Parts fitting clearances in acrylic and aluminum parts?

[jbarber]

Are there any standards or rules of thumb for machining clearances for slip-fit parts?

I'm currently making project parts from both acrylic and aluminum, and rather than guesstimating it would be handy to know for a given material how much tolerance to build in for fit. Thermal expansion/contraction, that kind of thing. I'd like to machine the parts for a good slip fit without slop, but not so tight that there's alignment and sticking problems during assembly.

I'm not a professional machinist, so please understand if I'm using the wrong terminology.

Thanks,
--jim