Since this thread is about accumulated knowledge and Z wobble caused by threaded rods. Why don’t anyone use belts for the Z-axis?
@Tom_Oyvind_Hogstad with belts, your X-axis (or bed, depending on the printer layout) would crash down as soon as the motors are turned off. With independent motors on each side, this would desynchronize them. With the typical Mendel - inspired layout, it would probably damage the hotend if not properly parked.
Another issue is that threaded rods provide a steep gearing, improving the resolution of the Z-axis. The gearing belts and pulleys offer wouldn’t give enough resolution to get consistent layers.
Aaaand of course, threaded rods are cheaper than belts.
I see. Actually found some printers using belts. Was thinking about it in a H configured printer. If the bed is moving in Z it won’t damage anything when you power of the motors and the bed sinks down.
Yeah, Z-belts are terrible for consistent layers.
https://plus.google.com/105705619434685566948/posts/deRxRkYGEac
@Tom_Oyvind_Hogstad for a H-Bot with just one motor (preferably 400steps/rev) and correctly set-up microstepping, a belt can work. It won’t work for a Mendel config.
400 rev stepper and double pulleys with GT2 /20 belts comes out at something like 0.05mm layers for a full step. The fun thing is trying and there will be quite easy to change to threaded rods or lead screw if it does not work out …
@Tom_Oyvind_Hogstad You mean GT2-2M belt, right?
Getting microstepping to work precisely can be quite challenging, so for such a coarse resolution it would be best to set the layer height to a multiple of 0.05mm (which is half-step resolution). @Jason_Gullickson can tell you a thing or two about that 
https://plus.google.com/103331171897037694195/posts/68XF8apjTQN
Maybe @Billy can show us the belt setup on his printer.
I meant the 2mm no backlash belts with 20 tooth pulley 
And apparently a double pulley will double the resolution. Giving a full step resolution of 0.05mm. I will be quite happy with layers from that and in multiples up.
I think such a setup could give really fast moves with Z lift, actually Z lowering with a H bot … ?
@Tom_Oyvind_Hogstad
And apparently a double pulley will double the resolution.
Sounds interesting, can you explain what a double pulley is?
t is sort of explained here http://www.thingiverse.com/thing:8852. I have not figured out the actual math yet as I found this today (And my physics is a bit rusty). Also check out http://en.wikipedia.org/wiki/Pulley.
Yep, i’ve seen that concept before. While it requires longer belts, it’s a totally viable way of doubling resolution.
Steppers have two positions per full step that are not affected by flaky microstepping - the original position with 71% current on both coils and the half-step position with 100% current on one coil and 0% on the other. So with the gun tackle arrangement, GT 20-2M pulleys and a 400spr motor, we’d get a “guaranteed resolution” of 0.025mm compared to 0.003125mm with an M8 rod and a 200spr motor. Not even the same ballpark, but also not an issue if you use layer heights that are multiples of 0.025mm.
Then it is even better than I thought Ordered a 0.9 deg stepper and are waiting for my account info from Misumi. I will probably have something working in a month or two.
Keep us posted!
I will
One more comment regarding the original topic: Mixshop is using the “Faerie Bottle or Bud Vase” by Whystler ( http://www.thingiverse.com/thing:11121 , http://www.mixshop.com/index.php?main_page=popup_image_additional&pID=145&pic=1&products_image_large_additional=images/large/products/ms-g1_11_LRG.jpg ), which is clearly licensed as “non-commercial”. I don’t think that’s cool.
It’s a Printxel. I didn’t go for double pulley on this printer for Z, but I did on its predecessor. I am using double pulley for torque not resolution. Its predecessor also use a single motor tied to both sides mechanically. On this printer it’s been the plan all along to have a second Z driver, but I’ve still not got around to it. Next design I’ll probably go back to how the predecessor worked.