On Sunday 04 September 2016 06:05:29 Gene Heskett wrote:
> On Sunday 04 September 2016 03:01:23 andy pugh wrote:
> > On 3 September 2016 at 23:24, Kirk Wallace
> <***@wallacecompany.com> wrote:
> > > I just finished a first pass at G76 tapered threading.
> > > My code is here:
> > > http://www.wallacecompany.com/tmp/G76/G76-7b.cc
> > Just so we don't tread on each-others's toes here.
> > You appear to be using D to define the taper?
> > I know why you chose this, it is because nothing else is available.
> > However it clashes with my (un-merged) multi-spindle patch:
> > https://github.com/LinuxCNC/linuxcnc/blob/andypugh/JA14_multispindle
> >/c onfigs/sim/axis/lathe_multispindle/README
> > Ideally I would use E for spindle number, but E is taken. I suspect
> > that entry and exit tapers are very rarely used, and that E is
> > "wasted" but we probably shouldn't go breaking existing G-code.
> I do use the E to define a retract speed within the ability of a
> stepper to achieve w/o losing a step. For some reason I've long
> forgotten, it was backing out at an apparent speed that was greater
> than the defined MAX_VEL and would occasionally slip a step.
> However, this may have been fixed at the same time the backlash moves
> were made subject to the MAX_ACCEL and MAX_VEL limits. As that fix
> was several 2.x versions ago, it is something I have not recently
> tested as I got into the habit of speccing an exit taper of (usually)
> .35. For my usage, entrance is generally a couple mm's off the end of
> the workpiece. That move is not under cutting forces load, and has
> never been a problem. On the little monster, thats a 435oz 8 wire
> motor wired parallel, so it can move right snappy. The E.35, at the
> spindle speeds involved is actually slower than the full retract to
> the 'drive line' for the retrace move as I was observing it running
> I have wondered about those usages, and it occurs to me that these
> usages of an alpha character should have their "scope" restricted to
> the life of the canned cycle being executed, to disappear with the
> stack cleanup as that particular canned cycle was exiting. The fact
> that its even being discussed tells me it is non-volatile. It IMO,
> should be a volatile value, eliminating the chance of cross-talk when
> one cycle sets it, and the other (possible the same) canned cycle used
> someplace else leaves it out as an option.
> > Perhaps the Cabal needs to decide who gets to claim D in G76 :-)
> > Is your pitch defined along the Z axis, or along the surface? Is
> > Steve B still around?
> For the usage I can imagine, pitch s/b along the Z axis on a (single
> spindle) lathe. On a mill whose head can be laid over, I have used
> G33.1 along the X axis several times so I know that works. But I've
> never tried G76 that way. Should it?
> It does seem to open a can of worms...
> Cheers, Gene Heskett
To continue this thread about G76 and E, I note that it says its an error
if E is more that half the drive line length. All this time I thought,
and have observed, was that it was the fraction of a full turn. Then I
grokked that programming a taper of K height would appear to be a matter
of speccing the drive length way out in the air, and programming E to be
49% of the drive line length. So all the taper would be done on the
workpiece. Longer tapers by moving the starting Z position in units of
the pitch P, and the starting X in K increments and running the same
line of code again. A time killer, but when in Rome...
When I get the little monster operational again, I will need some help in
arriving at a 7 degree included angle, eg 3.5 degrees at the workpiece,
as I think this is worth exploring. The solution to my tapered thread
requirement may have been right under my nose all the time!
Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>