# Lathe motor power calculator

URL: https://www.clove3d.com/tools/lathe-power/
Tool type: web calculator (runs in browser, no server, no login)

## Purpose

Calculates how much motor power a lathe needs to perform a specific turning operation.
Uses the Kienzle specific cutting force method with published kc1/mc constants by material.

## Inputs

| Field | Description | Unit |
|-------|-------------|------|
| Material | Workpiece material (preset or custom kc) | — |
| Cutting speed (Vc) | Surface speed at the tool tip | m/min or SFM |
| Depth of cut (ap) | Radial engagement per pass | mm or in |
| Feed per revolution (fn) | Tool advance per spindle turn | mm/rev or in/rev |
| Lead angle (κr) | Tool lead angle, default 90° | degrees |
| Drive type | Mechanical transmission type | — |
| Safety factor | Motor oversize margin | 1.0 / 1.25 / 1.5 |
| Existing motor (optional) | Motor to check for adequacy | kW or HP |

## Outputs

| Field | Description | Unit |
|-------|-------------|------|
| Required motor power | Motor nameplate rating to select | kW or HP |
| Net cutting power | Power consumed at the cut | kW or HP |
| Power at motor shaft | Net power / drive efficiency | kW or HP |
| Cutting force (Fc) | Tangential force on the tool | N or lbf |
| Specific cutting force (kc) | Force per unit chip area | N/mm² |
| Motor adequacy | Sufficient / Borderline / Underpowered | badge |

## Formulas

Chip thickness:
  h = fn × sin(κr)

Kienzle specific cutting force:
  kc = kc1 × h^(-mc)

Cutting force:
  Fc = kc × ap × fn  [N]

Net cutting power:
  Pc = Fc × Vc / 60,000  [kW]
  Pc = Vc × ap × fn × kc / 60,000  (combined)

Power at motor shaft (accounting for drive losses):
  P_shaft = Pc / η_drive

Required motor rating (with safety factor):
  P_required = P_shaft × safetyFactor

HP conversion: 1 kW = 1.341 HP

## Material kc1 and mc values

| Material | kc1 (N/mm²) | mc |
|----------|------------|-----|
| Aluminium 6061 | 350 | 0.25 |
| Brass (free-cutting) | 750 | 0.22 |
| Copper | 1100 | 0.26 |
| Mild steel 1018-1025 | 1500 | 0.25 |
| Carbon steel 1040-1050 | 1700 | 0.25 |
| Stainless 304 | 2800 | 0.21 |
| Cast iron (gray) | 1100 | 0.28 |
| Titanium Ti6Al4V | 1800 | 0.23 |
| Hard plastic (nylon/acetal) | 150 | 0.20 |

Source: Sandvik Coromant machining data, Machinery's Handbook, Kienzle (1952).

## Drive efficiency values

| Drive type | η |
|------------|---|
| Direct / VFD | 0.95 |
| V-belt | 0.92 |
| Gear head | 0.90 |
| Back gear | 0.80 |

## Safety factors

- 1.0: no margin (proving cuts only)
- 1.25: recommended for general turning
- 1.5: continuous duty or variable material

## Motor adequacy check

If the user enters their motor's power:
- Adequate: motor >= P_required
- Borderline: P_shaft <= motor < P_required (works but no safety margin)
- Insufficient: motor < P_shaft (motor will be overloaded)

## Related tools

- Lathe RPM: https://www.clove3d.com/tools/lathe-rpm/
- Feeds & speeds: https://www.clove3d.com/tools/feeds-speeds/