X-axis min limit switch issue

If I have a G55 setup to a fixed workholding device (i.e. table vise) and I have to tighten the X-axis belt I will be moving X-MIN for homing, altering what the G55 offsets should be. Am I missing something?

So the tensioner moves when you tighten the belt? I can’t really see the pieces, in the build photos, but does the limit switch hit the part that moves?

Yes, the tensioner is pulled taught by the screw that feeds into the captive nut. This does mean that the physical home position of the machine moves when you adjust belt tension.

Best thing I can figure, is keep track of the number of turns of the screw, and multiply by the 0.8mm thread pitch of the screw.

Not terribly dissimilar t the problem that 3D printers used to have with Z min. Every time you tweaked the bed levelling screws, you needed to re-zero your print bed – At least until sensors like the BLTouch came into more common usage – largely because of this problem.

This can be fixed, or at least bypassed. A small piece of aluminum (Strips from a can would do the trick) can be CA glued to the XZ plate and bent to make a consistent X zero point which would be entirely independent of the belt tensioner. I would do something like this if I had set a zero point to a fixed jig… But more likely, I’d make a set of stops that the machine can be moved to more as a block stop, or set up a touch pad on the table with known offsets to the jig.