So I’ve been printing flexible/elastic/rubbery filaments for the last few days. I’ve tested NinjaFlex, FilaFlex, and Flexible Polyester 40D Shore from Plastic2Print. I’ve been trying to compare them and figure out how to print them effectively.
My test object was the thick-legged octopus variant, sliced with slic3r. Slic3r isn’t best clever about how it should print the legs, so it performs quite a lot of retractions and travel. Which in most cases would be a bad thing, but in this case it makes for a handy test. If the print had no travel in it there would be no chance to evaluate and optimise the retraction and other settings.
The problems:
These filaments want to buckle when you compress them to drive them down the hotend. Printing too quickly, or having the slightest glitch in you extruder-hotend filament path will cause buckling.
The these filaments act like a spring when compressed and driven down to the hotend. If your hobbed bolt stops turning there is still stored pressure in the system and filament will continue to extrude/ooze.
The solutions:
You can stop buckling by fully constraining the filament in the X/Y direction. For this purpose I performed a very simple/easy hardware mod. I drilled out the hole where the filament exits my wades extruder from the bottom to a diameter of 4mm. This allows me to put in a piece of 4mm OD/2mm ID PTFE tubing that runs RIGHT up to the hobbed bolt, and runs down to the hotend. The tip of the tube where it meets the hob is carved to a 2D point such that it sits right against the hobbed bolt and idler. This gives the filament no option to buckle up.
You can’t eliminate ooze entirely with these filaments is the conclusion I came to, but there are strategies you can take that make a huge improvement to how they print. The first is to print at a completely constant velocity, for perimeters, infill, everything. Make it quite slow - around 30mm/s all round - don’t use a slower first layer. The reason for this is that we want to print this stuff in as much of a steady state system as possible. Changes in velocity and extrude rate affect the output flow rate of the extrudate in a drastic way. Travel moves should be made as quickly as your machine can handle them. Retraction should be aggressive and quite long. I usually use 0.5mm for PLA/ABS, for all the flex prints shown I used 1.5mm. Lastly you should watch your temps, higher temps make extruding easier, but the extrudate is runnier and oozes more. Try and print at as low temp as you can get away with.
My thoughts on the three filaments tested:
FilaFlex - Nice colours and lots of them, I chose orange.T he reel I got had consistent diameter all over but others have not been so lucky. The stuff is the softest of the 3 filaments tested. It only comes in 3mm, so that’s what I tested it in. The surface of the filament is quite high friction/clinging which might pose issues. The filament is so soft that I doubt they will be able to produce a 1.75mm variant that is functional. It extrudes nicely at around 210 for me, the ooziest of the bunch, with the most stringing. General print quality was ok, but not as good as the others. I don’t know what the formulation for this stuff is, but the clever money is on it being a thermoplastic urethane (TPU).You can print this stuff right onto blue tape. I used blue tape with a hint of hairspray, and the bed at 50C; it worked nicely.
NinjaFlex:
This stuff is made by a company called fenner drives who are mainly in the business of making TPU belts. However they have recently started making a flexible 3D printing material. I think it is safe to assume that this stuff is also a TPU. I purchased 1.75mm filament in blue. The experience fenner drives have in belting and motion seems to show through in their filament - they have done something to the surface that gives it a surface that has a very low tackiness, and low friction. It is matt in appearance, and almost feels like it has a powder on the surface. This low friction exterior is really a big help in reducing buckling and increasing print speed. Once printed the stuff comes out a glossy translucent colour. Much like you might expect PLA of similar colour. This stuff is “quite soft” (technical term) but more rigid than the filaflex, this makes it a little easier to feed. The material prints with some stringing and ooze, but less so than filaflex. I used 210C on the hotend with good results. You can print this stuff right onto blue tape. I used blue tape with a hint of hairspray, and the bed at 50C; it worked nicely.
Flexible polyester from http://plastic2print.com:
Comes in black or natural. Also comes in two difference levels of squishiness. I chose 40D. Despite 40D being their softer offering this stuff is a bit stiffer than either FilaFlex or NinjaFlex. This stuff prints absolutely beautifully at 200C, ZERO stringing or ooze. However it does warp, but this can be completely eliminated with a heated bed of around 90C. This stuff is definitely the easiest to print with, and gets the best looking results. It is however a bit stiffer than the others, still very much a rubber like material though.
Hardware/Software:
Mendel90 https://github.com/nophead/Mendel90/tree/master/dibond
E3Dv5 all metal hotend - http://e3d-online.com/
Slic3r 0.9.10b - http://slic3r.org/
Marlin - https://github.com/ErikZalm/Marlin
Method:
0.25mm layers, 3 perimeters, 3 bottom/top solid layers, 30% infill. All prints were done with the same GCODE file, but M221 was used to adjust for filament diameter variance.
