I've been asked to make a new set of feet supports for a pedal steel guitar (think xylophone, only waaaaay more complicated. And with strings instead of plates of tuned metal in primary colours...). Each support holds the leg at 12 degrees, to widen the base for extra support. The originals are aluminium, and the threads are tearing out, so I'm re-making them in Mystery Steel.
Anyway, I've honed my block of metal down to the right overall size, and before I cut the L-shape out of it (see pics), I want to drill and counterbore the leg support section; as once I've cut away the excess metal, it'll be a pain in the arse to hold in a vice. I would use my sine bar for this, but it's too wide... and I don't know where the hell it is, so I'll just use one of those digital angle whatsits. Correct to the nearest degree will be plenty close enough...
Anyway... using the original counterbore, I can set the Y axis position easily enough. However, I can't for the life of me figure out how to set the "X" axis centre spot, given that it's all at an angle from the flat. All I can tell you is the top edge of the deep side of the counterbore in the X axis is 0.075" from the edge of the block... I would be able to use an edge finder on the low side (once the block's in the vice), so I guess it's just trig from there?