Check how far a tool is stuck out relative to its diameter, and roughly how much more it will deflect compared to a sturdy 3:1 setup.
Ratio = overhang / diameter. Deflection scales with length cubed, so relative deflection = (ratio / 3)^3, using a 3:1 overhang as the sturdy baseline.
How it works
A tool acts like a cantilevered beam, and beam deflection grows with the cube of length, so even a modest increase in stickout can multiply deflection many times over. A 6:1 overhang is not twice as flexible as 3:1, it is roughly eight times as flexible.
FAQ
What overhang ratio is considered safe? Many shops treat 3:1 to 4:1 as comfortable for general milling, with anything past 5:1 to 6:1 needing reduced feeds and depths of cut.
Related Guides
CNC Calculators · Tool Deflection Calculator · Hole Depth-to-Diameter Ratio Calculator