Stickout is the length a cutting tool extends past its holder, and it’s one of the most powerful variables in machining because rigidity falls off dramatically as stickout grows. Tool deflection under cutting force scales with roughly the cube of the unsupported length — so doubling stickout makes the tool about eight times more flexible.
Why it matters
More deflection means chatter, poor finish, tapered or out-of-tolerance features, and shorter tool life. The practical rule is simple: use the shortest tool that can reach the feature, and choke the tool up in the holder so as little as possible is exposed.
When you need length
Deep pockets sometimes force long stickout. In those cases, reduce cutting forces (lighter depth and width of cut), consider a larger-diameter or necked tool, or use a more rigid holder — and accept that you can’t push a long tool as hard as a short one.
Frequently asked questions
Why does stickout matter so much? Deflection grows with the cube of length.
What’s the rule? Use the shortest tool that reaches; minimize exposed length.
Can I machine deep features? Yes, but reduce cutting forces and expect lighter cuts.