TAPS AND THREADING

The tap is used to cut internal threads. There are many forms of taps used in manufacturing work, but
the hand tap is the only one used in a home workshop. Three taps are used for each size of thread. The
Taper Tap is used to start the thread. This has a long taper ground on the point that will enter the drilled
hole and act as a pilot to guide and center the tap. Even with this self-guiding feature, you must hold it in
line with the hole or it will start crooked.

The tapered end will try to get it back to the center of the hole, and this will bend the tap and is liable to
break it.

Due to the long taper of the starting, or taper, tap, it cannot reach very far into the hole. A tap with a
shorter taper, called a Plug Tap, is used after the thread has been started with the taper tap.

It is possible to start a thread with a plug tap by carefully guiding it and using sufficient pressure. It is not
possible to start a thread with a bottom tap. If your budget does not permit the purchasing of the three
taps, get a plug tap and a bottom tap.

Taps are easily broken and must be handled very carefully. Never use a tap wrench too large for the tap
and do not force it as it cuts a chip. After the chip has formed, turn the tap backwards until it breaks the
chip. With very small taps, it helps to run the plug tap in as far as it will stand without breaking. Then
back it out and cut with the bottom tap until it reaches its limit.

This way, each tap cuts less metal each time and is less liable to be broken by twisting. It takes longer,
but is worth the extra time by saving broken taps.

It helps to have two small tap wrenches so the two taps can be left set up in the wrenches. Bending a
small tap sideways is one of the easiest ways of breaking it. Turn the tap with the finger tips of one hand
and use the other hand to steady the first by resting your wrist on the vise.

When tapping a hole where the tap must line up with a clearance hole, place the two parts together and
tap the thread through the clearance hole, which acts as a guide. If the two holes are not in line, the tap
will be forced against the tight side of the clearance hole and will cut threads that will allow the screw to
enter the threaded lower part.

These part threads cut in the clearance hole may prevent the screw from clamping the two parts tight,
and it may be necessary to remove them with a round file.

When a thread must be exactly parallel to a drilled hole, it is best to start the tap in the drill press before
the work has been released from the clamps used to drill the hole. Insert the tap in the drill chuck and
adjust the chuck so the tap will slip if it is biting too hard. Use a short rod that will fit into the keyholes of
the chuck to turn it, at the same time using a little pressure on the drill press feed to start the tap.