TECHNICAL TIP #27; END MILLS; OVERHANG AND DEFLECTION
End mills, being supported on only one end, are subject to
deflection. The amount of deflection is dependent on the material the end mill
is made from, the diameter, overhang, and the amount of radial cutting forces
acting on the tool. Steel has a lower co-efficiency of elasticity than cemented
carbide. Therefore, HSS end mills will experience more deflection than carbide
As a general rule:
A 20% overhang
reduction will reduce tool deflection by 50%.
increase in diameter will reduce tool deflection by 50%
Based on these rules
Use the largest end mill the work piece will allow.
the amount of overhang from the spindle nose.
Reduce feed per tooth.
Reduce radial or axial depth of cut.
Reduce number of flutes.
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