Worked this as one solid piece for as long as possible--this made it easier to line up through holes and threads. Drew some guidelines in the layout fluid and spotted a few (three) hole locations. Did my best guestimation of fastener sizes based on available space.
First drilled the center mounting hole with a #36--this is the tapping size for a #6-32. Drilled approx. half an inch deep.
Followed by a #2 bit to slightly recess the head of the bolt. Drilled about 0.125" deep, leaving an angle at the bottom of the hole.
Ground the point off the #2 drill bit and sharpened a cutting edge.
Used the modified bit to counterbore (make a flat bottom) in the hole.
Not shown, a #29 drill bit was used to drill approx. 0.250" deep for the through hole for the #6-32 mounting bolt. Here, I tapped the #6-32 thread to the very bottom of the half inch hole. Confusing, I know. I did as many steps as possible to the single piece. If I'd cut it in half first, I'd have had to do two times as many set-ups--and had alignment issues to consider.
A #43 bit was used on the two smaller holes. Drilled approx 0.250" deep.
Tapped #4-40 to the bottom of the holes.
Mounted the piece in an insert vise and bolted it to the Taig's crosslide. Couldn't get more than a singe bolt to hold the vise down, so I backed it with a steel block anchored into the T-slots. The vise couldn't twist against the backer. The slitting saw was mounted in a homemade arbor.
Slow speed, slow feed. Lots of cutting fluid.
The clearances around the slitting saw were super tight...
but it worked. Sanded the parts down to 400 grit, then cold blued.
A 5-minute epoxy glued the level into the mount.
Installed the #6-32 screw. This provides the majority of the clamping pressure to the dovetail.
The two #4-40 screws installed.
Mounted on a Benelli target pistol.
The #4-40 setscrews still need trimmed flush.
Test fit the level on several different guns. Seems to fit well on all the various .22 dovetails I tried.
As the mounting bolt is tightened, the block wants to hinge upward slightly--like a V. The two setscrews are screwed inward to cantilever the base back down until it's flat.
Very fine adjustments--and clamping security--are possible by varying the pressure between the mounting bolt and the adjustment set screws.
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