Burning on a model?

I'm getting some minor burn marks when I try to print this file : http://www.thingiverse.com/thing:633081

However, when I print other models I don't get burn marks on them...

I even changed the nozzle to a new one.

I just got this a week ago!

It's really annoying, any ideas?

Also the extruder gear teethers back and forth even though theres no filament. And when I load filament sometimes it will teeter and other times it will accept the filament and will load it successfully. But now when I try to print it won't extrude and I already recalibrated.

Also the extruder gear teethers back and forth even though theres no filament. And when I load filament sometimes it will teeter and other times it will accept the filament and will load it successfully. But now when I try to print it won't extrude and I already recalibrated.

Sounds like a defect extruder cable (or maybe it is not fitted correctly).

You can read much about it here: http://forum.zortrax.com/index.php?/topic/1204-extruder-stuttering-when-printing-raft/?p=17152

Install the twin fan and you'll never look back.

On that model in ABS, I'd go 0.19 or 0.15 with the fan at about 40% as it's more of a ornament than a structural part.

Mind you, with all the software/firmware upgrades I've noticed that using auto fan doesn't give some of the problems it used to.

Maybe just twin fans and auto even.

I've got some designs that used to burn a bit too, while others didn't.

Also the extruder gear teethers back and forth even though theres no filament. And when I load filament sometimes it will teeter and other times it will accept the filament and will load it successfully. But now when I try to print it won't extrude and I already recalibrated.

Most likely (I would say 90%) its ribbon cable. 

Ok thanks! :]

Also the extruder gear teethers back and forth even though theres no filament. And when I load filament sometimes it will teeter and other times it will accept the filament and will load it successfully. But now when I try to print it won't extrude and I already recalibrated.

Not sure about your feeder stuttering when there's no filament - might be a cable issue as others have suggested, unless there's something stuck around the gear.

As far as sometimes "accepting" the filament and other times not, that's a matter of cutting the filament end at an angle so that it hits the opening below the gear just right and goes in. Furthermore, if your filament has a curve to it, cut it so that the top of the cut is on the inside of the curve, and hold the filament so that it curves off to the right above the extruder.