What I think is causing so many feed failures at the raft layer

Just something that I hope others can watch for and check, about feed failures at raft time.

While printing the raft (high volume plastic deposition ) the hear temp dropped. This seems a common problem and appears firmware based, as though the controller loses track of the hysteresis measurement of the head temp, and is a major problem.

Anyway, if this happens during raft print, then when it thinks the head is warm again, it starts pushing plastic, very fast. The plastic in the head hasn’t reached temp yet though sometimes, if there’s a particularly bad printing pause, and so the head jams, and you hear the "click click click " sound as the drive gear rips a crescent of plastic out of the filament… And then print stops and it prints to air because it can’t grip the plastic anymore.

Can anyone else having this problem let me know if you observe the same factors when printing the raft?


@cj7hawk , this is a common problem with 8-bit controllers especially on the Cetus. The temperature-interrupts within the flow of gcode while printing is too far apart… the time between checking and adjusting the filament temperature is too long. It’s a balancing act that is too-slow on an 8bit controller where the firmware exists.

I’ve been running with stock Cetus MKII electronics for a year now, and will do-so until I publish my mod-package…then I will install a 32bit controller which handles all interrupts much quicker and reliably. The other solution is to install a tiny-controller(8bit) that handles the temperature tasks. Easily done and may be another project I undertake.

The solution I use is to increase the filament temperature until you see the temp you want to use constantly displayed within UPStudio. I’m setting the temperature for PLA+ at 224, and the temp displayed is a constant 220.

Another issue is heat-creep within the nozzle. Turning the extruder-fan off too-soon when a print is finished, will relocate the top of the heat-zone within the nozzle. The firmware thinks the temp is correct, but doesn’t know that further up the nozzle is where the top of the heat-zone actually is.


Which printer are having such problems with? Seems my Up Mini 2 prints the raft extra slowly, possibly tho help mitigate such an issue.

It still has the occasional feed problem, but usually due to imprecise z axis and uneven bed physically blocking the nozzle every now and then.

@cj7hawk, which printer did you experience this? Never happened with my Cetus MK3 printing a raft using UP Studio.

I’m having it with the UP300… Anyway, this only happened once, so I kept looking for reasons why I’m printing to air so much. I know I’m not the only one having this problem.

Usually I follow the following procedure after a jam.

  1. Swap the nozzle to a clean one, and clean the old one in MEK.
  2. Remove the feed mechanism and clean out the bits of plastic in the gear.
  3. Re-assemble.
  4. Change spool to a new one ( happened a lot with older spools. )

Usually when I start to get jams, I will continue to get jams until I do the above. ALL steps.

That last one has me curious. I get more jams with plastic as the spool gets used up. Today something strange happened while printing the raft. I pulled on the straw that guides the filament, and it resisted for a moment as if stuck, then came loose just as the printer jammed. This meant something is binding between the filament guide and the spool. I’ve been hearing a bit of noise from the filament compartment too at times - not loud, but the odd sound that sounds like something just jumped.

And I had a “Eureka” moment. I pulled out the filament and ran it on a pipe between two boxes without taking any action to clear the jam other than pushing the filament down a little into the head while extruding to get it going again.

So I designed and printed up a new spool holder that is within a millimeter of the ID of the spool all around, and just slots in after the spool ( eg, I put the spool in, put in the new axle which has two keys that fit through the slots, and turn it 90 degrees to lock it in place. )

Now the spool moves slowly and very steady while feeding at any speed, and I can visible see it turning without any problems and it’s as smooth as a second hand of a watch. No more jams for the rest of the day, even without cleaning the head.

Now it’s a bit early to say that this was the problem - I’ve had this with all spools, including Tiertime UP spools, especially as they get low. The only spool I didn’t have jams with was an aftermarket one that sat well on the holder… So I’m thinking maybe the spool holder is the reason I’ve been having so many problems to date. Anyway, so far so good. Straight back to printing, with the same spool and without cleaning out the bits of plastic in the gear drive, and it’s still going strong after 1/2 a day of continuous print.

So if anyone else has this feed problem, this is what I’m currently thinking it might be.


The clue that makes sense to me is…

If you open a new spool of filament and cut a length of at least 100mm and set it on a flat surface, and then, from a spool nearly empty, cut a length at least 100mm and set it on the flat surface near the other…you’ll see the natural-arcs of the filaments are different, one is relaxed and the other very-tight. The very-tight arc’d piece will create far more friction than the relaxed piece from the new-spool. When feeding these through tight filament-guides, the length of the guide the filament travels through matters, and if there are many feeder guides, the friction compounds. There are other forces at play here, especially when the filament is coming off the spool and is forced to straighten from it’s natural tight-arc…the energy becomes concentrated where it meets the rest of the filament on the spool, digs into the windings, and when forced to start straightening it’ll bind with the other filament-windings.

So, whatever your setup, reducing friction and allowing the filament to peel-off the spool without interacting with the other filament still on the reel is the key here.


I haven’t tried that test - I’ll wait to get the to the bottom of a spool and compare it to the next one.

Anyway, still no more jams, regardless of what is happening at the head. I need to make different sized axles though for different rolls. It works really well too with custom filaments which often come on a wider reel than the original axle will support.


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Good to hear that solution fixed your feed issue, sounds like the filament guides were not the most pressing issue…happy printing!


You need to contact the repair, I guess.

That’s not necessarily so. I think you definitely pushed my thinking in the right direction. Whatever the primary cause was, fixing the feed problems solved the jamming. The root cause of my particular feed problem however remaining unknown.

So your input was appreciated.

Hi Jamiereynoldss - The cooling down problem is a known issue. I expect that it will probably be resolved with a firmware update as TT has already acknowledged it.

Tks for the reply @cj7hawk , good to know some of my ramblings are helping folks!