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filament feed problems need help!

Posted by aduy 
filament feed problems need help!
October 29, 2012 02:20AM
hey guys so ive recently built myself a prusa mendel, and now i have everything working great except for the extruder. Im getting pretty frustrated since im not sure why its stripping and i have to baby each print to make sure it doesnt jam. its a direct drive 1.75mm from qu-bd.com, basically a mk7 copy, and the filament keeps jamming and stripping. i have some ideas as to why its happening. the hot end is cooled with a heatsink and fan, the motor is also attached to the hot end upper block, the motor gets pretty warm, and so does the filament drive gear. i think the drive gear is stripping the filament because its getting hot. another issue is it uses a metal plunger instead of a ball bearing or some slipper plastic. also it jams if i leave it sitting too long. any help would be greatly appreciated, thanks.

heres a link for the extruder. [store.qu-bd.com]
Re: filament feed problems need help!
October 29, 2012 02:27PM
Are you running the fan continuously? you should be for PLA even during warm up.
I would hazard a guess and say that the fan is not providing air motion over the relatively short thermal break and that's causing the PLA to mushroom and jam.
Does it still do it if you point a housefan or similar at the printhead during warm up and printing?
The reason I think it's the thermal break is that you state it jams if you leave it sitting too long. It's a relatively common problem with PLA and a whole host of hotends.
Re: filament feed problems need help!
October 29, 2012 03:22PM
i have always have the fan running at max, should i have another fan pointed at the stainless steel barrel too?
Re: filament feed problems need help!
October 29, 2012 06:55PM
The problems with the qu-bd extruder are pretty well documented over on the [www.fabric8r.com] forum

seem to be a few things causing what you are seeing

Definately the heatbreak, before I went to a more traditional extruder I had some better results with an additional fan blowing through the heatbreak, as well as the one on the heatsink, reduced temprature in this area from 30 to 25 degrees, but neither of these should have been an issue.

The grub screw on the extruder gear needs to be really well seated and loctited,

The grub screw that applies the pressure against the extruder gear has 2 issues.
A. the end of this grub screw needs to be a smooth curved shape, use some sandpaper or an emery board to make it a nicely smooth curved shape.
B. It tends to back itself out of the hole, a second bolt and nut on top to stop it backing out is also useful.

I have been keeping up with goings on over on the fabric8r foums, but beyond the first 4 days where I got nothing but issues with the extruder havent gone back to it. May even look at some of the accessible direct drive mk7 / 8 extruder designs that are around and think about replacing as this seems to be the biggest trouble area.

Re: filament feed problems need help!
October 29, 2012 09:37PM
thanks for the suggestion, i have some mini blowers and ill try pointing them at the thermal break, also i replaced the crap grub screw, by re tapping the hole with an m3 size, then i made my own set screw with an m3 bolt. ive also had some issues with my psu, i just bough a power resistor so i can load the 5v line in order to regulate the voltage.
Re: filament feed problems need help!
December 17, 2012 03:20PM
I had the following two problems:

1.) At the point where the filament screw is tight enough for the qu-bd gear to actually grab the filament (PLA), my 2.8kg/cm stepper could not keep up.
2.) The filament (PLA) constantly got stuck inside the peek.

I know qu-bd says that their filament gear is better than the MK7 drive gear. My feeding is much better and more consistent with the MK7 drive gear.

I drilled my peek to 2.5mm and inserted a PTFE tube which stopped the filament from getting stuck.

Before the qu-bd extruder I've had a ultimaker hotend with wades extruder (worked very well) and a lulzbot hotend with wades extruder (very flimsy hotend). Although the qu-bd extruder is a bit more difficult to calibrate it is much more robust and thus far getting realy good results.

Edited 1 time(s). Last edit at 12/17/2012 03:27PM by bluscape.
Re: filament feed problems need help!
December 17, 2012 03:33PM
I had the same problems; my solution was to sharpen the gear with a Dremel and build a "minimalistic mk8" style contraption out of wood instead of using the standard feeder block; it holds a 608 bearing against the filament. It's not particularly pretty, but it works.

I'd also check you hotend: mine became hard to push filament through. I cleaned it out as best I could (heat it up, use a needle) and applied oil to the inside- works great now!
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