Let's see, if I were going to make that the first thing I would want to know is how many need to be made. If it's just a one off then the steps involved are no big deal, but if making a lot of them then the steps involved would be critical.
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Ok let's see, back to reality. I don't have a Taig, but I'm sure you could pull this off with a Taig being that the part is so small. I'll assume you want to make a lot of them. I'd use this end mill:
That keeps you from having to make tool changes. As for clearance, humph! Well, I went to their site and they don't give any detailed specifications for their machines! That's strange. Oh well, in any case that end mill I'm recommending, or something similar, should be long enough and stiff enough to get around the clearance concerns associated with the chuck in the Z axis. Also, you'll have plenty of room to hold it in the chuck and still have clearance in the X axis. You'd be doing four operations at 90 degrees as you proposed.
They are stating 0.0005 inches repeatability! Ok, if that's true then you won't have to ream those holes out for the press fit bearings. But you could play it safe and leave 0.0015 inches of material and hand ream them to size. Or instead of making round holes you could make holes with undulating side walls varying by 0.0001 to 0.0005 inches from the 0.250. That would be a little harder to press the bearings in but it would work.
As for the center hole, yeah, I would do that separately on a lathe. I would start it with a center drill, then drill slightly smaller than the 0.275 and at a depth of about 0.250 and then I would use a 0.2756 or 7 millimeter end mill to square off the bottom and bring the ID to 0.2756.
Once the drilling was done I would part it off a little longer than 1 inch.
I'd also make an appropriately sized slightly smaller OD end stop to reside in the chuck to keep your 0.750 solid round bar stock in the same position for each operation.
Things I'm wondering about are:
What RPM will this turn?
How many do you need?
How strong does it have to be?
It's so tiny I'm thinking that it's not going to encounter very large forces. And there may be the possibility that you could make a silicone mold using the lost wax process and then centrifugal cast them in a low temp metal alloy or even a strong plastic casting resin. Also, along this line of thinking is the possibility to cast them in situ and have the whole assembly already assembled right out of the mold.