Hey Guys, just wanted to report back on a successful gib adjustment. I was having lots of chatter doing circular interpolation at 12 o'clock and 6 o'clock positions. Everything else seemed perfectly fine. Even at 50% of my commanded feed rates (which weren't anything too crazy, 42 IPM on 12L14 I believe), I was still getting chatter rounding the corner. Through some searching online, it seemed like it could be my y-axis gib.

I adjusted the gibs on all three axes and the problem completely went away. In fact, I cranked the DOC up and the feed rate and the entire cut still sounds great! Surface finish seems to be a little bit better as well, although that could just be my eyes playing tricks on me.

If you decide to adjust your gibs, I would definitely recommend using a small ratchet with a screwdriver bit for the back side of the y-axis and a very long flat blade screwdriver for the front. Once I started using the correct tools, it went very quickly.

The process I used:
  1. Attach an indicator to the table on a mag base and zero on the spindle nose (I used a 0.0005" DTI I use for gun work, seemed to work well for me here)
  2. Zero the DRO for the axis you are working on
  3. Jog the table IN THE OTHER DIRECTION in small increments until your DTI reads 0.001" of movement (I used 0.0001 steps in PathPilot)
  4. Verify the amount of movement on the DRO (this will be different from the actual movement, the difference is your backlash)
  5. IMPORTANT: Create a written table with the following columns (at least this worked well for me): | DTI Reading | DRO Reading | Number of Gib Turns |
  6. Loosen the gib quite a bit (Tormach recommends 8 turns). For the y-axis, this means loosen the front screw and tighten the back screw. IMPORTANT: Do not move the table while doing this, you must loosen one side and tighten the other with everything stationary. The right tools for the job REALLY help here (small ratchet / short screwdriver / long screwdriver / etc...)
  7. Jog to zero the indicator, zero the DRO, jog THE OTHER DIRECTION until the indicator reads 0.001", record the indicator reading, DRO reading and -8 turns on your chart
  8. Tighten the gib 1 full turn
  9. Jog to zero the indicator, zero the DRO, jog THE OTHER DIRECTION until the indicator reads 0.001", record the indicator reading, DRO reading and 1 turn on your chart
  10. Tighten the gib 1 full turn
  11. Jog to zero the indicator, zero the DRO, jog THE OTHER DIRECTION until the indicator reads 0.001", record the indicator reading, DRO reading and 1 turn on your chart
  12. .... repeat until you notice your DRO reading increasing for three consecutive turns on the chart
  13. Back the gib off until you get back to the starting number (or slightly above it)
  14. Jog to zero the indicator, zero the DRO, jog THE OTHER DIRECTION until the indicator reads 0.001", record the indicator reading, DRO reading and 1 turn on your chart
  15. If you're happy with the number being "back to the start" - then you're good to go!


Notes:
  • I was very frustrated until I slowed down and charted everything to visually see the changes, rather than just sweating in a Texas garage in the summer spinning screws in and out! Once you get to see the backlash on a chart, it helps a lot.
  • The whole "other direction" thing is important for measuring backlash. If you have done manual machine work, this will come naturally to you as you will feel "wrong" about jogging both ways during a zeroing operation =)


Hopefully this is helpful to someone else, I wish I had the above list when I started. Also, feel free to correct me anywhere I went wrong, but my machine is running much better now than before and the dreaded y-axis directional change chatter is gone!