On Friday 04 July 2014 00:28:07 Jon Elson did opine And Gene did reply: > On 07/03/2014 09:27 PM, Gene Heskett wrote: > > believe I need to figure out a way to certify its accuracy > > as g2 cut circles seem to have anywhere up to 3 thou, > > perhaps a bit more of almost random edge wibbles. > > Difficult when the only dial indicators I have are a 1" > > travel, .001" scale, and one of the Grizzly .0001" with > > perhaps a 13 thou range either way from zero. > > Well, I always make a rough cut first, then make a finish > pass of about .010" > to clean up the edge with minimal tool deflection. Small > HSS cutters can > deflect an amazing amount without breaking, but you will > have large > errors. Solid carbide cutters are much stiffer. > I've broken several of those 1/32 SC mills, trying to cut deeper than 1.5 thou per pass and faster than 2.5 ipm. Brass sheet (door kick panel from ACE Hdwe) is 1/32 thick so I'm doing 25 passes to get 45 thou down in case the wood backer isn't dead flat. It rarely is. Because the SC is so fragile in that size, there is no rough cut, particularly when dig cutting.
Obviously I could move faster with a faster spindle, but 2500 revs is wide open. I keep hoping to find a high speed motor thats 49.75mm in diameter so it would drop into the casting in place of the current spindle. But the smallest, a 300 watter at 12k r's & 50 volts, is 53mm in diameter. Sigh. > > So, how accurate might I expect to see with an ebay > > optical scale? Good enough to map these screws? Something > > like this: > > <http://www.ebay.com/itm/RSF-Heidenhain-Optical-Comparator-Video- > > Measuring-Machines-Scale-New-in- > > Box-/201105192906?pt=LH_DefaultDomain_0&hash=item2ed2cdb7ca> > > For a $150 bill. Thanks Jon. Cheers, Gene Heskett > > That's only a 10 um scale, hardly suitable for high accuracy > machines. > 10 um = .0004" or 2540 counts/inch. I'm running 20000 > counts/inch on > my Bridgeport in X and Y, and 40000 counts/inch on Z. > > Jon I won't waste any sheckles on that then, although its more accurate than I am atm, and I can't afford the higher accuracy stuff. I'm running, with the new screws, 25680 on XY, and -68571.4285714 on Z which isn't direct drive. Theres a (IIRC) 17 to 42 timing belt step down on a 10 tpi Acme with dual nook nuts for backlash adjustment in the z drive. Silly Q? There's a var you can set for display speed that controls the number of discrete points for a circle display. Is there something I can do to g2/g3 that would, by doing more and slower calcs, improve the circularity? Or is the math correct and I should attempt to map these screws after re- checking and redefining the backlash & gib snugness? That would likely involve using the limit switches as home position indicators to establish the initial screw orientation reference point. More hal trickery. ;-) Thanks Jon. 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> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ Open source business process management suite built on Java and Eclipse Turn processes into business applications with Bonita BPM Community Edition Quickly connect people, data, and systems into organized workflows Winner of BOSSIE, CODIE, OW2 and Gartner awards http://p.sf.net/sfu/Bonitasoft _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
