Editing Tap and die (section)

== Tap ==
[[Image:TapTypes.gif|thumb|From top: Bottoming, plug and taper taps (US usage), or plug, second and taper (UK usage).]]
[[Image:ThreadingTaps.jpg|thumb|Various taps.]]
[[Image:Tap and T-wrench.jpg|thumb|A tap and "T" wrench]]
[[File:WrenchTapBarT.jpg|thumb|Various tap handles (wrenches).]]
A ''tap'' cuts or forms a thread on the inside surface of a hole, creating a female surface that functions like a [[nut (hardware)|nut]]. The three taps in the image illustrate the basic types commonly used by most [[machinist]]s:

;Bottoming tap :The tap illustrated in the top of the image has a continuous cutting edge with almost no taper — between 1 and 1.5 threads of taper is typical.<ref name="taperthreads">{{cite book | author1 = Smid, Peter | title = CNC Programming Handbook | url = https://books.google.com/books?id=JNnQ8r5merMC&pg=PA210 | date = 2003-03-01 | publisher = Industrial Press | isbn = 978-0-8311-3158-6 }}</ref><ref name="tapdie" />  This feature enables a bottoming tap to cut threads to the bottom of a [[blind 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,<ref name="tapdie">{{Cite web | title = Taps: Technical information | url = http://www.tapdie.com/html/taps__technical_information.html | access-date = 2009-01-04 | url-status = usurped | archive-url = https://web.archive.org/web/20090113225928/http://www.tapdie.com/html/taps__technical_information.html | archive-date = 2009-01-13 }}</ref> or plug tap: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.<ref name="taperthreads"/> Plug taps are the most commonly used type of tap.{{Citation needed|date=January 2009}} 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 an intermediate tap but 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 the plug tap. The number of tapered threads typically ranges from 8 to 10.<ref name="taperthreads"/> A taper tap is most often used when the material is difficult to work (e.g., alloy steel) or the tap is of a very small diameter and thus prone to breakage.

;Power taps: The above taps are generally referred to as hand taps, since they are manually operated.  During operation, the machinist must periodically reverse a hand tap to break the chip (also known as [[swarf]]) that forms from cutting. This prevents the cut material from ''crowding'' and breaking the tap.

:The most common type of power driven tap is the "spiral point" plug tap, also referred to as a "gun" tap, whose cutting edges are angularly displaced relative to the tap centerline.[[File:spiral_point_tap.jpg|thumb|A spiral point plug tap ("gun" tap).]] This feature causes the tap to continuously break the chip and eject it forward into the hole, preventing crowding.  Spiral point taps are usually used in holes that go all the way through the material, so that the chips can escape. Another version of the spiral point plug tap is the spiral [[flute (cutting tool)|flute]] tap, whose flutes resemble those of a [[drill bit|twist drill]].  Spiral flute taps are widely used in high speed, automatic tapping operations due to their ability to work well in blind holes.

;Forming tap: A quite different kind of tap is a forming tap. A forming tap, aka a fluteless tap or roll tap, forcefully displaces the metal into a thread shape upon being turned into the hole, instead of cutting metal from the sides of the hole as cutting taps do. A forming tap has lobes periodically spaced around the tap which actually do the thread forming as the tap is advanced into a properly sized hole, and the threads behind the lobes are slightly recessed to reduce contact friction. Since there is no need to provide space for chips, these recesses are much more subtle than a cutting tap's flutes and the tap appears very nearly just like a plain thread.  Since the tap does not produce chips, there is no need to periodically back out the tap to clear away chips, which can jam and break a cutting tap if allowed to accumulate. This problem is particularly acute in blind holes, so thread forming is particularly suited to such applications. Forming taps only work in malleable materials such as mild steel or aluminum. Formed threads are typically stronger than cut threads. Note that the tap drill size is larger than that used for a cutting tap as shown in most tap drill tables, and an accurate hole size is required; a slightly undersized hole can break the tap. Proper lubrication is essential because of the frictional forces involved, therefore a lubricating oil is used instead of cutting oil.

