cut the bar into blocks, milled the ends flat. realized i forgot to tram1 in my vise so not really square. but luckily, it doesn't matter for these cuts, and the previous cuts were done such that they should have ended up reasonably square anyway.2
i'll tram it in before i do the next operations; which will be narrowing down one side of each block so it fits inside the tubing of the table. then i just gotta pop holes in them, tap them, and cold blue them, then glue them into the tubes (would have welded them, but this alloy doesn't weld well, and i don't want to redo the paint anyway)
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tramming in this case means using a dial indicator to line up the fixed jaw of the vise with the left/right axis of the table. then, if you make a cut by moving the table along the front/back axis, which is square to the left/right axis, you will also make a cut square to the fixed jaw, and therefore square to the side of the part up against the fixed jaw.
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i machined the bars from the top, so the orientation of the vise shouldn't really matter. if i did it right, it should have just depended on the squareness of the vise ways to its jaw, and the ways being parallel to the l/r-f/b plane of the mill table