Nylon jams in Cetus hotend

I am printing using the newer metal hot end but with the original 10CFM cooling fan and Nylon is the first filament material that I have given up on.

PC, carbon fiber PC, PP, PETG, ABS, flexible, etc all print great.
Nylon 12 will consistently extrude at about 10C over the Nylon suggested upper temperature range but it foams or bubbles as it extrudes so the print has no strength. This happens even if the Nylon is seriously vacuum dried at 1/10,000 of an atmosphere. Lower the extrusion temperatures the Nylon jams in the heater.

Just wondering if anybody, including Tiertime, has been successful printing Nylon with this hot end.

Are you using the steel nozzle? I had the exact same symptoms as you on a different printer with Bridge Nylon. I also dried the filament thoroughly, and increased the temperature in 5 degree increments up to 20C over recommended with no luck. I switched to a brass nozzle and it printed beautifully at recommended settings after that.

I’m new to Cetus though, and I just want to say thank you, Peter, for sharing so much of your knowledge.

You’re welcome.
The new heater with a steel nozzle. I did some test prints with replacement unit and compared them to older prints with the original broken extruder. I think the older extruder produced a better print so I repaired it and am now using parts from both. Basically it’s the old extruder with the new heater block. The old extruder repair requires a lathe and some small ball bearings. Not rocket science but you do need lathe.
To print at 300C you need better thermal insulation around the heater block and nozzle. The improved insulation takes about 4 minutes to reach 300C, without the improved thermal insulation the maximum heater temperature reached is about 260C after 5 minutes of warming up.
Pic cleaning out the filament path.

Cold end liner plastic tube or ???

If you print nylon and found the filament bubbling when extruded. This is evidence of absorption of water and it is very common for nylon to absorb water. This has nothing to do with hotend. I think the way you dry the filament is not effective, try use an oven to bake the filament for a while.

Hi Jason, I wish that the fix was that easy.

I happen to have a two stage, oil sealed, 50 liter/minute scientific vacuum pump. The vacuum reached is below 1/10,000 of an atmosphere which is much better than heating to eliminate moisture, plus low vapor pressure organic compounds, and air that has dissolved or diffused into the filament etc.

I don’t have a scale sensitive enough to weight the spool before and after drying to measure how much water was removed. The best indicator I have is using x10 optical magnification and inspecting the purge line of clear unblended hobby king polycarbonate printed at 290C. I don’t get any bubbles in the first 16 hours after vacuum drying, the next day I can see a few small bubbles in the purge line. Vacuum dried Nylon has no bubbles as long as I don’t exceed the maximum extrusion temperature. It is interesting how quickly above the maximum extrusion temperature the Nylon chemically breaks down and forms bubbles.

In the new cetus extruder, I think the Nylon melting point position between the cold and hot end just happens at a bad point and the Nylon sticks to something. I would do more experiments but I don’t think the white tube liner in my cold end will survive any more Nylon printing tests.

To be clear, I can heat and extrude Nylon at just over 260C and it still has no bubbles, but in the time it takes to move the nozzle and start printing the purge line it jams. Extruding at 270C it has no jams but you get a print full of bubbles with no strength so not a very useful print.

It would be good to know the maximum service temperature of the white liner material to be able to melt out filament jams!!!

Lastly it is possible that by simply changing the air flow over the cold end you could move the melt position up or down just enough to fix the Nylon sticking problem.

Best Wishes,


Hello Peter,

If you are sure the filament are dry, then I think the filament likely not compatible with the hotend.
We have tried esun, polymaker and Taulman nylons, we found the Taulman nylon (forgot which type) was very sticky in the hotend and cannot be extruded. The eSun and Polymaker filaments have no problems.

Hi Peter,

working here with a MK2 with stock brass nozzles and Nylon works great with mine. Even Nylon/GF combo printed nice. What I changed two years ago was the fan position. So I don´t cool the tip and the middle piece of the hotend only the top part next to the motor. Maybe this could be a worth a try…

Hi Folks,

Awhile back I was messing with NinjaTek Armadillo filament, I found the temperature tolerance was too tight for the stock heater-block setup. To print a flexible fabric at 0.4mm thick I needed a temp tolerance of +/- 2 degrees celsius. I installed an upper nozzle stabilizer post that lowered the heat-zone in the nozzle and allowed the removal of the two tubes that mount the heater-block to the metal bracket. Even though the tubes and bolts are stainless steel they are sucking heat from the heater-block and to make things worse from the side of the nozzle lacking enough heat for a uniformly melted filament. I have also reduced the cooling from hitting the nozzle tip.


From another post…

If there is black burnt residue in the nozzle there is something not aligned and/or a material’s temp rating does not meet the desired operating temperature of the nozzle.

An easy way to monitor the health of your nozzle is to notice how the filament is exiting the nozzle tip, if it comes out perfectly round and straight then things are likely ok inside your nozzle, if it curls or burps…well…things are not going well inside your nozzle.

Thanks for the suggestions.

I tested both the original MK2 heater and the replacement MK2.5 steel nozzle version. Unfortunately neither will print nylon and so I am moving on.

On the positive side I am very good at cleaning massive nozzle jams.

Two pics of vacuum drying nylon filament. The first is water gas condensation in the exhaust tube and the second is after an hour of ballast bleed air. Ballast air dries out the oil so you can get a better vacuum than just the vapor pressure of water. The vacuum is between 1 and 10 pascals in the second pic.