On Mon, 03 May 2010 22:48:52 -0400, Bob Engelhardt
wrote:

The same neighbor with the broken recip saw has a broken 7" angle
grinder that he'd like me to fix for him.

It's the switch on the grinder that's broken - the return spring on the
trigger has a broken end (it's an extension spring with hook ends).
I've checked the usual sources & can't find this one, but I have a good
repair, I think.

The repair is to make a plug with threads to match the coiled spring
profile. The plug would just thread into the broken end & have the
needed hook. The spring has a very high spring rate & extends very
little, so there would be little chance of the plug escaping during
extension.

As far as turning the threads on the plug, how closely do I have to
match the profile? Can I just use a standard 60 degree thread (with the
same pitch, of course), or do I have to use a form tool to get a
semicircular thread?

This will a small plug: the ID will be 3/32 & the pitch 24 tpi.

Anybody ever done this?

Thanks,
Bob
I've made spring ends with Cerrobend and Cerrosafe, alloys that melt
at temperatures well below what would affect heat-treat of a spring.
Think boiling water temp.

Drill hole in bit of scrap same as OD of spring. Insert spring into
hole. You could also have a center hole housing a hook. Pour in a
little molten alloy. It forms a plug that grabs a couple of turns of
spring, and in your case a hook. Or, you could drill the plug after
the fact and then insert the hook.

BTW - the spring is 3/16 OD, 1-9/16 OAL, .044 wire, preloaded - if
someone has a REALLY good source for springs (i.e., much better than McM-C)