Magnetic PTFE couplers with wire shelving brackets

I've found myself disconnecting and reconnecting PTFE tubes more times than I care to admit. Often it was to extract some wayward filament, but sometimes it was because I sliced a print to use filament #2, but this time, I want to use filament #4 instead without reslicing.

These magnetic couplers do an excellent job of helping keep multiple PTFE tubes organized when one needs to remove and reconnect the tubes with some frequency. They are particularly excellent for connecting my auto-rewinding spool holders sitting on wire shelving above the printers with the MMU2S's inputs.

The couplers come in two configurations. The wire shelving bracket has clips designed to fit the smaller bars of the shelving. The regular couplers can be screwed onto a standard 4mm OD PTFE tube. The threads inside the coupler should provide just enough grip to hold on well enough without deforming the tube.

Each configuration is available for use with 6mm or 8mm disc magnets (3mm thickness). Additionally, the Fusion 360 designs are available, and the designs are parameterized allowing for further customizations.

 

Embedding the Magnets

When slicing the print with PrusaSlicer, you want to find the first solid layer that will print over the magnets' holes. Looking at the G-code renderer, at 4.0mm, we see:

 

And at 4.2mm, we see the bridging across the holes:

 

After slicing your print, adjust the Z height in the renderer to 4.2mm, and right-click on the plus sign next to the height. There, choose “Add pause print” or “Add custom G-code”. I found that adding my own custom pause code was more compatible with OctoPrint. When printing, the printer should stop before beginning the layer at 4.2mm, move the nozzle out of the way, and let the extruder cool down (the bed should stay heated). 

 

⚠️	The current 3.10 version of the MK3S firmware seems to have an issue with continuing the print after it's been paused. Please keep this in mind when you print your couplers.

 

Here is the custom G-code that I use:

; Print informative message
M117 Place magnets
; Pause the print
M601
; Wait a period of time, just in case for OctoPrint
G4 S1

 

There are two recommended configurations for the magnets:

 

Heterogeneous

Magnets are placed alternating north and south sides up. This allows for any connector to mate with any other, however a 90º rotation may be necessary to align the magnetic poles. (This is how I've set up my couplers.)

 

 

 

 

Homogeneous

Magnets are placed either all north up or all south up. This allows for easier connections, but you have to ensure that you are mating a north coupler with a south one. I recommend printing the couplers according to their polarity to make it easier to match them up.

 

 

After the magnets have been placed, use the printer's menu to resume the print.

 

For the back of the MMU2S, I used short PTFE tubes, alternating 70mm and 85mm to allow room for the couplers (as they are much wider than the existing spacing).

 

Sharing from my own experience, I did not find that these magnets are strong enough to use them between the MMU2S and the extruder as they would separate upon sufficient force when the filament reaches the extruder gears. Stronger magnets would likely help, and there is an existing accessory that may work well here.