BIZOMAT MAKEOS · Manufacturing
Turning Cut Power Check (Equivalent Chip Thickness, Cutting Forces, Power, Speed Limit)
Will this turning cut fit within the lathe’s spindle power, what forces does it put on the tool, and how fast could I run before the power runs out?
Check of a turning cut against the lathe: the chip area, equivalent chip thickness, removal rate, cutting force, feed-plane force and its axial and radial parts and the cutting power (as the equivalent chip thickness cutting forces tool), the highest cutting speed the spindle power allows for the same feed and depth (as the full-power cutting speed tool), and the spindle speed for the work diameter, against the power available and the spindle speed limit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Feed per revolution | mm/rev | Feed per revolution. |
| Depth of cut | mm | Radial depth of cut. |
| Engaged cutting edge length | mm | Length of cutting edge in contact (from the tool nose radius, lead angle and depth). |
| Cutting speed | m/min | Cutting speed. |
| Specific cutting force at this ECT | N/mm² | Specific cutting force for the material at this equivalent chip thickness (from the tool maker). |
| Feed-plane force ÷ cutting force | Feed-plane force as a share of the cutting force. | |
| Chip flow angle | ° | Direction of chip flow, which splits the feed-plane force into axial and radial parts. |
| Lathe | ||
| Spindle motor power | kW | Rated spindle motor power. |
| Machine efficiency | % | Share of motor power that reaches the cut. |
| Work diameter | mm | Diameter being turned. |
| Spindle speed limit | rpm | Highest spindle speed of the lathe. |
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: Feed per revolution
- What it is
- How far the tool advances along the work for each turn of the spindle. With the depth of cut it gives the chip area.
- Units and format
- Enter a number in mm/rev: millimetres per revolution. The form accepts 0.000001 mm/rev to 10 mm/rev. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.8 mm/rev as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Chip area, cutting force and power rise in direct proportion to the feed.
- Get it right
- This is feed per revolution, not feed per minute.
What this means: Depth of cut
- What it is
- The radial depth the tool cuts into the work, half the reduction in diameter in one pass.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Chip area, cutting force and power rise in direct proportion to the depth.
- Get it right
- Depth of cut is radial: turning from one diameter to another removes twice this from the diameter.
What this means: Engaged cutting edge length
- What it is
- The length of the cutting edge actually in contact with the work, which depends on the depth of cut, the lead angle and the nose radius. The chip area is divided by it to give the equivalent chip thickness.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer engaged edge lowers the equivalent chip thickness; it does not change force or power here.
- Get it right
- Work it out from the tool geometry, or take it from the tool maker; it is not the insert edge length.
What this means: Cutting speed
- What it is
- The surface speed of the work past the cutting edge. With the cutting force it gives the cutting power, and with the work diameter the spindle speed.
- Units and format
- Enter a number in m/min: metres per minute. The form accepts 0.000001 m/min to 5000 m/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 m/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cutting power and spindle speed rise in direct proportion to the cutting speed.
- Get it right
- Enter it in m/min, not as a spindle speed in rpm.
What this means: Specific cutting force at this ECT
- What it is
- The force per square millimetre of chip area needed to cut this material at this equivalent chip thickness, from the tool maker’s data.
- Units and format
- Enter a number in N/mm²: newtons per square millimetre (equal to MPa). The form accepts 0.000001 N/mm² to 20000 N/mm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1500 N/mm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cutting force and power rise in direct proportion to it.
- Get it right
- Read it for the equivalent chip thickness the tool reports, not for an unrelated chip thickness.
What this means: Feed-plane force ÷ cutting force
- What it is
- The force in the feed plane, pushing back against the tool, divided by the main cutting force. It is split into axial and radial parts by the chip flow angle.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.5 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The feed-plane force and its axial and radial parts rise in direct proportion.
- Get it right
- Enter a plain ratio, not a percentage.
What this means: Chip flow angle
- What it is
- The direction in which the chip flows off the edge, measured in the feed plane. The tool takes the axial force as the feed-plane force times its cosine and the radial force as its sine.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 90°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter it in degrees as defined in your tool data; a larger angle shifts the force from axial to radial.
Lathe
What this means: Spindle motor power
- What it is
- The rated power of the lathe’s spindle motor, from the machine data plate or manual.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 10000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 18.5 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More motor power raises the power available and the highest speed at full power.
- Get it right
- Use the rating for the duty you are running, continuous or short time, and check it applies at your spindle speed.
What this means: Machine efficiency
- What it is
- The share of spindle motor power that reaches the cut after losses in the belts, gears and bearings, from the machine maker or your measurements.
- 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
- Lower efficiency lowers the power available and the highest speed at full power.
- Get it right
- Type the percentage itself, not a fraction.
What this means: Work diameter
- What it is
- The diameter of the work at the point being cut. With the cutting speed it gives the spindle speed.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller diameter needs a higher spindle speed for the same cutting speed.
- Get it right
- Use the diameter being cut; for facing, the spindle speed rises as the tool moves towards the centre.
What this means: Spindle speed limit
- What it is
- The highest spindle speed the lathe or the work holding allows. The spindle speed for the cut is compared with it.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3000 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Take the lower of the machine limit and the chuck or fixture limit.
Method and formulas
- Chip area = f a; ECT = area ÷ edge length; F_c = area × K_c; F_H = ratio × F_c split by the chip flow angle; power = F_c V ÷ 60 000 (as the equivalent chip thickness cutting forces tool).
- Power at the cut = motor × efficiency; highest speed = power at the cut × 60 000 ÷ (K_c a f) (as the full-power cutting speed tool).
- Spindle speed = 1000 V ÷ (π D).
- Example: the cut takes 12 kW of the 14.8 kW available, with 3,600 N cutting force; full power allows 246.67 m/min.
Limitations
- Specific cutting force must match the ECT and tool geometry used.
- Tool life, chatter and work holding limit the cut separately.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a roughing cut on a small lathe
- Find the fastest speed the motor allows
- Estimate tool and work forces for a setup
Who it is for
- Machinists
- CNC programmers
- Process planners
What you get
- Chip area, ECT and removal rate
- Cutting forces and power
- Power and speed against the lathe
Interpreting the result
- Thicker chips cut more efficiently: raising feed is a cheaper way to remove metal than raising speed.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1132–1141, 1084–1101. Topic reference; no source tables or recommended settings are reproduced.
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