Dimensional Accuracy on Y Axis

Mostly Printed CNC - MPCNC Troubleshooting
1

Okay so first off:

  1. Did you buy everything from here? Yes, about a year ago. I have not changed anything from stock.
  2. Are you using end stops? Nope
  3. Mac or PC? PC

I built my machine over a year ago and am only now getting around to actually learning how to use it. So far things have gone pretty well except I am noticing that I’m not getting the travel I would expect in the Y axis. I’m not noticing any shaking or binding in any axis, and my tensioner bolts are pretty loose. I’ve attached Gcode from two runs. Heartinkscape.gcode is an approximately 50x50 heart shape carved 2mm deep with a v-groove bit. As you can see in the attached image, there seems to be some shifting or something going on in the Y axis on the left bottom and top right side of the heart. The text, which was carved before the heart outline, seems almost perfect, except the right side of the “M” is a little high. The second job, square.gcode, is supposed to be a 100mm x 100mm square, and was cut as a part using a 1/8" diameter double fluted end mill. I don’t have my tool settings in front of me, but I know I used the conservative settings outlined in the set up guide. As you can see in that image, the X axis came very close at 99.4mm, but the Y axis only reached 95.5mm. It looks a little distorted in the picture, but I did verify it has perfect right angles at the corners, and the frame of the machine itself seems to be pretty square, so I’m not sure what is going on here. Any ideas what to check next? As I said, the hardware was bought from Ryan over a year ago - do I need to update firmware or anything? Thanks! - Jeff

MPCNC-Gcode.zip (17.8 KB)

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2

I would say try a very slow cut to make sure the bit can keep up. Cutting too fast can cause small size variations. The same with the heart, looks like you tried to move too fast or your machine is too loose.

Looking through the code the square is a bit deep per pass at that speed, the heart I am assuming is similar.

It is much easier to start slow and shallow and then test how far you can push it and watch the dimensions vary. You are really close but start a bit less aggressive. Cut the speeds in 1/3 and check your dimensions, and then you will get a good feel for your machines capabilities.

There are a few ways to make faster cuts but get a good slow one first.

3

I took your advice and dropped the speed down to 3mm/s. That made a huge difference. I’m going to keep fine tuning it but it looks like I’m on the right track now. Thanks for the quick reply!

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4

Awesome, of course that is way too slow but know you can get to your machines max speed/depth for the quality needed. The are a ton of variables rpm, tool quality , style, material, depth, etc.