Sunday, July 29, 2012

Prusa Build III

In the previous posts you can see the assembly of my Makerfarm Prusa up to the nearly complete frame.

I then installed the heated bed, electronics and extuder, making it look much more like a Reprap.  These were pretty simply assemblies, so I didn't bother taking progress photos.  The result is the hot-mess of wires and cable ties you see above.

Then the all-important first-turning-on, where you hope that you haven't connected something wrong and end up releasing the magic blue smoke that makes electronics go.  Amazingly, no smoke.  Installing the firmware, I had to invert a few axes in the configuration as well as recompute the mm-per-step, since I had used the SAE threaded rods rather than the M8.  All went pretty smoothly.

Finally it became time to test the extruder.  Heating it to 225, for ABS, I clicked 'extrude' in pronterface.  It worked great for a moment, then jammed, started skipping and chewed almost all the way through the filament.  So I increased the preload on the extruder: same result. So I increased the temperature: same result.  So I increased the current to the extruder stepper: same result.

At this point I was running out of ideas, so I piled the whole thing in the car and took it down to VHS.  There I asked the resident printer expert to take a look.  He spent some time looking at it, flipped my Y-axis mounts to give me more build-volume, disassembled the extruder, added thermal paste, but still couldn't figure out what was wrong.

So I contacted Colin from Makerfarm.  Within about thirty minute he had written back saying that he thought the issue might be related to running the extruder too quickly.  This made sense given the symptoms, good extrusion intially, followed by jamming shortly after.  So I dropped the extrusion rate from 300 mm/min (!) to the suggested 30 mm/min, and it worked perfectly!  I then tested to see how fast it could go, up to about 150 mm/min without problem.

So then it was time to start printing.  I could not get the prints to stick and didn't have Kapton tape.  I used some painters tape, connected the heated bed and tried again and got the following, encouraging result:

It came unstuck during the print, but I was pleased to see something resembling the box that I had tried to print.  So I retensioned the X-axis belt and tried again:

Much better, actually pretty good.  Tweaking some settings in Skeinforge improved this, specifically the flow-rate parameters, which I found produce the best prints when set to about 0.8-0.9.  So I tried a more challenging print, from my gear-generation script:

That actually looks pretty darn good!  As good as the Makerbot Thing-o-matic prints from VHS, if not better!  There are some blobs that I have to deal with, particularly where contours start and end.   So overall, as it stands, the printer has gone from left to right:

Overall, a pretty good improvement.  I will continue to try to improve the print quality, hopefully this will become a useful prototyping tool for future projects!

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