-11 .6250 17/32 (.5312) 9/16 (.5625) 21/32 (.6562)

3/4-10 .7500 21/32 (.6562) 11/16 (.6875) 25/32 (.7812)

7/8-9 .8750 49/64 (.7656) 51/64 (.7969) 29/32 (.9062)

1"-8 1.000 7/8 (.8750) 59/64 (.9219) 1-1/32 (1.0313)

1 1/8-7 1.1250 63/64 (.9844) 1-1/32 (1.0313) 1-5/32 (1.1562)

Coarse Threads - Metric

tap size major dia.mm (inch)

tap drill (mm) tap drill(inch)

clearance (mm) clearance inch (dec.)

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M1.6x0.35 1.6 (.0630) 1.25 #55 1.8 #49

M2x0.4 2.0 (.0787) 1.60 #52 2.4 #41

M2.5x0.45 2.5 (.0984) 2.05 #46 2.9 #32

M3x.05 3.0 (.1181) 2.50 #39 3.4 #29

M3.5x0.6 3.5 (.1378) 2.90 #32 3.9 #23

M4x0.7 4.0 (.1575) 3.30 #30 4.5 #16

M5x0.8 5.0 (.1969) 4.20 #19 5.5 7/32M6x1 6.0 (.2362) 5.0 #8 6.6 G

M8x1 8.0 (.3150) 7.0 J 9.0 T

M10x1.25 10.0 (.3937) 8.8 11/32 12.0 31/64

M12x1.25 12.0 (.4724) 10.8 27/64 14.0 35/64

M14x1.5 14.0 (.5512) 12.5 1/2 16.0 5/8

M16x1.5 16.0 (.6299) 14.5 37/64 18.0 45/64

M18x1.5 18.0 (.7087) 16.5 21/32 20.0 51/64

M20x1.5 20.0 (.7874) 18.5 47/64 22.0 7/8

M22x1.5 22.0 (.8661) 20.5 13/16 25.0 1

M24x2 24.0 (.9449) 22.0 7/8 27.0 1-5/64

M27x2 27.0 (1.0630) 25.0 1 30.0 1-3/16

Fine Threads - Englishtap size

(major dia. - threads / inch)screw

major dia.tap drill sizefor 75% .dia

tap drill sizefor 50% .dia

clearance drill

#1-72 0.073 53 (.0595) 52 (.0635) 46 (.0810)

#2-64 0.086 50 (.0700) 48 (.0760) 41 (.0960)

#3-56 0.099 45 (.0820) 43 (.0890) 35 (.1100)

#4-48 0.112 42 (.0935) 40 (.0980) 30 (.1285)

#5-44 0.125 37 (.1040) 35 (.1100) 29 (.1360)

#6-40 0.138 33 (.1130) 31 (.1200) 25 (.1495)

#8-36 0.164 29 (.1360) 26 (.1470) 16 (.1770)

#10-32 0.190 21 (.1590) 18 (.1695) 7 (.2010)

#12-28 0.216 14 (.1820) 10 (.1935) 1 (.2280)

1/4-28 .2500 3 (.2130) 1 (.2280) H (.2660)5/16-24 .3125 I (.2720) 9/32 (.2812) Q (.3320)

3/8-24 .3750 Q (.3320) S (.3480) X (.3970)

7/16-20 .4375 25/64 (.3906) 13/32 (.4062) 15/32 (.4687)

1/2-20 .5000 29/64 (.4531) 15/32 (.4688) 17/32 (.5312)

9/16-18 .5625 33/64 (.5156) 17/32 (.5312) 19/32 (.5938)

5/8-18 .6250 37/64 (.5781) 19/32 (.5938) 21/32 (.6562)

3/4-16 .7500 11/16 (.6875) 45/64 (.7031) 25/32 (.7812)

7/8-14 .8750 13/16 (.8125) 53/64 (.8281) 29/32 (.9062)

1"-12 1.000 15/16 (.9375) 61/64 (.9531) 1-1/32 (1.0313)

1 1/8-12 1.1250 1-3/64 (1.0469) 1-5/64 (1.0781) 1-5/32 (1.1562)

Fine Threads - Metric

tap size major dia.mm (inch)

tap drill (mm) tap drill(inch)

clearance (mm) clearance inch (dec.)

M8x1.25 8.0 (.3150) 6.8 H 9.0 T

M10x1.5 10.0 (.3937) 8.5 R 12.0 31/64

M12x1.75 12.0 (.4724) 10.2 13/32 14.0 35/64

M14x2 14.0 (.5512) 12.0 15/32 16.0 5/8

M16x2 16.0 (.6299) 14.0 35/64 18.0 45/64

M18x2.5 18.0 (.7087) 15.5 39/64 20.0 51/64

M20x2.5 20.0 (.7874) 17.5 11/16 22.0 7/8

M22x2.5 22.0 (.8661) 19.5 49/64 25.0 1

M24x3 24.0 (.9449) 21.0 53/64 27.0 1-5/64

M27x3 27.0 (1.0630) 24.0 1 15/16 1-3/16

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Tapping is a simple machining operation that many people overlook either because

we have broken a tap in a hole once and couldn't remove it (happens to all of us at

one time or other), or because it's simply a mystery. Well, it isn't a mystery and if

you've had a broken tap remain in a hole and couldn't remove it, well it's just a

tough apples kind of thing and we have to move on with our lives. Some folks have

had good luck with tap removal tools though, but others haven't. If we have had a

bad experience with this operation, then consider it an opportunity to learn how to

do it right rather than giving up on it.

