Now have the Z drive set up and working from the stepper motor.  The 10mm stainless steel axle makes a much better thing to wind up the cord onto.  The larger size and smooth surface makes for a much narrower wound up cord.

Good progress, Gina. I love your "make it up as you go along" methodology. I don't have the confidence to do that myself. I tend to take working designs like the Prusa and D-Bot and make improvements where possible. Best luck with your build

Thank you Dave

Here's a view from the front of the whole printer.

Now printing the bed frame on my Titan printer.

Two screenshots - one from SketchUp showing the frame right way up and the other form Repetier Host showing how the frame is actually printed.

Two photos of the frame placed on the Z carriage - one with the carriage at the top and one at the bottom.

The printed frame was the right size in length and width but a little too high so I've reduced the height by 2mm and added blind holes to tap for fixing screws.  Now printing the new version having changed the nozzle on my Titan printer from 0.4mm to 1.2mm to reduce the printing time.  Printing at 60mm/s it will take an hour and a quarter with 50% infill.

Didn't quite print properly so I've adjusted some of the CuraEngine slicer settings to correct this and now it's printing well   Increased first layer speed and reduced the others also increased the filament feed rate for first layer and reduced layer heights.  I'll post more details in my RepRap Titan printer blog.   Printing time is now 1.5 hours with 20% infill which I think will be enough.

Titan is playing up and I've picked up a bug so no progress.

It wasn't my Titan printer - it was me   It's working fine now.  And I'm feeling a little bit better   A few odds and ends arrived from Ooznest including brackets for the rear XY pulleys so I've now used them to attach the pulleys.  I'll have another go at the print bed frame shortly - Titan is currently printing a bracket for the camera on my widefield single imaging rig.

The print bed frame has finished printing on my Titan printer and seems fine.  I reduced printing speed to ensure success but I shall be experimenting with increasing the printing speed of the second and subsequent layers.   Printing time was 2 hours as predicted.

Since replacing the glass plate on the print bed of my Pilot printer I haven't been able to produce decent prints so I think I shall go all out to get this replacement printer working.  For smaller parts I can use a 0.4mm nozzle on my Titan printer.

Time to assess what still needs doing.  Still needing 3D printing are the two drive drums for the Core-XY system (if I had a better lathe I could turn them from brass or aluminium but my lathe just doesn't work well enough and 3D printing gives more accurate results).  I can't use the ones from the Pilot (which will be cannibalised to finish the Mini) as they are all different diameters.  Then the PSU, electronics box and LCD control/display need mounting plus a holder for the reel of filament.  After that it's just a matter of connecting everything up.

The drive drums could be a problem, as on thinking about it I don't think my present 3D printers would be accurate enough.  The Pilot printer has calibration problems (orthogonality of the X and Y axes) and the Titan printer only goes down to a 0.6mm nozzle as it uses an E3D Volcano hotend and the prints will have ridges.  Actually, any 3D print will have ridges from the layers.  Maybe I could try to improve my lathe.

With this being a new build I think I shall use it as a test-bed for the Duet Wi-Fi control board.  At least a test-bed initially but no doubt the Duet will stay.  I need to design the mounting parts for the control electronics and PSU etc. so it makes sense to try the Duet and make the parts to fit that.  The Arduino Mega and RAMPS etc. are "old hat" now

Might be a good idea to do initial build & test using a cheap RAMPS before hooking up the Duet

Having read up about the Duet it seems it's going to be much easier to mount than the Mega+RAMPS and I won't need the LCD display and control unit as it will be controlled via the web server.

17 hours ago, tekkydave said:

Might be a good idea to do initial build & test using a cheap RAMPS before hooking up the Duet

I have a spare Mega+RAMPS

I think I'll just print the XY drums on my Titan printer so that I can test all operations even though there may be some inaccuracy.

Still to do :-

1. Make XY drums and fit.
2. String up XY cords.
3. Print spool holder.
4. Print electronics box and bracket with cooling provision as appropriate.
5. Wiring.
6. Testing.

I've ordered some shaft couplers that I'm going to try as XY drums.  See if they fit the motor shafts closely enough.

The shaft couplers arrived today and they seem to be an adequately good fit on the motor shafts with less than 0.1mm play so I shall try these as the XY drums.

Now to calculate how many turns of cord it would take to cover the full range.  Worst case is from (0,0) to (200,200) or the other diagonal, making 400mm on the A or B drums.  Circumference is 16xPi ≈ 50mm so no. of turns ≈ 8.  The diameter of the cord is 0.48mm so 8 turns is > 4mm and the gap between the holes for the grub screws is 6mm so that should work out alright

now that's a novel z-axis

have you thought about using high poundage braided fishing line instead of string?

Braided fishing line is exactly what I'm using - this is rated at 80lb   There is 100lb rating I believe but it was out of stock when I bought this.

On 13/09/2017 at 15:35, Gina said:

It wasn't my Titan printer - it was me   It's working fine now.  And I'm feeling a little bit better   A few odds and ends arrived from Ooznest including brackets for the rear XY pulleys so I've now used them to attach the pulleys.  I'll have another go at the print bed frame shortly - Titan is currently printing a bracket for the camera on my widefield single imaging rig.

have you tried herringbone gears? i printed a couple off for lols and they mesh incredibly well.

Yes, and I agree that if printed well they mesh better and run more smoothly.  But they take more designing and they don't tolerate printing defects.  They also need aligning properly.  Plain spur gears are more tolerant of various problems.