I'm finding it's either too tight and prevents the motor from driving the filament, or it's too and doesn't put enough pressure on it to allow the motor to push it.
If I do find the sweet spot, it works momentarily but it just loosens itself.
Has anyone had this or know of a good solution?

I too am finding it difficult to get consistent extrusion. Currently I have the extruder resting on a box outside the case, and it seems to help. I have a hunch the problem might be the bowden tube fitting pushing on the filament inside the extruder?

I don't know the Fisher 1 extruder, (I had a beta), but what I can tell is :
* The RRP hobbed insert (on the Fisher 1) is quite good and while pressure properly adjusted, it doesn't slip. It was used on all RRP printers (except Fisher Beta)
* The spring is properly sized

Before RRP issued the Fisher 1, I have designed a geared extruder with mounting and position on the Fisher.
It does have a gear ratio higher than the Fisher 1 (3.1:1 instead of 2:1), which makes it more powerful. It was commented that such gear ratio may reduced the retract speed, but with the 19V of the Fisher power supply, I think this is ok, notably because the gear I use are those of the Ormerod extruder, which use the exact same stepper with only 12V.
I made a version to use the bearings of the Fisher 1 (MR93) and I improved the bearing holding, which reduced the gear play. Also, now there are integrated supports, so you don't need to set supports in the slicer (I always forget it ...). The bearing holding is better with MR93 than with 623.
However, these are small parts that I do recommend to print in PETG and not in PLA.
The only complementary supply you need is countersunk head screws M3x35, which are not part of the bolts and nuts of the Fisher.
Edit: and two M3x40 screws to push the spring.

It is here :
[github.com]
with details on assembly here :
[rouzeau.net]

Edited 1 time(s). Last edit at 01/31/2016 09:39PM by PRZ.