Hi Jonathan,

massive thanks for your answers. Here's a quick 3d drawing I've made to show the concept:



The orange bit is the bottom of the bearing which is pressed / pushed into the MDF. The light blue is the top of the bearing which sits against the shoulder (green, which will be higher up the shaft). The drawing is missing the locking nut above the bearings (the red sections).

I'll keep the points the same and fill them with my comments:

1) The seat I mentioned before will be 12mm deep so I'' be able to push the whole outside element of the bearing in it. The inside element (the rollers) will be pressed against a shoulder on the shaft. I reckon I can use a shaft collar to act as a shoulder? Then again the whole shaft will be machined, so adding a shoulder shouldn't be too hard

2) The reason I was asking about precision is because I've read about problems with alignment on diy CNC machines. I know it's probably harder to align things which are far apart as a small error grows as you move away from parts.

3) Am I correct to think that with this approach the shaft needs to have a thread on one side of the bearing? I've marked those in red on the sketch above. A 20mm shaft can have an M20 thread on it, but in order to get the nut where it should be there needs to be thread all the way up the shaft or the shaft needs to be thinner to let the nut through. Please correct me if this is utter rubbish:)

Cheers Jonathan!

Regards,
dsc.