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How to Use a Tap

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How to Use a Tap

Bottoming, intermediate, and taper taps.A tap cuts threads on the inside of a hole, to accept a machine screw or bolt.


Steps


Determine the size and depth of the thread that you want. What size screw will go into this hole?
Refer to a technical publication for the exact measurements for hole size. For example, if you want to use a 1/4-20 screw then you must use a #7 drill bit.
Drill the hole to the correct diameter and depth.
Secure the work piece firmly.
Apply an appropriate lubricant such as oil, WD-40, or a proprietary formula.


If the tap set has a separate handle or rod, insert it.
Hold the tap in line with the hole and turn it clockwise. You may feel the material breaking.
Every few turns, back the tap out (counterclockwise/anticlockwise) to clear away chips of loose material. This is especially important in a blind hole, one that does not go all the way through the work piece.


When the tap has reached the required depth, back it out, clean out chips and any cutting fluid or lubricant, and try your screw or bolt in it.

Tips


Small taps are extremely easy to snap. It takes about 4 pounds of force to break a 6-32 tap, so be very careful using small taps.


Larger taps, such as a 3/4-10, remove too much material to be used by hand unless you are very strong.
Take care not to change the angle of the tap, especially at the beginning. You only want to cut one thread.


For very thin material, it may be better to use a nut on the other side. A good rule of thumb is that at least three full threads should be in the material.

Warnings


Taps are made of hardened steel, which provides long life and a sharp cutting surface; however, this also makes them brittle. Taps are expensive and the work piece may be priceless. Always use lubrication and great care when performing tapping operations.


For load-bearing threads, always verify that the threads, fasteners, and materials are adequate for the job.

Things You'll Need
Work piece.
Lubricant.
Tap drill.
Tap.
Vise or clamp.


Chart of screw thread sizes.