I have make a little test with 4 dots aligned with A tower, B and C tower. Distance W and S are the same in the stl but not in the print. I have tried diferent values of diagonal root but S always is smaller than W, and all S are equal (more or less 38.20mm) and all W are equal (more or less 40.80). I expect that W and S will be 40mm. How can fix this problem?
Here is the stl I use: https://www.dropbox.com/s/2vwjbo387cmk5qa/DeltaCalibration%20v15.stl?dl=0
Update: I have replaced the steper motor in tower B but same result.
Well, you have two main issues:
1.- Your calculation for stepping is a little wrong, for example your firmware indicates 2315.84 when you need 2321.70 (REMEMBER this is an example and is not accurate), So you will see a diference about 2.0mm along your printing. If your printing is bigger more diference you will get.
2.- Misalignment, your printer is not angled correctly to 90° and also Z axe if has the same condition. with this uncalibrated parameter are you going to have pisa towers on every tall part. For delta Printers this not apply
3.- Tension. Your belts are a little weak; avoid weak tension band to eliminate something called backslash, of course this is for screw parts but is the same efect and even bigger. Also you will get an accurate dimension of the parts.