===Holes===

Whether manual or automatic, the processing of tapping begins with forming (usually by drilling) and slightly [[countersink]]ing a hole to a diameter somewhat smaller than the tap's major diameter.  The correct hole diameter is listed on a [[drill and tap size chart]], a standard reference in many [[machine shop]]s. The proper diameter for the drill is called the '''tap drill''' size. Without a tap drill chart, you can compute the correct tap drill diameter with:
:<math>TD = MD - \frac {1}{N}</math>
where <math>TD</math> is the tap drill size, <math>MD</math> is the major diameter of the tap (e.g., {{frac|3|8}} in for a {{frac|3|8}}-16 tap), and <math>1/N</math> is the [[thread pitch]] ({{frac|16}}&nbsp;inch in the case of a {{frac|3|8}}-16 tap).  For a {{frac|3|8}}-16 tap, the above formula would produce {{frac|5|16}}, which is the correct tap drill diameter.  The above formula ultimately results in an approximate 75% thread.

Since metric threads specify the pitch directly, the correct tap drill diameter for metric-sized taps is computed with:
:<math>TD = MD - \text{pitch}</math>
where <math>TD</math> is the tap drill size, <math>MD</math> is the major diameter of the tap (e.g., 10&nbsp;mm for a M10×1.5 tap), and pitch is the pitch of the thread (1.5&nbsp;mm in the case of a standard M10 tap) and so the correct drill size is 8.5&nbsp;mm. This works for both fine and coarse pitches, and also produces an approximate 75% thread.

===Tap sequence===

With soft or average hardness materials, such as [[plastic]], [[aluminum]] or [[mild steel]], common practice is to use an intermediate (plug) tap to cut the threads.  If the threads must extend to the bottom of a blind hole, the machinist uses an intermediate (plug) tap to cut threads until the point of the tap reaches bottom, and then switches to a bottoming tap to finish. The machinist must frequently eject chips to avoid jamming or breaking the tap. With hard materials, the machinist may start with a taper tap, whose less severe diameter transition reduces the torque required to cut threads. To threads to the bottom of a blind hole, the machinist follows the taper tap with an intermediate (plug) tap, and then a bottoming tap to finish.

===Machine tapping===
Tapping may either be achieved by a hand tapping by using a set of taps (first tap, second tap & final (finish) tap) or using a machine to do the tapping, such as a [[lathe]], radial [[drill]]ing machine, 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 achieved with 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.

Common reasons for tap breakage are:

* Tap-related problems:
** Wearing of tap cannot be easily quantified (use of worn-out taps)
** Use of tap with improper tap geometry for a particular application.
** Use of non-standard or inferior quality taps.
* Clogging with [[swarf|chips]].
* Misalignment between tap and hole.
* Over- or under-feeding the tap, causing breakage in tension or compression.
* Use of improper and/or insufficient cutting lubricant.
* Absence of a torque limiting feature.
* Improper or zero float for use with screw machines (recommended feed .1 slower to establish float for 40&nbsp;tpi or higher and .15 slower for 40&nbsp;tpi or finer<ref>Brown & Sharpe: Cam & Tool Design, p.11-12</ref>)
* Improper spindle speed.

To overcome these problems, special tool holders are required to minimize the chances of tap breakage during tapping. These are usually classified as conventional tool holders and CNC tool holders.

===Tool holders for tapping operations===
Various tool holders may be used for tapping depending on the requirements of the user:

====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 coaxial—in other words, going in straight instead of on an angle. The operator must get this alignment close to ideal to produce good threads and not break the tap. The deeper the thread depth, the more pronounced the effect of the angular error. With a depth of 1 or 2 diameters, it matters little. With depths beyond 2 diameters, the error becomes too pronounced to ignore. Another fact about alignment is that the first thread cut or two establishes the direction that the rest of the threads will follow. You can't correct the angle after the first thread or two.

To help with this alignment task, several kinds of [[Jig (tool)|jigs]] and [[Fixture (tool)|fixtures]] can be used to provide the correct geometry (i.e., accurate coaxiality with the hole) without having to use freehand skill to approximate it:

* 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 the spindle, and the operator turns the spindle manually via a handlebar. This fixture obviates the need for the operator to 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 basic principle is simply that of a jig or fixture to provide the correct alignment.

