What are your Heating - Cooling procedures?

Hi,

A little background first:
I have been fighting a MK7 clone extruder (QU-BD). Everytime I think I have it dialed in, it will start jamming again. I am printing with PLA (white from UM). I print a couple of parts that work great then the extruder will start jamming peridically. The last couple of times I took the extruder apart I found plastic in the stainless steel tube that connects the hotend to the cold end. Currently, I have gcode that backs the filament out right at the end of a print, but I am starting to wonder if I am pulling molten plastic in to SS tube when I do that. I think that the plastic left in the tube can cause the extruder to jam on the next part.

My question:
At the end of a print, do you back the filament out? Or leave it in? Leave the fan on while cooling or just shut everything off?

When I heat up the printer for a new print, before I re-insert the filament, a line of plastic about a inch long slowing extrudes (pulled out by gravity). Is that normal? Do all printers leave that much plastic in the nozzle at the end of the last print?

Edited 1 time(s). Last edit at 12/03/2012 02:14PM by pfinucan.

I generally leave the filament in the hot end and let the fan run.

pfinucan,
hi i don't know whats normal is as i have problems with some print going well and then the next ones are a mess.
but ... mine will run under gravity as the temp gets up to what i want. i then manually extrude a couple of times till is flowing well (filled back up)
and then go for it.
not sure what (if anything) special to do when finsihed a print.
but i don;t take the filament out or anything - just growl at it for making another crap print - turn off the light and grab a beer!
roger.

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Prusa 'Explorer' (3dStuffMaker), GEN6, J-head Mk III-B, Bowden Extruder, Marlin 1.0.0 RC2, Repitier-Host V0.84 and Slic3r 0.9.8, PLA. Live at Victoria, Australia.