On Sunday, May 06, 2012 09:15:18 PM Jon Elson did opine:

> gene heskett wrote:
> > On Sunday, May 06, 2012 02:33:08 PM Jon Elson did opine:
> > 
> > 
> > 
> > What is the best practice to establish the X zero on a lathe?  I am
> > making a test cut, measuring it and dividing that by half to enter in
> > a Touch Off.
> 
> If you have a quick-change toolpost,

I do.
> you should be able to set up X and
> Z offsets for each tool in the tool table.

That would require I get at least 3 or 4 more QC toolholders.  But then I 
am reminded that the QC post must be rotated in order to present the tool 
to the work at the correct angle, which is only as repeatable as eyeballs 
can make it.  OTOH, I do need more toolholders.  I could make a setting 
tool that would fix the reach out of each tool pretty consistent.  But 
before I tie a few hundred more up in holders for this flimsy post, my 
first inclination is to ditch the whole compound slide since linuxcnc can 
handle that rather nicely, and put a bigger, far more rigid QC post 
directly on the X cross-slide.  Something made out of real steel as opposed 
to the crappy, flexible alu this QC is made out of.

The thought also crosses my mind to mount a microswitch for homing that 
could be dropped into a locator on the carriage, but that would require a 
touchbar 3 inches long that was exactly on axis.  The alignment to keep it 
on axis while allowing it to swing out of the way, or be "unplugged" to get 
it out of the way would be fairly stringent though

As for z axis, I generally pick an arbitrary stickout suitable for the job 
and locate on the end of it, writing the gcode to run negative from there.
> Then, you leave the tool
> offsets on
> all the time.  X=0 is the center of the part, Z=0 puts the tool on the
> chuck (or wherever you decide to have the Z zero).
> 
> > Has anyone else come up with a better idea that might be more usable?
> 
> But, I don't have a CNC lathe setup, so the lathe users should have the
> exact things
> to do.

Maybe someone who does can spare a few words here? 

> Jon

Feature request:

Whoever has the touch-off code box, it sure would be nice if when you 
called it up, it displayed the current value separate the input box.  As 
is, I have to write it down, so I know where I am if I only need to adjust 
it say 0.0027 from where its at to get it exactly the right size for the 
next pass.  That would be almost as handy as bottled beer. :)

Thanks Jon.

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Cheers, Gene
-- 
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