Speeds and Feeds Calculator

Created by Steven Wooding
Reviewed by Dominik Czernia, PhD and Jack Bowater
Based on research by
Christopher J. Q. McCauley Machinery’s Handbook, 26th Edition, Chapter: Machining Operations (2000)
Last updated: Oct 09, 2022

Omni's speeds and feeds calculator helps you set the correct rotation speed and feed rate of your machine tool. It supports all of the following machine tool operations:

  • Drilling
  • Reaming
  • Milling (face, slab, and end milling)
  • Boring
  • Counterboring
  • Turning

So it's a reamer speed and feeds, milling speeds and feeds, and drill feeds and speeds calculator (plus more) all rolled into one.

Continue reading to learn about machine tool operations and the two principal speeds and feeds formulas that power this calculator.

Are you planning a general home renovation? Go ahead and check our stair calculator and the decking calculator – they may come in handy!

Machine tool operations

All machine tool operations consist of a cutting tool (e.g., a drill bit) and the workpiece that is being machined to make something. So, if you're drilling a hole in a piece of wood, then the wood is the workpiece.

This calculator supports the following hole-making operations:

  • Drilling – making an initial hole in the workpiece (make sure that the taper is right for the purpose!)
  • Reaming – slightly enlarges an existing hole to leave smooth sides
  • Boring – expands an existing hole by cutting around the side
  • Counterboring – enlarges the top part of an existing hole

It also handles the following milling operations:

  • End milling – the creation of an extended cavity in the workpiece, such as a slot or complex surface contour
  • Face milling – creates a smoother finish of a flat surface of the workpiece
  • Slab/side milling – creates large, broad surfaces that are parallel to the tool axis of rotation.

Finally, it supports the turning operation where the cutting tool is stationary, and the workpiece rotates. This configuration is the essential operation of a lathe machine, which is used to create symmetric circular manufactured items.

If your machine has a spindle, you may also be interested in the spindle speed calculator.

Speeds and feeds formula – Speeds

The "speeds" part of the speeds and feeds calculator is the rotation speed of either the tool (e.g., for drilling) or the workpiece (e.g., for turning on a lathe). For a given tool and workpiece material, there is a range of recommended cutting or surface speeds between the two materials. Given the surface speed, you can calculate the spindle speed in revolutions per minute (RPM) using the following equation (when using imperial units):

N=12VπD\small N = \frac{12V}{\pi D}

where:

  • NN – Spindle speed in RPM;
  • VV – Speed at which the tool travels relative to the workpiece, in units of feet per minute; and
  • DD – Diameter of the rotating element, measured in inches.

If you are using the metric system and have the surface speed VV in meters per second and the diameter DD in millimeters, the equation is:

N=60×1000VπD\small N = \frac{60 \times 1000 V}{\pi D}

Analyzing the equation, you might notice that πD\pi D is the formula for circumference of a circle. So we're dividing the speed at the circumference by the distance traveled during one rotation to get the number of rotations per minute.

Speeds and feeds formula – Feeds

The term "feeds" refers to the feed rate or the relative linear speed between the tool and the workpiece. For example, for drilling, it is the speed at which the drill bit travels down into the workpiece material. The equation for the feed rate is:

f=NCLnt\small f = N C_L n_t

where:

  • ff – Feed rate in inches per minute (IPM);
  • NNSpeed of the rotating element (either the tool or the workpiece) in RPM;
  • CLC_L – Amount of workpiece material removed per revolution per cutting edge; and
  • ntn_t – Number of cutting edges the tool has, also known as the number of flutes.

The chip load depends on the characteristics of the tool and the workpiece material. For example, a tool drilling a hole into a soft workpiece material will have a higher chip load than a harder workpiece material.

If you are not sure how many teeth your tool has, look at it end-on and count how many sharp cutting edges there are around the circumference of the tool.

