Prusa I3 confusion

The top of the Z threaded rods were wobbling around in the holes on my printer. This caused the rods to bow and the top to vibrate. I hadn't thought about it affecting print quality.

Anyway, I just popped one of these into the top of the frame on each side:



Only £0.20 each from eBay (5mm x 10mm x 4mm). Just needed a little electrical tape around the outside and it has a nice interference fit. Rods no longer bow or vibrate. Hard to comment on change in print quality as I've been testing many other variables in parallel.

Edited 1 time(s). Last edit at 01/29/2016 07:33AM by fiftyonenorth.

Amusing to see the very same errors that were known since the first CNC machines repeated with every new generation . When looking for a 3D printer, I discarded any vendor using ACME that is "inch" threaded rods because I knew about these rounding errors (or "inch" timing belts, gears...) that are inevitable. In fact any "inch" parts as it means the designers think "inch" and not metric. This leads to hard to find parts outside of the US, special tools, more expensive parts and even design errors.
Besides, a screw is not a guide. OK, a quality ball screw could be here but it would be overkill.

Edited 2 time(s). Last edit at 01/29/2016 11:17AM by MKSA.

Yes, that is what I have been finding in my research.

I knew very little about 3d-printing when I found this kit on eBay. What little research I did indicated that the Prusa I3 was a good design that I thought I'd be happy with for a first printer (and I am, don't get me wrong!) :-)

What I did not realize at the time, was that there are a ton of variations out there, and as a results in some pitfalls when buying from some random eBay seller.

Had I done a bit more research upfront, I likely would have selected a different kit from a different vendor.

I went through a similar thought process when I started on my printer. What I lacked was the historical context to place the Prusa designs into. The i3 is a popular design where a lot of the choices were made to simplify construction and make 3d printing more widely accessible. Any machine design involves a lot of trade-offs, and not all of those in the i3 favour print quality. And then, as you say, there are a lot of variants executed with varying degrees of success. Home 3D printing is still more a journey than a destination, but that's all part of the fun.

So, learning more as I go...

My Y carriage started to warp, so i purchased an aluminium replacement, which I started to install tonight. Then I realized my original belt is going to be about 2 inches short, because of how it mounts to the new plate.

After a bit of research, I discovered that my belt is a 0.08" MXL belt, on a 20T pulley, which turns out to be an odd combination. Giving 78.82 steps/mm (12.68749999999999 micron resolution)
And my firmware is configured for 78.74 steps/mm (12.7micron), which would be for a 0.2" XL belt using a 8T pulley... not correct, but so close it barely matters I suppose.

So, since I have to get some longer belts, I ordered a GT2 belt, with some 16T pulleys. I figure I can experiment with the 16T and 20T pulleys, but with either I will get some more even numbers for steps/mm. 80.0 (12.5 micron) for the 20T and 100.0 (10 micron) for the 16T.

The numbers being even, whole numbers, rather than fractions, should help improve things.

Just wish I realized this a day or two earlier, and had a chance to get the parts by this weekend.

Edited 1 time(s). Last edit at 02/05/2016 12:31AM by awdorrin.

Hi there I have the same model printer with the same z banding issue. is there any chance you could post the modified bracket you made so I can see if it solves the issues I'm having as well.

Ìanm sent me a pm to which I respond earlier (been swamped at work lately with no time to play) but for anyone else that may be interested, I posted the bracket here: [www.thingiverse.com]

My right threaded rod was just exactly like yours. I could roll in on the counter top and hear and see the bend.
I ordered a new rod from Graingers. I think it was about 36" long. Enough for three new rods. Not perfectly straight but much better.
It came in a heavy duty cardboard tube. I called one place they told me that they fastened theirs to a wood strip for shipment.

I replaced my threaded rods with a pair od t8 leadscrews that I ordered off eBay from China. They arrived sooner than I thought and I was able to install quickly and recompile the firmware.

No wobble in these at all and I do see a difference in the prints, but I still have some tweaking to do. The vertical motion is rather slow during the Z zero sequence.