The most expensive feature on your part isn’t the tight tolerance — it’s the second setup. Every time a part comes off the machine and gets refixtured, you buy a new datum error, a new opportunity for scrap, and another slice of lead time.

What 5-axis actually eliminates

Simultaneous 5-axis machining reaches five faces of a prismatic part in one clamping. For a typical aerospace bracket with compound-angle holes, that turns four setups into one, collapses the tolerance stack-up to a single datum structure, and removes two inspection gates from the router.

When 3-axis still wins

Flat plate work, simple housings, and high-volume 2.5D parts rarely justify the higher spindle rate. If every feature is reachable from two opposed faces, a well-fixtured 3-axis VMC with a tombstone will beat 5-axis on cost nearly every time.

The rule of thumb

Count your setups. At three or more — or any true compound-angle feature — ask for a 5-axis quote alongside the 3-axis one. On complex geometry we routinely see 5-axis land 15–30% cheaper per part, faster, with better Cpk on the critical features.