Most parts get cheaper on the drawing, not on the machine. These are the design decisions that decide whether a part is straightforward or expensive to make.
A rotating cutter leaves a radius in every internal corner. If the corner radius is smaller than the tool radius, the tool simply cannot reach it and the corner needs a second operation — usually EDM — at several times the cost. Design internal radii at or above the natural tool radius and the feature is machined in one pass.
Deep cavities have a similar constraint: a tool needs a length-to-diameter ratio to reach the bottom, and long slender tools chatter. Shallower is cheaper.
Thin walls deflect under cutting force and ring like a bell, which shows up as chatter marks and lost tolerance. Uniform wall thickness is far easier to machine than a wall that tapers from thick to paper-thin. Where a thin wall is unavoidable, we plan lighter passes and better support — but a design change is cheaper than a process fix.
A drawing that applies a tight default tolerance everywhere multiplies inspection and cycle time for features that carry no function. Tighten only the dimensions that matter, define datums clearly, and specify surface finish only where it is functionally required — roughness comes at a cost like anything else.
Every set-up adds cost and stack-up error. Design the part so as much as possible can be reached from one direction: features on one face, or on faces normal to it, are cheaper than features scattered across six sides. Where a part genuinely needs multiple faces, five-axis machining can often finish it in one set-up.
Aluminum and free-machining steels are forgiving; stainless, titanium and nickel alloys like Inconel are not, and engineering plastics behave differently again. Choosing the least difficult material that meets the functional requirement is one of the largest cost levers available — and one that costs nothing to pull early.