I have had trouble getting my machine squared, and thought I had gotten it better but then after being away from the machine for a while and trying to build something the other day I realized I had a major alignment issue when using the full length of the workspace.
I had set up my machine with a fixed plywood board on the lower left corner (green in this image), and cut out the actual square edges with the machine, which I expected should make things perfectly square to the board. Unfortunately an actual square shows the angle is slightly more than 90 so there’s some wiggle.
Next, I thought that at least one axis should be self consistent, right? So I set a board against the left fence but not the bottom fence, and then carved a straight line into it.
The distance between the fence and the start of the line is about 2mm less than the distance between the fence and the end of the line, which really stumps me.
Before all this, I attempted to square the machine by measuring the diagonals, and using some clamps to force the longer edge in until they were just about equal, but it’s hard to do this with more than ~1mm accuracy; is that still likely to be the source of the problem, or is there something else I should be adjusting? My best guess at what to do next is just take a lot more of the machine apart and try making sure its square as I put it back together, which obviously I’d prefer not to do.
When you use this method, once you release the clamps the amount of force applied by the clamps transfers back to the machine frame and causes it to be unsquare.
Loosen all the frame screws and shim where needed to get the frame square, then begin tightening screws in a three step sequence, then measure for squareness again. Repeat this process as many times as needed to get a proper square frame without applying force.
As to the test you show above (green board milled by machine) that might indicate something being mechanically loose.
Try using the machine with a marking pen or sharpie to draw two parallel lines.
Shims should only be necessary if the machine is pulled out of square when tightening hardware — if everything stays square while doing so, you’re good to go — if you encounter a fastener where tightening it begins to pull things out of square, check with support and if need be, add a suitable thickness of aluminum to prevent that.
