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Printing with Flexible TPE Filament

Posted by wozzy 
Printing with Flexible TPE Filament
March 15, 2014 01:47PM
I was asked earlier today, How I print Flexible TPE filament on my Mendel90.
I though it would be useful to repost my reply here:

For reference, I have been printing with NinjaFlex TPE on my Mendel90 Dibond kit.
I am using an E3D V5 hotend, however I was successful printing with the original J-Head.
I agree that it was not easy to print with at first, but keep in mind that you are pushing a flexible noodle with high compressive force.
Note that I don't think it possible to print flexible materials with a printer that uses a Bowden type extruder.

While NinjaFlex can be difficult to learn to print reliably, it has some really great properties that makes it worthwhile:
  - Amazing flexibility and toughness
  - Fantastic adhesion to a clean unheated bed 
  - Unbeatable inter-layer bonding
  - Zero curl and low shrinkage
  - Relatively low print-head temperature

The following are tips and settings that I've learned.
	-Feed slow, print slow: I use Repetier host, which has a speed slider. I typically set it 25 to 35% of the normal speed I would use for PLA/ABS.
	-When priming the print-head with TPE, I typically advance the filament 4mm then retract 2mm at 220C or 225C.
			-Keep doing this until the TPE flows freely and forms steady loops on the print-bed below.
	-Use Retraction: This seems to be the main factor in getting good prints. (*See below why I think this is important)
			-In Slic3r (Printer Settings / Extruder 1 / Retraction) I use the following settings:
					-Retraction Length to 10mm
					-Speed to 125mm/sec
					-Extra Length on restart to 0.1mm
					-Minimum Travel after Retraction to 1mm
			-Avoid large print areas with no retraction. If necessary add a feature to the design that will cause a retraction, or modify the g-code.
	-Print with Hot-end temp: 215 to 220 deg C: NinjaFlex has very good inter-layer bonding even at this low temp.
	-Hot-end and hobbed gear must be clean of all other traces of other filament (PLA, Nylon, ABS, etc). 
			-I usually use some Taulman 618 nylon to clean my print-head. First I extrude a little at 240C
			-Then I let it cool and then retract it at 120C. I repeat this until it comes out clean with the end intact.
			-I also use a hobby knife to clean out any pieces of old filament that may be stuck in the teeth of the hobbed bolt.
			-Just a little bit of ABS will cause problems because of the low print temp.
	-The filament path from the hobbed gear to the hotend must be smooth and free of misalignment.
	-The filament path from the hobbed gear to the hotend cannot have any excess clearance from the filament.
			-I had to print a new Wade's block for other reasons, and used the opportunity reduce the clearance, bring the feed-hole closer to the hobbed bolt, and smooth out the feed path with a drill.
			-I also glued a feed-tube holder to the top of the Wade's block to support the feed PTFE feed-tube since it would flop over otherwise.
	-Print on a cold or 40C print bed: the bed adhesion properties of NinjaFlex are excellent.
* I think that the difficulty with printing with flexible filaments is that they will kink up in the feed path between the hobbed gear and the hotend if you try to extrude too fast which
 allows the heat chamber to build, which caused the compression in the filament to increase. Once it starts to kink, unless you retract enough to undo the kink, you're done.
The Coefficient of friction of the flexible Urethane filament is so high, that there's no chance to push it through. The filament just continues to kink more and more until the total
 volume is filled. I've retracted kinked filament, and observed 10 or 12 kinks in only 10 or 12 mm

Good luck, and let me know how it goes.

Edited 1 time(s). Last edit at 03/15/2014 01:51PM by wozzy.
Re: Printing with Flexible TPE Filament
March 15, 2014 02:34PM
I just noticed there's another post on the topic on the RepRap Forums here: http://forums.reprap.org/read.php?1,269018
Re: Printing with Flexible TPE Filament
March 17, 2014 04:11PM
Hi Wozzy,

Thanks for this feedback on printing with NinjaFlex.

Your findings on the retraction settings are interesting. We are doing some playing with these settings now to determine what the optimal settings for retraction might be. The issues with the filament kinking if it is unsupported between the hobbed bolt and the extruder are also spot on. It is a classical engineering beam problem. Slower feeds and adding support are the best solutions currently available.

Stan Kulikowski
Applications Engineer - Fenner Drives
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