Chris Morley wrote: > > > I was wondering how the spindle sync works, roughly anyways. > > It sounds like emc uses the counts between index to track the spindle. > then the index must be just to reset the count and as a starting point > for threading. > How does the tracking work ? Check that every pulse the Z axis has moved > an appropriate amount? > > I think most machines just use the index as a starting point. The > problem with that is if u start threading then want to speed up or slow > down the spindle (usually because of chatter) it will start cutting in a > slightly different spot because of lag time. > > This is certainly the case for the okuma when I used the OEM control. > > Has anyone tried changing spindle speeds to see if it tracks correctly? > ( I would stop the threading program ,change the G code spindle speed , > then rerun the program.) They were doing REALLY rigid tapping at the CNC Workshop on the Mazak, and it did quite well. We think there is some software lag, as well as backlash in the Z axis that placed a load on the tap. What we believe we saw was that the spindle load and Z axis load were higher on the withdrawal of the tap than driving the tap into the hole. With the tap turning forward, it will cut its own way into the material, but backing out, the flanks of the threads will drag on the threaded material. So, this was a case of going from forward to reverse spindle direction, as well as forward to reverse Z feed. With a thousandth of an inch of Z backlash, you'd get a minimum of .002" error when you reverse the feed, plus any error caused by software lag.
Modest speed variations on a lathe should show much smaller effects than this case. I was using my mini-mill to demonstrate lathe threading, and varying spindle speed by at least 2:1 ratio, with no visible effect. I was running the servo cycle at 1000 Hz, and using an encoder providing 6912 counts/rev. Your old Okuma may have had a much slower servo cycle. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
