I understand your frustration. Making and threading holes is harder than most people think, especially when thousandths matter. Making and threading the holes first is a good strategy to overcome that difficulty because you can then accurately machine to the threaded hole locations.
If you can't make it precise make it adjustable.
When you can make things anyway you desire, do so.There are features commercial tools will never get, DIY opens that door.
I don't mind them tapped thru. Set narrow side in vise against a stop, and clock that for center line, long as they are close to equal width. However, this second operation can bulge the size enough to not fit slot anymore. Vise-held keeps that under control.
If you tap first, do them in pairs, triplet or more in length. Mill them into central not on parallels, but 2 equal size small drill blanks in the holes, and punch mark one side beforehand to keep track.
Make some as long as possible that still fit coolant trough. They have room for more than one thread size; very handy.
Total height ~.030-.050 shallow of flush, so they don't protrude as the stud pulls them up. Gage from corner edge, overall height is rather inconsequential.
A good chamfer on the bottom 4 sides & corners, and 4 corners of the actual 'T' makes life easier, lower edge just broken; functioning as partial T-slot cleaners.
It's worth sliding each ALL the way through each slot. Previous users of the machine could over tighten hold-downs and burr inner edge of slot.
No commercial T-slots are made to fit better than you can DIY, but casehardening or heat treatment is one advantage they have. Plenty of us do that too...
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Last edited by Toolmaker51; 08-12-2020 at 11:09 PM.
...we'll learn more by wandering than searching...
Paul Jones (08-14-2020)
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