Filament guide with runout sensor for Ender 3

This is a double roller filament guide with an optional runout sensor that uses the standard Creality (ender) end stop switch.

The guide can be attached to the X axis gantry without any screws. The runout sensor is positioned to be aligned with the stock extruder arm as well as to the all metal extruder arm in way that it avoids touching the Z rod.

The guide can handle both filaments running from the top (stock Ender 3) or from the side providing a smooth movement of the filament that reduces friction and increasing the effectivity and consistency of the extrusion.

I've attached the Fusion 360 Archives files 

Update - 19 October 2023

Updated the sensor case because after some use I noticed that due to the “sanding” effect of the filament on he dome nut I get false positives (as there is too much clearance between the arm of the switch and the bottom of the nut). I moved the switch 0.2mm closer to the hole so there is greater pressure that avoids these false positives.

Update - 2 November 2023

Updated the lower filament guide roller positions to better aim at the sensor hole as well as made tweaks to the sensor to avoid false positives (mainly by reducing tolerances on the guide hole)

Pringing

The model is optimized (designed and split into parts) that it does not need any supports. However, the some of the parts need reorientation before printing in order to be in their optimal printing orientation.

Can be printed in any material, I used Esun cold white PLA on the pictures.

Print two Roller and four RollerInsert. Everything else one.

I printed everything with 0.2 layer height with a 0.4 nozzle. The tolerance on the dovetail is 0.2mm.

Assembly and BoM

Filament guide (assuming both top and bottom roller guide is added):

• 2xM3 nuts and 20mm bolts
• 2x608zz bearings (one may be sufficient if filament is only fed from the top)

Runout sensor

• 2xM3 nuts and 16mm screws
• Creality endstop limit switch
• M3 Hex Dome Nut
• two small pieces of PTFE tubes (a min. 2mm piece and a min 10mm piece)

The screw holes for the runout sensor are covered with a 0.2mm high sacrificial bridge (to avoid supports). Those may needs piercing before inserting the screws.

Assembly is very simple, put the bearing into the Roller then the two RollerInserts go into the midhole of the bearing to adapt the hole to the M3 bolt. Then screw it to the Mount along with the RollerLock. 

The runout sensor and the guide can be connected by attaching the former vie the dovetail, the rest is self explanatory based on the pictures.

Once done the filament guide can be put on the X axis gantry. 

Not In case of using with one roller:

It is totally possible to use this with one bearing. But even in this case I recommend printing the 4 RollerInsert and use the bracket on the side to constrin the filament and to prevent it to potentially slipping off from the roller on a quick retract