True, I used to do a lot of helicoil repairs, (aircraft engine repairs)
but we usually used a 45 degree chamfer. With the proper installer(the
type that constrain the helicoil) the chamfer is not a problem. I can
see it helping if your using the standard screw type installer. We also
used to do a lot of twinsert repairs, a helicoil in a helicoil, for when
the previous repair had failed or the magnesium had corroded away.

Eric R Snow wrote:
On Sun, 28 Nov 2004 17:37:35 GMT, machineman
wrote:


Or could be used for chamfering any 60 degree threadform hole.

Eric R Snow wrote:



The 120 degree is also used for countersinking the holes for
Heli-Coils.
ERS

That's true, but usually the callout for chamfering a threaded hole is
45 degrees. In fact, I've never seen a 120 degree callout except for
the STI thread. Heli-coil says this is for ease of inserting the
heli-coil STI. But, since I've not seen every drawing I can't say it
isn't done. Or even that it's not common.
ERS