How to make something like this?

[lateAtNight]

So... does that mean its impossible to have right (or right-ish) angles at the bits that extrude out of the circle?

[John S]

Why worry?
If there is a radius in the corner then machine the external part with the same radius to match.

You don't want supa dupa accuracy on something like this anyway, you need a bit of bag to make assembly easy. Normally on a design such as this one or often both sets of tongues are slightly tapered in thickness so as it's turned into position it locks. making parallel tongues means it can keep rotating and never lock into position.

John S.