On Friday 24 January 2020 00:07:07 David Berndt wrote: > Hello All, > > I'm having a bit of an issue with some geometry not coming out as > expected. I suspect it's related to backlash and cutting forces moving > the table a bit but I don't have linear scales to monitor/correct for > that sort of thing so I'm left wondering a bit. I was hoping that > being able to see what backlash comp is doing on screen as my > toolpaths run might enlighten me some. Is there any pin or ?? that can > be monitored to give me more insight? > cutting forces vs backlash compensation are not a problem when digging cutting as the cutting farces are against the direction of travel, so backlash compensation always follows the direction. So when calibrating the scales, always do that with dig cutting.
Cutting tools OTOH, generally cut better and last longer when the bit is chopping down into fresh cut as it engages the metal approaching, but this means the cutting force may pull the table ahead, to the other side of the backlash. if the backlash is substantial then you will have errors. Generally I try to keep my own machinery at less than .002" for backlash compensation. That will often involve tearing down the thrust bearings which are the major source of that slop and adding some Reynolds wrap in the assembly to add just enough preload to get effectively zero backlash from that source. I bought a cheap C7 grade screw for z on the Sheldon, and wound up shimming almost 7 thou out of its thrust bearing. Thats what you get for buying a C7 grade 25mm Diameter. Chinese screw 1450mm long for under 200 dollars. And they are even cheaper today. I also put bellows over it to keep the swarf out of it so it s/b good for a long time. I also sealed up both above and below the bare x screw for the same reason. Yes, I am using z derived screw compensation, but its cross coupled to move the x, compensating for bed wear in a 70 yo lathe. Works well. > Thanks, > -Dave > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
