HOW to cut with dimensional accuracy?

Here there are the cad dimensions

And here the final cut dimension!
IMG_Tavola disegno 1_Tavola disegno 1|375x500 EDIT: THE 111,9mm dimension is 119 mm*. I wrote a wrong dim.

The cut was made with a DXF file and managed with ESTLCAM and PRONTERFACE
The bit is a 1/8" single flute

HOW CAN I REACH accurate cuts? I’ve checked the belts and seems to be fine

I’m Not able to make a cut with the FUSION post-processor since the machine moves strangely on the stock… and it starts to make dirty and apparently too fast cuts. (I left the Post Processor stock settings)

Is this a new machine or have you successfully cut things in the past?

DId you draw the crown? Have a pic?

That 120 turning into 112 is really worrying.

What cam settings did you use? Feedrate, depth of cut per pass, total depth?

It doesn’t look like skipped steps or the clamps came up.

I would start by just commanding the machine to move 120mm and make sure it actually moves that far. I can’t think of a reason it would repeatably be off by that far though.

It is actually 119 not 111,9. I put a wrong dimension

Yes I did it and it was good. BTW is a new machine and that it was the first good cut I was able to do

I’m far from expert at diagnosing CNC but believe with all machine problems, its history can be important. It’s interesting that your X and Y dimensions are both 1mm off from the drawing. Is the center slot cut as drawn or short/long? Did you measure the tool to make sure it’s dimension is correct?

I know nothing about Pronterface and have no idea if it’s in play as a source of errors. Hopefully someone will know one way or another?

Ok. Those errors are less than 1mm. That would say to me that it is very possible things are flexing. Totally different set of solutions.

  • Share some photos of the machine. That can help find issues.
  • In CAM. You can enable a finishing pass. It will do the rough cut fast and hard, and then just kiss the surface to remove the last 0.2mm. Combine with switching the direction of cutting (conventional vs. climb).
  • The belts do stretch a tiny amount. You can measure and tune this out. Attach a pen or a V bit. Move as far as you can in one direction and compare the distance it moved, then adjust your steps/mm. If you have to edit it more than about 1%, something else is wrong and you should get that fixed before doing this tuning.
  • You didn’t tell me your DOC and speed settings. This isn’t a $20k machine and it does have limits. If you’re trying to go full blast, it will flex. This is why a hard and fast roughing pass, combined with a full depth finishing pass is so great. Best of both worlds.
  • Are your bits sharp?