Please help me with my MMU2  

Re: Please help me with my MMU2

started another print and red had a problem right off the bat the tip is 2.03mm, grinding at the extruder.

Any reason why you've changed the ramming settings? I would suggest you go back to defaults.

Re: Please help me with my MMU2

started another print and red had a problem right off the bat the tip is 2.03mm, grinding at the extruder.

Any reason why you've changed the ramming settings? I would suggest you go back to defaults.

it seemed to help with stringy tips at normal / suggested print temps.

Re: Please help me with my MMU2

it seemed to help with stringy tips at normal / suggested print temps.

I see. Then I would suggest you try to go back to default ramming settings and lower the temperature instead.

Re: Please help me with my MMU2

it seemed to help with stringy tips at normal / suggested print temps.

I see. Then I would suggest you try to go back to default ramming settings and lower the temperature instead.

i have started to do that ramming is at 2.5 seconds temp is at 210. the trips are stringy but i want to see how long this print can run for. should i just drop the temp by a degree or 2 at a time?

Re: Please help me with my MMU2

it failed again with a tip that measures at 2.03mm ramming at 2.5 seconds temp pat 210. is there a reason not to just use a bigger PTFE tube(2mm ID) for the hotend?

IMG_20190111_195849389.jpg

Re: Please help me with my MMU2

it failed again with a tip that measures at 2.03mm ramming at 2.5 seconds temp pat 210. is there a reason not to just use a bigger PTFE tube(2mm ID) for the hotend?

I would go by 5C, like 205C, 200C, 195C
Sure thing, changing PTFE tubes is also an option. Couple people are doing that instead.

Re: Please help me with my MMU2

So I've been messing with this thing since writing this post and I'm in the middle of a print now. I'll let you know how it goes. So far (since last post), I've swapped back out to the original prusa mk3 heat-break (vs the E3DV6) and swapped to the original prusa nozel. When I started this print, on first load I got just a bit of grinding at the hot-end that seemed to correct itself by the time it got halfway through the pre-load sequence and was printing fine by the time it got to the purge block.

I've got my fingers crossed.

-Lynn

Re: Please help me with my MMU2

Well, it failed again, which sucks! The one bright spot, no grinding. This time it was failing at the load/unload sequence, and was successful up to about 25%.

Tips still seem to be good, so back the the drawing board...

Re: Please help me with my MMU2

is there a reason not to just use a bigger PTFE tube(2mm ID) for the hotend?

It is the "hot end" PTFE tube which determines the tip size. Increase the number of cooling moves and slow them down so that the tip is fully cooled in the smaller PTFE. It may be that your hot end PTFE tubing is stretched and may need replacing (with the smaller ID).

Peter

Re: Please help me with my MMU2

is there a reason not to just use a bigger PTFE tube(2mm ID) for the hotend?

It is the "hot end" PTFE tube which determines the tip size. Increase the number of cooling moves and slow them down so that the tip is fully cooled in the smaller PTFE. It may be that your hot end PTFE tubing is stretched and may need replacing (with the smaller ID).

Peter

We need more this type of explanation. There are numerous parameters in the slicer. People are just guessing what they do. I can't emphasize more the need of a detailed slicer manual.

Re: Please help me with my MMU2

is there a reason not to just use a bigger PTFE tube(2mm ID) for the hotend?

It is the "hot end" PTFE tube which determines the tip size. Increase the number of cooling moves and slow them down so that the tip is fully cooled in the smaller PTFE. It may be that your hot end PTFE tubing is stretched and may need replacing (with the smaller ID).

Peter

We need more this type of explanation. There are numerous parameters in the slicer. People are just guessing what they do. I can't emphasize more the need of a detailed slicer manual.

+1 from me. Until now I thought the tip is being cooled in the cold end (the cold side of the heatbreak).

Re: Please help me with my MMU2

I thought the tip is being cooled in the cold end (the cold side of the heatbreak).

Yes it is; the PTFE is located within the heat break close to the bottom of the heat sink.

I believe that the first (fast) unload after ramming is 15mm. This leaves a substantial amount of melted filament in the melt zone, thereby leaving the tip about 10 to 15mm above the heater block; just about at the bottom of the PTFE.

However after some use, the smallest ID of the PTFE is near to the top of the heat sink - where the PTFE lock is located. This is the place where you want the final cooling to happen, but it's difficult to achieve in Slic3r 🙁

Peter

Re: Please help me with my MMU2

I also miss a brief explanation how the whole tool change procedure works.
So far I saw following procedure:
1. Load to the extruder (before the gears) by MMU
2. Load into the nozzle (new filament is being pushed into the nozzle)
3. Purge
4. Print
5. Ramming
6. Pull out from the nozzle only couple millimeters
7. Cooling
8. Unload from the extruder
9. Retract by MMU

Please correct if I'm wrong somewhere.

It will be great to assign and/or mark the Slic3r settings to the specific steps so it's easier to understand what exactly you're changing there. The bare description what we have right now is more or less "try and see" approach.

