Eccentric spacer for Raise3D N2 extruder

UPDATE 03/02/16: I have replaced the original with a new version that can be used with a spring to dynamically tension the pinch pressure. This version requires that the original M3 12mm screw be replaced by an M3 18mm one. I replaced the acrylic cover thumbscrew with a longer cap screw and added a printed grooved spacer, also included here, to hold the spring. This version of the eccentric spacer also has a thinner shoulder that sits on the bearing inner ring and a bevel coming up from the bearing in order to help keep the filament from coming off of the flat bearing.

This eccentric spacer attempts to address a filament slippage problem with the fixed distance pinch mechanism on the Raise3D N2 printer. It requires swapping the original v-groove idler bearing with a 5mm x 10mm x 4mm flat bearing and drilling out the cavity over the bearing in the acrylic front plate. Once installed, the pinch distance can be adjusted by loosening the screw, turning the spacer wing, and then holding the wing while retightening the screw. I plan to make a scale that attaches to the acrylic plate to make it easier to keep track of known good pinch settings for different filaments. I will also try a version with two wings, for better grip while tightening, and upload that one here.

Print Settings

Printer:

Raise3D N2

Rafts:

Yes

Supports:

Yes

Resolution:

.1mm layer

Infill:

50%

Notes:

I printed this in PLA, but I plan to print one out of a stronger, higher temperature plastic - either nylon or PC. I printed it with the top down, but it would be worth trying it on its side with even smaller layer height. Also, if you can print with a narrower nozzle, that would probably be a good idea.

I used this bearing: http://www.amazon.com/gp/product/B00ART39CU

I drilled out the cavity in the acrylic plate using a standard 1/2" drill bit.

I drilled out the spacers after printing with a 3mm drill bit.

How I Designed This

This was inspired by a post by Ben Roj on the Raise3D community forum, where he described replacing the v-groove bearing with a flat bearing. I suggested the possibility of an eccentric spacer and then designed one to be machined, and I printed a test version of that one and also machined a test version out of brass. As my design evolved, You choi Cheung suggested the idea of making it thumb adjustable, and I came up with the winged version.