In this instance, the object is probably to produce a good surface finish, rather than to finish to a particular size?

If the bearing were pressure fed lubricated whitemetal (Such as Aluminium Tin, Aluminium/Silicon ), subjected to high rubbing speeds and loads, the clearances would probably be 0.002 to 0.004" (0.050 to 0.1 mm) with a surface finish of not more 6 micro inch Centre Line Average

The parts of a model are dimensionally small, so clearances of the order of 0..001 – 0.002" (0.025 – 0,05 mm ) would probably be more likely to be suitable.

In the case of a model, the lubricant is unlikely to be pressure fed, but to be applied manually to a steel / yellow metal bearing, not subject to high speeds and loads, but the pin will still need to be polished to a fine finish to avoid wear.

Barelling or taper, of the order of a few microns is unlikely to prove much of a problem.

Maintaining a small smooth radius in the fillets smoothly blended between pin and web will be beneficial avoiding stress raisers, although, again, fatigue failure should not be a worry in a model

The Great Western Railway were quite precise in their manufacture of locomotive parts, but when, many years later, King George Vth was rebuilt, it soon ran a hot box, because the clearances had been made too small!

Howard

I tend to finish crank pins with fine emery backed by a stick or flat metal bar which is a couple of mm narrower than the gap between the webs. Others tend to use a pair of flat sticks or oil stones and pinch the crankpin between those.