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Help printing usable pulleys

Posted by garyhodgson 
Help printing usable pulleys
April 18, 2011 02:28AM
Hi Everyone,

I'm having difficulty producing a usable pulley for my Prusa Mendel with a 0.5mm nozzle, and would like to ask if anyone has any special tips?

I have tried the standard pulley STL that comes with the Prusa, the modified version in Prusa's folder (pulleymod.stl), plus a modified version of the original by Greg Frost. The results are either warped spurs, or the spurs are too large to fit the 5mm timing belt. Also, the shaft for the spindle is usually too small (and so far drilling it out results in off-center shafts as I don't have a drill press).

I know that it's a case of improving the print quality through Skeinforge (v40), but I don't seem to be able to get the right combination of settings. I've tried reducing flow, reducing layer height, and feed rate, amongst many other tests, but so far nothing has resulted in something I could use as a replacement.

I do have a 0.35 nozzle (which I have yet to installed) and I presume that this will produce a usable pulley - but I would really like to know if I can produce one with the 0.5mm nozzle.

If anyone has any hints or a technique it would be appreciated, just so I know whether i'm heading in the right direction. I can also post photos and skeinforge settings later if it helps.



[Toolchain: Skeinforge 11.02.23 (40); Repsnapper 04.09.11; Tonokip; Prusa Mendel]
Re: Help printing usable pulleys
April 18, 2011 08:24AM
Your flow rate is probably too high. Please read the thread on SF 40: [forums.reprap.org] on how to optimize this.

Also, what are your feed rate, layer thickness, width over thickness ratio? You might want to go slow (feed rate and flow rate around 20 mm/s or lower with cooling on slow down if printing only one gear). Layer thickness of 0.3 mm and width over thickness of 1.5 has worked well for me with extruder gears.
Re: Help printing usable pulleys
April 18, 2011 11:40AM
This thread is also a good intro to setting up SF40 feed rae etc.

Re: Help printing usable pulleys
April 18, 2011 02:47PM
The holes will come out too small. You need to ream them with a reamer to get a precise fit. They have a taper at the start so they are self centering as long as the hole is bigger than the taper. I don't use a drill press.

Re: Help printing usable pulleys
April 18, 2011 06:09PM
Thanks for the advice guys.

I had already taken a stab at configuring Skeinforge after finding the discussion brnrd mentioned but I had only measured the amount of filament using 10mm lengths. Tonight I started from scratch using 100mm and found my initial e-steps was too low (539) and should be around 610. I also reduced the flow and feed rates right down (30/30 to 15/15), and even then the feed rate seemed quite quick so I used repsnappers multiplier to further slow things down. I was just starting to get better results when suddenly the filament got stuck in the hotend, and in my attempt to clear it I broke a Z coupling! Typical.

Thanks brnrd and geoffd for the suggestions - they've already helped. And thanks nophead for telling me about the hole sizes. Now I know I should concentrate on getting the spurs correct, and fix the shaft with some finishing.
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