@tgarr No worries about the thread digging, altough quite old, it is still as relevant as it was. In fact I just started a print with the exact same effector design as posted here. The 4th axis attachements are still evolving and I do have some minor changes planned to the effector design but noting major.
I don't use any special washers or something like that. Just the 6 screws (with a regular washer on top) that thread into brass heat set inserts.
In terms of calibration results here's the full DWC output string 🙂 . That is for a 180mm probe radius on a 400mm diameter bed.Calibrated 8 factors using 18 points, (mean, deviation) before (0.018, 0.046) after (-0.000, 0.043)
The results are certainly more consistent across the entire bed compared to the FSR's I used to use. I am honestly not sure if the 0.043mm deviation is considered good for a 400mm diameter bed.