# Feed Rate Calculator Lathe

Feed rate calculator lathe turning. Enter RPM or workpiece diameter, material, and cut type (roughing or finishing) to get feed per revolution (IPR), feed rate (IPM), mm/min, and MRR.

## What this calculates

Lathes program feed in IPR (inches per revolution), not IPM. This feed rate calculator lathe tool takes RPM (entered directly or computed from workpiece diameter and SFM) and a material-specific feed per revolution to return feed rate in IPR, IPM, mm/min, and metal removal rate. Works for roughing and finishing cuts on any common lathe material.

## Inputs

- **Spindle RPM Source** — options: Enter RPM directly, Compute RPM from diameter + SFM — Compute mode uses (SFM x 12) / (pi x D).
- **Spindle RPM** (RPM) — min 0 — Used when RPM Source = Enter directly.
- **Workpiece Diameter** (in) — min 0.001 — OD currently being turned. Used when RPM Source = Compute.
- **Workpiece Material** — options: Aluminum, Mild steel (1018), Medium carbon (1045), Alloy steel (4140), Stainless (304, 316), Tool steel (A2, D2), Cast iron, Brass, Bronze, Copper, Titanium, Plastic (Delrin) — Used for default IPR and SFM lookup.
- **Tool Material** — options: HSS, Carbide insert — Only used when RPM Source = Compute.
- **Cut Type** — options: Roughing, Finishing — Selects the default feed per revolution (heavier for roughing, lighter for finishing).
- **Feed per Revolution Override** (in/rev) — min 0 — Leave 0 to use the material/cut-type default. Enter a specific IPR to override.
- **Depth of Cut** (in) — min 0 — Radial depth per pass. Used for metal removal rate.

## Outputs

- **Feed per Revolution** (in/rev) — IPR applied. Used directly in lathe programs (G-code F word under G95).
- **Feed Rate (IPM)** (in/min) — Linear feed rate = RPM x IPR.
- **Feed Rate (metric)** (mm/min) — Feed rate in millimeters per minute.
- **Spindle RPM Used** (RPM) — RPM from direct input, or (SFM x 12) / (pi x D) when computed.
- **Cutting Speed** (SFM) — Surface feet per minute for reference.
- **Metal Removal Rate** (in^3/min) — MRR = 12 x SFM x depth x feed.

## Details

Lathe feed rate equations

  - Feed rate (IPM) = RPM x IPR where IPR is inches per revolution.

  - RPM = (SFM x 12) / (pi x D) for the compute mode, where D is the workpiece diameter.

  - MRR (in^3/min) = 12 x SFM x depth of cut x IPR (Sandvik turning math).

For a 2 inch mild steel bar turned with a carbide insert at 400 SFM: RPM = (400 x 12) / (pi x 2) = 764 RPM. Roughing IPR = 0.012, so feed rate = 764 x 0.012 = 9.17 IPM. At 0.050 depth of cut, MRR = 12 x 400 x 0.050 x 0.012 = 2.88 in^3/min.

Typical lathe feed per revolution (IPR)

  
    MaterialRoughing IPRFinishing IPR
  
  
    Aluminum0.0150.006
    Mild steel (1018)0.0120.005
    Alloy steel (4140)0.0100.004
    Stainless steel0.0100.004
    Cast iron0.0150.006
    Titanium0.0080.004
    Brass0.0150.006
  

IPR vs IPM on a lathe

On a lathe, chip thickness and surface finish depend on feed per revolution, not feed per minute. That is why G95 (feed per revolution) is the normal mode on a CNC lathe, with the feed value in IPR or mm/rev. G94 (feed per minute) exists for special cases like threading with a live tool or rigid tapping, but day-to-day turning is G95. A feed rate calculator lathe should return IPR as the primary number, with IPM as a reference.

Roughing vs finishing feed

Roughing prioritizes material removal: heavy depth of cut (0.050-0.150) and heavy feed (0.010-0.020 IPR). Finishing prioritizes surface finish: light depth (0.005-0.020) and light feed (0.003-0.006 IPR). Finishing also bumps SFM up 10-20 percent to keep chips formed cleanly. The calculator handles both by switching the IPR default based on the cut type you pick.

## Frequently Asked Questions

**Q: How do I calculate lathe feed rate?**

A: Feed rate in IPM = RPM x IPR (inches per revolution). For a 2 inch mild steel bar at 764 RPM and 0.012 IPR roughing feed, feed rate = 9.17 IPM. A feed rate calculator lathe does this step automatically once you enter RPM and pick the material.

**Q: Why do lathes use IPR instead of IPM?**

A: Chip thickness on a lathe is determined per spindle revolution, not per minute. Programming feed as IPR means chip thickness stays constant as RPM changes (for example under G96 constant surface speed). CNC lathes default to G95 feed-per-rev mode for this reason.

**Q: What is the right feed per revolution for stainless?**

A: Stainless roughing feed is 0.010 IPR and finishing feed is 0.004 IPR. Higher feeds keep the tool cutting below the work-hardened layer and reduce the chance of work-hardening. Lower feeds chatter and accelerate tool wear in stainless.

**Q: Should I enter RPM directly or compute it from diameter?**

A: If you already know RPM (from a separate SFM calc or from G96 reading), enter it directly. If you are starting from workpiece diameter and target SFM, use compute mode: RPM = (SFM x 12) / (pi x D). The calculator supports both.

**Q: What is MRR on a lathe?**

A: Metal removal rate = 12 x SFM x depth of cut x IPR, in cubic inches per minute. It is the number production shops optimize for. A 2 inch steel bar at 400 SFM, 0.050 depth, 0.012 IPR gives MRR = 2.88 in^3/min.

**Q: How do I convert IPR to metric?**

A: IPR x 25.4 = mm/rev. A 0.012 IPR feed = 0.305 mm/rev. Feed rate in mm/min = IPM x 25.4. A 9.17 IPM feed rate = 232.9 mm/min. The calculator returns both imperial and metric feed rate.

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Source: https://vastcalc.com/calculators/physics/feed-rate-lathe
Category: Physics
Last updated: 2026-04-08