SFM to Vc Calculator
Convert surface feet per minute to metric cutting speed, then cross-check diameter, spindle RPM, material range, and cutter style before setting the machine.
⚙Machining Presets
📏Inputs
🔬Material and Cutter Comparison
📊SFM to Vc Conversion Table
| SFM | Vc (m/min) | Best Use | Common Check |
|---|---|---|---|
| 80 | 24.4 | HSS in tough alloys | Slow, torque-heavy cut |
| 150 | 45.7 | Stainless or tool steel | Watch heat color |
| 300 | 91.4 | Mild steel carbide | General shop baseline |
| 500 | 152.4 | Aluminum or brass | Chip evacuation matters |
| 800 | 243.8 | Plastics or aluminum | Confirm tool RPM rating |
🔧Material Speed Reference
| Material | HSS SFM | Carbide SFM | Metric Vc Band |
|---|---|---|---|
| Aluminum 6061 | 200-400 | 250-900 | 76-274 m/min |
| Mild steel 1018 | 70-120 | 120-450 | 37-137 m/min |
| Stainless 304 | 40-80 | 70-260 | 21-79 m/min |
| Gray cast iron | 60-110 | 150-500 | 46-152 m/min |
| Titanium Ti-6Al-4V | 30-60 | 60-180 | 18-55 m/min |
| Inconel 718 | 15-35 | 40-110 | 12-34 m/min |
🛠Cutter Adjustment Table
| Tool Type | Speed Factor | Use Case | Notes |
|---|---|---|---|
| Carbide end mill | 1.00 | General milling | Balanced default for modern carbide |
| HSS end mill | 0.45 | Manual mill work | Reduce speed to manage heat |
| Carbide drill | 0.85 | Rigid drilling | Peck only when needed |
| HSS drill | 0.38 | Drill press or lathe | Conservative for tool life |
| Turning insert | 1.05 | OD turning | Use work diameter at cut |
| Slitting saw | 0.55 | Thin slotting | Diameter raises rim speed fast |
🔁Diameter and RPM Cross-Check Table
| Diameter | 100 SFM | 300 SFM | 600 SFM |
|---|---|---|---|
| 1/8 in / 3.18 mm | 3056 RPM | 9167 RPM | 18335 RPM |
| 1/4 in / 6.35 mm | 1528 RPM | 4584 RPM | 9167 RPM |
| 1/2 in / 12.7 mm | 764 RPM | 2292 RPM | 4584 RPM |
| 1 in / 25.4 mm | 382 RPM | 1146 RPM | 2292 RPM |
| 2 in / 50.8 mm | 191 RPM | 573 RPM | 1146 RPM |
✅Shop Notes
Machinists uses the term speed to refer to the velocity that occurs at the point where the tool edges is in contact with the material. The rate at which this velocity can be measured is in imperial units as surface feet per minute (SFM) or in metric units as cutting speed (Vc). Although both of these units represents the same measurement, the units of measurement are not the same.
The machinist must select the appropriate unit of measurement for a machining operation, as this will impact the tool life, the surface finish of the machined component, and the potential for chatter mark to develop along the components surface. Converting between SFM and Vc is a unit conversion; however, the variables that impacts such a conversion are more complex. The diameter of the tool impacts the relationship between RPM and cutting speed.
How to Pick the Right Cutting Speed and RPM
Two tools of the same RPM can have different cutting speeds if the diameter of each tool are different. The type of material that is being cut and the machinability of that material impact the tool speed. A cutting speed that is appropriate for 6061 aluminum may not being appropriate for 304 stainless steel.
Using the cutting speed that is appropriate for aluminum in a 304 stainless steel component can lead to the carbide drill bit overheats. You can use a calculator to input the cutting speed in SFM, the diameter of the tool, and the RPM of the machines spindle; using such a calculator remove the potential for mistake in the arithmetic involved in calculating cutting speed. An understanding of each individual element that go into calculating cutting speed is important.
The chip load for the tool tells the machinist the amount of material that each tooth of the cutting tool should remove during each revolution of the component; this is a necessary measurement for successful cutting. The engagement percentage for the cutter is important in determining how much heat is generate during cutting and how much the cutting tool may deflect from the cutting path. Other setup variable impact the speed at which the tool can operate before it break or the surface finish of the component suffers.
These variables are not abstract concepts to the machinist but have a direct impact on whether the component is completed in the time allowed or whether the cutter breaks or the component is completely scrap. Many people makes mistakes because they treat the surface feet per minute values listed in catalogues as rules. The value of feet per minute that is published in the catalog assume ideal conditions for the tooling and fixturing.
If you’re fixturing is not ideal, you can use the reduction factor in the calculator to find the RPM of your spindle that will provide the desired cutting speed under your actual condition. Similarly, if you are changing from high-speed steel tools to carbide or from carbide to high-speed steel, the material of the cutting tool will change the factor that you use to calculate the feet per minute value. This will tell you if your spindle is set to an appropriate RPM or if your tool will wear premature.
The reference tables to the right of the calculator provide a quick means of sanity checking your calculation. These reference tables show the relationship between different materials and high-speed steel and carbide tools. These reference tables also show the relationship between the diameter of a tool and the RPM of that tool traveling at a specific value of surface feet per minute.
These tables can help you confirm that the value from the calculator is a sensible one before you begin your cutting cycle. It is useful to run the calculation twice to ensure that the calculation is correct. You can calculate the target RPM using the catalog value of surface feet per minute.
Or, you can insert the RPM of your machine spindle into the calculator and confirm that the cutting speed comes within the band of speeds at which the material can be cut effectively. If the speed fall outside this range, adjust the feed or depth of cut rather than the RPM. This is a useful way of checking the RPM because machines may naturally run at different speeds for previous job or due to wear of the machine belt.
The use of this calculator force you to consider the cut as a system whose variables impact each other. The diameter of your tool, the material of your tool and workpiece, how much of your tool is engaged in the cut, and how your tool is setup on the machine impact on each other. By considering these variables together, the calculator will allow you to model your cutting process and determine the tradeoffs between each variable in order to produce your part correctly.
