extruder skipping with PLA

hello, i'm having a problem where the extrduer motor starts skipping steps (edit: the motor does not skips steps, it's the gears that slip past each other).. I'm posting here because i've already tried to crank up the extruder motor pot way too high already without success, and because it only happens when i print with PLA (with ABS it extrudes fine, but i can't get it to stick to the bed :< ). I would think that the problem is with my hot end, but i've already cleaned up the extruder (i've taken out the liner because it was too tight so i guessed that it generated friction and i haven't placed it back because the plastic is not oozing out).
i also get very severe biting of the filament on the hobbed bolt, so much some times that it will start sliding without pushing the filament..
could my thermistor temp table be wrong? why then would it print ok for ABS? besides, when it does extrude at 170° the filament looks pretty much ok, but if i turn the temperature at 190° then it looks really fluid when it comes out of the hot end..
Admittedly, my IR thermometer shows 150 as a max reading on the hotend when i turn it up to 190°, but the reading at surface is supposed to be colder.

Edited 1 time(s). Last edit at 07/16/2014 01:15PM by ansiomatic.

Picture of your hotend would help. It's likely that it isn't disapating the heat well. When PLA heats, it expands and will clog the hotend if it top is not kept cool. That's where active cooling on all metal hotends comes into play. Plenty can insulate well enough passively, with insulation and a good heat break.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

Right now i'm printing after taking the hot end apart and purging it.. at 175 doesn't skip, but the print warps a bit, so i'm reducing it now to 170. maybe the warping could be corrected with a fan pointing towards the print (which i took out because it made my ABS prints unstick from bed)..
Anyhow, here's my extruder.. Do you know where i can get better designs? i can't see any fan mounting holes in this one and every other design i found on thingiverse needs to print the whole extruder again.. i was thinking something like the groovemount with some screwholes for fans would suffice.
Thanks for the help

oh snap. after 20 mins or so of printing, it started skipping again
where should i put the fans? at the hobbed bolt, the body of the hotend or the tip of the nozzle?

i have no idea how i managed to post as Plastikschmelzer.. that was me talking

Groove mount like that, if you've got the money, just go get an E3D v6, all hotend problems solved if built and tuned properly.

If that's not an option you want to take; I don't have experience adding a fan to an extruder with insulation. In my mind it wouldn't dissipate the heat well enough, fan or not. You'll have to consult the more experience for that one.
On temps, my Solidoodle original hotend printed best at 162C. Each hotend is different. Some are such that they will never work with PLA. Some are such that they will never jam [as per E3D v6 reviews, I haven't heard about a single case of a jam on one, but it hasn't been around too long].

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

try to print with higher temp or slow down yours print and cool yours printed parts with fan

Edited 1 time(s). Last edit at 07/16/2014 08:46PM by premek.

Now i'm printing ok, although i have to recalibrate the extruder potentiometer as it heats up quite a bit (reminiscent from the times i thought that a pot turning was needed).
I'm printing with 0.2mm layer height, 2mm retraction, 170°C head and 100° bed (yea, i know it's a bit high for the bed, but i'm so frustrated from ABS bed unsticking i don't want to take any risks..) i tried printing an OK hand, and it did fine until it came to a point in the filament yarn where the filament was tied up so it stopped before printing the fingers.. the rest came up fine.
Now i'm printing a flexbot frame, which consists of many thin lines, to force the bed adherence.. The only thing that worries me now is that extruder motor heat.. Hopefully it won't do anything bad.
At what temp should i worry?
Thanks for the help. And i'll keep in mind that extruder when i have money to buy pimp up my printer, for now i'll do what i can with what i've got.

I would definitely get a heatsink and fan on that motor, by every means.
Also, 100C is insane for PLA, and will degrade your quality. I print at 45C, many print without heat. You'll find heat will help, but is by absolutely no means needed in similar fashion as ABS. You want PLA to harden as quickly as possible after it leaves the nozzle to reduce upward curling.

Edited 1 time(s). Last edit at 07/17/2014 10:22PM by MrDoctorDIV.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus

i think my thermistor is poorly calibrated (actually, i've never calibrated it. just went with stock thermistor tables on marlin) and i have a pcb-aluminum sheet-glass sandwich which further reduces the temperature.. IR thermometer on glass reads 70°, which i guess it's ok (but i have no idea how glass on aluminum affects IR readings, so yea.. it sticks and it doesn't appear to deform the prints)
First layer seems ok to me, and as i've said, i've been so frustated with bed unsticking when using ABS that i want to be absolutely certain it won't unstick for now since PLA is supposed to solve my problems. Maybe i can reduce bed temp by 5° every print i do until one unsticks..
Edit: sorry for my english

Edited 1 time(s). Last edit at 07/17/2014 08:38PM by ansiomatic.

yippies. Beautiful prints. a tiiiiny bit of oozing apparently which i think it's because a bridge got loose. Thanks for the help

Looks clean, nicely done.

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Realizer- One who realizes dreams by making them a reality either by possibility or by completion. Also creating or renewing hopes of dreams.
"keep in mind, even the best printer can not print with the best filament if the user is the problem." -Ohmarinus