Great thanks for the pointers! On Thu, Mar 14, 2019 at 1:32 PM Robert Ellenberg <[email protected]> wrote:
> Hi Curtis, > > There are a few major hurdles to doing rotary axis blending: > > 1. Blends between circular motions (that also have motion in other axes) > are not geometrically possible with the blending technique we use > (circular > arc segments), except for some special cases. This IS possible with line > segments, however. > 2. The blend arcs are parameterized using arc length; the distance in > ABC has to be included in the arc length calculation, or the blends > won't > match velocities properly with the segments they're blending. The > current > TP assumes in many places that "progress" along a segment means XYZ > motion, > and UVWABC motion is indirectly tied to this. > 3. It's difficult to define blend tolerances for ABC motion in a useful > way. For example, with 4th axis engraving program, the effective blend > tolerance depends on the diameter of the part. > > All that said, a while ago I extended the 2.7 TP to handle 6 linear axes > (which avoids problem 3, and doesn't try to blend any circular motions). > The branch is here if you want to try it out: > > > https://github.com/robEllenberg/linuxcnc-mirror/tree/feature/uvw-blending-2.7 > > This might help if you don't actually need rotary axis motion and can > pretend your 4th axis is linear. > > Best, > Rob > > > On Thu, Mar 14, 2019 at 12:56 PM Curtis Dutton <[email protected]> wrote: > > > I don't mind doing the G93 calculations. The problem for me is no > lookahead > > when using x,y,z,a > > > > Does anyone know why n-axis lookahead isn't easy to accomplish with the > > new TP? (I'm sure its complicated ! :-) > > > > On Thu, Mar 14, 2019 at 12:47 PM Gene Heskett <[email protected]> > > wrote: > > > > > On Thursday 14 March 2019 09:12:51 Les Newell wrote: > > > > > > > That does not help the trajectory planner lookahead problem. It just > > > > tries to correct the feed rates for each movement segment. > > > > > > > > Les > > > > > > No, it doesn't, so in that sense you're correct, Les, but its certainly > > > one way to solve the problem in terms of production time. This is > > > something I encountered about 4 years back when I attempted to make a > > > ship auger type drill bit on the G0704 while I was building us an > > > entertainment center. And again with a similar auger bit when I was > > > converting part of our front deck to a wheelchair ramp alittle over a > > > year ago so I could get the missus in and out of the house. In the > > > latter case I needed it capable of drilling a hole at a low angle into > > > the side of a 4x4 about 15" high, to anchor it solidly to the deck so I > > > could drop a 46" tall plastic rail post over it and make the safety > > > rails on one side of the ramp. Very solid feeling rail, it doesn't move > > > with my 165 lbs leaning on it as hard as I can. That was the general > > > idea. But it took many many hours with a 1/4" ball nose carving a 3/4" > > > piece of cold roll that needed sharpening about 4 times a hole. Cold > > > roll is not the ideal to make a drill bit from, but it got the job > done. > > > > > > I should have done something like calculating the speed by translating > it > > > to radius, then to inches a minute. But TBT, I was much more interested > > > in getting the job done, between the rapid dulling and time > > > resharpening, it took about a day for each of the 3 posts to get them > > > planted in a puddle of tightbond. Needless to say, I downloaded this > > > conversion utility. On of the things I intend to do with this big > gantry > > > is make a copy of a thumbhole gunstock I carved by hand for a 50 cal BP > > > rifle. Someday I'd like to find some purtier Maple. It shoots very > well > > > the way it is. > > > > > > My thanks to the author, apparently Shawn E. Gano. > > > > > > > > https://www.ganotechnologies.com/cnc/rapidrotary/ > > > > > > > > _______________________________________________ > > > > Emc-developers mailing list > > > > [email protected] > > > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > > > > > > 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 > > > > > > > _______________________________________________ > > Emc-developers mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > > > _______________________________________________ > Emc-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-developers > _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
