"Best" bowden extruder?

Hi

I am having a lot of trouble with my extruder. I am using the slightly more unknown brand 3d stuff maker/iprint creator. In short, the extruder is weak, which greatly limits my printing speed, and forces me to use high temperatures to get the PLA flowing as easily as possible. Usually I have to print at 215 degrees C which allows me to print at about max. 50 mm/s before the risk of stripping the filament gets too high.

I would like to print at, say, 190 degrees at 50 mm/s, or maybe 100 mm/s or higher at higher temperatures. I don't think this is unreasonable.

So I want a new extruder. Since the current configuration is bowden, and I don't believe there are any extruders made specifically for my printer, I believe that is the way to go since it requires minimal changes of the printer. The current extruder uses a NEMA17 motor which I'd prefer to reuse. However, there are still many to choose from.

What is generally regarded as the "best" bowden extruder for 3 mm filament, if there is one? By best, I of course mean strongest, and maybe things like ease of use might be factor as well, I don't know. Thanks.

If your extruder is weak, why do you want to reuse the motor? Also, perhaps the problem is not that your extruders is weak, but that your hotend requires too much extrusion force.

Edited 1 time(s). Last edit at 01/08/2013 12:11PM by Greg Frost.

If you're stripping filament with the extruder, it's more likely an issue with the hotend requiring too much force to extrude.

Edited 1 time(s). Last edit at 01/08/2013 12:23PM by Polygonhell.

Greg Frost Wrote:
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> If your extruder is weak, why do you want to reuse
> the motor? Also, perhaps the problem is not that
> your extruders is weak, but that your hotend
> requires too much extrusion force.

Well, I never said the motor was weak. The extruder as a whole is weak, meaning filament will start stripping, in my opinion too soon. The motor has plenty power.

Polygonhell Wrote:
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> If you're stripping filament with the extruder,
> it's more likely an issue with the hotend
> requiring too much force to extrude.


And what would one do about this? I mean, how complicated can a hot end be? It's really just a metal chamber with walls a certain temperature and a hole at the end. I don't see any way at all to do anything about this, except increasing the hole size, which obviously isn't the way to go.
And I know for a fact that other people usually are not limited to 50 mm/s because of filament stripping. Therefore my conclusion is that the extruder is poorly designed.
Of course I could be wrong. I would love it if anyone has anything to teach me.

I did clean out the hot end a few weeks ago, when I thought it was stripping unusually much. What I found was some grayish dust that seemed to be clogging it. However, I think I removed most of it. It got better, but not good enough.

Hot ends vary in how much force they require to extrude filament, it's a combination of how large the melt zone is and most importantly how long the nozzle orifice is.
If the nozzle orifice is too long it can require a tremendous amount of force to extrude even with a 0.5mm nozzle.
Look for the thread on JHead copies where people were having issues because of the longer orifice.
Buddaschnozles IME require very little force to extrude, JHeads seem to be pretty good, my SeeMeCNC hotend requires a lot more force to extrude, you can trivially feel the difference if you push the plastic through the extruder by hand.

If you are shredding plastic, the extruder is clearly overpowering the grip the hobbed bolt has on it, assuming the hobbed bolt is a reasonable design, then you need to reduce the amount of force that has to be applied, changing the extruder won't change that.

Edited 1 time(s). Last edit at 01/08/2013 02:16PM by Polygonhell.

Huh. Okay thanks for the info. I do not really have room for any more major projects now(As in changing the hot end entirely), so would it make sense to try and grind/lathe the nozzle a bit to reduce orifice length? Also how on earth would you even measure the orifice length? I can't really think of a simple way...

I started having the problem you describe and discovered it was my filiment.
Using filiment spec'ed as 3.0 +or - .1 mm worked ok for about 1/2 a roll and then my hobbed bolt started striping the filiment. I measured and found that the diameter had crept up to about 3.07mm and it would not fit through the tubing in my extruder. It was within spec but won't work with my extruder. I now use filiment spec'ed at 29mm +or- .1.

Are you actively cooling the cold end of the hotend with a fan. That can reduce the length of the rubbery plug that the partially melted plastic forms and hence reduce the extrusion pressure needed. As someone else mentioned, having the idler in the extruder too tight can cause premature stripping, as can having it too loose. To measure the orifice length Brian (the jhead man) made a stand using a narrow drill bit, measured the height of the bit and then measured the height of the nozzle when slid over he bit. If you have a long orifice (more than 0.5 mm) the. Grinding the tip may help.

Sounds to me like you need to change the hobbed bolt.

I don't think the filament is to blame. I have used two different brands of filament, with no real change inbetween. As far as I can see, the filament fits fine.

I might try cooling the cold end and see if it helps, but I doubt it.

The hobbed bolt is a hobbed bolt, and it is very much hobbed still. I don't see how a new one would change anything.

As everyone has said here there are several things that can cause this problem:

-filament is too large, measure with a caliper at several places an at different angles (filament can be oval)

-Hobbed bolt is of poor quality and doesnt have enough grip, see the following links for examples of good bolts
http://airwolf3d.com/wp-content/uploads/2012/08/3d-printer-hobbed-bolt-60-mm.jpg
http://farm8.static.flickr.com/7160/6708010499_82baf272e4.jpg

-The pressure applied to your filament to force it against the hobbed bolt may be too small, PLA requires more pressure than ABS, dont know what your extruder looks like but on most of them you can adjust the tension, set it higher, try as high as you can by hand, dont use a tool

-Your thermistor is not configured properly in your firmware or somehow giving you a bad reading so your hot end is not at the right temperature, as mentioned you should be able to push the filament in by hand, if its too hard to do remember only a small bolt is trying to push it through, too hard = it will strip. You may want to confirm the temperature using a probe.

-Your nozzle may be obstructed or badly drilled (unless your a machinist DO NOT try to correct it)


And after all that being said, I want to point out that all filament is different, I have some Chinese PLA that I print at 240C first layer then 220 for the rest. So you dont "NEED" to print at 190. If you want to lower the temp to fix overhang and curling make sure you are using a good fan with a proper fan duct to cool your print.

Also, if your filament is stripping, your stepper is strong enough.