====Heads for machine tool spindles====
* Tapping attachments: these may be normal (available in a range of tap sizes) or quick-change
* Quick-change drilling and tapping chucks (variations available for both CNC and manual-control tools)
* Rigid tapping attachments (for CNC)

Generally the following features are required of tapping holders:
* Twin chucking: tap is held at points of both its circular and square cross-section.  Gripping the circular section assures concentricity to the machine spindle, and gripping the square produces positive rotational drive.
* Safety clutch: The built in safety mechanism operates as soon as the set torque limit is attained to save the tap from breakage.
* Float radial parallel: small misalignments are taken care of by this float.
* Length compensation: built in length compensation takes care 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 source machinetoolaid.com [http://machinetoolaid.com/spindle-toolings/conventional-machine-toolings/tapping-case-studies.html]

====Tapping stations====
* Tapping stations are worktables with a tapping head attached to the end of a [[pantograph]]-style arm similar to that of a [[balanced-arm lamp]]. The operator guides the tapping head to each (already-drilled) hole and quickly taps it.
* ''Drilling and tapping centers'', whose name sounds similar to that of tapping stations, are actually light-duty, affordable [[Milling machine#Computer numerical control|machining center]]s of 2, 2.5, or 3 axes that are designed for a life of mainly drilling and tapping with limited milling use.

Double-lead taps and insert taps need different speeds and feeds, and different starting hole diameters than other taps. 

===Tap drill sizes===
{{Main|Drill and tap size chart}}

{| width="90%" border="0" align="center" cellspacing="5" summary="Tap drill bit size table"
|-
! Imperial tap and drill bit size table !! Metric tap and drill bit size table !!<ref>
{{cite web
 |url         = http://www.boltdepot.com/fastener-information/US-Tap-Drill-Size.aspx
 |title       = US Tap and Drill Bit Size Table
 |publisher   = BoltDepot.com
 |access-date  = 2006-12-03
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20061201191035/http://www.boltdepot.com/fastener-information/US-Tap-Drill-Size.aspx
 |archive-date = 2006-12-01
}}</ref><ref>
{{cite web
 |url         = http://www.boltdepot.com/fastener-information/Metric-Tap-Drill-Size.aspx
 |title       = Metric Tap and Drill Bit Size Table
 |publisher   = BoltDepot.com
 |access-date  = 2006-12-03
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20061110035435/https://www.boltdepot.com/fastener-information/Metric-Tap-Drill-Size.aspx
 |archive-date = 2006-11-10
}}</ref>
|-
| valign="top" |
{| align="center" border="1" style="border-collapse: collapse; text-align: center; nowrap"
