Cutting Odd Angles

This finderscope Bracket that I am trying to reproduce in acetal and not glued back together aluminum has one annoying aspect: the base is sort of a dovetail with a 77 degree angle on each side.  After a lot of struggle (geometry was the only B in high school) I believe that I figured it out.  The tilting table is set to 13 degrees and I positioned at the top of the rectangle and went down .09".  (This was determined by measuring, not by trigonometry. )

I think it worked.  This is the first side.  

Yes, the acetal is still a few hundredths too thick, but I want this to be a press fit into the receiver.   The angle feels right.

I cut the other side by moving the part and the tilting table until the angle was right.   I reversed the part in the tiny Sherline chuck that fits inside the Sherline tilting table, then moved the table to 77 degrees.   I experimentally achieved what opposite angles of crossing diagonal lines are equal should have told me.

It is not a press fit into the slot but is a heck of a lot tighter than factory.  

Another improvement is that the OEM part was held in place by friction from an M3x0.5 thumbscrew.   I am going to tap a hole for a thumbscrew in this part to screw into instead.  Far more secure.