Speed and Feed Engineering Calculator – Kennametal
These calculations are based upon theoretical values and are only intended for planning purposes. Actual results will vary. No responsibility from Kennametal is assumed.
Speed and Feed Calculator FAQ
- Speed (RPM) = (Surface Feet per Minute x 3.82) / Diameter of the Tool
- Feed Rate = RPM x Chip Load x Number of Teeth
- RPM = Of the tool or workpiece
- Chip Load = The amount of material removed, per revolution per cutting edge
- Number of Teeth = The number of edges, facets, or flutes.
Multiple factors affect the spindle speed (RPM) when milling steel, these include:
The type of steel:
- Overall hardness
- Heat treatment
- Alloying composition
The type of tooling:
- Material (high-speed steel, carbide, etc.)
- Shape
- Condition (new vs worn)
The type of milling machine:
- Use of coolant
- Stability of work holding fixtures
Most specialty steel manufacturers will make available machining information if it is not a common steel variant.
A CNC mill calculates speeds and feeds or SFM based on the information the user enters. The type of CNC mill, the type of machine controller, and the age of the machine will affect the amount of information that can be input directly into the machine. Historically G-code was created externally from a CNC machine and then loaded onto the machine. Externally created G-code was authored either with a dedicated CAM software or with a plug-in embedded in the 3D parametric modeling software. The user would input the same CNC machine they want to create the part on (with the specific work holding fixture), the type of tooling (manufacture, part number etc.), and the specific material being machined. The software generates the speeds and feeds based on the part's geometry and all the inputted information. This creates the optimal speeds and feeds or SFM tailored to the exact part and CNC machine.
Turning Feed Rate = Rotational Speed (N) x Feed Rate (fr)
Rotational Speed (N) = Cutting Speed (SFM) / π x Original Diameter
Feed Rate (fr) = Rotational Speed (N) x Feed (f). Note: Feed (f) is in distance/revolution.
Milling Surface Feet per Minute = (RPM x Tool Diameter) / 3.82
Turning Surface Feet per Minute = 0.262 x Part Diameter x RPM
Surface Feet per Minute = (RPM x Circumference) / 12
Note: The circumference unit is in inches and is dependent on if it’s a milling or turning operation. For milling operations, the circumference is of the cutter (tool in the spindle). For turning operations, the circumference is of the workpiece (the material in the chuck).
Surface feet per minute (SFPM or SFM) is the combination of a physical quantity (surface speed) and an imperial and American customary unit (feet per minute or FPM). It is defined as the number of linear feet that a location on a rotating component travels in one minute.
Inches per minute (IPM) is a speed measurement of how many inches traveled in a minute, without regard to direction. In machining, it is primarily used as a feed rate (imperial units).