Taps and Dies
are tools commonly used in
metalworking for the cutting of
different sizes, and types of taps.
The Tap is used to cut
a female thread on the inside surface of a predrilled hole.
The three taps in the adjacent image are of different sizes and types.
- The top
tap has the thread going all the way to the end of the tap and is called a
bottoming tap - it will tap to the bottom of the hole.
middle tap is an intermediate tap where the thread tapers off
before the bottom
lower tap is a taper tap where the thread has an even more
pronounced taper towards the end of the tap. This taper allows the tap to
ease into the freshly drilled hole in a gradual cutting action,
relieving the cutting pressure on the first few teeth of the tap.
To use, a hole is made
(usually drilled) that is the minor diameter for that sized tap. This
is the equivalent of the blank size (major diameter), less thread depth.
The order of usage when hand tapping is to use the taper tap first,
the intermediate next (if the material is hard and it is felt that
the tap is still working too hard), and finally the bottoming
tap is used to get the full form of the thread for the full depth of the
shank or hole.
The Die cuts a male
thread on a preformed cylindrical rod. The dies shown are
- top left
- and older split die, with top adjusting screw
left - a one piece die with top adjusting screw
- center -
a one piece die with side adjusting screw (barely visible on the full
- top and
bottom right - two dies without adjusting screws.
To use, a cylindrical blank,
which is usually slightly undersize 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 suffecient thread to pull itself along.
The adjusting screws allow the die to be compressed or expanded to
accomodate slight variations in size, due to material, manufacture, or die
sharpness. The two right most die images shown in the image have no
adjusting screws, however the die holder can be used to exert pressure and
close the cutting size down if required.
Each tool is used independently, but are usually sold in paired sets of both
types, one die and three taps. Some sets however may provide a lesser number
An ordinary Tap or Die
can also be used for repairing threads in stripped holes or bolts. Die
Nuts are dies made for cleaning up old threads, they have no split for
resizing and are made from hexagonal bar so that a
wrench or shifter spanner can be used to apply them (rather than the
purpose built die wrench)
A tap wrench is a hand tool used to operate any small tool that has
a square driving head as part of its body. These are usually cutting tools
of which the most common are
taps, however there are other small hand tools such as
hand reamers that they may be employed with.