Ok... I have been annoyed with the results when engraving on my little Taig CNC mill and I decided to make sure my mill bed was level end to end and front to back. A block of left over 3/8 aluminum plate, a couple Heli-coils, and some left over 1/4 x 20 field bolts did the trick. I whacked the aluminum on my miter saw, and drilled the holes with my cheap wobbly HF drill press. I spent some time thinking about it, and then basically freehanded the entire fixture from start to finish in about 20 minutes. I didn't measure anything. Just cut, drilled, and tapped. I did roughly level the block to the drill press.
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Net result