Trigonometry help please, plunge depth for a v cutter!

[Jonathan]

I didn't consider the flat spot at all. Wouldn't have been a disaster, but wouldn't have been correct either!
I asume if I use an insert v bit (such as CNC V Groove Miter Fold & Signmaking Insert Router Bit by Amana Tool) then I could just use Z=d/(2*tan(a/2)) as there would be no flat spot?

There's always going to be a flat of some sort, but for the tool you linked to I expect it would be neglegible. You might as well use the formula with the flat in your program, and just set f to 0 if the flat is insignificant as that results in the same formula as for without a flat.

If you've got the tool to hand, then one way to measure the flat is to spin it round and move the Z-axis down until it just touches. Retract the Z-axis and measure the diameter of the circle left - that's your f.

(haven't seen "LetMeGoogleThatForYou" before! Almost spat coffee on my keyboard when I clicked it!)

It's temping to link people to that quite often