I work with a robotics team and we got a new ShapeOKO XL last year. We had a problem during build season that the parts would be off by some small amount. I, of course, blamed the kids for not following the steps that I had shown them. But when I investigated I found that sometimes the Y axis would be off by exactly 1mm.
The test procedure was use the touch probe to find the corner. Then move the tool half width inward and see if the edge of the tool lined up with the edge of the material. I measured the offset a few times and it was always either right on or 1 mm off. I am having them move the tool low enough that the spiral flutes have to hit on on the side.
We are machining aluminum but it fails this test before cutting anything. I don’t think that 1 step is equal to 1 mm and because it is off before cutting anything I don’t think I have lost a step.
So I just always had them test it and adjust the home position by exactly 1mm when it seemed off.
The other mentor did not think we were getting good parts even after this and in general so I need to go back and make sure the machine is square.
I hoped it was something that would get addressed in a software update over the summer but there does not seem to be any newer software.
Any ideas if I am missing something obvious or what tests I should run?
I would think that if it were the flutes I would have a random error of less than 1mm. We also have this issue even if we drop the bit low enough that the twist of the flute ensures that the flute touches.
Does the end mill blank have other advantages? I also worry that the kids will knock it off a step while changing back to the real bit.
If you look at endmill geometry, there can be quite a bit of variation in the radius at any point. That will affect your probe results. The speed at which you probe, the temperature & humidity of the room / probe / endmill can affect your probe results. The labeled diameter vs actual diameter of your endmill can affect probe results. The conductivity of everything can affect probe results.
Are you probing stock of a specific size? Are you re-milling something an indexing off a corner? Are you probing between tool changes?
I know you said you think the kids will move everything on a tool change, but using a sharp point V-bit will get you closer than a mm.
Strange, mine is always off a small amount on x axis. I haven’t measured but it seems like it was around a 16th, which was noticeable to the eye. I don’t know if it is off on Y as well as once I discovered the X error, I only use it for z on any critical piece where I need things to be exact. I thought when things slow down for me this winter I will measure the error and then just build that into my projects going forward.