Re: CNC lathe threading?

[jmkasunich-at-ra.rockwell.com]

Ray:

AFIK, axis names, etc, aren't all that important.  Especially since I have
a Shoptask 3-in-1, so I will be using it as both mill and lathe.  I'll
probably
stick with the mill axis names, because most lathe work that I anticipate
is relatively simple, and I'll probably write the lathe G-code by hand.

It seems the real difficulty with threading is that instead of X and Z
(or Y) moving as a function of time, they have to move as a function
of spindle rotation.  The simplest solution might be to have the axis
continue to move as a function of time, but to start them when the
spindle is at a particular position.  The accuracy of threads cut that
way depends on the uniformity of spindle speed.

A more elegant and accurate approach would be to use the spindle
position to continuously drive the tool position.  Ideally, the code
would read the spindle encoder every 1mS and use the spindle
position to set the new position targets for the two axis.

Currently I am slowly putting my system together, but once I have
some hardware, I'll be ordering BDI disks and starting to look at
the code.  I have a fair amount of experience with real-time
control, so I'm hoping I can dig into and understand the low-level
real time parts of EMC.  I don't expect to grok the tcl/tk or g-code
parsing stuff - I'm really an embedded guy, not a GUI guy.  In fact,
I'm afraid the worst part of working with EMC for me will be the
work associated with maintaining portability.  I'm used to designing
hardware and writing code to run only on that hardware, to do a
specific task as efficiently as possible.  I have no doubt that I will
be able to hack EMC to thread on my machine.  However, I have
a real concern that the resulting code will be useless to anyone
else, and that I'll have to do it all over again for the next version
of EMC.

John Kasunich






Ray Henry <rehenry-at-up.net>-at-nist.gov on 03/10/2003 11:37:57 PM

Please respond to emc-at-nist.gov

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cc:
Subject:    Re: CNC lathe threading?




I can make a gui that shows x and z alone and can make x work in diameter
by
dividing the pulses per unit by two.  One place where I run into problems
is
with tool radius comp because it only works for xy moves.

It was suggested that we might want to modify the interpreter so that we
substitute axis names to get the same math used for the mill to work for
the
lathe.  As long as we are doing that to an interpreter we might just as
well
take out the mill routines and write some lathe specific stuff.

Ray


On Monday 10 March 2003 01:23 pm, John K wrote:
> I am also interested in what it would take to do threading in EMC.