How is the cutting speed when CNC milling calculated?

When using types of machining machines, especially cnc precision machining, calculating the speed of the milling knife for the cut material is essential because a lot of factors are related to each other such as the hardness of the material or the hardness of the milling knife. Each type of material will need a certain speed to be able to precisely cut the sizes required on the machining drawing.

So what is the cutting speed in CNC milling?

Cutting speed, also known as surface speed, is measured by SFM (Surface feet per minute) – this is the cutting speed on the surface per minute. All cutting tools work on the principle of surface footage

How cutting speed affects material details
How cutting speed affects material details

Read more: What is a CNC machine? Principles and types of CNC machines

Cutting speed is defined as the speed on the outer edge of the instrument when it is cutting. The cutting speed depends mainly on the type of material you are cutting and the type of cutting tool you are using. The hardness of the machining material is greatly related to the proposed cutting speed. The harder the working material, the slower the cutting speed. The softer the working material, the faster the proposed cutting speed. If two cutting tools of different sizes rotate at the same rotation rate per minute (RPM), then the larger tool has a greater surface speed. Surface speed, surface cutting step and surface area are all directly related.

Considering the hardness of the machining material, the cutting speed can be indicated as follows:

Aluminum > Lead > Iron > Steel

Judging by the hardness of the cutting tool, the cutting speed can be indicated as follows:

Carbon > Carbide > > Wind Steel

Cutting speed spreadsheet

Material type

Cutting Speed (SFM)

Low Carbon Steel


Medium Carbon Steel


High Carbon Steel


Free-machining Steel


Stainless Steel, C1 302, 304


Stainless Steel, C1 310, 316


Stainless Steel, C1 410


Stainless Steel, C1 416


Stainless Steel, C1 17-4, pH


Alloy Steel, SAE 4130, 4140


Alloy Steel, SAE 4030


Tool Steel


Cast Iron–Regular


Cast Iron–Hard


Gray Cast Iron


Aluminum Alloys


Nickel Alloy, Monel 400


Nickel Alloy, Monel K500


Nickel Alloy, Inconel


Cobalt Base Alloys


Titanium Alloy


Unalloyed Titanium










Brass and Aluminum


Silicon Free Non-Metallics


Silicon Containing Non-Metallics


Spindle Speed

When calculating the SFM cutting speed for a given material and tool is determined, the spindle can be calculated because this value depends on the cutting speed and knife diameter. We have the formula below:

RPM = (CS X 4) / D, in which:

  • RPM = Revolutions per minute: Number of spins per minute.
  • CS = Cutter speed in SFM: Cutting speed in SFM.
  • D = Tool Diameter inches: Instrument diameter in inches.
Know the information and speed when processing details
Know the information and speed when processing details

Speed of purification in milling machine

The speed of purification can be defined as the distance calculated in mm/min when moving working in a milling machine. The progress rate is capable of operating independently of the rotational speed of the spindle, in order to ensure maneuverability as well as a reasonable arrangement so that when the mill operates with different details the adjustment will become easier.

A number of factors affect the speed of purification of the milling machine:

  1. The depth and width of the cut.
  2. Types of cutters.
  3. Sharpness of the cutting knife.
  4. Embryonic materials.
  5. The strength and uniformity of the embryo.
  6. Requires fine processing.
  7. The necessary accuracy.
  8. The strength and hardness of the machine, the device holds and sets up the instrument.

Knife progression speed in milling machine

Knife progression speed is the amount of material that should be removed by each tooth of the knife as it rotates and enters the machining area.

As the cutting knife enters the machining area, each tooth of the cutter enters the machining area in equal amounts creating chips of equal thickness.

Chip thickness or machining salary per tooth, along with the number of teeth in the cutting knife, form the basis for determining the speed of knife progression.

The ideal knife progression rate for milling is measured in inches per minute (IPM) and is calculated according to this formula:

IPM = F X N X X RPM in which:

  • IPM = Feed rate in inches per minute: Knife progress rate per inch per minute
  • F = Feed per tooth: The amount of processing per tooth
  • N = Number of teeth: Number of teeth
  • RPM = Revolutions per minute: Rotation every minute

The conclusion

As such, we can already better understand how to calculate the cutting speed when milling CNC properly. To be able to accurately process the types of materials and product details you need to train a lot to be able to form a habitual mindset to operate correctly on CNC machines.

   VCC Molds, we specialize in precision mechanical engineering and mold fabrication design as required. If you have any questions or requests to exchange, please contact us immediately via Hotine/Zalo: 0934 683 166 and Email: or leave a message for us here. We will contact you again as soon as possible.  

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