On 2009-06-28, Michael Koblic wrote:
Jim Wilkins wrote:

[ ... ]

Plan the job so you can make the finish cuts on all surfaces without
loosening the chuck. It doesn't matter for roughing as long as you
leave an allowance larger than the runout.

Very good advice.

I doubt you will ever get the 3-jaw to run true enough that you can
reverse the work and make the cuts from both ends meet invisibly.
That's difficult even with a Set-Tru, 4-jaw or collets, and a good
reason to turn between centers. You could make a gnomon with extra
metal in the ends for the center holes and then part them off later in
the 3-jaw. Or turn to a step or groove from both ends, a little runout
won't show across it.


Thank you and all the others.

The critical bit of information seems to be that 3-jaw scroll chucks do not
necessarily hold true at all diameters thus trying to improve on the 4 thou
of runout would probably put me on the flat portion of the diminishing
return curve.

Yes. How close to 0.001" you get is a function of how much you
spend for the chuck -- and the precision of the lathe spindle setup too.
The Taig is likely to shift a bit every time you remove and replace the
chuck. Try it with a piece chucked up and see what happens.

I am not set up for turning between centres yet - that comes next and will
invove cobbling some sort of centre for the headstock and a dog (apparently
the cognoscenti like a hose clip for this).

Interesting -- but I guess that it will work. For the Taig, I
use a small dog which came with my Unimat SL-1000.

This will invove turning things
to a point so a compound slide will be in order.

Also -- ideally, you will want a live (ball bearing) center for
the tailstock end. That way you don't have to keep lubricating the
center.

Another issue is facing off
longish cylinders (the inner diameter of the spindle is only 5/16") and I
shall be needing a steady rest.

Yes -- you will.

But all of that had to be put on hold as I have not had a decent arrangement
to grind lathe bits. I finally finished it today.

:-)

This is worse than having a baby.

:-)

I wonder at what point one returns to some semblance of productive work
rather just continue making tools for tools...:-) It has become a running
joke in the family.

The primary purpose of *any* home shop is to make tools for the
tools. Any actual products other than this are a matter of luck -- or
testing the tools which you made. :-)

Enjoy,
DoN.

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