Yeah, Yeah. I know this has already been done.
Here is yet another linear bearing that I designed for my Anet A8. This version is my attempt at a lower friction design. The contact surface area is about a third less than what you find in most other commercial versions. They fit tightly against both retaining rings so as not to slide around in the housing. They also fit snugly around the 8MM Rod
Measurements: All are for 8MM Rod
Standard Bearing: 15MM OD, 24MM L
Standard Z Bearing: 15MM OD, 45MM Long
Long Z Bearing: 15MM OD, 60MM Long (fills Motor and Idler Mount holes)
I printed them in PLA. See my settings in the Print Settings section. I have to tell you, I wish I had done this much sooner. No more bearing noise, and it almost eliminated ghosting. I had noticed during my first assembly that the cheapo metal bearings wobbled ever so slightly as they moved along the 8mm rods. This was the cause of most of my ghosting on the X and Y axis. Use a dry lubricant like Teflon or graphite in the bearing if needed, but no liquid lubricants. These are nearly friction free, and almost silent.
I tweaked my printer settings specifically to print these, so if you print them, you may have to tweak yours a little for as tight a fit as possible.
Now on to reduce my motor noise.....hmmmm