small machining job??

[m_c]

The numbers that stick in my mind are 1thou per inch diameter.
1thou clearance for sliding fit, the same for press fit, or 1thou under for tight press fit.

Only way to get the exact size with a machine reamer is if it's perfectly aligned with the rotation axis. If it's off any, it'll cause an oversized hole, which can be handy, but also a PITA.

[AdieR]

You'll almost certainly need to ream out the 8mm, because you'll be lucky to find a boring bar that small - plus boring bars can "chatter" and cause poor sizing / finish. As a guide for reaming, the hole needs to be drilled 7.5 - 7.8 mm and finished with the reamer. Beware of putting an undersize diameter hole on an 8mm shaft, otherwise you may find they split and become damaged (esp with the 2 holes in the side, which will weaken it).

What are the two holes "pins or grub screws" for?

[Wobblybootie]

Thanks folks ... I have read all posts and will take the advice. Adie, the screws were to secure the shaft so that the sleeve and shaft turn as one. A member has agreed to knock these up for me and pointed out the same flaws in my design as everyone else did. So once again, thanks everyone, I will post to my build log/blog as progress is made, (Don't hold your breath though, my build is progressing with the speed of a striking slug!!)