On Monday 29 March 2010, John Figie wrote: >Years ago when with my first homemade CNC that used leadscrews I found > that I could get better results if after cutting the circle I then cut it > again but in the opposite direction. You may get much better results > because the cutting forces in the opposite direction will be opposite for > each 90 degree segment of the circle. > >John Figie
I didn't resort to that when I was cutting the bearing sockets for the thrust bearings in the alu blocks for my new Z axis for my HF micromill. I had them in and out several times and finally got them aligned to the holes I'd drilled for the grease fittings. I did have it all snugged up and was using around 2.5 thou of backlash comp in the x/y at the time. I could see the artifact, but could not feel it, and the bearings in and outs pretty well polished it away. The fit was pretty snug, taking at least 100 pounds to insert or remove them. I should have taken some pix when it was apart I guess, but didn't. >--- On Fri, 3/26/10, Jon Elson <el...@pico-systems.com> wrote: > >From: Jon Elson <el...@pico-systems.com> >Subject: Re: [Emc-users] accuracy question >To: "Chris Reynolds" <c_reynolds2...@yahoo.com>, "Enhanced Machine > Controller (EMC)" <emc-users@lists.sourceforge.net> Date: Friday, March > 26, 2010, 11:22 PM > >Chris Reynolds wrote: >> I have a quick question that I'm sure will be simple for one of the >> members out there. I've been using emc now for about a year and I'm now >> running it on my milling machine. I've got backlash set in the .ini file >> but I've noticed now that when I'm cutting around a circle that it's not >> coming out accurately. It's as if the motor when it changes direction >> while cutting a curve or circle speeds up to take care of the backlash, >> but then what's happening is that my cuts aren't coming out perfectly >> round. Any suggestions? > >Yes, this is one of the N reasons that backlash compensation really >doesn't work in any profiling application. It kind of works in hole >drilling applications where you don't do anything with multiple axis >coordinated moves. The problem is, for the most part, only solved by >fixing the backlash. In your case above, every time an axis changes >direction, the motor is required to instantly move from one side of the >backlash to the other. This requires two instantaneous accelerations, >which are of course physically impossible. So, anything the CNC program >does is already wrong, attempting to do the impossible in the least >awful manner. What is worse is that backlash leaves the table >unconstrained by the motor/leadscrew. So, any time the screw is driving >the table in one direction, cutting forces could pull the work further >into the cutting tool. Just an overall bad situation. > >Jon > >-------------------------------------------------------------------------- >---- Download Intel® Parallel Studio Eval >Try the new software tools for yourself. Speed compiling, find bugs >proactively, and fine-tune applications for parallel performance. >See why Intel Parallel Studio got high marks during beta. >http://p.sf.net/sfu/intel-sw-dev >_______________________________________________ >Emc-users mailing list >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users >-------------------------------------------------------------------------- >---- Download Intel® Parallel Studio Eval >Try the new software tools for yourself. Speed compiling, find bugs >proactively, and fine-tune applications for parallel performance. >See why Intel Parallel Studio got high marks during beta. >http://p.sf.net/sfu/intel-sw-dev >_______________________________________________ >Emc-users mailing list >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users > -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) But what can you do with it? -- ubiquitous cry from Linux-user partner ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
