The hardest part of machining a bevel gear - or any gear - is the spacing between teeth. You can make the bevel portion easily with a lathe (watch the video) - but you need a 4-axis mill to make the spacing, or at least to do it “the right way.”
Of course, it can still be manufactured with a 3-axis mill if the vise can be rotated precisely: put the gear on a shaft in the vise, cut a slot, rotate it the correct number of degrees, cut the next slot, and so on. The tricky part is when you run out of vise freedom - you have to align the gear again to continue cutting.
You can make it even better if your mill’s head can be rotated - this will allow a consistent depth with the bevel gear grooves, rather than being far deeper at the wider portion (which would reduce strength).
Or, if your vise doesn’t turn, there’s always trig - with a CNC machine, shouldn’t be too hard. However, a rotating head won’t help, so you will have a gear with deeper grooves at the bottom than the top.
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