On Thu, 7 Jun 2012 09:39:12 -0400, you wrote: >I did notice yesterday while cutting that 4mmx0.7 thread, which btw came >out real nice, that the spindle speed you start at should not be changed >during the run as it will widen the cut thread, leaving a distorted profile >at the root of the thread.
That should not happen? I thought LinuxCNC compensated for spindle speed change by using an encoder and modifying the feed to suit? One of the selling points over Mach I'm told ;) >I had started it at an S200 and had run it up >to 300 with the spindle override for a couple of loops as I was touching >off to the final size. Slowing the spindle back down to 200 put it back on >track and it cleaned it up nicely. As for cutting, with that fine a >thread, I could have cut it at 600+ rpms, z was not speed challenged. > >My guess is that there is a get up to speed lag in the z accel after seeing >the index before z is actually phase locked to the spindle. I have always >started a thread well off the end of it in air, and I'm thinking this >phenom could be backlash related. To that end, would it be possible to >incorporate in the retrace motion of G76, and extra 2 thousandths of an >inch to the right of its park & wait for index, which is then brought back >to the z starting position with a 2 thou move to do nothing but take up the >backlash while it is waiting for the index. This 'turn around' move would >then take up the backlash, hopefully preventing this spindle speed related >slippage between the spindle and Z. If the index arrives while the backlash >move is in progress, skip it and wait for the next index of course. Starting off the actual end off the stock is normal for threading and the carriage should have all the backlash gone by the time the tool hits the work. I always start my threads 5mm off the real start point and never have a problem. I would think the minimum distance would have to be considerably larger than the actual backlash amount to be certain. That said I never use G76 and only have a couple of tenths of a thou backlash (0.005mm) on both axis on my lathe. Steve Blackmore -- ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
