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!
Fan turned off?
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.
They are three different prints. The tower has 1/4" wall thickness which gives two internal and external perimeters with some infill.
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?
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.
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.
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
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.
And the answer is...?
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.
