MMU3 / MMU2S MK3S+ PC4-M10 Extruder Anti-Twist Screw-Adjustable IR Sensor Adapter
Description
PDFThe aim of this is to both allow the use of a PC4-M10 (1/8BSP) PTFE pass-through adapter and eliminate frustration in calibrating the IR sensor.
As it was a much-improved version with the addition of an adjusting screw, I printed the MMU3 IR sensor Prusa printed parts. But I still found the adjustment process frustrating. The adjuster body rotates during calibration and even when accidentally bumping the chimney, altering the calibration setting.
In the Prusa assembly, the cover screw is used to both fix the chimney to the adjuster and fix the adjuster to the extruder body. The result is that after turning the adjuster screw and tightening the cover screw, the adjuster body tends to rotate, altering the the desired IR sensor adjustment. I can understand a reluctance to update the extruder body and motor plate as it creates more work and requires re-calibration of the printer.
The IR Sensor Chimney for the MMU takes a lot of space, making fitment of the PC4-M10 challenging. The PC4-M10 is buried deep into the extruder body, under the adjuster, with the PTFE tube extending down to bottom of the MK3S+ Adapter-Printer block.
A new 1/8BSP threaded Adapter Printer holds the PC4-M10 in place.
Both the Prusa extruder body and the Prusa motor plate (R6) have been modified to accept the enlarged Adapter Printer. The MK3S+ magnetic sensor and cover screw fixing voids in both parts have been filled in. This was necessary to accept new fixing screws for a modified IR sensor adjuster.
The MK3S+ extruder cover screw no longer extends into the extruder body.
Two screws have been added to fix the adjuster to the extruder body and eliminate rotation. This also prevents the new PC4-M10 – Adapter Printer assembly from moving vertically.
A new Chimney locking screw and nut are placed close to where the cover screw used to be. The adjuster body no longer rotates when this screw is tightened.
The IR sensor cables have been re-routed into a channel in the top-rear of the modified extruder body.
The adjuster body covers and holds the sensor cables in place.
This arrangement of the IR sensor adjuster is that the locking screw can remain tight when removing the adjuster sub-assembly form the extruder. This preserves the adjustment. I have removed the sub-assemble a number of times and no re-adjustment was needed when I put it back.
The Prusa MMU3 IR sensor adjuster and chimney were used as a starting point but have been heavily modified due to adding PC-M10 PTFE adapter, relocating the adjuster screw, chimney locking screw and the adjuster fixing screws.
Please note that tolerances on the adjuster and chimney are intentionally tight to allow all sliding surfaces to be smoothly finished using pin files, removing printing artifacts.
As the extruder body and motor plate are modified, the extruder hot end needs major re-assembly and calibration.
For me at least, this extra work is justified by being able to use the PC4M10 pass-through adapter and not have the IR sensor chimney / adjuster rotate both during calibration and when the chimney is accidentally bumped.
Note:
I recommend pin file finishing printed parts and per-assembling all new printed parts and hardware as a sub-assembly away from the printer. This will prove smooth adjusting operation prior to disassembly of the MK3S+ extruder and reassembly with the new parts.
Parts:
The PC4-M10 PTFE adapter was sourced her:
While two M3x20 screws are required to fix the adjuster to the extruder body, it is possible to use M3x25 screws instead.
The chimney lock requires an M3x10 screw and stand M3 nut.
The adjusting requires an M3x30 screw and M3x9x0.8 Mudguard Washer.
Three Thin Square Nuts, DIN562-M3, are required.
These were sourced her:
These are 1.79mm thick and should easily press into place. Prusa nuts, typically 1.72mm, will also work. I have intentionally not opened up the nut slots to accept out-of-spec 2.2mm nuts currently being sold on eBay and Amazon. Doing this makes the above nuts, and especially Prusa nuts, to fall out when the assembly is inverted.
The IR sensor, screw and Prusa chimney cap will be needed to complete the assembly.
I am using a modified IR sensor board with an LED and a clear cap.
https://www.printables.com/model/653244-led-state-indicator-in-chimney-cap-for-the-mmu3-mm
Assembly:
I have not provided detailed step-by-step assembly instructions. I recommend reading the Prusa assembly instructions carefully to gain a good understanding pf that process before attempting assembly of the new parts.
Options:
The front arm of the chimney has a small cross-section, making it somewhat flexible. An option would be to increase its width, over the top of the extruder motor body.
While that would make it stronger, there might be problems with some printers where that area has been used for other purposes, such as a heat-sink for the stepper motor. For that reason I have not made that alteration even though it would improve the chimney front arm strength. As it is, pin-filing a smooth operation is the best thing that can be done.
Model origin
The author remixed this model.
Differences of the remix compared to the original
- Enlarged Adapter-Printer with 1/8BSP threads to accept a PC4-M10 PTFE adapter.
- Added fixing screws for the IR sensor adjuster to prevent rotation.
- Re-routed IR sensor cable into a channel in the extruder body
- Modified extruder body and motor plate to accept the enlarged adapter printer and new fixing screws and removing the existing fixing screw nut.
- Modified chimney and screw adjuster for a central PC4-M10 PTFE adapter and re-located adjuster fixing screws.
- Creation of an IR sensor sub-assembly with dedicated locking screw and nut, able to be removed with the sensor adjustment preserved.
