Didn't get a lot done today but did come up with a more predictable process. All 4 posts now have tenons milled on them. Sorry, too dark when I finished to take a picture.
I did spend considerable time getting two mortises housed and fitted. That was the most predictable process. First I draw out the post position on the header. Then I mark of the center of the holes to be drilled to hog out the waste. I set out the outline with a 1 1/2" chisel and a dead blow hammer.
After drilling the holes, I chopped out the waste. Getting holes to the right depth eluded me for a while until my brain kicked into gear and I set a few gauges to measure the depth. Trying to remember numbers and read rulers each time is a recipe for error. Set the gauge and then I don't need to remember the number.
Part of the problem was that I intended to house the post and that 1/2" more in depth didn't translate to the hole depth until the first tenon didn't fit for depth! Re-drilled and cleaned out the bottom and I was good to go.
Somebody mentioned no routers up to this point. Well, here you go! I sawed the housing for depth and then set the router bit depth to clean out the housing.
Purty, ain't it?
And, the final fit.
Next up are the knee braces. This out to be interesting.