Tap and Dies

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Group member :

M. Syafie

M. Nurhisyam

Abd. Haiman

Ismail Yakin

*

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*

*Bottoming

*Plug

*Taper

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*T Wrench

*Various tap handle (wrench)

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A tap cuts a thread on the inside surface of a hole, creating a female

surface which functions like a nut. The three taps in the image

illustrate the basic types commonly used by most machinists:

*Bottoming tap or plug tap

Has a continuous cutting edge with almost no taper between

1 and 1.5 threads of taper is typical. 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.

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*Plug tap, second tap, or Intermediate 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.

*Taper tap

Similar to a plug tap but has a more pronounced taper to

the cutting edges. This feature gives the taper tap a very gradualcutting action that is less aggressive than that of the plug tap.

The number of tapered threads typically ranges from 8 to 10. A

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

difficult to work (e.g., alloy steel) or the tap of a very small

diameter and thus prone to breakage

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*The processing of tapping begins with forming and slightly

countersinking a hole (usually by drilling) with a diameter

somewhat smaller than the tap's diameter. The correct holediameter may be determined by consulting a drill and tap

size chart, a standard reference item found in many machine

shops. If the hole is to be drilled, the proper diameter is

called the tap drill size.

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

compute the correct tap drill diameter as follows:

*where TD is the tap drill size, MD is the major diameter of the tap(e.g., inch for a "-16 tap), and N is the number of threads per inch(16 in the case of a "-16 tap). For a "-16 tap, the above formula

would produce 516 as a result, which is the correct tap drill diameter

for a "-16 tap. The result produces a tap drill size that results in an

approximate 75 percent thread.

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*The correct tap drill diameter for metric sized taps is computed as:

*Where TD is the tap drill size, MD is the major diameter of the 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) and so the correct drillsize is 8.5 mm. This works for both fine and coarse pitches.

*With soft or average hardness materials, the common practice is to

use an intermediate (plug) tap to cut the threads. If the threads areto extend to the bottom of a blind hole, the intermediate (plug) tapwill 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. Frequentejection of the chips must be made in such an operation to avoidjamming and possibly breaking the tap. With hard materials, the

machinist may start with a taper tap, whose less severe diametertransition 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 tapwill be followed by an intermediate (plug) tap and then a bottomingtap to finish the operation.

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Machine tappingTapping may either be achieved by 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 drilling machine, bench type drill machine, pillar type drillmachine, vertical milling machines. Machine tapping is faster, and generally moreaccurate because human error is eliminated. Final tapping is achieved with singletap.

Research has shown that the important reasons causing tap breakage are asfollows:

* 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 chips

* Tapping does not follow the pre-tap hole (misalignment)

* Mismatch of machine feed and tap feed may cause the tap to break in tension orcompression.

* 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 .1slower to establish float for 40 tpi or higher and .15 slower for 40 tpi or finer[5])

* Improper spindle speed

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Tool holders for tapping operations

To overcome the problems, special tool holders are required to minimize the chances of tap breakage during tapping.

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.

The operator must get this alignment rather close to ideal in order to (a) produce good threads and (b) avoid tap

breakage. 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 will follow. To help with this alignment task, several kinds ofjigs and fixtures can be used

to provide the correct geometry without having to use freehand skill to approximate it:

o 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

25 error.

o 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

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

o Quick-change drilling and tapping chucks (variations available for both CNC and manual-control tools)

o Rigid tapping attachments (for CNC)

Generally the following features are required of tapping holders:o Twin chucking: tap is held at points of both its circular and square cross-section, holding it steady and providing positive rotational

drive.

o Safety clutch: The built in safety mechanism operates as soon as the set torque limit is crossed to save the tap from breakage.

o Float radial parallel: small misalignments are taken care of by this float.

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

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Tapping stations

*Tapping stations are worktables with a tapping head attached

to the end of a pantograph-style arm similar to that ofa balanced-arm lamp. The operator guides the tapping head toeach (already-drilled) hole and quickly taps it.

*Drilling and tapping centers, whose name sounds similar tothat of tapping stations, are actually light-duty,

affordable machining centers of 2, 2.5, or 3 axes that aredesigned for a life of mainly drilling and tapping with limitedmilling use.

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*

Five die sizes and types

The die cuts a thread on a preformed cylindrical rod,

which creates a male threaded piece which functions

like a bolt. 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

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A cylindrical blank, which is usually slightly less than the required diameter, is

machined with a taper (chamfer) at the threaded end. This chamfer allows the die

to ease onto the blank before it cuts a sufficient thread to pull itself along.

The adjusting screws allow the die to be compressed or expanded toaccommodate slight variations in size, due to material, manufacture, or die

sharpness.

Each tool is used independently, but are usually sold in paired sets of both types,one die and three taps. The common sets shown are designed for hand operation,

but different types such as helical or spiral may be used in production tools suchas CNC machining tools, which employ die heads to make large volumes of

threaded parts.

Die nuts, also known as rethreading dies, are dies made for cleaning up damaged

threads, have no split for resizing and are made from a hexagonal bar so that a

wrench or shifter spanner can be used to turn them. Die nuts cannot be used to

cut new threads.

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Step by step to used tep

* Step 1: Determine the Threads Per Inch

Tapping is when you threads are cut into a hole. A die set is used to cut threads onto a cylinder(bolt). To use a tap or a die, first determine the number of threads per inch (TPI) of the part to

be fixed. A gauge system that has a number of different pins can be used to calculate the TPI of a

bolt or nut. After determining the TPI of a bolt, choose the die that corresponds to it. A tapered

die will tell which side to begin using. The die fits into a special wrench that holds and guides the

die.

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* Step 2: Create New Threads

To use the die to create new threads on a worn out bolt, place the bolt into a vise to hold it as

the wrench is turned over it. Cutting metal with metal can create heat, so put some cutting oil

on the bolt to lubricate it. Place the die over the bolt and hold it horizontally. Turn the wrench.The die will catch on the threads already cut into the bolt. Every couple of turns, reverse the

wrench about a half a turn to clear the threads so that the die will cut better. Also, re-apply

cutting oil throughout the process. Turn the wrench until the bolt comes past the top of the die.

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* Step 3: Turn a Steel Rod Into a Bolt

o A die set can also be used to turn an ordinary steel rod into a bolt. To do this, the rod must

have a beveled end. If necessary, chamfer the end of a rod on a grinder to get a bevel. The die

will not work very well with a flat-ended rod.

o Lubricate the rod often, as when cutting into a worn bolt. Make turns slowly. Have a little bit

of patience with this process to achieve the desired results.

* Step 4: Use a Tap

To use a tap, choose the size that is appropriate for the size of the bolt or the hole you want to

thread. Place the tap into the special wrench and tighten it in. Then, place the cutting end of

the tap over the hole and turn. Use cutting oil to lubricate the tap. As with the die, once the tapis started, make a slight reverse turn every now and then.