UPDATE 17DEC2017: I have added a new frame that is larger, "Spinner Press XL". This is to accommodate larger spinners but also because I've found it handy to use the press for other purposes entirely. Also, I have changed the thread pitch of the large screw. It now offers more mechanical advantage and is much easier to turn. I have removed all older designs to clean up the downloads.
I designed this to make it easier to press fit the bearings in to fidget spinners. It presses them in to be perfectly flush.
This works for pressing large ball bearings in to place as well. I tested it with 1/2" ball bearings. You can also use it to remove those bearings.
To use, hand press the bearing in to the spinner a little and then insert in to the press and turn the screw until it's flush. I have found it easier to insert the bearing from the top side of the printed spinner as the bottom tends to flare out a bit on the first layer of printing.
I over engineered this a bit as I wanted to ensure that I wouldn't break it. It's thicker because I didn't want it to bow or bend and I added material around the screw to prevent stripping of the threads.
1 x 608 bearing for main screw
1 x 5mm ID / 10mm OD / 4mm High bearing for removal screw
This is over engineered so you probably shouldn't need 50% infill. The standard 20% will probably be fine. I wasn't sure so I did 50% and it's super strong. You'll only print it once so you might as well just print it at 50% so it will last forever.
At 50% infill, it took me 5 hours, 41 minutes to print. 20% infill estimated at 4 hours, 30 minutes. 100% infill was almost 7 hours.
Print the new main screw bearing cap at 100% infill.
Print the new removal screw bearing cap at 100% infill.
DO NOT USE SUPPORTS! Support is unneeded and will cause a lot of issues in the threads
I tested the deflection (amount of change) when the main screw is tightened as tight as I could turn it and also without any pressure at all.
Not tight: Gap 24.8mm
Tight at 50% infill: Gap 25.1mm
Tight at 20% infill: Gap 25.6mm
So it looks like 20% infill is strong but it allows for a 0.5mm deflection. For the sake of a little longer print and a little more plastic, I'd print at 50% infill and never have to print it again.