OmniTurn   CNC Lathes Made in Oregon
 Fast... Precise... Affordable... Home Contact

The World’s Most Cost-Effective Turning Machines

OmniTurn G3 CNC: Size-holding Issues

Size-holding Problems

Your parts are not maintaining size; measurements are different part to part. If the size variation is wandering back and forth within a limited range, the issue is probably mechanical. If it tends to accumulate errors in one direction or the other it's probably electrical (a motor or control problem). Use Ctrl-C & Ctlr-H tests for motor or control problem; skip down to Mechanical Tests for mechanical problem.

Using Ctrl-C & Ctrl-H to diagnose repeatability problems

These two tests (Ctrl-H and Ctrl-C) will determine if the problem is in the control or the axis motor without needing any additional tooling or indicators.
NOTE: before starting this check to see that all connections on the MC-2 and servo cables are clean and have no obvious defects. Check to see all pins on the axis cables are level and not pushed back.

Ctrl-C and Ctrl-H are diagnostic tools to help determine the cause of repeatability problems.

If Ctrl-C does not indicate zero, the problem is internal to the MC2.
If Ctrl-H does not indicate zero, the problem could be the motor encoder or encoder circuitry on the MC2.

  1. Establish Home as normal, by pressing 9, then Cycle Start.
  2. Move slightly away from Home, then establish Home again by pressing 9, then Cycle Start. (Homing twice clears all registers).
  3. Load “smaltest”, which is a test program which makes a one inch circle inside a one inch square centered one half inch from machine home.
  4. Set Cycle Repeat and let it run twenty times. Go to Jog Mode when program is done.
  5. Press H key, then X, then Z to send slide home.
  6. Press Ctrl-C (press and hold Ctrl Key, then press C Key). X and Z readings should be zero.
  7. Jog the slide a little ways from home, then Establish Home by pressing 9, then Cycle Start.
  8. Press Ctrl-H (press and hold Ctrl Key, then press H Key): X and Z readings should be zero.
    • If the axis you’re having trouble with is not zero, the problem could be a bad MC2 card or a bad motor encoder. Write down the axis which is not zero.
    • If the either Ctrl‑C or Ctrl‑H reports non-zero, write down the axis which is not zero.
  9. Press E‑Stop to shut servos off.
  10. Swap motor connections at back of CNC and test again (go back to step 1, above).

Mechanical Tests

To see if it is a mechanical problem, turn servos on and position the slide close to the spindle. Mount an indicator on the tooling plate so it touches the headstock, zero out the indicator and then push and pull the slide with servos on. The indicator should show some movement as you push and pull on the slide. However it should return to zero when you let go. If the slide does not come back to zero then there is something loose, (Slide, Ballscrew nut, Ballscrew support bearing, etc).

To check repeatablilty, write a program to rapid back and forth in the axis you’re testing. Mount an indicator on the tooling plate and zero it at the program end location. Be sure to slow down the feed before the indicator hits. Run cycle repeat for 100 cycles and see if the indicator is zero at the end.

After running the program and studying the way the indicater responds, you should have an idea of what your mechanical problem could be.

If the indicator repeats, you could have a tooling issue: Maybe the part is moving, check your work holding fixture; be sure the tooling is held tightly; if you have an attachment, see if the slide might be loose on the lathe.

If the indicator doesn't repeat, email the factory and describe the type of error that you are seeing, for example: constant creeping in one direction, random movement in both directions, jumping.

Back to Top
Back to Troubleshoot G3
Back to Support Page