Most of the cost of a machined part is decided before anyone cuts metal. A few choices on the drawing set the number of setups, the tools and the time on the machine. Here are the ones we see most often.

Internal corners

A milling cutter is round, so an internal corner always has a radius. Ask for a radius a little larger than a standard cutter, 3.2 mm instead of 3.0, and the tool can sweep through the corner instead of stopping in it. The finish improves and the cycle shortens.

Deep pockets

A pocket deeper than four times its width needs a long, slender tool that has to run slowly. If the depth is not functional, reduce it. If it is, widen the pocket or open one side.

Tolerances

• Put tight tolerances only on features that fit something
• Leave the rest at the general tolerance of the drawing
• Give position tolerances from datums the part can really sit on

A single ±0.005 mm bore is routine. Twenty of them on one part is an inspection project.

Setups

Every time a part is turned over, it costs handling and a small error. Features reachable from one side, or from five sides on a 5-axis machine, come off cheaper and more accurate.

If a feature is hard to draw a dimension to, it is usually hard to machine and harder to measure.

Send it early

A fifteen-minute review of an unfinished model often removes a third of the cost. We do that for free on every quote, and we mark up the drawing so you can see why.