N2 Printer PolyFlex Filliment Problems

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N2 Printer PolyFlex Filliment Problems

Postby masonj12 » Wed May 02, 2018 8:12 pm

Hello, I'm a student at Foothill High School and have been having trouble with the filament called PolyFlex on the N2 printer. We've followed the instructions for temperature on the box but it keeps jamming by the time it gets to the second layer. Right now, the filament won't even eject from the printer as the gear keeps slipping. I've looked around this forum and can't find any answers. Does anyone have any advice for both print settings and removing the stuck filament? Thanks!


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Re: N2 Printer PolyFlex Filliment Problems

Postby Targo » Thu May 03, 2018 6:32 am

where is the PTFE hose? It is always needed to ensure even transport, no matter what material.

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Re: N2 Printer PolyFlex Filliment Problems

Postby Jetguy » Thu May 03, 2018 11:43 am

masonj12 wrote:Hello, I'm a student at Foothill High School and have been having trouble with the filament called PolyFlex on the N2 printer. We've followed the instructions for temperature on the box but it keeps jamming by the time it gets to the second layer. Right now, the filament won't even eject from the printer as the gear keeps slipping. I've looked around this forum and can't find any answers. Does anyone have any advice for both print settings and removing the stuck filament? Thanks!

First, we absolutely want to help you resolve this, just that there are a couple of things going on here.
#1 as pointed out, you are not using the factory supplied guide tubes that go from the right top side of the printer where the filament passes through the hole from the spools below and then over to the extruder. Depending on when this printer was purchased early units had short but fat 6mm guide tubes only at that pass through hole- later models of the exact same printer included smaller 4mm long guide tubes.
What is important here is understand why you need it in the first place. When the extruder moves from being nearer the spools on the right hand side and uses some filament, and then rapidly moves to the left, this can jerk on that filament to unroll more off the spool rapidly. This additional jerk and force can lead to skipped step and shifted layer on the printed object. That's also not to mention, you can see the sharp curve of the filament right there at the entrance to the extruder. That causes the filament to bind and drag while trying to be pulled into the extruder. Again, the total combination of a flexible type of filament (often a little bit rubbery or grippier and thus drag on anything it touches in the path from the spool), the lack of a guide tube allowing potential jerking of the extruder head when it tries to move, and the extra drag of the filament making a sharp right angle into the extruder, and then being that flex filament, a potential extreme amount of drag at times as it binds. Another option if you do not have the guide tubes and if this is the schools printer and you are not allowed to really touch it is use an overhead filament spool mount. The spool is placed at least 18 inches to maybe even 2 feet above the printer so the filament pulls straight down off the spool and has very little angle to enter the extruder as it moves anywhere in the build area of the printer.
Just as a note, I personally recommend changing the factory supplied white guide tubes now with Capricorn brand specialty coated super slick guide tubes. They do make a massive difference if you continue to use the side mounted spools. The Translucent series is slightly larger diameter internally and since it is translucent (not unlike the white factory tubing) you can see the filament during pushing it through. https://www.captubes.com/shop/#!/TL-Ser ... ort=normal
FWIW, also sold direct or at my favorite online store Filastruder https://www.filastruder.com/collections ... tfe-tubing

#2 You have a basically stock printer extruder feeder. One of the things about that feeder is that it has a fixed distance between the drive gear biting and gripping the filament and the little V groove bearing. Depending on the filament, you made need to slightly adjust the motor position by removing the acrylic clear cover, accessing the 4 motor screws to only loosen them, Move the motor towards the V groove bearing, and then tighten the 4 motor screws and put the cover back on (sorry, should have said all with filament unloaded at the time).
extruder head.jpg
extruder head.jpg (35.05 KiB) Viewed 825 times

Again, the issue here is that with a fixed distance setup like this, depending on the exact filament diameter (and yes, it can be different between different filament brands and spools, not to mention different filament types) coupled with different filament is different hardness (ability to smash it sideways) and so that drive gear may not optimally grip the filament. This topic and adjustment is covered here called "Flexible Filament Help" viewtopic.php?f=2&t=879&p=8367&hilit=paper+shim#p8342

There is also a shim method to further make more grip here viewtopic.php?f=4&t=867&p=8229&hilit=shim#p8229
Motor shim1.jpg
Motor shim1.jpg (25.42 KiB) Viewed 825 times
motor shim2.jpg
motor shim2.jpg (21.87 KiB) Viewed 825 times

Again, the reason why this is so important is such a simple concept, the software is going to command that motor to only turn a certain distance and assumes it grips the filament and pushes it in. If it does not grip and slips, then you do not get the correct amount of plastic into your print. The second thing is, that when it slips and grinds against the filament, it can grind a divot out of the side of the filament. This is like a car stuck in the mud that keeps spinning the tire digging a deeper hole. With a fixed distance idler (the v-groove bearing pushing the filament against the drive gear) when you grind a divot, then the side pressure is now near zero, so it never can grip again without user intervention. This is why the new Pro2 comes with an upgraded Bondtech feeder and a spring loaded idler that also spins and grips the filament so both sides push.

