Ok, I did one better. I took measurements every 10mm - measuring a total of 10 dots at a time since that should equate to 100mm which is what I calibrated the machine steps to. I put this into a graph, which ended up being VERY interesting.
It looks like a sine curve. What the heck does that mean???
See my graph I posted. Since the variation is non-linear would this approach still work?
Can you provide the data in a cumulative fashion: X-axis target and X-axis as measured which might look something like this:
| Target X | Result |
|---|---|
| 0 | 0.0 |
| 50 | 50.0 |
| 150 | 150.0 |
| 320 | 319.7 |
| 420 | 419.3 |
| 540 | 538.6 |
| 640 | 638.0 |
Iāve seen this before. I know exactly what that is.
Demonic possession. Common problem with a Chinese system.
In all seriousness, thatās likely going to be a complicated problem. Quite possibly a combination of problems. To help diagnose, Iād suggest running the test a few more times in each direction. Is the problem reasonably repeatable and is it the same in both directions? Have you tried it faster or slower?
If you grab the head and push/pull it along the x axis is it tight? Can you put your hands on the moving components while the machine is moving (donāt loose a finger, belts are fān dangerous!) and feel if anything is grinding? Have you confirmed that your bed/test piece/x axis way are reasonably straight? Are you positive that thereās no calibration file (either present or missing) to help with something like this? CMMās need a calibration file. Have you checked your belt tension?
Belt stretch or a loose belt. The distance between the head and stepper would explain the variation. It will likely always be there to some extent. Rack and pinion doesnāt have that problem.
Thanks for everyones help, I have corrected the issue to a range that is acceptable.
End game it was 2 things - the root cause was belt stretch in my opinion caused by the pulleyās being out of alignment with the rail. I fixed that and it still didnāt work, but that second issue was when I was shimming pulleys and such I knocked the machine out of alignment.
Last night I was able to get it back in alignment and while its still not cutting perfect, its pretty close - I think getting it perfect may be impossible with this machine without due to some design flaws.
Thanks again everyone!
So, free beer toasting party at DMS in lieu of $100 hours??
Kidding!
Glad it worked out for you. Belt driven machines are always going to have some slop and are particularly susceptible to hysteresis due to inertia. Iām not sure what the spec is, but if it can hold a half mm total I would think thatās pretty good.
Gladly! Let me know when and where to bring the beer!!!
Across 700mm its about .5mm off still. Iām good with that, although I will say the thunders are much more precise and are also belt driven - they appear to have a much more stable pulley system in place than my machine. Thanks again for your help!
