Hi, my old green screen Okuma LB15 is behaving strangely. I started her up yesterday to cut a couple of threads on a few hydraulic cylinder rods...something I did last week without issue, & discovered that it is no longer cutting the programmed thread pitch.
The control is a OSP5000L &I have cut many metric & imperial thread on it over the years.
This one was a M30 x 2mm pitch external thread. My threading line looks like this
G97S400M42M3T0303
G0X40Z20M8
G71X25.26Z-50H2.44D.3U.07F2M22M33M74
After cutting the first thread I checked it with the mating nut & it wouldn't go...no worries I thought & adjusted my tool offset & ran it through again. When it still wouldn't fit (but felt a bit loose at the start) I grabbed my thread pitch gauges & to my surprise it was out.
I ran a few more test pieces at various pitch, including a 12TPI thread using F25.4J12 with the same result. A 2mm pitch over 20 threads looks to be about 0.7mm out of wack & the 12TPI over 1 inch was about 12&1/2 TPI.
I pulled the cover off & checked the encoder running off the spindle & while the belt looked good & had good tension, I pulled it off anyway & found a small piece of swarf under one tooth. After a good clean, I put it back on, checked the cable & ran another test part...no change.
The piece of swarf has left a small bump in the belt but I don't think that would cause my problem??
What do you guys think...encoder problem? The machine tracks (chases) the thread spot on each pass (I re-cut a couple to check) & the error appears to be progressively consistent along the length of the thread...its just not cutting the programmed pitch.
Is there a way of checking the encoder or any other checks I can do?
Regards Bruce