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 > > <[email protected]> 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 > yesterday. > > 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> ------------------------------------------------------------------------------ _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
