widen 3mm barrel for hot end?

I've bought a couple of 3mm brass barrels from mixshop (http://www.mixshop.com/store/index.php?main_page=product_info&cPath=11&products_id=45) for the hot-end of my extruder. The barrel is too too narrow for the filament unless I widen it a bit (say to 3.5 mm) with a drill bit.

I purchased 3mm filament from the same supplier.

In your experience, do the 3mm barrels for the hot end need to be widened a bit to accomodate 3mm filament? (I'm having real difficulty with the extruder hot-end, and don't want to buy a replacement barrel or filament from this supplier until I understand this issue a bit more.)

The barrel should be slightly wider than the filament, but not as big as 3.5mm for 3mm filament as you get too much back flow.

I use 3.3 or 3.2mm for 3mm filament that is +/- 0.1mm. The problem is some suppliers sell "3mm" filament that is only about 2.85mm to fit 3mm barrels and then that is too small.

Edited 1 time(s). Last edit at 01/26/2012 08:32AM by nophead.

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I bought the same brass tube from mixshop and I had to drill and ream the bore out to 3.5 mm to extrude PLA. The PLA swells when heated and presses against the inner walls of the tube and creates too much friction to extrude.

BTW I also had to upgrade the (cold side) of the hotend because the PTFE is not mechanically stable at the normal operating temp of the extruder. It worked for about 8 hours before failing.