May Puzzler
Submitting on behalf of Matthew:)
The May puzzler is yet another mystery. Above is a picture of three calibration prints. The ones on the left and right are normal but the one in the middle has a spiraling appearance.What is causing this? Reply with your answer below and the first correct answer will receive a 5lb spool of PLA. Good Luck!
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Fan turned off?
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These are three separate prints, right?
Also - I can't exactly tell by the photo, but I assume that the apparent spiraling isn't simply from helical, single-wall printing.
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They are three different prints. The tower has 1/4" wall thickness which gives two internal and external perimeters with some infill.
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I just registered in the forums, just in time to still answer the puzzle (still May!) :-)
I think this is due to a leveling problem, either the nozzle or the bed.
As it is not a random pattern, I would say the culprit is the bed being tilted in angle, producing the leveling issue. As the gigabot has a "floating" bed, the nozzle will not clog in the area closer to the bed surface but just push it instead, creating the pattern.
Am I right?
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The bands appear to be to be a 'macro' issue - not necessarily banding of each layer, but I can't tell from the photos.
If it were simple leveling, then I would expect the effect to be worse at bottom then correct as the layers replicated a surface parallel to the nozzle travel. (This change in the visual slope from bottom to top may actually be happening - hard for me to tell from the photo.) In any case, the angle of the banding appears to be around 5-degrees - that much bed tilt would cause immediate failure.
If it's mechanical, then I'd look for hysteresis or slop somewhere, but I don't think that's it.
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Humm ... going that way, I had a similar patter some time ago due to a loose timing band, but it was in a delta printer, so, I am not sure what the results would produce similar failure in a granty printer.
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Here's my wild guess...
The temperature coefficients for the nozzle thermocouple weren't set right, causing a larger than normal sinusoidal variation in the nozzle temperature.
Darrel
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I would guess temperature fluctuation as well. I get banding like this when my heater is bouncing too far above and below the set temperature. Seems to affect where the extrusion lays down on curving paths.
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And the answer is...?
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Thanks for the prod Darrel, I was really stumped when I first saw this and immediately blamed temperature variation. I re-tuned the PID for the hot end and printed it again. At the same time I noticed the extruder was extruding about 15-20% too much material and I reduced the extruder calibration. The next print came out great. In reality I changed two variables at the same time (like a mad scientist) but I would bet the strange pattern has more to do with the PID tuning than the over-extrusion. Temperature variations can cause the printed part to look more glossy or mat with just 5-7C temp difference.
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