Hey Martin,
by wanting to reproduce your precisely determined gap, you place a demand on precision from the machine. You should consider
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that a hand trim router is the cheapest type of milling motor you can ever get (and it’s not even allowed for use in a stationary machine).
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Due to the design of the Onefinity and the position of the trim router, the cutting edge of the cutter is unnecessarily far away from the attachment point on the Z-axis (and therefore also from the X-axis), resulting in unnecessarily high leverage force exerted on router/Z gantry assembly, and subsequently in more freedom to be diverted by the counterforces during milling. One would like to clamp the router closer to the bearing to at least reduce this distance a bit, but this is not possible because the router would then hit the top of the z-stepper’s cage:
If you think of switching to a serious milling motor aka spindle, be aware that with 65 mm stock motor mount, the problem with the motor not clearing the stepper will persist:
Image: A 65 mm spindle does not clear the stepper and therefore has to be slid much downwards inside the 65 mm stock motor mount in order to not bump the stepper cage with its back 