Both XY drums now replaced and cords re-threaded.  XY drives now work perfectly    Test print run in process.  BUT filament had lumps and the nozzle caught on it and caused a move in origin

The first layer printed fine and stuck to the aluminium bed but the second was patchy.

I've swapped filament to PLA - see how that works - also changed settings to suit.

If you're used to it PETG will do just as well.

I think you're right - the PLA won't stick to the bed.  I'll try the rigid.ink PETG extremely good filament.  Or watch Sky at Night or both

Hmm...  The PLA won't come out or retract.  Shouldn't have tried it - I've had that problem before!!!!   Have to strip down the hotend tomorrow and drill the PLA out I expect.

I wonder why PLA seems to have this problem but other types of filament don't.

I managed to clear the hotend just by heating.  Disconnected the Bowden tube and extracted some filament so that I could cut it just above the heatsink.  Then heated the hotend to 210°C and was able to push the filament out with a thin Allen key.  Then replaced the filament with PETG and extruded a bit.  Have now set up parameters for PETG for the Giant printer and about to try a print.

The PETG is printing and much better than ABS.  I think it needs higher temperatures though.  I'll see how this test print goes.  I shall want to increase speed as ATM it would be quicker to print with a O.6mm nozzle and Volcano on my Titan printer.  We may need a longer heater block and nozzle but I have still to tweak settings - it's early days yet.  I don't think I'll use ABS in the Giant printer until I have it boxed in and fume extraction.  Little prints on the Mini printer are one thing but this is "a whole different ball game".  The Titan has fume extraction and still will have when rebuilt.  If I want to use ABS in the Giant it will have to be in a different room and/or boxed in with fume extraction.

I have the print bed just perched on pieces of wood across the frame ATM but it will have to be fixed properly because the rough laid filament is catching the nozzle has pushed the bed to one side.  Higher temperatures might help and I'll try that tomorrow.  The bed should be heavy enough to stay put by its own weight at 4Kg but I was intending to fix it anyway.  The XY frame and fixed bed system seems fine otherwise.  So far I haven't needed to increase the motor power from the default 800mA except for the extruder which I increased to 1.5A to get enough power to drive the extrusion.  Of course, I'm only running at very low speed currently.

PETG sticks very well to the aluminium bed.  The first layer is not a problem - at least not at this low speed.  Second layer is still troublesome.

Filament was still stuck to the bed when cold but was quite easily pulled off.  Next test run will be at twice the speed with 40mm/s the fastest and higher extrusion temperature for second layer onwards.  With PETG I have the first layer height at 2mm so the extrusion rate is high but the nozzle heating is coping well but this also means that the ratio of speeds between first layer and the rest wants to be greater.  Other layers are now set at 1.8mm with the 2mm nozzle, previously 1.5mm, though I might be going the wrong way

New test run.  Hotend took just over a minute to get from room temperature to 280°C and the bed 4m to 120°C.  Better but still leaves a lot to be desired.

With a cold bed I have removed the print with a little difficulty.  The first layer is alright but second layer is worse so it seems the second layer height needs reducing.  Bed adhesion of the first layer is more than adequate and the speed can be increased - currently 25% of the 40mm/s of the main peripherals.  Think I'll try 33% and leave the main speed alone.  That speeds up the first layer but the only change for the second layer will be layer height.  ie. changing just one parameter at a time per layer.

Made a new start yesterday and made much better progress.  First layer is now alright but other layers, particularly the wall need more tweaking.  Also made a new, stronger Y carriage for one that had broken and raised the bed to relieve tension on Bowden tube.

I believe it to be the Bowden tube (or end fittings) that are causing the problem and have decided to change to direct feed.  Also when I tried PLA it produced too much drag in the tube and wouldn't extrude.

X carriage redesigned to arrange for putting the extruder on.  Here are some photos of the assembly.  Parts just placed roughly in position and not yet screwed together.

Latest print after plenty of tweaking and trial runs.  150mm diameter and 30mm high.  PLA.

For faster printing this printer needs some "beefing up".  Changing from cord to timing belts and pulleys, larger wheels made of steel, double width X rail and all printed parts more bulky and made of PETG.  I shall also probably change to trapeziodal screw rods for the Z drive for greater accuracy.

Here are screenshots of the X and Y carriage models in SketchUp.  I have yet to add the belt clamps to the X carriage.

Recommend getting single-start screws for resolution. Also stops any back-driving causing bed to sag. Also recommend using 3 screws to give a stable z axis.

Yes, single-start screws are what I want Dave.  Been looking through your D-Bot thread as I thought you mentioned it there but not found it as yet.  Can you please post a link to your source of single-start rods?  I'm planning to use 4 as my XY frame isn't very rigid at the corners.

@tekkydave I've found the part of your D-Bot thread referring to the single-start 8mm rod but no link to where to get them.

This is the one. I bought 3.

Thanks Dave   Hmm... Slow boat from China and not really long enough for my Giant printer.  Would do for my Titan printer though, just.  Nice and cheap

The same seller does longer lengths - even 1000mm.