Based on feedback from from Guy153 I’m still showing a design using laser cut sheet metal brazed together. Based on feedback from JMY the max delta is 34mm, with 17mm also. Based on other posts in this forum I focused on 160mm and 180mm rotors. The dropout body (w/o the braze-on flat mounts) is 154g, vs a Paragon offering at 115g for comparison.
The 160mm adaptor’s threaded and non-threaded holes are deliberate. Via shifting the adaptor 17mm the caliper is shifted 17mm. Via then rotating the adaptor 180 degrees the caliper can be shifted to the final 34mm. The hex screws’ position and direction is like a puzzle, but I think I got it correct.
I needed the 180 adaptor to have height to allow room for the hex bolts to be threaded into the caliper. Two of the upper holes are slotted to help wiggle the hex bolts into place, but at least one caliper bolt is always in a non-slotted hole.
The bottom image demonstrates a rotor at the longest effective CS for a 160mm rotor, and the shortest effective CS for a 180mm rotor. Not at once…just showing spatially the two extremes that the rotor translates. The math says the derailleur would need an extra 6 links of capacity to accommodate the two extremes (34X2 / 25.4 X 2 [links per inch] rounded up to 6).
This meets my goal of the rear axle passing through an actual 12mm hole integrated into the frame for robustness, vs a flip chip or sliding dropouts. I otherwise cast no doubt on those designs. I really do now like the “go big” option of 34mm, and now think of 17mm as more fine tuning road/gravel, which was and remains my motivation. It’s sort of the dropper post of CSs, if you know what I mean.