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Milling inside corners

Milling inside corners

Milling inside corners requires careful considerations concerning the suitable arc of cutter engagement as well as the appropriate feed rate.



  • When feeding the cutter into internal corners, the radial arc of engagement will increase, which places extra demands on the cutting edge
  • Often, the process becomes unstable, creating vibrations and an insecure process
  • Wobbling cutting forces often result in undercutting of the corner
  • There is a risk of frittering the tool edges or total tool breakdown

Traditional corner milling
Corner radius = 50% x DC

Solution – limit the arc of engagement

Use a programmed radius (circular milling) to reduce the arc of engagement and a radial cut to reduce the vibration tendencies, which will allow higher depths of cut and feed rates when milling inside corners.

  • Mill a bigger corner radius than stated in the drawing. This can sometimes be favorable, as it allows for the use of a bigger cutter diameter in roughing, which maintains high productivity
  • Alternately, use a smaller DC cutter to mill the desired corner radius
Mill a bigger component radius
Corner radius = 75% x DC
Use a smaller cutter
Corner radius = 100% x DC


A programmed radius of 50% DC is optimal.


For finishing, it is not always possible to have such a large radius; however, the cutter diameter should be no larger than 1.5 x component radius, e.g. corner radius 10 mm (0.394 inch) = max 15 mm (0.591 inch).

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