I have started using my Primo for some jobs that were waiting for the new machine (after I melted my Burly leaving it out in the sun one day this summer). I’m pretty sure that my Burly was cutting jobs to size. The Primo seems to be cutting small for some reason. It makes no sense because the Rambo and motors are the same and I think the new drive gears are the same diameter and the belts are the same, however, what was just an odd couple of jobs that I needed extra sanding to get them to size has become an epidemic. I’m milling out a square hole in some wood that should be dead nuts on 3 5/8". It’s not, it’s 3 9/16, which is really strange. Is there some kind of scaling magic incantation I need to type into the Rambo when moving to Primo for some reason?
1.7% is not a lot, but this is driving me a little crazy. Ideas?
You can always adjust the steps per mm. It can be done in configuration.h, but you can also adjust them using g-code. A M92 can be used to set steps per mm, and an M500 can be used to save that setting. The default is 100 for X and Y.
But before you make firmware changes, you might want to look for mechanical or other issues that might be causing the problem. I found my Primo also not cutting to size when I finished it. I traced my problem to bad adjustments on the core giving the Z axis too much play resulting in significant deflection. A starting point could be to put a pen back on your Primo and have it draw some circles and squares and measuring the result.
It sounds like you are experienced so I hesitate to mention it, but there are CAM settings in some programs that leave extra stock. Or a wrongly defined end mill can result in larger or smaller cutouts.
A hole coming out too small may be the tool deflecting while cutting. Are you using a finishing pass?
A loose pulley or a loose joint can cause backlash. Which could also be causing this issue.
I am hesitant to adjust steps/mm because most times, it isn’t proportional error and adjusting that can make it look right in some places and double wrong in others.
The electronics and the (Marlin) software don’t cause this kind of problem.
I pulled the Gcode into Excel and it looks like the code is wrong. I think Robert’s idea that I have some offset in my CAM is right, but I can’t find it. I’m guessing that Fusion360 is trying to “help” me somehow, but I can’t locate where the help is coming from. I’m using the adaptive clearing, with “stock to leave” set to 0 explictly and I’m taking little bites (just 1mm per pass in walnut with a 1/4" single flute carbide end mill.
Max X 209.947mm
Min X 123.825mm
Difference 86.122mm
Render back to inches 3.390638"
Add cutter diameter (0.25) = 3.641"
Drawn dimension = 3 5/8 = 3.625"
Which is about 1/64 too small, which is what I’m having to correct in my drawing. Odd…
I was going to mention checking if there was a tool offset. I had to figure that out, because my tool was cutting centered on the line, which caused the cutout to be oversized by half the cutter diameter.