Breaking off a tap?!

[Derek <dereklola@yahoo.com>]

I recently needed a half inch deep 10-32 tapped hole in the
head end of an 7/16 Allen bolt. The tapping would start OK
(the inside of an Allen bolt isn't all that hard) but at
about 3/8 deep it would bind and trying to unscrew it would
just break the tap.

Solution? I ground off the periphery of the tap threads
after about 6 full threads. In other words the six threads
did the tapping and after that the ground threads didn't
bind in the already tapped section. It didn't weaken the
tap because it's fluted much deeper than that anyhow.

Result? I now have several spare 10-32 taps which I bought
for contingency reasons.

Question. Why do taps have such long threaded portions? I
can understand the tapered lead-in section but why the long
parallel section?

Derek

.

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