Elastomeric ("rubber") Filaments

Today I tried Ninjaflex and another experimental elastomeric filament that I'm not allowed to discuss publicly at this time on my gMax. Both failed due to the large gap between the feed gear and the filament entry tube. The large I.D. of the entry tube may also be a problem even if the gap is closed.

The extruder can only push. With rigid filament pushing is not difficult, but with these soft filaments it's like trying to push a wet noodle, i.e. very difficult. Ninjaflex is extremely soft and tricky to print with on any printer (although I've heard it works well on MakerBots). This new stuff (the white one) is considerably stiffer than Ninjaflex and it feeds very well on my Afinia (Ninjaflex doesn't, without modifying the printer) but the gap below the gMax's feeder is just too much - the filament buckles as soon as it hits the nozzle.



Staff member
the ecoflex seemed a bit stiffer and I has less of the noodle effect. I tried increasing the temp and lowering the speed which allowed me to print. I can increase the height of the barrel to see reduce the gap as much as possible which may help. Swapping the motor bracket can happen without having to remove the whole extruder assembly.
I can increase the height of the barrel to see reduce the gap as much as possible which may help. Swapping the motor bracket can happen without having to remove the whole extruder assembly.
Excellent, I will print the new design and test as soon as you publish it :)

P.S. Maybe reduce the barrel I.D. as well so the filament can't buckle inside the barrel and has nowhere to go but down toward the nozzle.
I had success today printing Ninja Flex with the gMax printer.

As Julia showed in her posts above, the space between the extruder's drive wheel and the filament support shaft is too large to effectively contain the Ninja Flex as it is being pushed into the Hot End.

I solved the issue using a Paper Mate Ballpoint pen, a 9/64" drill bt, a 3/32" drill bit and some acetone (to clean my fingers - that ball point pen ink is a mess)

In simple steps, the process was:

1. Remove the Extruder Lever (the part that has the bearing attached that presses against the filament)

2. Remove the Extruder Motor Bracket, which (as Gordon said) can be unbolted from the extruder motor and the extruder platform without taking anything else apart.

3. Find a Papermate ballpoint pen and remove the point and the ink tube from the outer shell.

4. Cut off about 1/2" of the ink tube off the end opposite the point to get rid of the plug in the end, then cut another piece about 2 inches long. Watch for the ink. Be careful. Don't wear white. You just want an empty tube nub without any ink trapped inside. Acetone works well to dissolve the ink, but it can still be a mess.

5. Check the outer diameter of pen tube nub - mine was 9/64". Then drill out the filament hole in the Motor Bracket using a 9/64" drill bit - I just turned the bit into the hole by hand, holding the drill bit with a pair of pliers. No need for a power drill.

6. Remount the motor bracket, tighten the screws that clamp the bracket to the hot end and the acrylic base plate and push the pen tube nub into the drilled out hole until it bottoms out on the top of the hot end.

7. Loosely mount the extruder motor with the drive wheel in position and touching the pen tube nub. Take a utility knife blade and partially cut through the tube right at the drive wheel, trying to maximize the length of tube that would extend past the wheel without impeding the motion of the wheel.

8. Remove the pen tube nub and finish the cut. Then reinsert the nub into the motor bracket.

To be continued ...


9. Take a length of 1.75mm filament (PLA or similar - not Ninja Flex) and insert it into the pen tube nub and push it into the hot end. If you can feel the filament hanging up at the top of the hot end right as it exits the nub, you can try to ream out the tube/hot end interface a bit. I used a 3/32" drill bit to ease the transition. (Again by turning the drill bit with my fingers - no power tools) I just inserted the drill bit until it hung up on the interface point, then rotated it several times while applying light pressure. After a couple of passes, the transition was smoothed out and the filament passed freely into the hot end.

10. Remount the Extruder motor and tighten the bolts carefully.

11. Loosely mount the Extruder Lever and before you install the spring, press the bearing against the tube nub and slice the top of the nub in the other direction so that the top of the nub is pointed and fits right between the drive wheel and the bearing. I had to shave it twice to get the right angle and length and not hang up the bearing.

12. Finish mounting the Extruder Lever.

13. After rigging the Ninja Flex filament spool where you want it, preheat the hot end to 230 degrees (ABS temperature) and press down the Extruder Lever and insert the Ninja Flex filament into the top of the pen tube nub. It should slide easily down to the hot end.

14. It will be tough, if not impossible, to push the Ninja Flex through the hot end with your fingers, so I used the LCD display to control the extruder stepper in 0.1mm steps slowly push the Ninja Flex through the hot end. It will take a while to clear out the previously extruded material that is still trapped in hot end. Continue to extrude until the extrusion is 100% Ninja Flex. Stop. Wait for the ooze to stop. Clean the tip of the hotend before sending the extruder head back to the Home position.

15. You are ready to print. I set the temperature at 230 degrees for my first print, and had the speed dialed way back. I will include the Slic3r configuration file I used to print a stretchy - which used a spiral vase pattern with only a single perimeter. I haven't had time to try other objects yet.

Hope that helps.

Rick Palmer


Awesome, thanks! I've got some teflon (PTFE) tubing laying around from other printers (commonly used for bowden extruders and filament guides) so maybe I won't have to get messy with ball-point ink :) I was kind of hoping Gordon would release a new extruder bracket design that would extend the feed tube upwards but i know he's busy. Great to know that NinjaFlex can be gotten to work with the gMax! I've got a spool of FilaFlex from Recreus to try now too - many more color choices than Ninja.



Staff member
That's some great work Rick. I agree with Julia that PTFE might work even better but it looks like yours is running great. For reference, McMaster-Carr has PTFE tubing. I also just uploaded the updated extruder motor bracket (v1.2) with the longer barrel. It definitely helps but it doesnt extend as far as your mod which still gave me some headache when printing with ecoFlex (which isn't as flexible as ninjaflex). It might be worth us investigating using PTFE through the whole barrel.
Awesome mod to get Ninjaflex to work!

Has anyone tried Semiflex? Will it have the same problem? I have ordered some and plan on giving it a shot, would like to use my gMax instead of my other printer if at all possible.
I would think that with the extra hardness/stiffness with SemiFlex that it wouldn't have quite the same problem as NinjaFlex. That being said, I HIGHLY recommend either the tubing fix Rick did, or get an E3D hot-end which comes with PTFE tubing that feeds all the way through to the nozzle, and can easily be trimmed with an exact-o knife to get the same shape shown earlier in this thread.

Once I can pick up a spool of SemiFlex this summer (hopefully June) I'll post here and let you know how it goes.


Ok.. I am finding threading filament in to be a challenge the way it is right now with standard stuff. I can't imagine trying it with Semiflex.

I have some ordered actually, should be here by Friday. Little leery taking the thing apart right now, since I JUST literally got it working 2 days ago, but if I must, I must I suppose. I have thought about getting an E3D hot end as well, but I would like to get the Cyclops, and I don't have the skills to design a carrier that would work with it I don't think.