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  1. @DonMilne A knurled wheel + two rubber wheels may work better than the belts. I've been debating if I want to modify my extruder design to use two rubber wheels instead as the rubber belts causes a number of issues if the belts have too much slack. The idea behind the belts was that the more contact area = more friction against the filament but there are more variables to consider if the belts are not 100% tightened. One thing to note is that the filament will slip even if the filament does not jump back (ie. stepper motor does not skip) so just using two knurled wheels by itself may not solve the problem if there are a large number of consecutive retractions. I'll likely try to modify my design to use http://www.mcmaster.com/#2473k11 and a http://www.mcmaster.com/#4747a61 rather than belts in the near future.
  2. Sorry, I don't think I have the original file of the spacer that I'm currently using. It should be fairly trivial to make one though as it's just a rectangular box ~12mm in height.
  3. I just want to clarify a point mentioned here in case others get the wrong impression about the point of my extruder design. The belt system does not improve the result of the UM2 extrusion test. In fact, it should perform worse due to the increased friction from the gearing system. The entire point of the design was to improve extrusion reliability and accuracy. The extra reliability only comes into play when printing retraction-heavy prints which more often ends up stripping the filament partway through a print. Most people seem to be printing fairly simple designs with few to no retractions (especially when combing is turned on) so they won't be seeing any benefits from my extruder. For those who like to print with combing turned off or complicated prints with a large number of retractions, thats where my extruder design shines. For reference, I've been printing retraction heavy prints at 50 micron layer heights for >200 hours now with no underextrusions and no occurrence of filament stripping. Changing filaments is certainly a hassle, but its not an issue that I'm planning to fix as it would add unnecessary complexity to the extruder design. I'm not advertising this design as a solve-all-problems upgrade. It's really only meant for a small niche set of users who are intent on squeezing every bit of quality out of their prints.
  4. The belts were from McMaster-Carr in the US. Unfortunately they don't stock metric belts so it may be hard to source if you're in the UK. Direct link to the belts is here: http://www.mcmaster.com/#7887k71.
  5. I've actually had the same issues described in this thread when I first started using the UM2, but I've implemented a different fix using two parts. The printer that I have has the issue where one corner (front right in my case) was ~4mm higher than the other three corners and so the printer wobbled when printing. I didn't want to completely take apart the printer to fix the issue, so I came up with an alternative fix instead. The first part consists of length adjustable legs that attached to each corner to stabilize the printer: The second part was the actual fix for the heated bed and involved a printed spacer wrapped in kapton tape to prevent the spacer from melting/warping. By wedging the spacer into the back left corner between the PCB and aluminum plate, I've turned the three point leveling system into a four point one with one corner being set at a fixed height. By tightening the rear screw, the height of the back right corner can be adjusted without affecting the back left corner. This adjustment is also independent from the front corners. It takes a bit of time to get it levelled this way, but once the bed is calibrated it stays pretty consistent from my experience (I print at 0.05 - 0.1mm layer heights). Wish there was a more permanent fix, but it doesn't seem like there is one without taking apart and reassembling the printer.
  6. I wanted to wait till I finalize the design before making the STLs more widely available. I just wrapped up and tested rev. E of my design and verified that it's working as intended. The files are posted on YouMagine.com now if anyone is interested in testing it out: https://www.youmagine.com/designs/belt-driven-ultimaker-2-extruder
  7. Hey guys, long time lurker here. I've been following some of the alternate designs here for a replacement filament feeder as I've had a lot of filament stripping and/or underextrusion issues on prints. I've been working on my own replacement for the filament feeder and I've finally gotten it to the point where it actually works better than the original feeder design. This is more of a proof-of-concept design if anything, so I wouldn't recommend actually trying to assemble the current version. I'm still working on improving the design, but in the meantime I'd like to put what I have out here for critique. Full developement history, design files, other details, and pictures + video can be found at my post here: https://0x7d.com/2014/07/improved-ultimaker-2-material-extruder/.
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