#3 Flexible filament is a challenge for any 3D printer. This is because since the extruder feeder grips and pushes the filament into the actual hotend and nozzle to create the pressure at the nozzle. Rigid normal filament under this compression passing through the center of the central crossing block helps it stay straight and rigid and not bind and buckle against the side walls of the guide path. Flexible filament on the other hand is like trying to push a rope through a pipe horizontally. At some point, it tries to snake back and forth and the friction against the walls is so great it eventually cannot be pushed any farther. The second thing is that the guide system of the extruder on the N series is made of several components that work together as a system. Just like I said the filament guide tube from the spool to the feeder was changed from early units to later newer units, the same is true here inside the central crossing block. As such, depending on some specific details of version, you may have a small gap or gaps in path there the various parts all work together.
extruder cross section.jpg
extruder cross section.jpg (46.45 KiB) Viewed 825 times

These gaps allow flexible filament a place to buckle (bend sharply) and jam. This topic here viewtopic.php?f=4&t=2276&p=16789&hilit=cone+shaped#p16789
And another picture showing the minor but important difference in versions of the internal guide part that makes the gap bigger on earlier machines viewtopic.php?f=4&t=2276&p=16789&hilit=cone+shaped#p16801
That newer style longer part is sold in the store and is relatively cheap to upgrade ($9.99) https://www.raise3d.com/collections/3d- ... eding-tube
New VS old, New longer on top, old drilled and modified on bottom
Newguide VS old.JPG

#4 To remove the stuck filament, first use the control panel to preheat the extruder. As a general rule, always attempt to feed filament to extrude some before attempting to unload. The reason for this is that while heating up or sitting idle (not extruding), the filament melts for some distance inside the hotend of the nozzle. When you just attempt to unload after heating, this extra long section of melted filament can be pulled up with the hard rigid filament and then break off in the gap area or just weld itself stuck against the walls in the cooler section of the path. The point is, feeding first before unloading pushes fresh solid filament down, pushes the melted liquid filament out and creates a much shorter melted end on the hard filament. This way when you immediately unload, you reduce the chance of pulling up a longer hot noodle of filament only to have it break off and get left inside this path inside the extruder.
Since you may have ground a slight divot or we know the motor is not gripping the filament well, you may have to manually assist here to resolve this jam. In other words, first preheat the hotend, then use the filament unloading menu but choose the load option to feed some filament first, then at the same time, push on the filament by hand or with pliers into the extruder feeder up top until it begins feeding. let it extrude at least an inch or two of filament before stopping and immediately unloading.

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Re: N2 Printer PolyFlex Filliment Problems

Postby tja » Thu May 03, 2018 5:48 pm

Does anyone have any advice for both print settings and removing the stuck filament?

I have had the same problems you mention using flexible filament and I dare say everybody has who has tried it.

Try printing slower, flexible filament doesn't like to be hurried. I print the first layer at 15mm/sec and the rest around 25 mm/sec.
Turn the heat up, the warmer it is the better it will flow. I don't take too much notice of the manufacturer's recommendations and frequently find I need to print 10 or 20 degrees hotter. When you get it printing okay you can always turn it down for subsequent models if you get more stringing than you want.
Turn off retraction, or set it to the minimum.

To clear the blockage, heat the extruder up (+10 or 20 degrees over when it got stuck). Remove the clear plastic front of the extruder (3 screws). You will find that the polyflex has wrapped itself around the extruder pulley. Using the needle tweezers, unravel it and if it isn't too mangled, try pushing it down into the hot extruder using the tweezers (be careful NOT to pull it up out of the hot end because you may end up blocking the cold end). You will likely feel it move down quite easily and see it coming out of the nozzle. (This is actually a good test of extruder temperature - if it flows easily when you feed it with the tweezers you are at the right sort of temperature). Keep going until you have pushed all the troublesome filament through the PTFE tube. Fit the clear cover, making sure you don't trap the filament anywhere, then use the load filament routine in Utilities (remember to keep the temp up).

When you have finished printing, don't leave flexible filament on the printer. Take it off and store it in a dry box. It absorbs moisture rapidly from the air and this causes a whole series of issues.

Even following these steps I still have times when flexi filament just wont extrude first time, preferring to wrap itself around the extruder pulley! So I'm upgrading my printer to a Bondtech extruder to see if that will fix it.

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Re: N2 Printer PolyFlex Filliment Problems

Postby masonj12 » Fri May 04, 2018 8:00 pm

Thanks for all the advice! I'll report back and tell you how it goes.

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