Mill upgrade plans

After a loooong time mostly away from the shop (a job hunt, a new job…then another new job) I had been considering selling the mill and moving onto some other projects. After sitting down and really looking at the whole picture, I realized that the mill will help me complete these projects quicker, but it’s gotta work better than it does now. Holding a thou with this thing is basically impossible, so the question at this point is how much better can I get it. There are a few things that aren’t quite right:

  • Backlash:
    • X: 0.002″
    • Y: 0.002″
    • Z: 0.006″
  • Spindle perpendicularity (to table): currently off by about 0.001″/1″ (about 1 mrad or 0.000017°). This doesn’t sound like much, but with a 2.5″ face mill it’s very noticeable on a single pass.
  • Z-axis perpendicularity (to table): unknown at the moment.

The testing looks like this:

  • Put indicators on X-,Y-,Z-axes and ballscrews simultaneously (one axis at a time)
    • Determine if screw is able to move independently of axis structure.
      • If so, need to pull screw and repack with larger balls, or order new ballscrew and nut.
    • Determine if mounting block is moving relative to saddle.
      • Need to reinstall screws with Loctite.
  • Measure Z-axis perpendicularity
    • Put indicator in spindle and 123 block on table, determine if movement is perpendicular.
      • Shim column or rotate head to achieve best perpendicularity.
  • Measure spindle runout
    • Measure runout of taper
    • Measure stack-up by installing TTS holder with ground rod in it
  • Test higher spindle speeds, up to 10k RPM
    • Measure top bearing temperature and noise, compare to previous values

So the first step is to resolve these, then do some further testing. This will not only give me a more useful machine, but also is helping me think through issues on one of the projects I’m working on.

In addition, I’m working on upgrading to LinuxCNC. I have a computer which is being setup with it now (slowly but surely), using Mesa hardware (7i76 and 6i25). I’ll note here my comparison of control upgrade options:

  1. Upgrade to LinuxCNC ($300)
    1. Buy Mesa 7i76+6i25
  2. With steppers including encoders ($720+):
    1. New steppers (~$50 each)
    2. New encoders (~$65 each)
    3. Design and manufacture or buy mounting bracket ($??)
    4. Convert to LinuxCNC using Mesa 7i76+6i25+7i52 (~$370)
  3. With direct servos ($1780+)
    1. New servos ($240 each)
    2. New servo drivers ($218 each)
    3. New mounting adapters for motors ($??)
    4. Convert to LinuxCNC using Mesa 7i77+6i25 (~$300)
  4. With servos and pulleys (1:3 or 1:4) ($1200+)
    1. New servos ($150 each)
    2. New servo drivers ($138 each)
    3. New mounting adapters for motors ($??)
    4. Pulleys and belts ($??)
    5. Convert to LinuxCNC using Mesa 7i77+6i25 (~$300)

Finally, I’m whipping up an oil mist eliminator because of the crazy amount of oil mist that comes from using the minimum quantity lubricant system. This seems easier than completing the modifications I made to get flood coolant (and will probably be valuable with that system should I go to it, anyway).

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