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## Selecting Speed and Feed Rates and Depth of Cut

The following items must be selected by the machinist when using endmills.

- SFPM – cutting surface speed
- Chip Load – material removal rate
- Depth of Cut – depends on specific part applications requirements
- Considerations – cutting depth never to exceed flute length

Excessive depth of cut will result in tool deflection.

As the depth of cut increases, use the largest diameter cutter available to maintain a depth to diameter ratio of 1 : 1.

Width of Cut – (maximum amount should not exceed 2/3 x Cutter diameter)

**MACHINING FORMULAS**

S.F.M. = 0.262 x D x R.P.M.

R.P.M. = (3.82 x S.F.M.) / D

I.P.R. = I.P.M. / R.P.M. or CHIP LOAD x F

I.P.M. = R.P.M. x I.P.R.

CHIP LOAD = I.P.M. / (R.P.M. x F) or I.P.R. / F

F=Â number of flutes

D=Â diameter of cutter

R.P.M=Â revolutions per minute

S.F.M=Â surface feet per minute

I.P.M=Â feed rate: inches per minute

I.P.R=Â inches per revolution

**IMPORTANT TERMS**

**Chip load** – The amount of material removed by each flute of the cutter.

**Feed Rate or Feed per tooth** – The inches per minute of workpiece movement toward the cutter between each tooth

**Inches Per Minute (IPM)** – The number of linear inches the cutter passes through the workpiece in one minute

**Depth of Cut (DOC)** – The depth of cut of the end mill into the part surface axially. With CNC milling, it is measured in the Z axis direction.

**Inches Per Revolution (IPR)** – Feed rate of the cutter for each revolution of the cutter. In the inch system, the feed rate of the cutter can be calculated for each revolution of the cutter.

I.P.R. = Chip load x Number of flutes

**Millimeters Per Revolution (MMPR)** – Feed rate of the cutter each revolution of the cutter. In the metric system, the feed rate of the cutter can be calculated for each revolution of the cutter.

M.M.P.R. = Chip load x Number of flutes

**Meters Per Minute (MPM)** – The cutting speed of the end mill. This system is used in all countries that use the Metric system. MPM represents the rate of the surface of the cutter passes over the surface of the part. Cutting speed is measured in Meters per minute.

**Revolutions Per Minute (RPM)** – The spindle speed rate of the cutter. This value will be calculated from a selected S.F.P.M. or MPM.

**Surface Feet Per Minute (SFPM)** – The is the cutting speed of the end mill in the United States. It is the number of feet per minute that a given point on the circumference of a cutter travels per minute.

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