I give up, this is too messy and difficult designing my own extruder, gathering the hardware, CADing and printing the parts, etc.
I found a good solution on ebay:
link to ebay extruder. It's a little pricey, but in the end may be the cheapest solution for me, who has been struggling forever to get a 3mm Kossel Mini kit to work (a kit I bought as a newbie; see the MakerGeeks Kossel Mini - Junk! thread. The only benefit from that is I am now quite knowledgeable about printer engineering since I have replaced or redesigned virtually every single part of that kit!)
Here is why I think this is best solution, point out any logic I screw up please!
--To maximize torque from my existing direct-drive (as a 3mm requires), I wanted to stick with my MK8 hobb. The 624UU was supposed to give me better backing than a (small) flat bearing.
--But, I found a very nice pre-built for 3mm. It looks like it comes with a larger hobb like the MK7. Normally that would give me less force from the motor, but I realized today that is also spreads out the filament contact, which improves gripping force without destroying the filament. Also, the backing bearing is huge so strong clamping forces won't cause as much pinch-off as the 624UU, despite its groove.
Of course, this puts a bigger load on the direct-drive motor I was trying to reuse, plus the driver and I am intolerant of chew OR skip, but this setup comes with a geared stepper, so I'm back to better grip, stronger torque, a nice quick-release and mounts directly on the frame without a bracket.
I was even today looking at the cost of switching to a 1.75 setup and selling or eating the cost of all my 3mm investments, especially the hotend, which I had ALREADY re-bought to replace the junky one from the kit.
It costs more than I originally wanted but I can keep all my 3mm investment, which saves me money, preserve the possibility of soft materials (which are almost impossible with 1.75 over a bowden), the extruder is a nice looking assembly, dual-spring adjustable-load with quick-release. They also have some nice-looking dual versions, which I am really interested in pursuing once I get normal printing working well. I immediate learned to HATE HATE HATE dealing with overhangs and support material, which always looks horrible after I trim it away, if I can even get to it.
As usual, money solves the problem, if you have it. I'm just really glad they had 3mm versions.
I already upgraded the chassis to all metal corners with 2020 extrusions so it is very square now, quite a beast. Hopefully this means I can run at high speeds too.
Wish me luck.
