Optimize Machining Time


Feed and Speed rates need to be determined to optimize machining time, surface finish, and tool life. Speeds and Feeds along with required horsepower can be calculated using the machinist’s handbook and a series of formulas. Information in the Machinists Handbook assumes production speeds: i.e. an average tool life of fewer than two hours.

Production speeds state the maximum production for the cost of tooling, though they are sometimes impractical for the small jobs done at the machine shop. However, calculated speed and feed rates do give a useful reference in determining what rates should be used for our purposes. The following demonstrates how to calculate Speeds and Feeds for a surface milling or slotting operation.


Input Air Turbine Spindles® governed speeds from 25,000 to 90,000RPM and you will see the scale of savings these direct drive spindles can achieve in your application.

Comparison of Cutting Speed with a 1.5mm End Mill

Standard Machine Spindle at 12,000 rpm = 2.22”/min (56.5 mm/min) advance

Air Turbine Spindles® 625 Series at constant 50,000 rpm = 9.28”/min (235.6 mm/min) advance

Your Cutting Speed is increased 4.2x with Air Turbine Spindles®!

In addition to reducing cycle time, the accuracy of the cutting tool is improved and its life extended

Cutting Speed = (D × π × Spindle Speed )/1000

Cycle Time Cut in Half on DMG HSC 55

Linear Milling Depth: Row depth 2.0-0.13 RA

Material: 1.2344 Steel – HSC 30/70

Tool: Ball Nose End Mill R 2, 0.03mm/z


Standard DMG HSC 55 Spindle – 25,000 rpm

Advance: 1,500 mm/min = Cycle Time: 60 minutes


Air Turbine Spindles® 625HSK Spindle – 50,000 rpm

Advance: 3,000 mm/min = Cycle Time: 30 minutes

Machinist Handbook Values

SFM (ft/min): (Surface Feet per Minute)- Also called Cutter speed. Speed of a point on the outside diameter of the tool. Value depends on the material.

FPT (in): (Feed Per Tooth)- Also called Chip Load. Amount of stock removed by each tooth during a single revolution. Value depends on stock material, tool size, and tool material.

HPF (HP*min/in3): (Horse Power Factor) – the number used to calculate power requirement. Value depends on the material.

Other Variables

D (in): Diameter of tool

N: Number of teeth or flutes

DOC (in): (Depth Of Cut)

RPM: (Rotations Per Minute) Spindle Speed

IPM (in/min): (Inches Per Minute) Also called Feed Rate. The rate at which the workpiece is moved into the tool.

MRR (in3/min): (Metal Removal Rate) Rate of volume removal

HP: (Horse Power) necessary power


RPM = SFM*12/(1.618*D)




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