|- class="infotableheader" bgcolor="#eee8c6"
! Tap !! Fractional drill bit !! Number drill bit !! Letter drill bit
|-
! 0-80
| {{frac|3|64}}  || -  || -
|- bgcolor="#EEEEEE"
! 1-64
| -     || 53 || -
|-
! 2-56
| -     || 50 || -
|- bgcolor="#EEEEEE"
! 3-48
| -     || 47 || -
|-
! 4-40
| {{frac|3|32}}  || 43 || -
|- bgcolor="#EEEEEE"
! 5-40
| -     || 38 || -
|-
! 6-32
| {{frac|7|64}}  || 36 || -
|- bgcolor="#EEEEEE"
! 8-32
| -     || 29 || -
|-
! 10-24
| {{frac|9|64}}  || 25 || -
|- bgcolor="#EEEEEE"
! 10-32
| {{frac|5|32}}  || 21 || -
|-
! 12-24
| {{frac|11|64}} || 16 || -
|- bgcolor="#EEEEEE"
! {{frac|1|4}}-20
| {{frac|13|64}} || 7 || -
|-
! {{frac|1|4}}-28
| {{frac|7|32}}  || 3 || -
|- bgcolor="#EEEEEE"
! {{frac|5|16}}-18
| {{frac|17|64}} || - || F
|-
! {{frac|5|16}}-24
| -     || - || I
|- bgcolor="#EEEEEE"
! {{frac|3|8}}-16
| {{frac|5|16}}  || - || -
|-
! {{frac|3|8}}-24
| {{frac|21|64}} || - || Q
|- bgcolor="#EEEEEE"
! {{frac|7|16}}-14
| {{frac|23|64}} || - || U
|-
! {{frac|7|16}}-20
| {{frac|25|64}} || - || -
|- bgcolor="#EEEEEE"
! '''{{frac|1|2}}-13'''
| {{frac|27|64}} || - || -
|-
! {{frac|1|2}}-20
| {{frac|29|64}} || - || -
|- bgcolor="#EEEEEE"
! {{frac|9|16}}-12
| {{frac|31|64}} || - || -
|-
! {{frac|9|16}}-18
| {{frac|33|64}} || - || -
|- bgcolor="#EEEEEE"
! {{frac|5|8}}-11I 
| {{frac|17|32}} || - || -
|-
! {{frac|5|8}}-18
| {{frac|37|64}} || - || -
|- bgcolor="#EEEEEE"
! {{frac|3|4}}-10
| {{frac|21|32}} || - || -
|-
! {{frac|3|4}}-16
| {{frac|11|16}} || - || -
|- bgcolor="#EEEEEE"
| colspan="4" | <span style="font-size:87%;">Drill sizes are for 75% depth of thread.</span>
|}
| valign="top" |
{| align="center" border="1" style="border-collapse: collapse; text-align: center; nowrap"
|- class="infotableheader" bgcolor="#eee8c6"
! Tap               !! Metric drill !! Imperial drill
|-
! 3&nbsp;mm - 0.5
| 2.5&nbsp;mm  || -
|- bgcolor="#EEEEEE"
! 4&nbsp;mm - 0.7
| 3.3&nbsp;mm  || -
|-
! 5&nbsp;mm - 0.8
| 4.2&nbsp;mm  || -
|- bgcolor="#EEEEEE"
! 6&nbsp;mm - 1.0
| 5.0&nbsp;mm  || -
|-
! 7&nbsp;mm - 1.0
| 6.0&nbsp;mm  || 15/64
|- bgcolor="#EEEEEE"
! 8&nbsp;mm - 1.25
| 6.8&nbsp;mm  || 17/64
|-
! 8&nbsp;mm - 1.0
| 7.0&nbsp;mm  || -
|- bgcolor="#EEEEEE"
! 10&nbsp;mm - 1.5
| 8.5&nbsp;mm  || -
|-
! 10&nbsp;mm - 1.25
| 8.8&nbsp;mm  || 11/32
|- bgcolor="#EEEEEE"
! 10&nbsp;mm - 1.0
| 9.0&nbsp;mm  || -
|-
! 12&nbsp;mm - 1.75
| 10.3&nbsp;mm || -
|- bgcolor="#EEEEEE"
! 12&nbsp;mm - 1.5
| 10.5&nbsp;mm || 27/64
|-
! 14&nbsp;mm - 2.0
| 12.0&nbsp;mm || -
|- bgcolor="#EEEEEE"
! 14&nbsp;mm - 1.5
| 12.5&nbsp;mm || 1/2
|-
! 16&nbsp;mm - 2.0
| 14.0&nbsp;mm || 35/64
|- bgcolor="#EEEEEE"
! 16&nbsp;mm - 1.5
| 14.5&nbsp;mm || -
|-
| colspan="3" | <span style="font-size:87%;">Drill sizes are for 75% depth of thread.</span>
|}
|}

