rubber grinding

Hello guys, maybe somebody can shed a light on this issue.
The other day, I tried to print an object using rubber but my prusa started grinding it and the filament won't get into the nozzle smoothly.

Indeed, when I took apart the hotend I found out that it made several senseless "loops" around the extruder's gear.
I think it could have been caused by the fact that the filament is quite soft and tension on it was weak.

Do you have any suggestion which can help me out?
How do you usually adjust your extruder's spring?

Thanks

Edited 3 time(s). Last edit at 07/21/2015 06:05AM by gianni21.

Rubber???
I seriously hope you mean flexible filament like Ninjaflex...
If your extruder is not designed for flexible filaments you will have little chance to use it.

It's Flexible TPU
and at least on paper, it should be compatible with TPU's

Edited 2 time(s). Last edit at 07/21/2015 09:16AM by gianni21.

Flexible material only works properly on some extruders. Basically it needs to be held in place on the sides while it's pushed into the hotend, if your extruder has an open gap between the hobbed bolt (or gear) and the hotend entry then it's not going to work with that setup. It takes some pressure to get the hotend to force the material out the other end so if the filament can go elsewhere easily then it will do that instead.

Try an old trick, although it only woks with some extruders:
Using a lighter heat the end of your flex filament and the end of a normal piece of PLA.
Once the tip starts to melt press them together - it helps to have a piece teflon with a little groove in it.
Once cooled trim the excessaround the fused bit so it is even with the filament again.
Feed the PLA into your extruder, use a very low pressure on the bearing.
Slowly let the PLA work the way down until it extrudes, if you are lucky enough and your extruder is not all bad (for flex) it should now go where you need it instead of curling up.
Keep an eye on the pressure and try printing at quie low speeds until you worked out how to treat the flex on your printer.

Nice tip I'm gonna try it, by the way let me say that when I park my hotend and extrude some TPU, it flows smoothly.
The main problem pops up only when I start printing.

Probably, I should dispose off that part of filament already grinded because it seems softer than its original shape.

Edited 1 time(s). Last edit at 07/22/2015 03:00AM by gianni21.

I had the same problem trying to print ninjaflex. I took apart a few pens until I found one with an ink tube with an ID of approx 2mm (filament should slide through nicely). Then, I pushed it down into the filament hole right up to the hot end (gregs wade accessible extruder), and cut a window where the hobbled bolt would grab. This tube supported the filament the whole way down to the hot end, which allowed me to print well (albeit at low {20mm//s} speed). Also I found that using an oiler on ninjaflex helped in my case. I'm not sure if you could use a piece of ptfe tube or if the OD of that would be too large. Others have done the same with a brass tube successfully.





Good luck!

Slow your print down.
I have also used the TPU Flex. I found a couple of times it would buckle inside the extruder. I think the extruder was trying to push it into the nozzle faster than it could ooze out the other end. I slowed the print down and the problem went away.

I'm using slic3r, which speed parameters should I tweak?

I didn't do a lot of printing with Flex. Once I had the part I wanted I went back to plastics. But some observations I made when I was using it:
Flex TPU sticks well to clean glass.
My perimeters I printed 10mm/sec and infill at 15mm/sec (external perimeters at 50%).
First layer at 120% extrusion width.
I had bed at 60 degrees and hotend at 220 degrees.
I had to increase my extrusion multiplier. I had it at 1.1 and I'm not sure it was enough even at that.
I also found that overhangs were good, but bridging wasn't.
And it is very sticky. I had some paper towel ready to wipe the nozzle from time to time.

A bit more experimenting would get you better settings, but that was as far as I got. Hope it helps.