I was perusing a bearing website to locate some high-quality bearings to use for idler pulleys because I'm sick of crunchy bearings. Then I discovered these magical needle bearings tickling my creative mind. Little bit of tinker-cation and I determined the right combination of components to replace the current ball bearing setup with needle bearings! No more crunchiness!
What is needed:
(3) Drawn cup needle roller bearing ID:8mm, OD:12mm, W:10mm
(3) M6 x 12mm Shoulder Bolt
(3) M6 Locking Nut
(1) Grease (Optional)
UPDATE - 2018-06-02
I've converted all my machines back to normal pulleys and here's why. I love the durability of needle bearings and never once encountered a failed bearing. Unfortunately, the bearings don't have sides and the belt will likely gravitate to one end which will wear the belt, make awful rubbing noises, and (the deal breaker) skew the accuracy of the print ever so slightly. I'm constantly fiddling and printing new washers or squirting some sewing machine oil to quiet the washers down (even though I printed graphite ones). It's just not worth the hassle.
UPDATE - 2018-04-26
V5 - I've been running this for several months now and I think I have them down to a science. Applying the KISS principle, you really only need 2 washers and I would recommend either buying nylon washers from the hardware store or printing with a self-lubricating material like IGUS or even Proto-pasta's conductive filament (it's a graphite composite and what I'm currently using). You can tap the plate, but I can tell you the metal is soft and will cause the post to bend (which is why the previous designs were failing me). I do recommend the greasing the bearing since the needles are exposed.
UPDATE - 2018-02-25
V3 - Tapered for guiding and form fitting around the head of the bolt. No supports are needed. I just printed and installed on latest TLM rebuild and am VERY happy with the results!
I'm currently using Proto-pasta Conductive filament since it contains graphite.
I used an M6 tap to thread the hole (no drilling required). If you purchase the hardened steel shoulder bolts it'll self-tap since the bracket is soft aluminum. Put a dab of grease on the shaft or inside the bearing, assemble based on the image, tighten the shoulder bolt enough the washers and bearing move freely and use the locking nut to keep it in place. Enjoy!