MMU2 filament goes up and down and up and down and doesn't load
I have a solution for two recurrent problems with the MMU2:
- Failure to load filament into the MMU2
- Filament goes up and down nd up and down the Bowden-like tube and then fails.
Like many people, I have said some swear words at and about the MMU2. It's constant failure to load at the MMU2 and failure to load into the hot end make it a truly horrid product for some. But there seems to be answers for both problems which were non-obvious and which other didn't suggest when I raised these concerns a few months ago:
Failure to load filament into the MMU2
I have found that the failure to load filament within the MMU2 is primarily caused by curvature of the filament. As the filament goes through the MMU2 it exits a hole, then crosses over a gear, and then must enter a hole on the other side. When filament is curved (typically from being close to the end/core of a spool or on a 300g spool) the curvature is enough that the filament won't pass straight through and it will miss the hole on the other side of the gear.
The solution is that you need to hake the curve out of the filament and ensure that it is straight for the first 10cm or so.
This could have been avoided by a better design that controlled the filament within the MMU2 and/or had a funnel at the far end of the sprocket.
Filament goes up and down nd up and down the Bowden-like tube and then fails.
When the filament goes up and down and up and down the Bowden-like tube this seems to be cause by one thing: The IR sensor is not being tripped. This sensor detects that the filament has passed over the sprocket within the hot end. The up/down action is an attempt to reload.
To make things worse, this up/down action wears the filament and is somewhat likely to cut a notch in the filament so that it doesn't load properly. But this is not the cause of the original problem...the original problem is a little known (or discussed) mis-adjustment.
When the filament passes over the sprocket in the hot-end it operates a teeter-totter lever that blocks an IR beam that indicates that the filament has been loaded.
What I didn't realize and what isn't widely discussed that there is an important adjustment that is critical for reliable MMU2 operation. The adjustment positions the IR beam relative to the teeter-totter lever.
To do the adjustment you need to adjust the chimney at the top of the hot end. When you lose the screws the chimney can slide from left-to-right by about 1~2mm (⅛"). While a very small amount, it is critical to get this perfect.
Go the menus and find the hardware sensor status screen. It will display the status of the IR sensor as well as others. It will display a "1" or a "0" depending upon whether the beam is blocked or not. (It updates in real-time).
Now, remove the Bowden tube from the top of the hot end and insert a piece of filament. Push and pull it until you can feel it going over and out of the sprocket and notice the teeter-totter lever moving.
- Keep pushing and pulling the filament over the sprocket and slide the chimney from far-left towards center. Note the position where the 1 and 0 on the display begin to change.
- Next, move the chimney to the far left and begin to slide it towards the center until you see the 1 and 0 on the display begin to change. (You and continuing to push and pull the filament over the sprocket.)
- You now have identified the left and right extreme positions that the chimney can operate. Move it to the middle of these two positions and screw it down tight. You have centered the sensor.
In Summary:
- Curved filament will cause a load failure because the filament will not be able to enter the hole on the far side of the sprocket within the MMU2. The curvature on a fresh 1kg role is not enough to be a problem, but towards the core as the roll entries, or on a 300g spool, the curvature is enough to cause loading problems. Straighten the end of the filament and it should load and stay loaded.
- The chimney on the top of the hot end is adjustable and this is a critical adjustment. It can be centered by using the display on the i3 to show the sensor status and by manually passing a piece of filament over the hot end sprocket.
I hope these instructions save others the grief I have gone through.
Best Answer by SeattleDavid:
I have a solution for two recurrent problems with the MMU2:
- Failure to load filament into the MMU2
- Filament goes up and down nd up and down the Bowden-like tube and then fails.
Like many people, I have said some swear words at and about the MMU2. It's constant failure to load at the MMU2 and failure to load into the hot end make it a truly horrid product for some. But there seems to be answers for both problems which were non-obvious and which other didn't suggest when I raised these concerns a few months ago:
Failure to load filament into the MMU2
I have found that the failure to load filament within the MMU2 is primarily caused by curvature of the filament. As the filament goes through the MMU2 it exits a hole, then crosses over a gear, and then must enter a hole on the other side. When filament is curved (typically from being close to the end/core of a spool or on a 300g spool) the curvature is enough that the filament won't pass straight through and it will miss the hole on the other side of the gear.
The solution is that you need to hake the curve out of the filament and ensure that it is straight for the first 10cm or so.
This could have been avoided by a better design that controlled the filament within the MMU2 and/or had a funnel at the far end of the sprocket.
Filament goes up and down nd up and down the Bowden-like tube and then fails.
When the filament goes up and down and up and down the Bowden-like tube this seems to be cause by one thing: The IR sensor is not being tripped. This sensor detects that the filament has passed over the sprocket within the hot end. The up/down action is an attempt to reload.
To make things worse, this up/down action wears the filament and is somewhat likely to cut a notch in the filament so that it doesn't load properly. But this is not the cause of the original problem...the original problem is a little known (or discussed) mis-adjustment.
When the filament passes over the sprocket in the hot-end it operates a teeter-totter lever that blocks an IR beam that indicates that the filament has been loaded.
What I didn't realize and what isn't widely discussed that there is an important adjustment that is critical for reliable MMU2 operation. The adjustment positions the IR beam relative to the teeter-totter lever.
To do the adjustment you need to adjust the chimney at the top of the hot end. When you lose the screws the chimney can slide from left-to-right by about 1~2mm (⅛"). While a very small amount, it is critical to get this perfect.
Go the menus and find the hardware sensor status screen. It will display the status of the IR sensor as well as others. It will display a "1" or a "0" depending upon whether the beam is blocked or not. (It updates in real-time).
Now, remove the Bowden tube from the top of the hot end and insert a piece of filament. Push and pull it until you can feel it going over and out of the sprocket and notice the teeter-totter lever moving.
- Keep pushing and pulling the filament over the sprocket and slide the chimney from far-left towards center. Note the position where the 1 and 0 on the display begin to change.
- Next, move the chimney to the far left and begin to slide it towards the center until you see the 1 and 0 on the display begin to change. (You and continuing to push and pull the filament over the sprocket.)
- You now have identified the left and right extreme positions that the chimney can operate. Move it to the middle of these two positions and screw it down tight. You have centered the sensor.
In Summary:
- Curved filament will cause a load failure because the filament will not be able to enter the hole on the far side of the sprocket within the MMU2. The curvature on a fresh 1kg role is not enough to be a problem, but towards the core as the roll entries, or on a 300g spool, the curvature is enough to cause loading problems. Straighten the end of the filament and it should load and stay loaded.
- The chimney on the top of the hot end is adjustable and this is a critical adjustment. It can be centered by using the display on the i3 to show the sensor status and by manually passing a piece of filament over the hot end sprocket.
I hope these instructions save others the grief I have gone through.