Thanks for the comments wersy, Quotewersy Are you quite sure that you first had all aligned with equal care as now incl. levelling of HBP? I am sure you didn't use bearings on top for the lead screws. Yes, and yes, the tops of the screws were free. But those screws were visibly bent on arrival from PBC Linear. It was always a matter of trying to fix something that wasn't great to begin with. Tby justine.haupt - Developers
FYI, dc42 made said update. Happy multi-zone bed user here.by justine.haupt - Developers
Hi the_digital_dentist, -Why 4 screws and not 3: In part, a messy design heritage. I knew I'd need at least 2 screws, and I couldn't find closed-loop GT2 belts big enough to get around three at a time. Three was also geometrically awkward for my frame. Understand that the machine's footprint on the floor is 1m x 1m. I settled on four screws driven by two motors, and after parts were machined thby justine.haupt - Developers
Quotenewbob There's one other situation I can think of that could cause this: in four screw arrangement, periodically, one screw could take over from the other (due to backlash between nut and screw bed would not lock out) making vertical movement uneven. You know, in practice I don't see that happening. All four screws are always moving in unison, and with precise leadscrews with the nuts all aby justine.haupt - Developers
Hi newbob, No. The problem described above was never about Z-wobble. I think the initial post wasn't clear enough in this regard, so sorry for that. The banding was from layers expanding and contracting in a periodic way from the Z axis making movements less than and more than the layer height. It's an issue of compression of the filament as it's extruded onto the previous layer, and the distanby justine.haupt - Developers
Thank you Michael, Quotewersy It would be interesting to know what the reason really was. You think it was caused because the pulleys are eccentric. Maybe it is possible to proof this with a disc like a clock face and a pointer mounted on the lead screw. In similar way we tested the clocking of stepper motors. In retrospect it had nothing to do with the pulleys. I changed to machined aluminum pby justine.haupt - Developers
Quotedc42The 1.20RC1 firmware for the Duet WiFi/Ethernet that I released yesterday supports multiple independently-regulated bed heaters. Wow great news! Thanks for the update!by justine.haupt - Developers
Update, FYI: The problem was eventually fixed by going with 4 "powered leadscrews" from Thomson Linear (stepper with leadscrews instead of conventional shafts). I went with narrower screws with 10mm diameter and 2mm thread pitch, and mounted with the motors on the top-side and the bottom of the screws free-hanging. Positioning accuracy as measured with a digital dial indicator is now +/- 3um. Aby justine.haupt - Developers
If you really don't want to go custom you might also consider a mosaic of 4 square silicone heaters. Perhaps you could find 9x9", I don't know. This is the route I went for a 610mm square bed using four 12"x12" pads. I'd originally planned on an off-board closed-loop controller for each zone, but the pads are consistent enough that I've been running all four off one thermistor using the stock heby justine.haupt - Developers
Hello all, Last year I discovered that any carbon-filled material allows one to print parts with machine screw threads that are usable. It occurred to me that this might not be common knowledge. Actually, I can't believe how well it works. I've successfully incorporated the technique on most of my recent projects with thread sizes as small as M2.5 when oriented vertically on the build plate andby justine.haupt - General
Hi o lampe, There's NO Z wobble. The banding is a periodic dilation (expansion and contraction on all sides of the print), not an offset. The problem is that there's a residual motion in the Z movements so that sometimes layers are more compressed and sometimes less, leading to variation in the effective extrusion width, causing the bands.by justine.haupt - Developers
Thanks Jerry. I already have the new version worked out, but this is a picture of what I have now: The belts are loose there as I took the picture during assembly, but you get the idea. It's a printed polycarbonate double 60T GT2 pulley that the leadscrew threaded right into. I'm pretty sure the pulleys are eccentric, as I can see the belt breathing in and out a little as it rotates. The linby justine.haupt - Developers
Hello, I've been commissioning a homebrew large format printer for a couple months now, pulling my hair out with redesigns to fix various mechanical issues as I go. The machine in question is large (24" square build surface) and I went with a 4 linear shaft + 4 leadscrew arrangement belted to 2 motors. Learning an alignment/setup process has been painful and hindsight is 20/20, but long story sby justine.haupt - Developers