Gina

Mounted the bed plate with some very strong PETG brackets.

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

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.

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.

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.

The Mk2 will use the standard timing belts and pulleys for the CoreXY drive system and also the common trapezoidal screwed rods for the Z axis. These will be driven by a timing belt and pulleys from a single Z drive stepper motor. I now have all the parts for this.

Do you lubricate your trapezoidal screw rods @tekkydave?

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.

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.

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

All rod stabilisers installed. One is causing binding so I've loosened it off and it seems to be better.

Now printing the last TPU rod stabiliser.

Seems the XY carriage has to be very closely level with the bed for the grid compensation to work. And Z probe height is also critical.

The rods are definitely slightly bent but there seems to be enough flex in them that they should be alright restrained to be straight. Whether the rods will bend straight (oxymoron??) or the TPU flexible bearing blocks will move remains to be seen

X and Y axes aren't right and I've realised that I haven't recalibrated since changing to timing belts. Motor timing pulleys have 20 teeth and the belt is 2mm pitch so the belt will move 40mm per revolution. Microsteps per revolution is 200x16 = 3200 so steps/mm = 3200/40 = 80. That should be precise.

Now printing TPU. Wiring up and testing under way. Corrected steps/mm setting for Z and that's right now. X and Y homing correctly.

I think I'll print the bottom rod stabilisers in TPU to give a bit of flexibility in case the alignment isn't perfect.

Added simple clamping and been testing the Z motor drive. If I set the speed high the very slight deviation from perfectly straight means that the rods suffer from centrifugal force and when the carriage gets near high up the unsupported ends of the rods start splaying out and shaking the whole printer! Maybe with 500mm rods this is not a problem but with metre long rods it seems I shall need to support them at both ends. This is only a problem with fast movement - during printing operations the Z movement will only be small and there will not be time for vibrations to get going.

X, Y and Z now moving correctly One motor needed reversing. Probably not surprising as one motor is upside down I haven't measured it but it seems that the Z calibration needs adjusting though the X and Y seem to be about right. With motor drive, friction is not sufficient to hold the Z adjuster wheels when the carriage is being lowered so clamping is needed as I suspected.

X, Y and Z motors connected plus power to the Duet control board and been testing the Z drive. Needed to increase the motor current but it's working. The timing belts are working fine with the present tension.

Here's a photo of the top of the printer with the Z drive belts, pulleys and rods plus the XY frame etc. The XY frame which is also the Z carriage is shown very near the top here where I adjusted the height at the four corners with the adjuster wheels (yellow) to level the carriage. It won't come up this far during printing due to the space required for the bundle of wires and water cooling tubes. The belts already have some tension and that may be enough but I have planned for tensioning idler pulleys if required. The amount of wrap around the timing pulleys seems entirely adequate.

Just printing the last piece to complete the Z drive. Photos to follow shortly.

Here are some photos of the back Z drive blocks also with XY idler pulleys. Top views and from underneath showing the adjuster wheels.

Gradually designing & printing all the parts needed for the Z drive.

Excellent