Jamming on 2nd print of the day.

[Video Storm]

I have a very consistent problem.

My rep2 always fails to start extruding at the beginning of a print after the machine has warmed up.  It can be resolved 75% of the time by unloading and reloading the filament then starting again.

Looking at the unloaded filament ends (see attached pic), the filament seems to be getting stuck at the opening of the extruder (right after the pulley) because of a slightly larger diameter at that point.  I think this is happening because the filament is getting too hot and melting a bit at the top of the extruder, so if it sits there between prints it will jamb immediately on the next print.

Anyone else have the same issue?  How did you deal with it??

[DHeadrick]

What do you do at the end of your last print?  Do you just turn off the bot?  If you do that, the cooling fan does not keep cooling the block down and instead the filament cooks in the nozzle.  This may not be your issue, but just curious.

[Video Storm]

Usually I am printing again, so I just start another print.  Apparently the 2-3 minutes in between is enough.

[Gary Schroeder]

Filament jamming-this is mostly a result of filaments not maintaining a round cross section throughout the roll, especially at the end of the roll. My Replicator 2 fails when I use cheaper filament rolls that may not be wound to the filament spool carefully. What happens is the nicely extruded round filament gets deformed into an oval shape as it is spooled under tension and is formed over the spool center as a curved filament, possibly while still warm from the extrusion process. The problem shows up when the feeder tries to pass this through the 2.00mm dia. hole in the entry to the Makerbot heated extrusion head. I have measured these filaments being as high as 2.06mm in the largest dimension as an oval shape with the smallest dimension being 1.65mm at the same point in the filament. A formula for disaster, that has happened on several roles of filament. The fix, for me, was to buy a precision reamer from McMaster Carr (on-line).p/n 8803A14, a small chucking reamer Hss wire gauge for #48 wire with a diameter of .081". I reamed out the extruder tube after removing it from the tip using a slow speed on a battery driven drill and a little cutting oil. I now have a tube that measures 2.08mm ID and allows deformed filaments to pass through to the heater tip without jamming. It did not have any detrimental effects on my parts, as the rate of extrusion did not change because the cross-section area of the filament did not change. Makerbot should do this change immediately to prevent many users from being frustrated with a failed part that did not complete due to filament jam, the most common failure I, and most users, experience.

[Connor Wilkinson]

Also, if it isn't the inconsistent diameter Gary talked about, I saw someone else fix this with a thermal paste between the heat fins and the heating block, since he was getting thermal bleed through that started melting the filament way too soon. I haven't done this with my extruder, but if you don't want to ream it out just yet, you could try the paste. Course, I think either will work fine for the early melting, but only reaming it out will give you compensation for variable filament diameter.

[Ryan Carlyle]

Lord, please don't tell people to do this. The 1.81mm diameter of the upper thermal barrier tube is deliberately designed to be a tight fit so you get good thermal contact between the barrier tube and filament. That in turn reduces heat-creep softening of PLA in the upper thermal barrier, which is the #1 cause of all extruder jams with PLA. The stepped internal thermal barrier tube (1.81-2.00) is empirically much more reliable with PLA than 2.00mm barrier tubes sold by other manufacturers. Reaming out a good thermal barrier tube to let you use crappy filament is a bad idea. Just spend $5/spool more and get good filament. 

Or if you really want a 2mm tube diameter to run crap filament, switch to a PTFE-lined thermal barrier (eg FlashForge) which is demonstrably more reliable with off-size filament. Failing that, you can buy 2mm thermal barrier tubes from QU-BD, Robotdigg, and many other retailers. But they aren't as reliable.

Back to the question at hand -- if you're getting filament softening above the hot block, your cooling bar is probably not getting sufficient heat shedding through the heat sink. You're not getting jams DURING prints because fresh filament feed is keeping cool, solid filament in the upper section of the tube. But this is very unreliable and prints with lots of retractions will likely jam. Stuff to try:

• Check the interface between the cooling bar and heat sink is making good contact -- you can add a little bit of thermal grease if you have it.
• Verify your extruder fan is blowing onto the heat sink (no sticker visible on the fan). 
  
• Print out a filament lubricator from Thingiverse and put a thin film of canola oil on your filament as it feeds. This improves heat transfer from the filament to the thermal barrier and lubricates any minor jams that do form.