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 Manufacturing Engineering and Technology

  Machinery's Handbook

  Marks' Standard Handbook for Mechanical Engineers

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The calculation of spindle speed in milling uses the same formula as that for turning to convert from linear cutting speed.

i.e.:

N = 1000 x S(m/min)

     p x D (mm)

Where D = diameter of milling cutter in mm.

Where a lathe has a single tool and feed can simply be expressed as feed per revolution; milling cutters generally have more than one cutting edge – introducing the concept of tooth loading, or table feed per tooth.

Generally table feed can be provided in one of two ways (either, in the case of C.N.C. milling). Either by a separate motor – in this case table speed is expressed in mm/min; or by the spindle motor, expressed in mm/spindle rev.

In the first instance:

Tablefeed(mm/min)=  Feed (mm/tooth) x No. of teeth x N(rev/min)

In the second instance:

Table feed (mm/rev) = Feed (mm/tooth) x No. of teeth

Example 1:

A 100mm diameter shell mill with 16 teeth is to be used to machine Aluminium at a cutting speed of 45 m/min.

The recommended tooth loading for this particular cutter is 0.1 mm/tooth. Find table feed in mm/min.

First calculate the spindle speed.

N = 1000 x 45

      p x 100

=143rev/min  

Next calculate the table feed (mm/min)

Table feed (mm/min) = feed/tooth (mm) x No. of teeth x N(rev/min)

= 0.1 x 16 x 143

= 228 mm/min

Example 2:

A 16mm diameter end mill with 6 teeth is to machine mild steel at a cutting speed of 28m/min. The recommended tooth loading for this tool is 0.05mm/tooth. Find table feed in mm/rev.

This is a simpler calculation:

Table feed (mm/rev) = feed (mm/tooth) x No. of teeth.

= 0.05 x 6

= 0.3 mm/rev.

Tooth loading will remain the same regardless of whether the correct cutting speed is used or not.

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