Saturday, October 06, 2007

 

Tha intakes are clogged wi' dust, Capt'n

The standard CAPA filament is reasonably pliable and doesn't form dust. PLA, on the other hand does. The reason for a recent extruder jam was that the bearings had filled with PLA dust. I wondered if we might open up the extruder a little behind the screw drive to let dust and debris fall out?

Update: Dust prevented and feed improved by lightly lubricating the filament with SAE 30 oil.

Vik :v)

Comments:
I have some extruder parts on order. I plan to make an extruder which can handle either filament or granules. I think the correct solution to the drive is to use two metal gears (possibly with sharpened teeth to dig into the plastic) which run in opposition to each other.

The problem with the screw drive (as I see it -- but of course I could be wrong) is that the teeth are constantly scrubbing against the plastic. Prototyping talks, bullshit walks, so we'll see if I'm right after my stuff arrives from rrrf.
 
We tried gears. We found that CAPA needed three pairs of metal gears to prevent slippage. See the Wiki and blog for details on the Mk I Extruder.

Vik :v)
 
You mean as described here:
http://staff.bath.ac.uk/ensab/replicator/Downloads/extruder/extruder.html

Well, I may be screwed, but I'll give it a try anyway. I'm hoping that because I'm driving granules rather than a rod that I'll have less slippage.
 
Has the Mk1 Extruder ever been used with an extruded filament, i.e. one with a constant diameter? HDPE?
Seems to me the superior design, compared to Darwin.

I strongly doubt, though, if a design like this will work with granules. Even if you use sharp cogs instead of rolls, the pressure will be too unsteady.

The trouble with the screw drive comes from the friction between filament and wall, i think. You need pressure to avoid slippage, which increases friction, so you need more power on the drive, and again more pressure on the filament ....
Maybe one could place some rolls on the wall behind the filament (static friction > dynamic friction). They┬┤d have to be >< - shaped (how do you call this in english? egg-timer?), though.
 
I agree with you that it might not generate an even flow. Only way to find out for sure is to try it!
 
Right you are!
Im looking forward to find myself proved wrong on this. Would be great for this project if I was.

Greets,
Karl
 
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