Massage Roller v2 - multiple rollers - smooth grip - Covid-19 usable - 50mm wide - with or without 608 bearings

This is a remix from https://www.thingiverse.com/thing:398515

I initially printed the 608 bearing version of the original design. After showing it to my physician, I decided to do a v2 to include all the recommendations I got:
- wider design (50mm), it easier for larger hands and to apply more pressure
- rounded edges of the shell, so it smother grip
- multiple roller designs to address different use cases (my physician prefers the regular spheres)
- COVID 19 useability: increased tolerance of the shell, so the roller can be easily disassembled and disinfected if you want to use it for professional purpose on multiple people. (Use No bearings roller or 608RS bearings instead of 608 or 608zz).

I also added some design improvements:
- rollers have a built in edge to make sure the bearing is not pushed in too much
- rollers have a solid core which normally speeds up printing
- improved tolerances on bearing to shell interface (less diagonal movement of roller inside the shell

There is also a "plain" roller included in STEP, so you can add your favorite surface if its not already there.

Assembly (see pictures):
- push the two 608 bearing im place (if you are using the bearing rollers)
- slide the two shells together while putting the rollers on the axles
- if you not want to disassemble the roller (COVID 19 use design) you might want to add some superglue to stop the shells from sliding open again

Upon request: No bearing rollers added. So if you dont have the 608 bearings ready or just want to use the massage roller occasionally, you can also use the no bearing rollers. The are also allowing for an even better disinfection. ......just add some oil and the rollers should spin as good as with bearings. You will just have some wear after hrs of use...

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