Cutting double keyways

[protrxrptr17]

I need some pointers on cutting double keyways in a shaft. Its a 2 7/16 with 5/8 keys 180 degrees apart. I've been doing it by scribing lines across the end with a center finder and lining it up with a level. Theres gotta be a better way. It has always worked out OK, but I just don't feel like its the most accurate way to do it. I'm cutting it with a knee mill and a 5/8 end mill. The lumber mill is waiting on me right now, so a quick reply would be much appreciated.

[Andre' B]

I have clamped a large V block to the shaft, and cut one keyway with the block sitting on one side on the machine table and the shaft clamped in a vise. Us parallels and shims as needed to level things up.
To do the other keyway just turn the shaft over so the V block is sitting on it's other side.

Even if you do not put the keyway perfectly on center the second one will be exactly 180° as long as it is a good V block and you do not change the distance from the cutter to the fixed vice jaw.

[Mcgyver]

on smaller shafts I've done the V block thing, but that’s a big one. Why not clamp to the table, in a t slot, and use a keyway cutter, run it up and down both sides with one set up....it'll do a better job than an endmill. Move clamps as necessary to complete

[crabbass]

On long pump shafts with keys spaced 180 apart, I have used a Miracle Point.
It is a magnetic Vee with a point to the centerline of the shaft. It has a mercury balanced dial. This isnt my preffered method, but the miracle point is a damn handy tool in the shop