nozzle geometry and filament bukcling.
January 11, 2013 10:34AM
For some time I have been getting buckling of the feed filament in my extruder. Fiddling around with the various settings, temperature etc., seems to cure it for a while, but it keeps coming back. Although it seems to be fairly free when I push filament therough by hand, during a print there comes a point when the back pressure increases sharply, buckling the filament, but returning to normal if the filament is pulled right out and a clean bit installed.

Two possible new theories (of which I have had many) come to mind: The nozzle hole is 0.25mm diameter and 2.5mm from tip to melt chamber. I read somewhere (on this forum I think) that the length of this hole should be about 10 times the diameter to give clean flow, but I don't see any examples where the hole is particularly deep.

Carefully drilling out the nozzle by hand, (0.25mm carbide drills are staggeringly fragile) I notice that the first approximately 1mm feels like drilling into plastic, but after that it feels crunchy, possibly something is being deposited on the walls of the nozzle hole? If this is the case, why does it go away when the filament is withdrawn?

For the time being I am using a new nozzle with a hole 0.35mm diameter by 1mm deep and filament feeds very freely - but many times before i have thought that I had it licked.

Any thoughts on other possible causes would be greatfully received.

Mike
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