CMV wrote:When I want to true up a small part with a square face in the chuck I use the back of an insert turning tool to do it. Put the tool in the tool holder so its inline with the lathe bore but the cutting end is facing away from the work. Put the part in the jaws, align best you can by eye/feel, and loosely tighten the jaws - just enough to barely hold it in place. Turn the lathe at low RPM and gently bring the back side of the tool into the work, just kissing it. Then stop the lathe with the tool still in contact with the work. Tighten the jaws securely. As you're doing this, you'll see the part go from wobble to stable as it's spinning.
This won't get it dead nuts, but it will be very close to it. Some guys make a special tool to do this with a roller at the end so there's less chance of marring the work, but the back side of a tool seems to be ok as long as it's square & not driving a corner into the face of the work. If the tool is set at the right height for cutting the back end is pretty high from center so it's not really trying to cut into the work - just pushes it in.
Only hard part is getting a feel for how tight "barely secure" in the jaws is. Too tight & it won't square up or the jaws will mark the outside as it's pushed in a little. Too loose & the jaws just spit the part out.
I've done kind of the same thing with a center in the tailstock. If the part has a center hole, loosely chuck it and then push it in with the tailstock center as it spins. When it looks good, stop & secure the jaws. For something like a K with a very skinny face that way works better.
If the "wrong" side is the square end, I put 2 parallels between the work and the chuck. Pick a size that gets the work exactly where you want it in the jaws. Push the piece against the parallels firmly while snugging the jaws. REMOVE THE PARALLELS before starting the machine (unless you want them violently flung toward you) and you should be really close. Again, not dead nuts, but very close.
There's probably a "right way" to get a small part perfectly indicated back in but since I'm just figuring out how to do things as I go, these are things I've found to work for me. I don't expect to hold tenths in my work - I'm just not good enough. Hell, I probably can't accurately & repeatedly measure tenths anyway. ± .001-.002 is perfectly acceptable to me when I'm trying to be precise. A real machinist will tell you .005 may as well be a quarter mile & in some cases it is. So far I'm happy with how my projects turn out with ± .002 tolerances and can live with "close enough". Blasphemy....
Brilliant! Just what I needed for starting to make a small gear for a very old clock and I was
bedeviled on how to set it up without buying an expensive disposable chuck or
making a special holder as the talented Enfield does so often.
For a larger piece I pressed a small bearing onto a SS pin I salvaged from
a computer printer board which I then pressed into a piece of drill rod.
Held in my Aloris, as you, I set the RPM at lowest setting, and rotated, say, 1.5"
disk true to chuck. Obviously does not work on a smaller part.
Also a 'chuck spacer': <<
http://www.chaski.org/homemachinist/vie ... 42&t=98304 >>
Thank you again for sharing such a 'why did I not think of that before' solution.
Best.
