Gina

A bed weight of several KG would be better supported on 3 threaded rods I reckon and guided with metal wheels on two 20mm x 20mm V-Slot extrusion rails.

Plywood Cutting.

Finished clock.  Apart from changing to gear drive from the motor I've cut out the ball bearing on the moving hours gear - it's sufficient to run PLA on a stainless steel bolt with washers either side of gear.  With such a low speed, wear will be insignificant.  (Bolts and washers are not shown in this model.)

Fixed hour and minute gears are attached to base plate with three countersunk bolts.  Then washer, moving hour gear, another washer and all retained by a 6mm SS bolt into the base plate.

Seconds gear drive.

Now for some calculation for a pair of spur gears for the seconds drive.

1. Seconds wheel wants to turn once a minute = 60s.
2. Stepper motor driven by TMC2100 in it's quietest mode takes 3200 microsteps per revolution.
3. With a 6:1 reduction ratio (16t motor pinion and 96t seconds wheel) motor takes 10s per revolution.
4. This means 320 microsteps per second.
5. In the Arduino sketch above the 1600 pulses in a half-second becomes 160 (which agrees with the 1/10th speed of the motor).

Now looking at another clock to go in the kitchen.  Just slightly smaller dial and hands.  May go for spur gear drive to seconds wheel rather than ratchet.  Maybe a slightly smaller gear unit would look better in the smaller space.

I'm no longer sure about using the C-Beam and Gantry Plate system in view of the cost mainly though if I decide to change the Z axis on the Concorde I would have most of the parts to transfer from Concorde to Giant.  The Concorde printer Z drive system does not appear to be performing as well as I had expected though I'm not sure the rail system is the cause, I have some investigations to do.

This screenshot shows the latest XY Carriage with the partscooling fan and air duct moved underneath so that it no longer sticks out beyond the frame.

Latest assembly.  XY Carriage with running rods added and also drive shafts with timing pulleys.

The hotend heatsink cooling on this printer uses a radial fan without any ducting to concentrate the airflow through the fins.  To test that this would be adequate I made a small modification to the same part on my Concorde printer then checked the heatsink temperature when printing PETG at 240°C - it ran quite cool even with only half the heatsink being cooled.

Now to work out what depth the printer needs to accommodate the extra Y dimension.  The full Y range can be produced with a 362mm Y bar and 2x 13mm thickness of mini linear rail.  This gives a total of 362 + 26 = 388mm.  To allow for tolerances I think I'll make this 390mm.

Next to work out how this can be cut from the 900mm x 900mm x 18mm sheet of plywood.  The inside width has already been determined as 410mm.  Since the back, front and base fit inside the sides, this will be the cut width.  Overall height of the box (outside) will be half the height of the ply less cutting, so a little less than 450mm.  Width of the side panels will be 390mm (from above) plus twice the plywood thickness ie. 390 + 2x18 = 390 + 36 = 426mm.  Base will be 410mm x 390mm.  This gives a total width of plywood of 410 + 426 + 5(ish) = 841mm Add another 5mm for the cutting gives 846mm and therefore just 54mm wide strip left.

Adding up the back and base from the height of the board, we get 457.5mm + 5mm + 390mm + 5mm = 857.5mm leaving a strip of about 42.5mm.  I was hoping it would be 100mm to use as the top front piece.  However, I have some 18mm plywood left over from making my Concorde printer that I can use in necessary.

Went on to design the XY Carriage - what on a standard 3D printer would be the X Carriage but in this case runs on two round bars at right-angles.  This carries extruder & motor, hotend with heater block and nozzle plus Z probe and cooling fans for the hotend heatsink and parts-cooler.  Four linear bearings run on the two cross-bars.  As a result of the design model and comparison with the print bed size, the depth has had to be increased a bit to give full bed cover.

Here are some screenshots.

The X and Y drive systems.

Update...

If the belts run with centre line 25mm from the sides of the box, the pulleys and hence want to come to 20mm from the box sides.  So with X=440 and Y=340 the axles will be 400mm and 300mm.

Assembly with box hidden.

Started printed parts production starting with the bracket that attaches to the mini rail slider and takes the cross-bars for X and Y.  The holes on the top are to take bolts and straps to hold the ends of the timing belt.  Design was altered to make 3D printing easier.

Front.

Back

Assembly update.

Cutting pattern for the plywood.

Filament spool in bottom of box.  It will be supported on a centre spindle running on ball bearings and central axle.

Drive belts and bed.

I'm going to try a smaller box and see how that goes.  This is using the length of round rods I have on order which can be attached to the sliders with 3D printed brackets.