α≈4

The taper is 4.

You roughly make an isosceles trapezoid, then make a high line, and in a right triangle, solve it with the tangent value. You are (12-5)/2. Don't you understand? Just make a picture and you will understand!

My major is also mold design and manufacturing. Mathematical knowledge is needed in many places of molds. So don't forget math @! The key is to draw the picture, so it is easy to understand!