Cool idea!
Here is an idea I had for a feed mechanism. Please excuse the drawing I'm on hols with the family and only have the kids pens to work with
The sketch shows two taper wheels one being the drive and the other driven by the gear at the base of the taper. The filament in orange is pressed into the taper by a profiled bearing that is sprung.
The mechanism has two interesting benefits.
1. The bite provided by the two tapers should allow for much greater pushing force before slipping. (it's used on most feed systems for bar peeling where force and bit are critical)
2. Now this is the interesting bit. The taper means that a thicker filament moves out on the taper to a smaller diameter i.e feeds less. Thinner filament moves into the taper to a larger diameter i.e feeds more.
Point two should provide a more consistent flow through the nozzle with no need to monitor filament diameter prior to the feeder to correct for inconsistent filament diameter.
Now the angle of the taper is critical to the function of this system. I'm only at the idea stage so far and would really like to know what everyone thinks.
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My extruder had stopped pushing filament entirely because there was not enough pressure on it to move it, so I made an ugly hack mod to the existing extruder. It is printing/feeding very consistently now.
First, I printed a pulley type cover for the idler bearing (on a different printer, since my UM2 wouldn't print). It's a small circular pulley type wrap for the bearing which fits on it tightly. It is 2mm thick at both edges, and 1mm thick in the middle. Second, I cut away the entire left side of the casing between the two bolt holes, to remove all of the areas of the casing which might rub on the new, larger pulley/bearing assembly.
Here is how it looks now, with the nasty edges and everything. LOL
Edit: Oh, I also adjusted the metal filament drive cylinder so that the biggest teeth were centered on the filament while it rides in the groove of the pulley.
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