Replacement IR sensor holder and selector for i3 mk3s mmu2s

by frimmel Apr 10, 2019
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I ordered the MMU2 the first day and got it very early. I have so many problems I almost tossed it. MMU2s helped but I still had problems. Your sensor tower allowed me my first unaided print since I bought it. I made one change for my setup. I lengthen the flag by .5mm.

I did the print and upgrade on Saturday, your design is better, my issues were solved. You can also add in your comments, that your design also is best in preventing filaments that generate particles, from interfering with the IR sensor's ability to read loaded filaments, leading to extruding stationary blobs/layers into the purge tower, ruining the print. Thank you again! I'll try some of your other mods!

...and how exactly did you remove the brass thread from the original cover? It seems to be melted into the part. I'm trying to use a knife to cut it out.

I used a soldering iron on low (or not fully heated) placing the til in the hole of the original cover and walking it back and forth until it cale out. I then used the soldering iron to push it into the new piece.


The brass thread is simply pressed into the plastic. I carefully removed the plastic using pliers bending and removing piece by piece (only took a few minutes) - as the mmu2s contained a NEW item, I did this on the OLD threaded item just to have the new as a backup.

Thank you again! Just to let you know, I had issues with the IR sensor reading the filament during the middle of a print, actually every 45 min into the print. I had the IR sensor on the LCD screen, just to monitor if it was reading the loaded filament, and what would happen is the sensor would sporadically stop sensing the loaded filament in between changing filaments for a print, and the extruder would just extrude a blob on the purger block. I had prusa send me a replacement sensor and when I installed it, the same issue continued. What I tried was stopping the print when this happened, and then I'd remove the idler door and blow out the extruder interior, then the print would resume, but because of the filament extruded into the blob, then the print would skip layers and was ruined.

I'm not sure if using 2 wood filaments created particles that would affect it's reading from time to time. I'm printing your design this evening. I'll share the final results.

Please clarify what you mean, 'print with the tower in VERTICAL position'. It looks perfectly set on the plater view in slic3r, as is, once it's loaded. And the sensor cover, should I re orient it so that it's printed face down, as it will be once it's installed?

I assume you could print it directly as when loaded in slic3r. However, I printed it (and designed some details) for printing it with the tower in vertical (standing) position, i.e. the same direction as it should later be mounted. And yes, please re-orient the sensor cover, thank you for noticing this.

Using the IR-sensor tower and the new idler (see separate thingiething), I successfully MMU2-printed an item with flex98, filaflex and ninjaflex in the same print. I would love to hear your response, if these items work out for you also. Remaining problem is the wipe tower - it still looks horrible and I need to adjust the wiping temperatures a bit.

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