Friday, January 7, 2011

Mendel Axis Pulleys

Telling the Truth / Lying to machines

It's likely that most of my thought processes, no matter what I'm doing, are colored by my conception that I'm an artist.  As such I'm most often interested in how to use a reprap.  To me this new tool isn't just something where I can find the best settings in Skeinforge, and click print with each new object. There are varying scales and best ways, little hacks to get best prints. I think at this point I understand enough about the process and settings in Skeinforge that I can start exploring the many ways to print. An artist is not defined by what medium they use, but how the medium is used.

I'm starting small, while within the scope of printing other repraps and reprap parts. Yesterday I was fully focused on an Axis Pulley. I have printed about 10 of these in the last couple months, never happy with the results. They come out, they're usable but it always seemed It was possible to make them better, but I couldn't articulate to the computer how.  Starting with the assumption that the hardware machine is limited, but nothing could be done to get about these limitations, I started looking to firmware and software.

top usable, but ... bottom aesthetically pleasing
From hardware up; the firmware is still a work in progress of hacking from an older standard reprap code. There were a few things I thought I could get working that would make my prints higher quality. Namely; 1. a working heated bed, 2. better extruder control 3. fewer pauses 4. quicker prints.

1. a working heated bed, I know how this works and had a low temperature heated bed working previously, but not cost effective for finishing in a day.

2.The extruder works, but for some reason... likely because I'm using old code intended for a DC motor, the stepper motor will not reverse.

3. fewer pauses... This could be fixable in just code, but the code possibilities are limited by the hardware, so this is out.

4. quicker prints. This is really dependant on hardware and the two previous points working

SOoo... the extruder firmware code; I managed to get some of the functions from a more recent reprap firmware intended for an Arduino Mega with a stepper extruder.  I cannot run all the code intended for a Mega on the much smaller and weaker Arduino 328p, but the algorithms and a couple functions could be adapted and in the end I managed to get the extruder to go in both directions. WOO HOO!

But still my pulleys looked unfortunate. So software. What can i do in Skeinforge? I played with this all yesterday, really 90% of the day went to adjusting things in skeinforge, trying different infill ratios and patterns. No matter what I did the pulleys still came out about the same, with gaps in the gears. So then I tried lying, which comes just before sledgehammer solutions. I told skeinforge the plastic coming out of the nozzle was less than it actually was. the setting originally was .48mm for a .50 nozzle, I dropped this to .45 then .42 and I started lowering the flowrate in speed from 5.6 to 5.4 and 5.3 I finally end up at a layer height of .36 and a flowrate of 5.0 an 11% reduction in flow and 25% lie in layer height. But it worked you can see the difference in the pictures above.

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