===US tap and drill bit size and reference chart===
{{Main|Drill and tap size chart}}
A comprehensive reference for US tap and drill bit sizes can be found in the chart provided by Albany County Fasteners. This chart includes detailed specifications for machine screw size, threads per inch, major and minor diameters, and appropriate drill sizes for different materials.

{| class="wikitable" style="text-align:center; width:90%;" align="center"
|+ '''US tap and drill bit size and reference chart'''<ref>{{cite web
|url=https://www.albanycountyfasteners.com/Fastener-Reference-Tables-s/drill-tap-size-charts
|title=US Tap and Drill Bit Size and Reference Chart
|publisher=AlbanyCountyFasteners.com
|access-date=2024-03-06
}}</ref>
|-
! rowspan="3" | Machine screw size
! rowspan="3" | Number of threads per inch (TPI)
! rowspan="3" | Major diameter
! rowspan="3" | Minor diameter
! colspan="4" | Tap drills
! colspan="4" | Clearance drill
|-
! colspan="2" | 75% thread for aluminum, brass, & plastics
! colspan="2" | 50% thread for steel, stainless, & iron
! colspan="2" | Close fit
! colspan="2" | Free fit
|-
! Drill size
! Decimal equiv.
! Drill size
! Decimal equiv.
! Drill size
! Decimal equiv.
! Drill size
! Decimal equiv.
|-
| 0
| 80
| .0600
| .0447
| 3/64
| .0469
| 55
| .0520
| 52
| .0635
| 50
| .0700
|-
| 1
| 64/72
| .0730
| .0538/.0560
| 53
| .0595
| 1/16
| .0625
| 48
| .0760
| 46
| .0810
|-
| 2
| 56/64
| .0860
| .0641/.0668
| 50
| .0700
| 49
| .0730
| 43
| .0890
| 41
| .0960
|-
| 3
| 48/56
| .0990
| .0734/.0771
| 47
| .0785
| 44
| .0860
| 37
| .1040
| 35
| .1100
|-
| 4
| 40/48
| .1120
| .0813/.0864
| 43
| .0890
| 41
| .0960
| 32
| .1160
| 30
| .1285
|-
| 5
| 40/44
| .1250
| .0943/.0971
| 38
| .1015
| 7/64
| .1094
| 30
| .1285
| 29
| .1360
|-
| 6
| 32/40
| .1380
| .0997/.1073
| 36
| .1065
| 32
| .1160
| 27
| .1440
| 25
| .1495
|-
| 8
| 32/36
| .1640
| .1257/.1299
| 29
| .1360
| 27
| .1440
| 18
| .1695
| 16
| .1770
|-
| 10
| 24/32
| .1900
| .1389/.1517
| 25
| .1495
| 20
| .1610
| 9
| .1960
| 7
| .2010
|-
| 12
| 24/28/32
| .2160
| .1649/.1722/.1777
| 16
| .1770
| 12
| .1890
| 2
| .2210
| 1
| .2280
|-
| {{frac|1|4}}
| 20/28/32
| .2500
| .1887/.2062/.2117
| 7
| .2010
| 7/32
| .2188
| F
| .2570
| H
| .2660
|-
| {{frac|5|16}}
| 18/24/32
| .3125
| .2443/.2614/.2742
| F
| .2570
| J
| .2770
| P
| .3230
| Q
| .3320
|-
| {{frac|3|8}}
| 16/24/32
| .3750
| .2983/.3239/.3367
| 5/16
| .3125
| Q
| .3320
| W
| .3860
| X
| .3970
|-
| {{frac|7|16}}
| 14/20/28
| .4375
| .3499/.3762/.3937
| U
| .3680
| 25/64
| .3906
| 29/64
| .4531
| 15/32
| .4687
|-
| {{frac|1|2}}
| 13/20/28
| .5000
| .4056/.4387/.4562
| 27/64
| .4219
| 29/64
| .4531
| 33/64
| .5156
| 17/32
| .5312
|-
| {{frac|9|16}}
| 12/18/24
| .5625
| .4603/.4943/.5514
| 31/64
| .4844
| 33/64
| .5156
| 37/64
| .5781
| 19/32
| .5938
|-
| {{frac|5|8}}
| 11/18/24
| .6250
| .5135/.5568/.5739
| 17/32
| .5312
| 37/64
| .5781
| 41/64
| .6406
| 21/32
| .6562
|-
| {{frac|5|8}}
| 11/18/24
| .6250
| .5135/.5568/.5739
| 17/32
| .5312
| 9/16
| .5625
| 41/64
| .6406
| 21/32
| .6562
|-
| {{frac|11|16}}
| 24
| .6875
| .6364
| 41/64
| .6406
| 21/32
| .6562
| 45/64
| .7031
| 23/32
| .7188
|-
| {{frac|3|4}}
| 10/16/20
| .7500
| .6273/.6733/.6887
| 21/32
| .6562
| 11/16
| .6875
| 49/64
| .7656
| 25/32
| .7812
|-
| {{frac|13|16}}
| 20
| .8125
| .7512
| 49/64
| .7656
| 25/32
| .7812
| 53/64
| .8281
| 27/32
| .8438
|-
| {{frac|7|8}}
| 9/14/20
| .8750
| .7387/.7874/.8137
| 49/64
| .7656
| 51/64
| .7969
| 57/64
| .8906
| 29/32
| .9062
|-
| {{frac|15|16}}
| 20
| .9375
| .8762
| 57/64
| .8906
| 29/32
| .9062
| 61/64
| .9531
| 31/32
| .9688
|-
| 1
| 8/12/20
| 1.0000
| .8466/.8978/.9387
| 7/8
| .8750
| 59/64
| .9219
| 1-1/64
| 1.0156
| 1-1/32
| 1.0313
|-
| {{frac|1|1|16}}
| 18
| 1.0625
| .9943
| 1.000
| 1.000
| 1-1/64
| 1.0156
| 1-5/64
| 1.0781
| 1-3/32
| 1.0938
|-
| {{frac|1|1|8}}
| 7/12/18
| 1.1250
| .9497/1.0228/1.0568
| 63/64
| .9844
| 1-1/32
| 1.0313
| 1-9/64
| 1.1406
| 1-5/32
| 1.1562
|-
| {{frac|1|3|16}}
| 18
| 1.1875
| 1.1193
| 1-1/8
| 1.1250
| 1-9/64
| 1.1406
| 1-13/64
| 1.2031
| 1-7/32
| 1.2188
|}