Re: Please help me with my MMU2

I also miss a brief explanation how the whole tool change procedure works.
So far I saw following procedure:
1. Load to the extruder (before the gears) by MMU
2. Load into the nozzle (new filament is being pushed into the nozzle)
3. Purge
4. Print
5. Ramming
6. Pull out from the nozzle only couple millimeters
7. Cooling
8. Unload from the extruder
9. Retract by MMU

Please correct if I'm wrong somewhere.

It will be great to assign and/or mark the Slic3r settings to the specific steps so it's easier to understand what exactly you're changing there. The bare description what we have right now is more or less "try and see" approach.

OK, not quite:

1. MMU loads filament to precalibrated distance
2. MMU and Bondtechs start to load filament into extruder
3. Bondtechs finalise loading into nozzle
4. Purge
5. Print
6. Ram
7. Quickly retract 15mm
8. Cooling
9. Unload too much to ensure filament is above Bondtechs
10. MMU unloads to sensor
11. MMU unloads to parking position according to set distance compiled into firmware

Steps 2 to 9 can (to varying extent) be controlled within Slic3r

Peter

Re: Please help me with my MMU2

it failed again with a tip that measures at 2.03mm ramming at 2.5 seconds temp pat 210. is there a reason not to just use a bigger PTFE tube(2mm ID) for the hotend?

I would go by 5C, like 205C, 200C, 195C
Sure thing, changing PTFE tubes is also an option. Couple people are doing that instead.

so as a follow up to this i did order some extra hotend PTFE tubes that are 1.85mm and now i am getting tips around 1.90mm. it would seems that if you have a stock MK2.5 like me you need this tube as the heat break is 2mm ID. my printing has improved as a result of this. but i am still running into issues. i think part of my problem now is related to the filament sensor cap. i have printed the the following and i am trying it out now.

https://www.thingiverse.com/thing:3129388

Re: Please help me with my MMU2

so nice update. the PTFE tube ended up getting stretched out again and tearing down the hotend confirms that the tip cannot be re-inserted into the heatbreak. so does anyone know what can be done in terms of settings to keep the tip from getting too large? it kind of sucks if the PTFE tube is going to be a consumable part.

Re: Please help me with my MMU2

There are various work-arounds for this already posted here.

A couple I use is to use a 2.5mm ID "Bowden" and taking this tube into the top of the extruder body, removing the lower Festo and optical filament sensor.

Peter

Re: Please help me with my MMU2

There are various work-arounds for this already posted here.

A couple I use is to use a 2.5mm ID "Bowden" and taking this tube into the top of the extruder body, removing the lower Festo and optical filament sensor.

Peter

my mistake. i was referring to the PTFE tube that sits in the hotend. the one that has an inner diameter of 1.85 mm. also i dont get how i am supposed to limit the tip size so my filament wont get so big in the first place?

Re: Please help me with my MMU2

my mistake. i was referring to the PTFE tube that sits in the hotend. the one that has an inner diameter of 1.85 mm. also i dont get how i am supposed to limit the tip size so my filament wont get so big in the first place?

No, not your mistake.

The hot end PTFE will wear down/expand, but after a time it does so much less. There's not much point in changing it every few weeks if you can work-around the problem, hence my answer.

There are other things you can do to help reduce the expansion, like slowing down the retractions and cooling movements, but it will always happen.

Personally, I have just accepted the wear and allowed the printer to work "normally" with slightly larger tips - up to about 2.05mm diameter.

Peter

Re: Please help me with my MMU2

my mistake. i was referring to the PTFE tube that sits in the hotend. the one that has an inner diameter of 1.85 mm. also i dont get how i am supposed to limit the tip size so my filament wont get so big in the first place?

No, not your mistake.

The hot end PTFE will wear down/expand, but after a time it does so much less. There's not much point in changing it every few weeks if you can work-around the problem, hence my answer.

There are other things you can do to help reduce the expansion, like slowing down the retractions and cooling movements, but it will always happen.

Personally, I have just accepted the wear and allowed the printer to work "normally" with slightly larger tips - up to about 2.05mm diameter.

Peter

i apologize if i sound rude but i fail to see how the bowden tube being 2.5 mm helps with the tip size. the problem is that my hotend PTFE tube(brand new from prusa with an ID of 1.85mm) wore out after week, allowing for the tips to get larger than 2mm. once this happens the tip cannot be physically reinserted into the heat break as the tips gets over 2mm in diameter.

what i am trying to find is sli3cr settings for people that have a working printer. it would be nice to get a slic3r config export to remove any doubt. but what has been posted else where seems to create the desired tip shape but at least in my case the HOTEND PFTE tube is now a consumable part.

my printer is a mk2.5 and otherwise completely stock with the exception of the following
the bowden tube is 2.5mm
selector has been replaced with this https://www.thingiverse.com/thing:3337120
the selector also has springs that other users on this forum are using and larger 2.5mm tubes