non repetitive Z axis

[jcastro]

I have a colchester storm 300 turning center with a Fanuc OT controller. When running repetitive parts against a common spindle stop, I get an incremental shift in the program anywhere from .007 to .010 per part. The entire program shifts in the z positive direction. Can any one give me some direction. The company says its impossible due to the encoders being absolute. Any help would be greatly appreciated.

[hitachibos]

whats your set-up? collet or chuck jaws?

[jcastro]

I am currently using soft jaws.

[hitachibos]

is there an undercut on your jaws or a decent champher on your part?

[jcastro]

Yes on the jaws. We undercut the back side to eliminate corner issues. The problem seems to be a complete work shift issue. If I run some 20 pcs the parts progressivly grow in length. After 20 pcs I may be as much as .250 longer than when I began. The work shift dimensions will still show the same but in acutuality has moved in the Z positive direction. Thanks for your interest.

[Nastyzen]

Sure sounds like the part is moving during cycle.Clamping pressure, feedrate slowdown could help.When you use a common spindle stop,do you mean you load the part in the chuck indexing it against the turret?If that is the method then it must be in the program.Are you bar pulling?
In bar pulling the parts tend to be shorter than longer...
Good luck

[jcastro]

I would agree with your conclusion that the part may be moving during the cycle. If this were the case the parts would progressivly grow as they may be moving into the spindle. Our parts are being stopped however on the spindle side. I have an adjustable stop that runs through the spindle and stops just prior to the end of the chuck. The materiel passes through the chuck and rest againt the stop thus establishing a fixed point. As the parts are being run they will progressivly get longer as I run the job. It is not just the first tool I use to face the length but every tool following.
Right now I am running a job using 32" lengths of 6061 Aluminum without a stop. I am turning a part on one end, turning the material around and cutting an additional part on the other. The parts are then saw cut and the process repeated. I am setting the stick out length using a combination square. At the beginning of the run I had the square distance set at 5 1/4 inches. 20 some odd pieces later I had to adjust the stick out length to 5 1/2 or the part length would not clean up. I'm not the sharpest tool in the shed here but am thinking of contacting "unsolved mysteries" Any advice would help!

[hitachibos]

do you know if you have a MAN/ABS switch if you do try pushing or fliping the switch. if not look in the setting page it might be there.