I used a C12-ER11A-100L cut to length and cut a 12×1.25mm thread on the end, pressed/glued (Loctite) the connection rod into the end of ERA11 (a little more than 8mm diameter and turned it to 8mm after installation)
The bearing case is turned from 25mm Aluminium.
The biggest problems I had with the bearings. First I used IBU 7201 12x32x10 mm, but they get very hot after a few minutes at 30k rpm. Then I used noname(china?) bearings 61801ZZ /12x21x5mm, still very hot. Now I use FAG 61801ZZ bearings which stay cooler. Nevertheless I redesigned the printed parts to route the cooling air of the built-in fan of the brushless motor over the bearing case. The brushless motor sucks the air into the bottom holes and over the bearing case and blows it out at the top.
Don’t have much hours on it at the moment, so I can’t say anything about durability of it.
1. 1 Upper case printed part ABS
2. 1 Lower case printed part ABS
3. 1 Bearing case turned part 25mm Alu
4. 2 Bearing FAG 61801ZZ
5. 1 Collet chuck holder C12-ER11A-100L (cut to length)
6. 1 Connection rod Steel 8mm
7. 1 Nut self locking M12x1,25
8. 1 Flexible coupler 8mm to 6mm
9. 1 Brushless Motor Turnigy 600 H3763 Brushless outrunner 1330kv
Can give you the step files if you like.