After lots of faffing about I've at last got the mesh grid compensation (auto bed levelling) working.  Now I'm having trouble with the grub screws in the pulleys working loose.  May have to use Loctite

I've found an easier way of adjusting the XY frame for level - take the belts off the pulleys and turn the rods by hand while checking the distance between frame and bed near the corners.  When as near as I can get that way I put the belts back on and run the mesh grid compensation then tune the levelling by taking a belt off and turning the appropriate pulley the required amount etc.

The adjuster wheels proved awkward to clamp so I'm removing them and screwing the nuts onto the blocks.  Removing the drive belts from the pulleys is far easier than fiddling with adjuster wheels anyway.

The TPU rod restraining bearing blocks were too rigid so I've redesigned them and printing a new set.

That's the way I do it to get the z carriage level. I have extra adjusters on the corners of the heated bed for fine adjustment of the bed itself.

Do you lubricate your trapezoidal screw rods @tekkydave?

Yes - lithium grease. You only need the tiniest amount.

All four Z support blocks modified for fixed nuts with tapped holes for M3 screws.  XY frame set up level using a short length of extrusion as a guide and timing belts replaced on Z drive pulleys.  This means the Z carriage (XY frame) is level with the bottom frame members.

I'm now looking at a proper support system for the heated print bed.  This is a 500mm square aluminium plate with 400mm square heater attached to the underside.  Currently I have it supported on two pieces of wood sitting in the front and back main frame members.  I have positioned the bed for maximum available movement in the X and Y directions which results in the final values of 430mm X and 400mm Y.  A bit less than the earlier arrangement with string drives but this should give better accuracy while still retaining a reasonable printing area.  From the inside of the main frame the bed plate is 20mm from the front, 50mm from the back, 110mm from the left and 90mm from the right.

I'm going to try PETG printed brackets from the front and back rails of the main frame.  I'm hoping creep won't be a problem.

The acrylic sheets have not arrived and the quoted latest delivery time has passed.  Maybe the package will be delivered tomorrow.

Quote

Delivery By Hermes Logistik Gruppe

Mounted the bed plate with some very strong PETG brackets.

Here are the Automatic Calibration Results before fine tuning.

After a bit of fine tuning.

A bit more tuning and I think this should be good enough.  RMS error less than 0.25mm.

Decided to have another tweak of the Z drive rods and this is the result.  I think that is as far as I can go - the errors now are mainly the plate not being quite flat.  This is with the bed cold - I shall repeat with the bed hot and see what difference I get.

Z probe calibration next.  Had to screw the Z probe in a bit to make it higher before calibration would work.  Two things need setting roughly right before Z probe calibration will work - level bed (or XY frame in this case) and Z probe height relative to nozzle.  There is some tolerance on these but not a lot.

That's all the calibration finished - next to connect up the rest ready for printing.

Extrusion test done.

Bed connected up and heating.  Trying a print run

Adjusted nozzle height 0.4mm lower and first two layers were fine but but the spiral vase wall went wrong.

Still experimenting with settings but ...

Here's a photo of most of the printer.  Above is a mess of wires and water pipes, a couple of power supplies, the Duet control board and spool of filament on stand.  All this needs tidying up and sorting out.

I'm afraid there won't be any more photos as I appear to have used up my allocation on SGL   I didn't realise there was a limit or I might have been less lavish with my photos and videos.

EDIT - Later... Found a way round it using Dropbox - slightly more to do but at least it works.

I am now looking into how to arrange the PSUs and Duet control board plus a few other odds and ends.