Reprap Extruder & 3D Printer Update

Posted on October 1st, 2013 by George Moore

Reprap Extruder Update.

In last weeks post, Reprap Extruder-Making it Better, I discussed my design of a new, better reprap extruder for my 3D printer, to overcome some issues I had with my old extruder. This week I’ve been putting the extruder through its paces on the printer. This has uncovered some issues with the new design but has also inspired some improvements. I also made a video of the printer at work, see below, as a bit of visual proof that the design works. I even managed to upgrade a couple of the parts since last week.

3D Printer News.

I’ve had a bit of a mass gremlin attack this week on the printer, with a series of minor and major issues. This kept me busy for much of the week, troubleshooting, although I did manage to print a few novelty pieces and a couple of new parts for the extruder.

Here’s some of the problems I ran into:-

  • Horizontal ripples on sides of 3D prints.
  • Vertical ripples around holes and near corners.
  • Random stalling on Y-axis over several days followed by complete failure.
  • Filament Grinding.

It was hard work but I eventually managed to fix these problems:-

  • I tracked the horizontal ripples back to the x and y axes drive pulleys, which were printed on my old printer. These were running eccentrically on the motor shafts, also the motor shafts had no flats ground on them to prevent slippage. The cumulative effect was the regular horizontal ripples. I solved this by printing some new, concentric, pulleys and grinding flats on to all motor shafts on the printer.
  • The vertical ripples around holes and at corners, I diagnosed, following a bout of research on the web and some toying with the jerk speed settings in the firmware, were being caused by flexing of the belts due to a too high jerk speed. This I corrected by reducing the jerk speed for the x and y axes from 15mm/s to 12mm/s.
  • The random stalling of the y axis stumped me for a while until it finally stopped mid-print. First I checked the driver and motor were OK by swapping the axes wiring around. I then continuity tested the extension wiring and found one of the wires was snapped off in both end connectors, but was held in contact by the wire insulation. I carried a quick repair of the connections and now the motor is running better than ever.
  • Stopping the filament grinding turned out to be the quickest fix this week. I had replaced my newly made hobbed bolt with another one I had produced with the mini-lathe hobbing tool I 3D printed last week. It seems the teeth, although cut deep enough to shave off filament at an alarming rate were not deep enough to bite into the filament. Reverting to the previous hobbed bolt instantly fixed the issue. The issue, I reckon, stems from a lack of rigidity in the 3D printed tool causing it to flex away from the cutter in the chuck. This I put down to only using 0.25 infill which also reduces the compression strength of the tool preventing me from clamping it tightly enough in the lathe toolpost.

What’s Next?

In the interests of developing a practical, reliable reprap extruder and helping my fellow makers , I have decided to make the design for my new reprap extruder open-source under a creative commons license. Therefore, in the next few weeks, I will be uploading the .stl files for the Motomach Reprap Extruder to Github. I considered using thingiverse and youmagine, both excellent 3d printing file repositories, but I felt that github would be better for collaboration and file management. I look forward to future developments of this reprap extruder.

I will also be working on a better hobbed bolt tool for my mini-lathe to replace my current one, which is lacking in both strength and repeatability at the moment.