The Meticulous Z-Axis

Maslow Community
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I (finally) finished up the work I needed to do on my siding! I am so relieved to have that behind me! :sweat_smile:

I have a short little window now between that and getting back to working on my plow truck before I’m going to need to use it for winter, so I’m trying to bring my Maslow back to life.

This week I did manage to get a new, adjustable top beam mounted up on my frame, so I can now pick up where I left off on post 206 with my spindle clamps. :astonished:

Tonight, I got my linkages mounted:

IMG_20190906_204453
IMG_20190906_2044534032×3024 3.97 MB

And my Z-axis motor mounted:

IMG_20190906_204518
IMG_20190906_2045184032×3024 3.13 MB

The motor bracket I cut on the waterjet at work, and used a press brake to get the 90* bend it in. Made it a breeze to get a good tension on the timing belt. I used 10-24 threaded inserts into the plywood, because I will be adjusting that tension a lot when it comes time to test different ratios.

Speaking of ratios, I am currently running the set of pulleys that give me closest to 1:1 from what I have on hand, just to get it up and running. The motor is running a 40 tooth pulley, and the leadscrew a 30 tooth pulley. This gives me a ratio of 0.75.

Some weirdness happened with my calibration attempts. My current Z-axis pitch is set to -9.48, but I’m not fully convinced that’s 100% dialed in. I’ve gotten it accurate to ± 0.1mm across 8mm. I only have 10mm of stroke on my test indicator, and I didn’t want to max it out on a move. The weird part is that I saw a small amount of variation in the move commands. I ended up bouncing up and down a little bit on my pitch as I went. I’m not sure what the resolution of the motor is with my current gearing, but my indicator was picking up errors as much as 0.06mm in a move command at 8mm. That’s only 0.75% error as in, less than a percentage. That error translates to slightly more distance in a 20 mm deep cut, like a sheet of plywood. If you use a retract height of 0.250", or 6.35mm, that’s almost 0.2mm of error on that entire cut.

So, I have three questions:

  1. Does the Z-Axis motor have a lower resolution than my indicator? I looked for something in the spec, but didn’t see anything listing resolution.

  2. How significant would this error be at a more extreme gear ratio? I’m guessing that it would be a factor of the ratio, but I’m not learned enough to calculate what that would be.

  3. Assuming that I do want higher resolution (maybe later on, if I think it’s a priority), would it be worth getting a better (higher resolution) servo motor?

All that being said, I’m hoping next week to get chains hung and the machine calibrated, so I might soon have a functioning Maslow again! :smile: :smile: :smile:

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