That was probably the most pressing question I wanted answered, when I got a mill. And the answer seems to be 0,01mm if your very careful.

Not the accuracy of the mill itself - I felt very sure, that straight out of the crate, the mill would be way out of tram, and that certainly was the case! Rather, given a properly trammed mill, to what tolerances should I be able to machine stuff? Give and take how many tenths, hundreds or thousandths of a millimeter should I reliably be able to produce a part of a certain length, width, or height?

Part of the answer was pretty straight forward. Commonly available - and affordable - measuring instruments (calipers, micrometers, height gauges) have a resolution of 0,01mm (digital micrometers and some dial indicators resolve to 0,001mm) and with a repeatability of about 0,03mm - so the answer is at least close to those numbers.

The other part of the answer was found in this very excellent categorization over at CNCCookbook of which measurement instruments are usable when working towards different tolerances, and his personal notes on what tolerances he can achieve on his IH mill (a very nice RF-45 clone) given 10 years of experience.

Straight out of the crate, the column of my SX3 was 0,6mm out of tram over a range of 250mm side-to-side. My target for tramming the column is 0,01mm over 150mm.

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