Re: How do I stop TPU coming out the side of the extruder?
Joan, I wonder why you suggest reducing the screw tension on the Bondtech clamp? In spite of all that I've done, I'm still having difficulty printing TPU. The filament always "escapes" on the idler side, and it occurred to me that maybe the filament is actually pushing against spring tension and literally moving the idler away from the drive gear. So my next experiment will be to try increasing the spring tension.
I think the idea is that you want to grip the filament without deforming it. The flexible filament deforms very easily, so minimizing the tension reduces the deformation.
Another thing is adjustment of the length of the PTFE tube in the extruder body. Apparently you can assemble the extruder and think that you have the PTFE tube just about touching the Bondtechs, but the flexible filament will find a way to push down on it. So the next time I install a new tube (tomorrow?) I'm going to push down on it very firmly by hand before I decide whether it's the right length and installed correctly. I've made a jig so I can cut the tube with two 45 degree slopes so the top of the tube has "ears" that constrain the filament from going astray along the axis of the Bondtechs.
And yet another thing I'm going to do: I now have plenty of PTFE tubing so I'm going to do a "reverse bowden" from my dry bag all the way to the top of the extruder to keep the filament really dry.
If you haven't done it yet, I strongly suggest that you upgrade to the R3 extruder parts. The changes in the R3 version were specifically intended to reduce problems with flexible filaments, and it worked for me. R3 gives you a much more constrained filament path below the bondtech gears. Flexible filament stays in place because it simply has no place else to go.
Well, yes, I have upgraded to the R3 parts. In fact, in the last couple of days I even made my own mod to add more plastic inside the zone where the Bondtech extruders have their channels (like the Skelestruder, I think).
But I'm STILL having difficulty. I'm down to a Volumetric Rate of 2.0 and no part fan, which seems successful so far, but I don't know how much margin of safety I have. I'm trying to print a commercial part that when completed at the volumetric rate of 2.0 will take about 27 hours to print. And the "pancake" part that seems most likely to fail comes at the end, so I hate to waste a full day and a quarter of a roll of filament again and again and again.
I think there's a tradeoff of spring tension. Obviously if I squeeze too hard I can make the filament oval and then it won't fit going down the PTFE tube. But if I have too little spring tension, then the filament can just push the idler roller aside and make its escape.
Re: How do I stop TPU coming out the side of the extruder?
But I'm STILL having difficulty. I'm down to a Volumetric Rate of 2.0 and no part fan, which seems successful so far, but I don't know how much margin of safety I have. I'm trying to print a commercial part that when completed at the volumetric rate of 2.0 will take about 27 hours to print. And the "pancake" part that seems most likely to fail comes at the end, so I hate to waste a full day and a quarter of a roll of filament again and again and again.
How soft is the TPU you're trying to print? For really soft TPU, 2.0 doesn't sound unreasonable.
One thing I usually do when I'm trying to troubleshoot a tricky print is create a test object that isolates the problem part of the print and fails quickly. If you just print the pancake part and nothing else, does it still fail?
Re: How do I stop TPU coming out the side of the extruder?
Hi Jay,
excess tension on the extruder screws, tends to distort the TPU and cause it to pop out between the bondtech and the PTFE...
your mileage may vary
reverse bowden sounds like it will keep your filament dry!
I have printed R3 parts for the extruder. but not fitted them why modify a working printer...
I am expecting my MMU2, soon, so I will do the R3 extruder parts then.
the R3 parts are supposed to work better with TPU.
I only have cooling problems where the layer time is very short... some of my parts have little peaks at the top, which require full cooling and reduced speed... you can set your fan to come on, at higher layers, and less speed, in Slic3r or another slicer
good luck, Joan
The more I think about it the more I wonder... Although TPU is easy to deform, it is also very elastic, meaning that as soon as the force is removed it bounces back to its original shape. So I'm definitely going to try experiments with the extruder screws tightened at least to the same place that's used for PLA and PETG; I'll even try higher tension just to see what happens.
Re: How do I stop TPU coming out the side of the extruder?
Back again in the continuing saga. I feel pretty confident of success now. I'm printing MatterHackers Pro Series TPU with a Hot End temperature of 250C and a Volumetric Extrusion rate of 2.0. I don't turn on the Print Fan, and I have a desk fan beside the printer blowing across the machine to keep the Extruder Motor cool. (I have heat sinks on the motor, and with the fan blowing it's barely perceptibly warmer than room temperature.)
I think the final victory came from making a little cutting jig and repeatedly trying out different lengths for the PTFE tube inside the extruder body. The one I have now is essentially in contact with the Bondtech rollers, but not pressing against the rollers hard enough to jam them. You can see the little hump I added to the extruder body in this picture, as well as the extension of the PTFE tube above the printed body. Although the entry for the tube is not tapered, I haven't had any problem feeding filament into the extruder.
I also implemented a "reverse Bowden" carrying dry TPU filament from my bag with desiccant right to the top of the extruder. This PTFE tube is not actually anchored down firmly on either end, but the very slight drag of the filament passing through it seems to keep it well butted up against the top of the extruder body entry. I do have a "guide" so that the PTFE tube is constrained to approach the top of the extruder in a perpendicular direction.
Truly dry TPU is really beautiful. But an exposure of only an hour or two to ambient air makes it rough and grainy.