BIZOMAT MAKEOS · Manufacturing
Inch Milling Setup Check (Speed, Feed, Removal Rate, Spindle Power)
For a milling cut set up in surface feet and inches per tooth, what spindle speed and table feed do I program, and does the machine have the speed and power for it?
Check of an inch-unit milling setup: spindle speed from surface speed and cutter diameter and table feed from teeth and feed per tooth (as the inch speeds and feeds tool), capped at the machine’s top speed with the surface speed and feed that result, then the metal removal rate from width and depth of cut and the spindle power from a unit power for the material, against the machine’s motor power and efficiency.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Surface speed | ft/min | Surface speed recommended for the cutter and material. |
| Cutter diameter | in | Diameter of the cutter. |
| Number of teeth | teeth | Number of cutting teeth (flutes). |
| Feed per tooth | in | Feed per tooth (chip load). |
| Cut and machine | ||
| Width of cut (radial) | in | Radial width of cut. |
| Depth of cut (axial) | in | Axial depth of cut. |
| Unit power of the material | hp per in³/min | Power to remove one cubic inch per minute of the material (from the tool or machine maker). |
| Spindle speed limit | rpm | Highest spindle speed of the machine. |
| Spindle motor power | hp | Rated spindle motor power. |
| Machine efficiency | % | Share of motor power that reaches the cutter. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Surface speed
- What it is
- The speed at which the cutting edges pass over the work, in surface feet per minute, chosen for this cutter material and workpiece material. The tool converts it to spindle speed using the cutter diameter.
- Units and format
- Enter a number in ft/min: ft/min. The form accepts 0.000001 ft/min to 100000 ft/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 400 ft/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Spindle speed, table feed, removal rate and power all rise in proportion to it until the spindle speed limit is reached.
- Get it right
- Take it from the cutter maker’s data for your tool coating and work material; a carbide figure used with a high-speed steel cutter will burn the tool.
What this means: Cutter diameter
- What it is
- The cutting diameter of the milling cutter or end mill, measured across the cutting edges through the axis. It turns surface speed into spindle speed and limits the width of cut.
- Units and format
- Enter a number in in: inches. The form accepts 0.000001 in to 1000 in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger cutter needs a lower spindle speed for the same surface speed, so the table feed falls; the width of cut must not exceed it.
- Get it right
- Use the actual cutting diameter, not the shank diameter; a reground cutter is smaller than its nominal size.
What this means: Number of teeth
- What it is
- How many cutting edges (flutes or inserts) the cutter has around its circumference. Each tooth takes one chip per revolution.
- Units and format
- Enter a number in teeth: a whole number of teeth. The form accepts 1 teeth to 500 teeth. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 teeth as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Table feed, removal rate and spindle power rise in proportion to the number of teeth.
- Get it right
- Count only effective teeth; on some insert cutters not every pocket cuts at full depth.
What this means: Feed per tooth
- What it is
- The distance the table advances for each tooth that passes through the cut, also called chip load. It sets the chip thickness each edge takes.
- Units and format
- Enter a number in in: inches. The form accepts 0.000001 in to 1 in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.002 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Table feed, removal rate and spindle power rise in proportion to it.
- Get it right
- Enter the feed per tooth, not per revolution: divide a per-revolution feed by the number of teeth.
Cut and machine
What this means: Width of cut (radial)
- What it is
- How far the cutter is engaged sideways into the work, measured across the cut at right angles to the cutter axis (radial engagement or stepover).
- Units and format
- Enter a number in in: inches. The form accepts 0.000001 in to 1000 in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.25 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Removal rate and spindle power rise in proportion to it.
- Get it right
- It cannot exceed the cutter diameter; the tool flags a width larger than the cutter.
What this means: Depth of cut (axial)
- What it is
- How far the cutter is engaged along its own axis, measured from the cut surface to the lowest point of the cut (axial engagement).
- Units and format
- Enter a number in in: inches. The form accepts 0.000001 in to 1000 in. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 in as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Removal rate and spindle power rise in proportion to it.
- Get it right
- For a side cut with an end mill this is the length of flute in contact, not the depth into the side wall.
What this means: Unit power of the material
- What it is
- The power the spindle must deliver at the cutter to remove one cubic inch of this material per minute. It reflects how hard the material is to cut.
- Units and format
- Enter a number in hp per in³/min: hp per in³/min. The form accepts 0.000001 hp per in³/min to 20 hp per in³/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 hp per in³/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Spindle power needed rises in proportion to it.
- Get it right
- Take it from the tool or machine maker’s data for your material; the limitations note that a dull tool can need up to half as much again.
What this means: Spindle speed limit
- What it is
- The highest speed the machine spindle can run. If the speed worked out from surface speed is higher, the tool runs the spindle at this limit and recalculates the surface speed and feed.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 1000000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8000 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lower limit caps the spindle speed, which lowers the table feed, removal rate and power needed.
- Get it right
- Use the spindle’s rated top speed, or a lower limit set by the tool holder or the cutter maker if that is lower.
What this means: Spindle motor power
- What it is
- The rated output of the spindle drive motor, the power available before losses in the belts, gears and spindle bearings.
- Units and format
- Enter a number in hp: hp. The form accepts 0.000001 hp to 10000 hp. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 hp as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the continuous rating from the machine plate or manual, not a short-time peak rating.
What this means: Machine efficiency
- What it is
- The share of motor power that reaches the cutting edge after losses in the spindle drive, belts, gears and bearings.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 1% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Power needed at the motor is the cutting power divided by this share, so a lower efficiency raises it.
- Get it right
- Type the percentage itself (80 for 80 %), not a fraction; take it from the machine maker if known.
Method and formulas
- Speed = 12 × sfm ÷ (π D); feed = speed × teeth × feed per tooth (as the inch speeds and feeds tool).
- Speed capped at the machine limit; surface speed and feed recalculated at the capped speed.
- Removal rate = width × depth × feed; power = removal rate × unit power ÷ efficiency.
- Example: 3,055.8 rpm and 24.446 in/min remove 3.0558 in³/min, needing 3.8197 hp.
Limitations
- Unit power varies with tool sharpness, rake and chip thickness; dull tools need up to half as much again.
- Tool deflection, chatter and work holding limit the cut separately.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check an end mill setup on a small mill
- See whether a cut needs a bigger machine
- Work out the feed after the spindle speed is capped
Who it is for
- Machinists
- CNC programmers
- Process planners
What you get
- Spindle speed and table feed
- Removal rate
- Spindle power against the machine
Interpreting the result
- When the spindle speed is capped, keep the feed per tooth and accept a lower table feed rather than raising the chip load.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1013–1017, 1084–1101. Topic reference; no source tables or recommended settings are reproduced.
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Open the Inch Milling Setup Check (Speed, Feed, Removal Rate, Spindle Power) calculator