The calculator will produce a recommended range of feed rates. Generally, it would be best if you started at the lower feed rate and slowly increase it from there. For an operation such as milling, the slower the feed rate (and cutting speed), the smoother the finish on the workpiece will be.

Example of a milling speed and feeds calculation

Let's go through an example of how to calculate speeds and feeds manually, using the speeds and feeds formulas discussed above. Your tool is half an inch in diameter and made of high-speed steel, and you are end-milling a block of aluminum. Looking up the average surface speed between the cutting tool and the aluminum, you find it to be 600 feet/min. Using the imperial speeds formula, you would perform the calculation:

N=12VπD=12×6003.14159×0.5=4584 rev/min\small \begin{align*} N &= \frac{12V}{\pi D}\\[1em] &= \frac{12 \times 600}{3.14159 \times 0.5}\\[1em] &= 4584\ \text{rev/min} \end{align*}

Next, let's calculate the average feed rate at 4584 RPM, given that your tool has two teeth, and it has an average chip load when milling aluminum, which is 0.004 inches:

f=NClnt=4584×0.004×2=36.7 IPM\small \begin{align*} f &= N C_l n_t\\[.5em] &= 4584 \times 0.004 \times 2\\[.5em] &= 36.7\ \text{IPM} \end{align*}

Ideally, you would also calculate the minimum and maximum speeds and feeds, so let's see how our calculator can work out everything for you in super-quick time.

How to use the speeds and feeds calculator?

The speeds and feeds calculator has two modes of operation: preset mode and manual mode.

In preset mode, you can select the operation, tool material, size and number of teeth, and the workpiece material. The calculator contains a range of recommended cutting speeds for different materials, allowing it to calculate the rotation speeds. It also has the corresponding chip load data to calculate the feed rates.

In manual mode, you can set the cutting speed (usually in surface feet per minute – sfm), and it will output the rotation speed in rotations per minute (rpm), therefore converting sfm to rpm. You can also set custom chip loads to calculate the feed rates. Let's look at each mode in detail next.

Preset mode

With the calculator in the default preset mode, follow these steps to get your speeds and feeds result:

  1. Select the type of machine tool operation you wish to perform.
  2. Select the tool material, either high-speed steel (commonly used for drill bits) or a carbide-based tool.
  3. Select the workpiece material.
  4. Enter the diameter of the rotating element. For all operations apart from turning, this will be the tool's diameter. Since with the turning operation, the workpiece is rotating, the workpiece diameter should be used in that case.

You will then see results for the range of speeds you should use. For the best outcome, start at the minimum speed and gradually increase it to the average figure. If you want a quick, but rough finish, carry on up to the maximum speed.

Next, enter the number of teeth the tool has to get the range of feed rates to use. The feed rates shown are for the average rotation speed. To calculate the feed rates at a different speed, enter the RPM into the custom rotation speed field. Similar to rotation speed, the slower the feed rate, the smoother the finish of the operation will be.

Manual mode

With the calculator mode set to manual mode, you need to enter the minimum and maximum surface speeds and chip loads. The specification sheet for the tool you are using may contain this data. Here's what you should do:

  1. Enter the tool/workpiece diameter as in preset mode.
  2. Enter the minimum, and maximum surface (or cutting) speeds, commonly found in units of surface feet per minute. You'll then get the rotational min and max speeds straight away.
  3. Input the number of teeth your tool has.
  4. Enter the minimum and maximum chip loads for your tool, operation, and workpiece material.
  5. You will then see the min and max feed rates at the average rotation speed.
  6. As in preset mode, you can then enter a custom rotation speed which you would like to calculate the min and max feed rates for.
Steven Wooding
Calculator mode
Preset mode
Machine tool operation
Drilling
Materials and geometry
Tool material
High-speed steel (HSS)
Workpiece material
Aluminum
Tool/workpiece diameter
in
Speeds
Min rotation speed
rpm
Avg rotation speed
rpm
Max rotation speed
rpm
Feeds
Number of teeth
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