Square hole round peg.

image of alumium part

It is hard to cut a square hole with a round tool. Here are some tips that might help you get close.

Types of Machines

image of cnc mill

The following is a breakdown of various types of mills and lathes that might be of use to you when designing parts and looking for machine shops that can fabricate them.

The Ideal Part

image of a part and some calipers

If you as a designer can limit yourself to as few setups as possible the cheaper your part will be.