On Fri, 31 Aug 2007 13:46:23 -0700, Grant Erwin
wrote:

Wes wrote:

Well, it is once again time for me to use an engine lathe to single point
thread. It seems to be something I do every couple years so I've never
realy mastered it.

I'm restoring a Clausing 6903 lathe that uses a varidrive.

The driven sheave has a crack in it.
http://wess.freeshell.org/clausing/6...it_a_crack.JPG

My bud tried to gas weld it with cast iron rod but it wouldn't close.

http://wess.freeshell.org/clausing/6903_gas_welding.JPG

Not much of a picture, cell phone camera though a welding helmet.

So then we tried brazing.

http://wess.freeshell.org/clausing/6...rning_down.JPG
http://wess.freeshell.org/clausing/6...wn_brazing.JPG

It looks like the crack filled but since gas welding didn't work I don't
feel like trusting it. There could be dirty metal in crack. So plan #2
forms.

I'll replace the hub by turning it off, boring and threading sheave for a
1045 steel hub followed by loctiting with 271 and driving two pins in mating
diameter.

Here is a drawing.

http://wess.freeshell.org/clausing/C...ave_repair.pdf

So last night I took a practice pass at threading to get my brain
configured. Compound at 29 degrees, crossfeed set at 0, infeed with
compound, hand on halfnut lever and pulling out and pulling up on lever at
end of thread.

I ended up blowing a pull out once. There wasn't a shoulder and if you
looked at drawing their will be one. The only other thing I can think of to
improve my chances is to put a dab of paint marker on shafting so I can have
a timing mark to pull out.

I'm open to suggestions on any other tricks to thread up to a shoulder, I've
already put in an undercut and the slowest speed is 45 rpm and the machine
is a Leblond servoshift so going out of gear at the last part and cranking
by hand isn't an option.

A lot of guys in the magazines advocate adding a hand crank to the back side
of the headstock spindle, and slowly cranking it towards the end of each
pass. They use an expanding rod arrangement to lock a shaft inside the
headstock tube, the shaft of course having a crank handle fitted.

GWE
=======
For one way to do this click on
http://mcduffee-associates.us/machin...ndle_crank.htm

One word of warning -- if possible disconnect or loosen the drive
belts as the crank will whack the crap out of you or anyone in
the area if you turn the lathe on.


Unka' George [George McDuffee]
============
Merchants have no country.
The mere spot they stand on
does not constitute so strong an attachment
as that from which they draw their gains.

Thomas Jefferson (1743-1826),
U.S. president. Letter, 17 March 1814.