Simple rule of thumb is that when using the full width of the cutter don't use a depth of more than D/4 that's diameter divided by 4. You can go a lot more than this particularly as cutter dia increases but stick to D/4 for now.

So for your 1mm dia cutter you could go sideways if milling the half circle in say 0.2mm thick brass shim using a single pass but would not want to do that if it were 3mm gauge plate you were cutting. Even if plunging don't do it in one go with a small cutter like that gradually move the work sideways say 0.1mm per plunge

Either way do as suggested in the other thread and drill a 1mm hole then file or mill back to half way.

Edited By JasonB on 21/09/2020 17:34:59

put up a drawing

Again a lot will depend on thickness of the material being cut, if thin (less than 1/4 of cutter dia) make one pass from the end.

If thick then you have two options, firstly set the cutter to take the whole 1.5mm width then lower the cutter say 0.75mm then take a cut stopping at a specific handwheel reading which looks like it would be 4.5mm from the end of the work then back the cutter out of the work. Lower it another 0.75mm and feed in again to your handwheel position.

The other method for thicker work would be to use more of the side of the cutter but less width typically 1/10th the dia, So locate the end and edge of the work, move work 0.3mm sideways and then feed in to your set handwheel position then back out. move over another 0.3mm and take the next cut and so on. The disadvantage of doing it this way on a cut that does not go right to the far end of the work is that as you get towards the full width there will be a larger area being cut as you get to the handwheel position (cutter engagement) and this can make the tool chatter resulting in a poor finish on the curved part of the cut. The main advantage is it uses more or the cutting edges so you get more use out of the cutter rather than just blunt the end.

I would not use a plunge type cut for that shape.

Edited By JasonB on 21/09/2020 18:41:39

here you go Chris, the two methods I describe in previous post but using an 8mm cutter rather than 3mm as it's easier to see.

First option I'm doing all the required width eg half the cutter dia in this case 4mm by D/4 = 8/4 = 2mm height each pass

Second option hull height but 10% of cutter width 8/10 = 0.8mm per pass.

Both stopping 6mm in from the end.

Should not get any error unless user generated. I just used DRO as it was easier to show what was going on particularly doing it one handed.