calibration

[Jonathan]

what do we win Jonathan (tool changer for free) LOL

No idea...but chip won it. The ATC mechanism seems solid, just need to solve issues with the bearing arrangement and it'll be ready to go.
The general idea is to incorporate two tool racks hidden *inside* the gantry, one either side with 8 tools on each and have it so the Z-axis retracts inside the gantry, tool holder slides under spindle and rotates to the right tool ... tool is changed then the Z-axis drops down to carry on as normal. The only issue with this plan is it will add overhang to the Z-axis, reducing rigidity, and loose a bit of travel. I've got 400mm of travel to play with, so that's not a big deal. Using 760mm profile rails. I've had the profile rails for a long time but not been able to decide or afford to mount them properly.

I haven't got a clue Jonathan maybe the belts have stretched a bit ?? but it was out about 6%

Timing belts don't stretch by 6%! Even if they did it's the number of teeth that determine the ratio. What number is in step/mm for the Y-axis under config-motor tuning?

Mine involves a piece of wood but it's even more techni-not than that.!!. . . . 13 nails with heads snipped..

So you've only got the metric collets.