Suggested Percentage
Of Full Threads In Tapped Holes
It stands to reason that it takes more power
to tap to a full depth of thread than it does
to tap to a partial depth of thread. The higher
the metal removal rate, the more torque required
to produce the cut.
It would also stand to reason that the greater
the depth of thread, the stronger the tapped
hole. This is true, but only to a point. Beyond
that point (usually about 75% of full thread)
the strength of the hole does not increase,
yet the torque required to tap the hole rises
exponentially. Also, it becomes more difficult
to hold size, and the likelihood of tap breakage
increases. With this in mind, it does not make
good tapping sense to generate threads deeper
than the required strength of the thread dictates.
As a general rule, the tougher the material,
the less the percentage of thread is needed
to create a hole strong enough to do the job
for which it was intended. In some harder materials
such as stainless steel, Monel, and some heat-treated
alloys, it is possible to tap to as little
as 50% of full thread without sacrificing the
usefulness of the tapped hole.
workpiece
material
deep
hole
tapping
average
commercial
work
thin
sheet stock
or stampings
hard or
tough cast steel
drop forgings
Monel metal
nickel steel
stainless steel
