Extruding Inconsistancies

I was wondering if anyone has had the same experience or could suggest a remedy.

While printing perfectly fine, every 5 min or so the PLA will extrude really fast with a more liquid consistancy and then go back to normal after a few lighter lines.

I build the machine from Botmill's kit. I have installed 2 small computer fans on the extruder to try to prevent the heat from rising in the chamber.
Right now the temp is set to 185. I imagine lowering could help but I found that the plastic does not bond well at the lower temps on my machine.

Thanks for any help!

-Will

Edited 1 time(s). Last edit at 05/04/2012 03:02PM by kwdelre.

Are you using bang-bang temperature control or PID? I found that bang-bang can easily have 5 degree swings +/- of the target temperature. That shouldn't be enough to completely explain what you are seeing, but could be a contributing factor. Have you had this PLA for a while, and is it in a temperature and humidity controlled environment? If it has not, then perhaps the PLA has absorbed humidity from the atmosphere and you are seeing the results of flash-steaming that within your melt chamber. Again, not enough to completely explain, but could be a large contributing factor. Have you measured the filament to confirm it is uniform in diameter along its length, and is round? An oval section, perhaps due to the way it was wound onto the spool, could cause uneven feeding of filament into the melt chamber, and again be a contributor to the results you a seeing.

I did read about the moisture issue with PLA. I had this spool in my garage for about a week before I became aware. The temps were very comfortable and not very humid. I live in Houston so even indoors there is humidity. Does the PLA absorb moisture that quickly? If so, it's very surprising that it would be so popular...

I have never had any issues with moisture and I live in B.C. (one of the worlds largest rain forests). I keep my filament in my house out in the open most of the time (some in bags) .

---

FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
Tantillus.org	Mini Printable Lathe	How NOT to install a Pololu driver

That's encouraging