Anyway don't let bad luck or the fear of mystery drive you away, come back and

take another look at this operation. First let's see why we should even consider

tapping holes for our fasteners in the first place. Why not through bolt everything?

Well, because it isn't always feasible, that's why. Also drilling and through bolting

may only be a quick and dirty way to acomplish something on a work that you've

spent many a caring hour on and the result could very well be quite nasty looking in

relation to the finish on the rest of the work. Often the look of a work is ruined not

by an attractive bolt head but rather by the nut and protruding stem of the bolt on

the backside of the work.

There are times when a part or piece that is either removable or needs to be

secured in place at a later time requires a tapped receiver hole. Maybe there isn't

room to add a nut behind the work or there needs to be a clean way to remove

and/or replace a part, especially if there are adjustments or repairs to be made

later. There are a number of good reasons for tapping including into blind holes and

it's really obvious why to the most rudimentary of metal workers.

Okay, we now are convinced, what next. Each tap and bolt size usually has two

distinct threads, a fine thread and a coarse thread. The most common type that we

use is the coarse configuration and without going into endless detail about the why's

and wherefore's of each type let's simply move on. What's good for the goose is

good for the gander, same with tapped holes. Most likely you will be tapping for

coarse threads most of the time, if not always, unless you do a bit of machining

work. If you do that kind of thing then you already know everything here and should

move on to read about forging stuff or something like that.

Each tap has a recommended drill size for predrilling the receiver hole. Sometimesyou may find this size stamped on a tap itself, or you may have to look up the

mating drill size on either a chart or somewhere else. What you may find is that the

drill sizes are often number/letter sizes and not fractional sizes which we normally

keep around the shop. What to do? Well you don't have to run out to the

neighborhood hardware store (chances are they don't have what you're looking for

anyway) so you will then have to use the next larger drill bit size that closely

resembles the recommended number/letter drill size. Again refer to a chart for the

decimal sizes/fractional size conversion chart.

It probably would help to put up a metric/number/letter/fractional drill size chart

here in the Bramblebush sometime and if there is a demand for it, I may do that,

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but in the meantime let your fingers do the walking and find your own chart.

Chances are however, that if you bought a matched set of drills and taps then

everything is already set up for you in the package.

Okay, I'm going to get to the tapping part in a minute but first I want to say

something about drilling holes, then we'll move on.

Drilling is a simple operation, however there may be a couple of things that could be

helpful in improving your drilling techniques. One thing is predrilling and an

application here is when you may be drilling into heavy stock or using a large drill,

(1/2" or larger). It helps enormously to predrill a smaller hole first and that hole

could be about the size of the two flats on the point of the large drill, or a little

larger. Doing this aids in spotting the drill for accuracy to begin with and also speeds

up the drilling operation for the larger drill bit considerably. After predrilling, less

pressure is also required for a larger drill bit, a handy thing to know when you may

have to use a hand drill rather than a drill press. Life is good. Oh, don't forget topunch mark your drill location, but I probably didn't have to remind you of that

though.

Alright, now a word about breaking through the drilled hole while drilling. This is

kind of important, especially if breaking wrists or thumbs and getting bruised by

spinning unclamped metal smarts too much. Whenever a drill is beginning to break

through the far side of a piece of metal, always back off the pressure a bit. Many

folks do the opposite and find themselves in serious trouble.

What the hole looks like from the other side is something more like a ragged tear

and easily grabs the bit with heavy pressure bearing down on it. If the final pass is

lightly taken, then whatever metal is trying to grab the bit is only a few thousands

thick and is easily defeated, even if you are not clamping the work down on the

press. This is especially good to know whenever you are manhandling a powerful 3/4

hp hand drill instead of a drill press. That drill can spin itself around and your wrist

with it if you aren't careful. Oh, by the way, it always helps to use a lubricant when

using a large drill bit except into cast iron, then you drill that dry.

Ahhh.....now we're getting back to the tapping thing again. Well, tapping is an

operation that requires one to be very sensitive with their fingertips. When starting

to tap a hole, the taper on a plug tap easily works itself into the hole then begins to

resist. What you need to do is to back off the tap every time you advance it about

an eighth turn or so in order to release the curled chips that are forming inside the

hole. Otherwise the tap is going to get jammed, and boink! it breaks. Also use a

lubricant every time you tap, and for each new hole started.

