First part to size, next part not

Mostly Printed CNC - MPCNC Troubleshooting
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Hi all,

2 part question :slight_smile:

  1. I’m investigating a cut issue that I think is multifaceted, but while looking at it, I noticed that the bearing on Tention Bolt A seems to flop around during travels.

Video demo:

I followed directions to tighten the nut until just the nylock is engaged. I also measured and squared as best I could. My cuts are generally accurate in the XY too.

  1. That leads to the next question. My first piece cut was accurate to CAD, second piece was off by 1mm in each X/Y (so inner pocket 86mm was 88mm, outer 100mm was 102mm). There is a bit of a trapezoid to the cut too. Is it possible I dulled the 1 flute endmill with a 1mm DOC on cherry wood so that the next piece turned out dimensionally inaccurate? See two attached photos. Same CAD/CAM for both parts (F360) and same speeds. I did a 2nd lid (big open pocket) at about half the speed and the finish was nicer, but still 1mm too large in each direction from center. Trapezoid still there but greatly reduced at slower speed. I ran this at ~6k rpm as best I can tell (need a tach) since I was getting some burning at higher speed.

Any help appreciated, Thanks! Also, I plan to shrink my machine, I haven’t used the full space, so down to 2’x2’ from 2’x3’ when I get time.

20200413_110412 20200413_110435

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Hard to really say for sure but I would at least put a little tension on that bolt. Typically you can always slow down the CAM to fix most build issues but it is still good to find the build issues. That bearings should not be able to move so I suspect a few might be a little looser than they should be.