Found some orange PETG so I'm printing the carriages in that.

The modified Y carriages with moved pulleys mean other changes such as the X carriage timing belt attachment points and the rear mounted pulleys.  The latter just needs longer screws and some spacers but the X carriage now needs another re-design and print.

I think I know why many 3D printer makers use an established design rather that the "make it up as you go along" approach that I use!!    Mind you, I haven't seen a design for a printer this size.

I think I have the X carriage and back plate designs done and now printing the back plate.  I've come to the conclusion that this is not just a Giant printer but also a Giant Project!!

X carriage main part and its back plate printed and assembled.  Looks alright so far.

CoreXY timing belts and pulleys all threaded up and a small amount of tension applied to both belts.  Having threaded one belt, I cut the extra off and found it was just sufficient for the second belt so I didn't actually need the two lengths of 5m as I estimated and bought.  Still, better to overestimate the amount needed than to find I didn't have enough.  I feel that's a bit of a milestone

X carriage almost fully assembled.

More photos.

I think the next job is to sort out the Z drive.  The trapezoidal screwed rods will go in the corners just inside the XY frame (Z carriage).  I plan to mount the associated nuts in 3D printed brackets fastened in the corners of the XY frame.  At the top will be ball bearings mounted in 3D printed brackets attached to the main frame, to take the screws with a short spacer and timing pulleys (60t 8mm bore).  As shown in a diagram above, the four pulleys will be driven by a pair of timing belts on a pair of 60t pulleys on the Z drive stepper motor, mounted in the middle of the top.  Idler pulleys will provide for tensioning the belts and also improve the amount the belts wrap around the motor pulleys.

I think the easiest way to adjust the Z carriage for level (to get it well within the limits of the automatic bed level compensation) will be to have thumb wheels on the trapezoidal nuts, maybe with clamps to hold them in position once levelled (vibration could cause movement otherwise).

Will the XY frame be constrained in the X-Y plane purely by the wheels in the 4 corners? If so you may get binding issues with the screws unless the XY frame is free to float on them.

I had issues with my D-Bot when I had wheels in all 4 corners and 3 screws. I eventually removed the wheels at the front as the rear wheels were providing sufficient constraint in the X-Y plane. The screws were then purely moving the bed up/down and keeping it in the same plane.

Maybe I have misunderstood your design.

Checked the maximum printing area with the new carriages and it's 450mm x 415mm (X x Y).  Can't yet say what the height will be but 600mm looks likely, possibly more.

18 minutes ago, tekkydave said:

Will the XY frame be constrained in the X-Y plane purely by the wheels in the 4 corners? If so you may get binding issues with the screws unless the XY frame is free to float on them.

I had issues with my D-Bot when I had wheels in all 4 corners and 3 screws. I eventually removed the wheels at the front as the rear wheels were providing sufficient constraint in the X-Y plane. The screws were then purely moving the bed up/down and keeping it in the same plane.

Maybe I have misunderstood your design.

I think you have understood my design alright.  I think you are right that two V-Slot wheels would be sufficient to constrain the Z carriage in the XY plane.

Are the wheels just on one side of the v-slot. Mine are on both (3-wheeled) so stop it moving in either X or Y. 

I wouldn't rely on the screws to constrain the movement, just move it up & down.

Here are a couple of diagrams - first the arrangement I have ATM and the second with just two wheels.

Here is another idea for the Z drive belts and pulleys which uses just two idler/adjustment pulleys but still provides good wrap around the pulleys.  The motor has two pulleys and the belts are at different levels.  I've added a second diagram showing just one belt round the motor pulley.

9 minutes ago, Gina said:

Here are a couple of diagrams - first the arrangement I have ATM and the second with just two wheels.

Will the 2 wheels be able to keep the XY frame constrained in the Y-plane. I wouldn't rely on the leadscrews to constrain the bed.

The problem with just two wheels may be that the frame could go off-square.  The second pair of wheels were to prevent this.  Hence the design with four wheels and four rods allows for any lack of rigidity in the corners of the XY frame.

Just checked the delivery tracking and the estimate is for tomorrow (24th April) and the shorter ones for my Titan printer upgrade have been included in the same package   That's rather better than the original delivery quoted for the 500mm rods to fit the Titan printer

Quote

Estimated delivery Thu, 03 May - Tue, 22 May

Been looking into the Z drive system and laid out the pulleys and one of the belts on the acrylic sheet on the top of the printer.  With the rods where I'm thinking of near the inner corners of the XY frame, the belts may not quite be long enough with the motor over near a side.  As the motor is moved towards the centre of the top, the belt length required reduces which leads to a slight change as shown in my latest digram below.  I can't really make parts until I know the exact dimensions of the nuts.

I've attached a 2ft (610mm) square acrylic sheet to the top of the frame.  It's a bit short as the width is 740mm but I can fill that in with something.  I couldn't find a source of 740mm or 750mm x 610mm as this is basically a mix of Imperial and metric.  (610mm is really 2 feet and a size of shed window).  At first I was going to place it centrally but the supports would interfere with the Z drive.

I have a test setup installed on the acrylic sheet for a timing belt and pulleys and checked for the best place for the Z drive stepper motor.  Here's a quick photo - not very good I'm afraid.  Distortion is due to wide angle on zoom lens.

Here's a better photo.  This is from the RHS - the front of the printer is on the left of the photo and the back on the right.  ie. the motor will be near the back.  I have taken the XY frame with carriages, motors etc. out of the frame.

Here is a starting design for the LH back trapezoidal nut holding block.  The big hole is to take the shank of the nut and a guess ATM.  I think the RH back block will be the same but inverted.  The thickness of the top and bottom parts of the block provides spacing for the XY timing belt idler pullers.  These are the holes that are offset top to bottom, the other holes are for fastening the block to the frame.  The gap is to take the rails of the frame and should be a nice snug fit.

Yippee!  Trapezoidal screws and nuts are out for delivery.  Just hours to wait now