Ripples in Print

[jesse]

Does anyone know how to remove ripples in a print?

http://i.imgur.com/93L54KX.jpg

I'm pretty sure it's a firmware/lag issue between Gcode commands.

[geneb]

Do you see the same ripple when printing from the SD card?

I've got this same issue, but it's less pronounced and doesn't really bother me. (My machine has enough horsepower to feed three printers at the same time, but my desk shakes like a mofo. *laughs*)

g.

[jesse]

I don't think the problem is with my pc. The RAMBo might be overloaded with the print and updating the LCD.

[626Pilot]

The RAMBo is "falling behind" if you can see the print head stopping dead. Normally it will never stop moving. Is that happening?

There is always some ripple with these printers. It could be the 200 frames/sec resolution limit in Repetier, or resolution limits with the axis motors, or oscillations in filament pressure due to the extruder drive motor very slowly moving in sharp, discrete steps. I think it may be a combination of all three to varying degrees. I don't have a Bowden-fed Cartesian printer so it's hard for me to test.

What I've observed is that the ripples always show up in the same places if the layer configuration doesn't change, but as soon as the layer configuration does change the ripples will be in different places. I've also noticed that the faster I print, the less convolutions there are. There are other drawbacks that show up the faster you print so it's a tradeoff.

It's possible that upgrading to an ARM-based controller (a few of which are around, and more are showing up) or upgrading the extruder drive motor to something with more steps per degree could help. (Our motors are 1.8 degrees per step, but you can get them all the way down to 0.25 per step.) With an ARM-based controller you get way faster clock speeds, so it can translate from Cartesian to delta coordinates ten (or a hundred) times more frequently without disturbing anything else. It can also cache more g-code instructions because it has plenty of memory, so it will not starve. With the RAMBo you get 16MHz and 4KB of RAM and that's it! However, I haven't tried either of these things so I can't tell you whether they would make any difference. They might not! It could be something else entirely.