IDEAL MMU2S FRICTION FORCE TO EXTRUDER GEAR
Hello,
I was experiencing some random under extrusions, using the MMU2S tubes path & buffer system.
Since I was not sure if it was due to effective temporary clogged nozzle, or simply under extrusion caused by filament shifting in the extruder gear due to excessive force required to pull the filament from the buffer, I decided to do some tests.
- After the under extrusion, in some cases it was enough to pause the print, and extrude some material (from settings LCD menu) to verify that the nozzle was not really clogged.
- In others that operation was not enough, I had to open the MMU2 cover, detach the tubes, an manually pull the filament, from the buffer, and then it could be extruder as in case 1.
- With thermal camera, I verified that during the print, the extruder motor often become very hot, more than all the others, and this is the symptom it has the biggest effort.
- Today I used a dynamometer to measure the effective force required to pull the filament from the MMU2/buffer and (actually) it is around 2N.
I have now some open questions:
- What is the ideal/standard force required to pull a filament from the Prusa i3MK3S+MMU2S in N ?
- What PRUSA expects to be the force in Newton ?
- Is 2N a bad or good value ?
Regards
RE: IDEAL MMU2S FRICTION FORCE TO EXTRUDER GEAR
This question is pretty complex. First of all you need to differentiate between force required for initial pull and then you need to consider the acceleration. Most likely you just measured the force required to pull with constant speed while moving.
Anyway, based on my experience if you can drag it by hand then the extruded will handle it without any issues. If you think, that extruded is slipping, then you should hear a prominent “klick” sound. But it sounds more like a regular heat creep issue.
Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram
RE: IDEAL MMU2S FRICTION FORCE TO EXTRUDER GEAR
The point, I did not mentioned in the first topic, is that when the issue appeared, I think the stepper motor was perfectly able to apply all the full N force to the filament, but unfortunately was the filament that did not support such force applied to a small lateral surface by the grinder, becoming powder.....
RE: IDEAL MMU2S FRICTION FORCE TO EXTRUDER GEAR
The gotcha is not just whether it can move, but how quickly. If it can't move fast enough for the retract due to friction you'll get crap tips and stringing that leads to jams...
RE: IDEAL MMU2S FRICTION FORCE TO EXTRUDER GEAR
That's what it makes this questions difficult. Ideally there will be zero friction.
I understand what you're asking for. But you can get this data only if all people who does not experience this issue are measuring with the same method. Unfortunately most of the people does not have such a device.
I can only tell you that I'm still using stock setup with the autorewind spool holder. It adds up a little bit friction but I had no such issues so far. So the friction of the tubes wouldn't be my first spot to look at.
Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram
RE: IDEAL MMU2S FRICTION FORCE TO EXTRUDER GEAR
At the moment, I noticed that the friction is generated after a while on the tubes, not immediately. I noticed that:
- all the filaments tends to be link a circular spring: that can't just stay straight but become curved shaped.
- the more the spool is finishing them more the bending angle is
- the PTFE tubes are of course in a curved shapes (e.g. buffer in high position with tubes that curve and fit in the lower MMU2)
- the filament due to usage, rotates on its axe, AND the bending angle can become opposite of the PTFE tube bending angle; then the friction becomes incredible.
- is it impossible at the moment have a way to rotate the filament on its axe to keep it always to match the PTFE curved angle.
I am currently working on those problems.
Regards