Taps are made of a very hard and brittle steel so they are not very forgiving when

over stressed. This is where fingertip sensitivity comes into play here and it's

important that you develop the feel for taps and how much they may be turned

when tight in a hole before backing off. You have to be aware of just how limited the

twisting can be and yes, a hardened tap can twist a little bit before breaking.

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7/28/2019 Tap and die

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5/16-18 F

3/8-16 5/16

7/16-14 U

1/2-13 27/64

9/16-12 31/64

5/8-11 17/32

3/4-10 21/327/8-9 49/64

1"-8 7/8

1-1/8-7 63/64

1-1/4-7 1-7/64

1-1/2-6 1-11/32

1-3/4-5 1-35/64

2"-4-1/2 1-25/32

----------------------------

1/4-28 #3

5/16-24 I

3/8-24 Q

7/16-20 W

1/2-20 29/64

9/16-18 33/64

5/8-18 37/643/4-16 11/16

7/8-14 13/16

1"-14 15/16

1-1/8-12 1-3/64

1-1/4-12 1-11/64

1-1/2-12 1-27/64

1-3/4-12 1-43/64

2"-12 1-59/64

----------------------------

TAPER PIPE SIZES - NPT----------------------------

TAP DRILL

SIZE SIZE----------------------------

1/8-27 R

1/4-18 7/16

3/8-18 37/64

1/2-14 23/32

3/4-14 59/64

1"-11-1/2 1-5/32

1-1/4-11-1/2 1-1/2

1-1/2-11-1/2 1-47/64

2"-11-1/2 2-7/32

2-1/2-8 2-5/8

3"-8 3-1/4

3-1/2-8 3-3/44"-8 4-1/4

----------------------------

STRAIGHT PIPE SIZES - NPS----------------------------

TAP DRILL

SIZE SIZE----------------------------

1/8-27 S

1/4-18 29/64

3/8-18 19/32

1/2-14 47/64

3/4-14 15/16

1"-11-1/2 1-3/16

1-1/4-11-1/2 1-33/64

1-1/2-11-1/2 1-3/4

2"-11-1/2 2-7/32

2-1/2-8 2-21/32

3"-8 3-9/32

3-1/2-8 3-25/324"-8 4-9/32

----------------------------

METRIC TAP DRILL SIZESRecommended tap drill sizes (for approx. 75% thread)

METRIC COARSE SIZES----------------------------

TAP DRILL

SIZE SIZE----------------------------

1mm x .25 .75mm

1.1 x .25 .85

1.2 x .25 .95

1.4 x .3 1.1

1.6 x .35 1.25

1.7 x .35 1.3

1.8 x .35 1.45

2 x .4 1.6

2.2 x .45 1.75

2.5 x .45 2.05

3 x .5 2.5

3.5 x .6 2.94 x .7 3.3

METRIC FINE SIZES----------------------------

TAP DRILL

SIZE SIZE----------------------------

4 mm x .35 3.6mm

4 x .5 3.5

5 x .5 4.5

6 x .5 5.5

6 x .75 5.25

7 x .75 6.25

8 x .5 7.5

8 x .75 7.25

8 x 1 7

9 x 1 8

10 x .75 9.25

10 x 1 910 x 1.25 8.8

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4.5 x .75 3.7

5 x .8 4.2

6 x 1 5

7 x 1 6

8 x 1.25 6.8

9 x 1.25 7.8

10 x 1.5 8.511 x 1.5 9.5

12 x 1.75 10.2

14 x 2 12

16 x 2 14

18 x 2.5 15.5

20 x 2.5 17.5

22 x 2.5 19.5

24 x 3 21

27 x 3 24

30 x 3.5 26.5

33 x 3.5 29.5

36 x 4 32

39 x 4 35----------------------------

11 x 1 10

12 x .75 11.25

12 x 1 11

12 x 1.5 10.5

14 x 1 13

14 x 1.25 12.8

14 x 1.5 12.516 x 1 15

16 x 1.5 14.5

18 x 1 17

18 x 2 16

20 x 1 19

20 x 1.5 18.5

20 x 2 18

22 x 1 21

22 x 1.5 20.5

22 x 2 20

24 x 1.5 22.5

24 x 2 22

26 x 1.5 24.527 x 1.5 25.5

27 x 2 25

28 x 1.5 26.5

30 x 1.5 28.5

30 x 2 28

33 x 2 31

36 x 3 33

39 x 3 36

----------------------------

Handy Helpers!Tap Drill Sizes (inch) for a 75% ThreadIn general, you can find the tap-drill for any size 60 degree thread, subtract one pitchlength from the major diameter.

Formula: Major Dia. minus One Pitch Length equals tap-drill size

English Example for 3/8-16 thread: .375 - .0625 = .3125 tap-drill (5/16)

Metric Example for M6 X 1 thread: 6mm - 1mm = 5mm tap-drill