>> This caused me to wonder... How many encoder pulses per inch does a professional CNC machine use.
My lathe - a commercial "hard turn" machine that I bought from Timken only has 2450 pulses per inch of travel on both axes. It was originally setup to turn semi hard bearing races prior to heat treating and grinding. The encoders are mounted right on the axes ball screws. So I guess they figured that they will cut the races to within a couple of thou, then heat treat them and grind the bearing cups to much tighter tolerances. The machine was really setup for high volume production with a 20' bar feeder, parts catcher, pressure lube on all of the ways etc, etc. So as John said I think it all depends on the machine and what it is designed to do. Dave cogoman wrote: > Thanks to Sven Wesley I was impressed by the AMT102-V Versapak > quadrature encoder available at Digi-Key. With 2048 PPR, which could > get 8192 quadrature increments it could give me a possible solution to a > router axis drive. Using skateboard bearings to support a 5/16" rod, a > DC motor could drive the rod with O-rings and pulleys. A fine steel > stranded cable wrapped around the rod many times would release about 1" > of cable per revolution. With 8192 steps per revolution, there would be > about 250u inches per encoder step. > > This caused me to wonder... How many encoder pulses per inch does a > professional CNC machine use. > > When we were swapping drive cards on our FADAL 4020, I seem to > remember the following error getting to around 60 encoder pulses (or at > least I think the controller was listing error in pulses) at a fairly > fast feed rate, and the machinist said that was in the normal range. We > recently discussed this and it seems that cutting around the outside of > a square part, which is usual for us, the end mill would come to a stop, > allowing the servo motor to catch up, before the 90 degree turn to mill > the next side. Also, the final cut is usually at a lower feed rate > which should have less error. > > So, are there enough encoder pulses per inch to make 60 pulses off a > very small error around 200u inches, or could it be that having a servo > that's behind by a couple of thousandths during heavy material removal > doesn't adversely affect the size achieved during the final finish cut. > > Or, in the immediate application, could an encoder count that gives > 250u inches per encoder pulse allow the system to cut with accuracy > better than .001" in the final part. > > ------------------------------------------------------------------------------ > Come build with us! The BlackBerry(R) Developer Conference in SF, CA > is the only developer event you need to attend this year. Jumpstart your > developing skills, take BlackBerry mobile applications to market and stay > ahead of the curve. Join us from November 9 - 12, 2009. Register now! > http://p.sf.net/sfu/devconference > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9 - 12, 2009. Register now! http://p.sf.net/sfu/devconference _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
