Making keyways in gear blanks. if you don't have all the big cutters.

[Toolmaker51]

re Your Keyways, Captainleeward...the arc shouldn't cause any issue. The depth at corner and width of slot are the real 'make or break' considerations. Width of course is a backlash type of action; hammering away at whatever is softer, wheel, key, or shaft. Depth is what keeps the key in place for greatest engagement of shaft and wheel.
Getting excess material out of the way is a challenge sometimes. Theory is fine, but can affect the final result, usually because there isn't enough to work the next cutter well. Drilling the material center is better idea than trying to drill small holes inboard of corners. Did you cut keyways in the lathe or by shaper vertically in the drill. Good too; but how did you regulate movement and depth of cut?