Filament getting chewed up by extruder gear

Pic of chewed up filament [oi59.tinypic.com]
Pic of extruder & bowden [oi61.tinypic.com]

My printer has an ~8' bowden on it. Recently I switched to a clear PLA, and it sticks to the bed great, but it seems to get eaten by the extruder's hobbed gear easier than other colors.

The extruder is powerful, if the PLA gets jammed it won't lose it's grip or slip, which is good most of the time, as it allows me to extrude at high rates, but, if the PLA ever gets solidly jammed, the extruder gear will keep turning, will grind through the filament, so no more filament will come out until I come back to the printer to pause it and pull the damaged filament out.

So, where I'm at now, is that I can't leave prints unattended, because the extruder will inevitably eat the PLA and the print won't complete.

Just lower your extruder feedrate a little. You can also play with the acceleration rate for the extruder so it grab better.

Why is the Bowden tube so long? The longer it is the more friction there will be between it and the filament running through it.

If the hot-end is jamming maybe you need to look at the hot-end design or placement in your machine. If it starts to jam after running for a while with PLA, I suspect heat is creeping past the thermal break and causing the filament to swell and jam. Does the hot-end have a fan and heatsink?

Well it seems I fixed it pretty simply.. I adjusted the hobbed-gear/bearing part so that it isn't clamping down on the PLA so hard and things seem to be running ok now.

If you were truly seeing chewing to the point where it took a semicircular bite out of the filament, then relaxing the tension wont solve the problem. It will only result in slippage and will most likely not dig into the filament.

If your filament is getting chewed up, the likely cause is that your print speed is not in line with your hot end temperature. Your hot end can only melt plastic at a certain rate. If you exceed this rate you will not be able to push the filament into the extruder - there simply is no room for it. What will happen is that the hobbed bolt/gear will start to slip on the filament, and - if it is tightened enough - it will dig into the filament. Slow down the print speed (which will result in a lower extrusion speed) or raise the temperature a bit. Don't get too carried away with the temperature either - too high can result in other problems.

I generally print at about 60mm/s and I use 185 degrees for PLA and 225 for ABS. This has worked well for me.

8 foot Bowden?!