Reamers

A set of small tools I bought relatively late is a set of reamers. A reamer is a five sided, sharp edged, tapered steel tool. With it you can ream, widen, holes that are too tight. Good etched always make their etched holes too too small. The accuracy of the etching process is not predictable enough to etch holes exeactly to size. So having a good kit neccesitates a reamer set. Drilling then? No, drilling is less accurate. If you want holes to have a perfect fit, ream them. And the more accurate the holes, particularly in the driving components, the better the performance of your loco.

My set ranges from 0,65 to 4,0 mm. The reamers overlap in size.
As said, a reamer is tapered, but only slightly. Once you made one hole to a perfect fit, which needs patience and a lot of trial fitting, mark the depth on the reamer and you'll be able to reproduce this hole size endlessly.