Mill slide in what angle?

[tedahlenius85]

Hello, in what angle should the slide be mille on a Tanfo for red dot?

 

89’ or even closer to 90’?

What is the downside of going parallell with the top of slide?

[Yondering]

Mill it parallel with the plane of the top edge of the sights. You could set a thick straightedge on the sights and indicate to that, or just indicate to the top edge of the sights directly. If done accurately, a centered optic mounted that way will point the the same place as the sights. I'm not sure what the exact angle is, I haven't measured it. 

Edited September 24, 2019 by Yondering