[etpm]

Using the G84 command on this 15XT machine used to work fine but lately the feed seems to be inconsistent. The mill does not have the rigid tap EPROMs but does have the Baldor drive that is necessary for rigid tapping. I am using tension/compression tap holders. What is happening sometimes the tap holder will extend too much, all the way to the limit. For example the mill is tapping a 1/4-20 hole .900 deep. But once the tap is engaged in the hole, and the Z axis has moved down about .400, the holder will be at maximum extension. Then the tap starts to pull out of the holder, which tends to ruin the tap collet among other things. I have checked the RPM while tapping is in progress and it is as programmed. So this must mean that the feed is too slow. And then sometimes the hole gets tapped to depth with no excessive extension of the holder but when the spindle reverses and the Z axis rises the holder will once again extend way out, as if the feed is too fast. I am running repeat jobs with no program changes, programs that have run well for years. If I adjust the Z offset for the tap in the positive direction so that the tap only enters the part about a quarter of an inch the holes will be different depths. But then sometimes the machine will run several parts in a row and the tapping will be perfect. If I was experiencing feed problems on either the X or Y axis I would try swapping the servo amps to see if the problem changed to the other axis but I don't know if I can safely swap the Z axis servo amp with either the X or Y amps. Anybody here have any ideas?
Thank You,
Eric

[jon_fallon]

Had the same issue on the 4020 here when the extension tapping head was first used. It was fixed by entering SETP, scrolling to the RPM factor, and adjusting the RPM factor until the extension head tracked the tap.

[etpm]

Greetings Jon,
When the problem first occurred I tried adjusting the RPM factor. But it didn't help. The feed seems to vary from hole to hole. So holes will be tapped just fine and then the tap holder will extend too far while the tap is entering a hole or it will tap the hole perfectly and then the holder will extend too far as the tap is reversing out of the hole.