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Thursday, November 05, 2009

An end to ooze II


Ages ago, I put code to reverse the extruder at the end of plotting a sequence of line segments into the Java host software, thinking, "That might be useful someday." I set the default so that it reversed the motor for 0ms to turn the feature off, and forgot about it. Seeing Erik and Nop's post below, I thought I'd better finally try it out...

Above is the result - perfect! (Ignore the dark splodge in the middle of the square; that was crud on the extruder falling into the build; I should have cleaned it first.) Normally there'd be loads of string between the L-shaped nozzle-wipe bit and the block being made. Now there's none.

I'm running at an XY feedrate of 3000 mm/minute. At that rate setting ExtruderN_Reverse(ms) to 200 and ExtruderN_ExtrusionDelayForPolygon(ms) to 400 seems to work nicely.

The delay figure is how long the extruder runs before starting an XY move; this allows the polymer to move back down the barrel to take up the slack.

7 comments:

  1. It looks good but why are the two delays not equal to put the filament back where it was?

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  2. The start-up delay deposits a small splodge to stick things down and make sure that everything is running right before moving in XY. The code always places this in the middle of a solid region on a part of the hatch pattern, even when it's doing outlines (in that case it then plots a bit of the hatch up to the outline then plots that). That way it gets a good start, the outline is clean, and the splodges are buried in the finished solid out of the way.

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  3. What are the specs on your stepper, and the diameter on your pinch wheel? My first attempt at a stepper driven pinch wheel won't go much above 1000 mm/min, but I don't think my stepper was up to snuff.

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  4. Good code design then ;-) That's a fairly huge free-fix!

    If ooze is totally eliminated do you think the wipe fence would be needed any more?

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  5. Wade - It's a NEMA 17 with a 5mm knurled shaft. The motor is this one:

    http://www.motioncontrolproducts.co.uk/pdf/FL42STH47-1684A-01.pdf

    which has a holding torque of just over 0.4 Nm. That seems to do 3,000 mm/min quite comfortably.

    Ed - Great that you got the knives back! I think we'll keep the fence for a while at least: it adds only a trivial time to the build, and it clears the extruder's throat before each layer...

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  6. i was going to try adding the code to do that myself once i got my reprap up and running, but i am glad to see that some one beat me to the punch there, i think it makes a big difference in the quality of the output.

    i just wish i could get the parts i need faster :(

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