⚙️ Lathe Cutting Speed Calculator
Calculate RPM, surface feet per minute (SFM), feed rate, and material removal rate for any lathe operation
⚡ Quick Presets
🔧 Calculator Inputs
✅ Calculation Results
📊 Material Properties Reference
📈 Speed & Feed Reference Table
| Material | Tool | SFM Range | Feed (in/rev) | Depth of Cut (in) | Brinell Hardness |
|---|---|---|---|---|---|
| Aluminum 6061 | HSS | 200–400 | 0.005–0.020 | 0.010–0.150 | 95 |
| Aluminum 6061 | Carbide | 400–600 | 0.010–0.030 | 0.020–0.200 | 95 |
| Mild Steel 1018 | HSS | 60–120 | 0.005–0.015 | 0.010–0.100 | 131 |
| Mild Steel 1018 | Carbide | 200–400 | 0.010–0.025 | 0.020–0.150 | 131 |
| Stainless 304 | HSS | 30–50 | 0.003–0.010 | 0.005–0.060 | 201 |
| Stainless 304 | Carbide | 60–80 | 0.005–0.015 | 0.010–0.080 | 201 |
| Brass | HSS | 150–300 | 0.008–0.020 | 0.010–0.100 | 55–73 |
| Cast Iron | HSS | 50–70 | 0.010–0.020 | 0.010–0.100 | 180–220 |
| Cast Iron | Carbide | 150–300 | 0.015–0.030 | 0.020–0.150 | 180–220 |
| Copper | HSS | 200–300 | 0.005–0.015 | 0.010–0.080 | 35–45 |
| Titanium | Carbide | 80–110 | 0.003–0.008 | 0.005–0.040 | 300–370 |
| Hardwood | HSS | 300–500 | 0.010–0.030 | 0.020–0.200 | N/A |
🔧 Tool Insert Reference Table
| Tool Type | Insert Grade | Speed Multiplier | Best For | Max SFM | Coolant |
|---|---|---|---|---|---|
| HSS | M2 / M42 | 1.0x (baseline) | Steel, Brass, Wood | 150 | Recommended |
| Cobalt HSS | M35 / M42 | 1.25x | Stainless, Hard Alloys | 200 | Recommended |
| Carbide (Uncoated) | C2 / K10 | 2.5x–3x | Cast Iron, Aluminum | 600 | Optional |
| Carbide (TiN Coated) | P25 / M20 | 3x–4x | Steel, Stainless | 800 | Recommended |
| Carbide (TiAlN) | P15 / M15 | 4x–5x | Titanium, Hardened Steel | 1200 | Air or Dry |
| Ceramic | Al2O3 / SiN | 5x–10x | Cast Iron, Superalloys | 3000 | Dry only |
📏 Common Lathe Operations Reference
| Operation | Typical Stock Size | Recommended SFM | Feed (in/rev) | Est. Time |
|---|---|---|---|---|
| Aluminum OD Turning | 1" dia x 6" long | 300–500 | 0.010–0.020 | 1–3 min |
| Steel Shaft Rough Turn | 2" dia x 8" long | 80–120 | 0.015–0.025 | 4–8 min |
| Stainless Finish Turn | 1.5" dia x 4" long | 60–80 | 0.005–0.010 | 3–6 min |
| Brass Facing | 3" dia face | 150–300 | 0.008–0.015 | 1–2 min |
| Cast Iron Boring | 2" bore x 3" deep | 100–200 | 0.010–0.015 | 3–5 min |
| Steel Threading (1/2-20) | 0.5" dia x 1" | 30–50 | 0.050 (20 TPI) | 5–10 min |
| Aluminum Parting | 2" dia | 150–250 | 0.002–0.005 | 1–2 min |
SFM = (π × Diameter × RPM) / 12. To find RPM from SFM: RPM = (SFM × 12) / (π × D). Carbide inserts can run 3–5x higher SFM than HSS, dramatically reducing cycle time on production runs. Always use the midpoint SFM for unfamiliar materials and adjust based on tool wear and surface finish.
Material Removal Rate (MRR) = Feed Rate × Depth of Cut × SFM × 12. For finishing passes, reduce feed by 50% and depth by 75% from roughing values. Increase feed before increasing depth of cut to improve tool life. For threading operations, feed per rev equals the thread pitch (1/TPI in inches).
The cutting pace is the relative motion between the knife and the surface of the workpiece. One measures it in square feet each minute (SFM) or metres each minute. On a lathe the cutting pace depends on the diameter of the bit and the RPM, in which it spins.
With a bigger bit, one must lower the RPM to keep the surface pace right for the knife.
Cutting Speed and How to Find RPM
The working pace for metal cutting is based on two things: the material of the knife and the hardness of the material that one cuts. Every type has its own cutting pace. One commonly finds that value on the packaging of the tool maker.
When one knows the cutting pace, one can count the RPM by means of a simple equation.
A practical thumb-rule is made up of multiplying the cutting pace by 3.82 and then dividing by the diameter of the workpiece on a lathe. On a mill, one instead divides by the diameter of the knife. Another way to say that: RPM matches the cutting pace times 4, divided by teh diameter of the bit.
For lathe work, always count the biggest diameter of the cut part, use that in the math and do not pass that RPM.
Here is a sample using the metric system. If the diameter is 50 mm and the steady pace 700 RPM, the cutting pace results around 110 metres a minute. The equation is: cutting pace matches pi times diameter times RPM, divided by 1000.
High surface paces make more stress on the knife and more heat. With materials easy to cut, like aluminium, high surface paces work well. But with stainless steel, going two or three times the suggested surface pace will burn the tools quickly.
For gentle steel with high-speed-steel tools, the thumb-rule is around 90 surface feet a minute. Carbide tools can handle four too six times that pace.
Going too slowly also can cause troubles. If the RPM is too low, the knife will not cut well and could be pushed away from the cut. One calls that bending of the tool.
Indeed, higher pace can help the knife cut better and bend less. On the other hand, many people turn too quickly, when the bit is not perfectly round, what causes shaking. And shaking really can rip the bit from the chuck.
To reach nice surface finish, several things play a role. Generally, higher pace or smaller step gives better result. Also the depth of the cut matters, some materials need shallow cuts, while others need deeper.
Using steady pace helps, because it makes up for the change of the diameter during the turning, keeping the surface feet a minute steady. Honing the edge of ahigh-speed-steel knife can remove little bumps that stay after milling, thus improving the finish.
