sketching from a 2d blue print.

Ok, in my class we are following a book by Paul Tran. I had a question on why he chose to draw the part the way he did and my instructor and i seem to think it has something to do with machining the part.

Here is a picture of the part with fully constrained dimensions. It will be revolved around a center line to make a alignment pin.

Ok, here is what it will look like after the revolve, then i can ask my question.

So, here is my question. What was the purpose of the 59 degree line???? I could have made this part with a straight line rather than that angled line. If you look in the part through the smaller hole at the bottom, you will see the cone shape that the 59 degree line makes, but it serves no purpose for the function of the part.

So my original guess was that if the part is machined on a lathe, this is where the drill head would have carved out material. I have only had a few months exp with a manual lathe, but this is my only reasoning to why the book says to draw it this way. I do find it important to why i am doing what i am doing in this book haha. if i dont ask questions, then i am just taking pauls word for it..

thanks