Ok, So I've been fiddling around with the x-carve for a couple of weeks. (My schedule doesn't allow much during the week, but on the weekends I get some fiddle time).
I find that calibrating using calipers without cutting and cutting and measuring a cut square give two different results. Is this normal?
With Calipers I screw them to the waste board put the end mill in the jaws, and then command moves and monitor the results. I do this for x and y. It's reasonably accurate this way and I get some errors but they average out.
Then I tried to cut a 50mm square 6mm deep in MDF. To eliminate any other software issues I generated the g-code using Inkscape and gcodetools, then checked in CAMotics that I was in fact getting 50mm square. I used really conservative feed of 400mm/min so as not to put too much strain on the machine.
Using this method I measured the square being cut both inside and outside, calculated the tool width from the difference, then calculated the distance of center to center of the cut to find the square is undersized! (0.2mm in x, and 0.25 in y*)
(the square has different length y sides too (49.76 & 49.69) but I may need to work a bit harder on squaring the machine for that one and I think I know what to do there).
But the real question is should I update the steps per mm based on the cut square or is should the movement without cutting distance and cutting distances be the same and there is something else wrong?