[TheForge] Re: post vise repair

[Mike Spencer]

> ...repairing a post vise, and fixing up a new thread. Some new key
> stock was wound into the thread and then brazed into the tube with
> brass,...

A couple of factoidal anecdotes, for whatever they're worth.

At a workshop circa 1978, Dimitri Gerakaris described, repairing a
post vise by wrapping 2 pieces of 1/4" square side by side on a
mandrel, then brazing one inside for the female thread and the other
onto the/a mandrel for the male.  Great success reported.  A couple of
years later, when I saw Dimitri again, I asked about it and he said it
hadn't held up well in the long run.



I had a square-thread rod (but no nut) and wanted to make a wood vise.
1/8" cold rolled fit in the threads very nicely.  But when you bend
square cross section as sharply as that (you all know this already) it
gets stretched on the outside and compressed on the inside of the
curve.  Result is a trapezoidal cross section resembling an Acme
thread, not what you want for a square thread -- doesn't fit right or
make good contact with the opposing thread.  If you draw-file the
piece of stock to a trapezoidal cross section *before* wrapping and
then wrap with the narrower of the parallel faces in, the distortion
brings the shape back (more or less) to square.

This all worked fine for my wood vise, only I got way too much brass
in the tube/threads.  Lots of time with a dental drill, reaching in
with a little wheel and cleaning up.  Once the male thread wold go
into the tubular threaded part at all, it was time for lapping
compound.  That fixed up the fit pretty good.

I didn't have compressed air or a gas forge when I did this.  I'm
guessing that I could have made a more tidy job of the brazing with
the gas forge and could have blown out some of the excess brass with
compressed air while it was hot.



FWIW,
- Mike

-- 
Michael Spencer                  Nova Scotia, Canada       .~. 
                                                           /V\ 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^