# CNC Turning Cycle Time and Metal Removal Rate Calculator

> Source: https://netray.co/tools/cnc-turning-cycle-time-and-removal-rate-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Calculates spindle rpm, passes, cutting time, metal removal rate and parts per hour for an OD turning operation, with a surface speed sweep.

## Category

mes-shop-floor

## Industry

Precision Machining

## Audience

- CNC programmer
- Process engineer
- Estimator

## Tool

**Kind:** calculator

**Currency:** $

**Inputs:**

#### Workpiece diameter

**Key:** dia

**Type:** number

**Default:** 1

**Min:** 0.05

**Step:** 0.05

**Unit:** in

#### Length of cut

**Key:** len

**Type:** number

**Default:** 2.5

**Min:** 0.05

**Step:** 0.1

**Unit:** in

#### Surface speed

**Key:** sfm

**Type:** number

**Default:** 400

**Min:** 20

**Step:** 10

**Unit:** SFM

**Help:** Choose from the insert maker's data for the material. Mild steel with coated carbide is often several hundred SFM.

#### Maximum spindle rpm

**Key:** max_rpm

**Type:** number

**Default:** 4000

**Min:** 100

**Step:** 100

**Unit:** rpm

**Help:** The lathe and chuck limit. The calculator caps rpm at this value.

#### Feed per revolution

**Key:** feed

**Type:** number

**Default:** 0.008

**Min:** 0.001

**Step:** 0.001

**Unit:** ipr

#### Radial stock to remove

**Key:** stock

**Type:** number

**Default:** 0.125

**Min:** 0.005

**Step:** 0.005

**Unit:** in

**Help:** Total on the radius, not the diameter.

#### Radial depth of cut per pass

**Key:** doc

**Type:** number

**Default:** 0.05

**Min:** 0.005

**Step:** 0.005

**Unit:** in

#### Approach and overtravel per pass

**Key:** over

**Type:** number

**Default:** 0.1

**Min:** 0

**Step:** 0.025

**Unit:** in

#### Non-cutting and other operations time

**Key:** other

**Type:** number

**Default:** 20

**Min:** 0

**Step:** 1

**Unit:** sec

**Help:** Rapids, tool changes, drilling, grooving, threading and part handling.

**Outputs:**

#### Calculated rpm

**Key:** rpm_calc

**Expr:** 12 * sfm / (pi * dia)

**Format:** integer

#### Spindle rpm used

**Key:** rpm

**Expr:** min(rpm_calc, max_rpm)

**Format:** integer

**Primary:** true

**Description:** Calculated rpm limited by the spindle maximum.

#### Actual surface speed

**Key:** sfm_act

**Expr:** pi * dia * rpm / 12

**Format:** integer

**Description:** Lower than requested when rpm is capped.

#### Passes

**Key:** passes

**Expr:** ceil(stock / doc)

**Format:** integer

#### Cutting time

**Key:** cut_min

**Expr:** passes * (len + over) / (feed * rpm)

**Format:** minutes

**Description:** Passes times path length divided by feed rate in inches per minute.

#### Metal removal rate

**Key:** mrr

**Expr:** 12 * sfm_act * feed * doc

**Format:** decimal

**Description:** Cubic inches per minute, using 12 x SFM x ipr x depth of cut.

#### Cycle time

**Key:** cycle

**Expr:** cut_min * 60 + other

**Format:** number

**Primary:** true

**Description:** Seconds per part.

#### Parts per hour (100 percent)

**Key:** pph

**Expr:** 3600 / cycle

**Format:** decimal

**Chart:**

#### Cycle time (sec) vs surface speed

**Type:** line

**X:** sfm

**From:** 100

**To:** 800

**Steps:** 36

**Series:**

- cycle

**Disclaimer:** First estimate only. Cutting time assumes a constant diameter and ignores acceleration and spindle speed changes on a constant surface speed control. Confirm speeds and feeds with the tool maker's recommendation for your material.

## Content

**Intro:** A quote starts with a cycle time, and a turning cycle starts with spindle speed, feed and the number of passes. This calculator works from surface speed to rpm, cutting time, metal removal rate and parts per hour.

**Sections:**

#### How to use it

**Body:** Enter the diameter, length of cut, surface speed and feed per revolution from the insert supplier, and the radial stock to remove with the depth of cut per pass. Enter the spindle limit so the result does not exceed what the machine can do, and an allowance for non-cutting time such as rapids, tool changes, grooving and handling. The result shows rpm, passes, cutting time, removal rate, cycle time and parts per hour. Use the chart to see how much a speed change really saves.

#### Formulas used

**Body:** Spindle rpm equals 12 times SFM divided by pi times the diameter in inches. If the result exceeds the spindle maximum, the maximum applies and the actual surface speed is recalculated. Passes equals the radial stock divided by the radial depth of cut, rounded up. Cutting time in minutes equals passes times path length divided by feed rate, where feed rate is feed per revolution times rpm. Metal removal rate in cubic inches per minute equals 12 times SFM times feed in inches per revolution times depth of cut.

#### Reading the speed sweep

**Body:** Doubling the speed does not halve the cycle, because the non-cutting time stays fixed and, on small diameters, the spindle cap limits rpm. The chart flattens out when either happens, and that is where more speed gains nothing. Higher speed also shortens tool life, so use it together with the tool life cost calculator before pushing speeds up. Feed and depth of cut are usually better levers than speed for roughing.

#### Common mistakes

**Body:** Mixing diameter and radial depth of cut is the most common error: stock on the radius is half the diameter change. Leaving out the approach and overtravel makes short cuts look too fast. Using full catalog speeds with no rigidity allowance gives times a real machine cannot hold. Also do not forget that constant surface speed on facing makes rpm climb towards the centre. Feed these cycle times into your ERP routing as run standards, then compare them with actual job reports.

**Cta:** If your routing run times come from estimates, Netray can help compare them with actual cycle data captured in your ERP or MES.

**Faq:**

#### What is the formula for rpm from SFM?

**Answer:** RPM equals 12 times surface feet per minute divided by pi times the diameter in inches. The commonly used shortcut of 3.82 times SFM divided by diameter is the same value rounded.

#### How is metal removal rate calculated for turning?

**Answer:** In inch units, metal removal rate in cubic inches per minute equals 12 times surface speed in SFM, times feed in inches per revolution, times depth of cut in inches. Multiply by roughly 16.4 to convert cubic inches to cubic centimetres.

#### Why does the calculator cap rpm?

**Answer:** Small diameters need very high rpm to reach the target surface speed, often more than the spindle or chuck allows. Capping rpm gives a realistic cycle time and shows the actual surface speed you get.

#### Does it handle facing or threading?

**Answer:** Not directly. Put those operations into the non-cutting and other operations time using your CAM time or past jobs. This calculator is for the main OD turning passes where most of the cutting time lives.

## Search terms

cnc turning cycle time calculator, turning time calculator, metal removal rate turning, sfm to rpm calculator, lathe cutting time formula, turning feed and speed calculator, cycle time estimate lathe, turning mrr formula

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