Printing NinjaFlex on a @nop_head Mendel90
After lots of trial and error I’m starting to get some pretty good results with NinjaFlex (even on complex shapes like the Android below) and I thought I’d share my settings to help others get a starting point because for some reason there seems to be a lot of strange advice out there which didn’t match my experiences at all.
Intro
NinjaFlex seems to be a really nice product, its stretchy, compressible and yet amazingly strong. It reminds me a bit of the soft silicone cases you get for mobile phones but its not quite the same.
How is it different to PLA/ABS when printing?
The first thing you will notice is you have the opposite problem to usual when it comes to adhesion to the bed. Instead of having to use heat, hairspray, glue and things like that to try and get your print to stick you will find yourself trying to get it to not sick as hard so you can remove it afterwards! In my case plain glass and zero heat worked perfectly. I learnt the hard way after wasting a few sheets, DO NOT use Kapton, you will never be able to get it off afterwards!
What about temperatures?
As I said above, no bed heat is needed. For the extruder its recommended that you use temps between 210c and 225c, however I found that with the geared spring loaded extruder on my Mendel 90 those temperatures were a non starter. The issue appeared to be that the flexibility of the raw material meant it was difficult to apply pressure in the hot end and it would simply squidge/buckle up and often get stuck. However increasing the temperature up to 240c completely solved the problem, resulting in a reliable extrude every time.
Retraction
One of the pieces of advice I saw quite often was “don’t use retraction with NinjaFlex” accompanied by photos of really stringy prints from people that didn’t use retraction. I can only think this is aimed at people with Bowden style extruders or something like that(?) because I cranked up the retraction both in distance and speed on my Mendel and got far better results. One of the issues is the squidginess of the NinjaFlex accompanied by the slightly higher heat means it tends to dribble. At the moment I’m running a 3mm retract (prime/suck) at 40mm/s and as you can see from the photo its achieving quite good results. I need to experiment and find out what the sensible limits on my Mendel are as faster and further seems to be the way to go.
Flow
The other thing I noticed was I was getting waaay too much flow. I set up my slicer with the measured raw material diameter (2.85mm in my case) and it just wasn’t right at all. I’m not sure why NinjaFlex is like that, maybe its due to expansion during heating? At the moment I’m down to a flow tweak of 0.9 and I may even lower it a tad more. (Interestingly enough I noticed by chance that if I had kept the diameter in the software set at 3mm the flow would have been much closer to correct. I do wonder if the manufacturer is aware of the expansion and hence made the material undersized deliberately, that would make sense as it would give beginners a better chance.)
Starting
One thing I did notice which caught me out at first is NinjaFlex is a bit of a slow starter. Due to its compressibility you need wind the extruder quite a bit before you get any material coming out. I found personally that heating up the hot end and turning off the motors so I could hand crank it around a couple of times before a print helped, the other option was to print plenty of skirt loops so you get some flow before you start printing your actual print.
Final thoughts
Over all it seems quite an easy material to manage, in the Mendel 90 anyway. If you are having trouble getting started I found starting off with thicker layers such as 0.3mm made things easy. Once I got the settings closer I then dropped down to 0.2mm.
Anyway I hope this helps you guys out as it took me a while to get things going and at one point I almost threw the towel in, but I’m glad I didn’t as its really cool stuff 
