On 27/07/09 02:32, Chris Reynolds wrote: > I'm new to the group and I could use some help with a problem that I'm > having. I just built a new cnc machine and I keep running into a problem that > I can't figure out. I've been doing some test cuts, > problem is they always come up short on one end. I thought it was a > backlash problem so I put the dial indicator on the machine and ran it to an > inch. It came up like .040" short. So I > tried adding a backlash command to the ini file and that didn't fix it, > so it wasn't a backlash problem. Then I tried messing with the steps > and finally got it to come out right. Run it to an inch, dead on 0, run it > back to 0 and end up dead on 0 again. So then I run the > program again and the whole thing is now to long. It always seems to > come up short on one end. Checking the math the steps are right, I have a 20 > tooth pulley on the motor and a 40 tooth pulley on the leadscrew, running in > full step mode, so that comes out to 1600 steps per inch, which is what I > have in the program. It's almost like it's a compounded problem, like it's > off a small amount but then when you cut through the whole part it adds up. > But the weird thing is that it's off on one end. The part I'm cutting > resembels a comb, where you have slots cut into the part every so often, > there's a wider section at each end, on the far end it's right, on the 0,0 > end of the part that wider section is to short. > > I'm using an older hobbycnc driver that I've had for a number of years, it's > not one of the newer pro boards. I've done a number of checks and backlash > doesn't seem to be the problem. Any help anyone can provide would be greatly > appreciated. > > Chris > > > http://www.blowyourbrassoff.com > http://www.builderofstuff.com > http://www.myspace.com/builderofstuff > http://www.myspace.com/builderofbluesharps > > > Just a man, his shop, and a long list of unfinished projects... > > > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users >
check your 1 inch steps across your screw. If its a cheapy screw it may be ~10 TPI at one end and closer to 11 at the other (probably not that drastic but enough to notice) IE do a 1" move at one end, get it all good, go down the other and do another 1" move. nice and slow like so you shouldn't drop steps or anything like that. ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
