Speed & Feed Recommendations

RPM charts and surface speed tables for rotary files, burs, and countersinks

The RPM Formula

The correct spindle speed for any rotary cutting tool is calculated from the recommended Surface Feet per Minute (SFM) and the tool diameter:

RPM = SFM × 3.82 ÷ Tool Diameter (inches)

Where 3.82 is the constant derived from 12 / π (converting feet to inches and accounting for circumference). This formula applies to all rotary cutting tools including Midget Mills, Junior Mills, Lab Mills, countersinks, and Carbo-Mills.

Important: These are starting recommendations. Adjust based on your specific setup, rigidity, coolant availability, and desired finish. When in doubt, start slower and increase speed gradually.
Quick Reference
  • HSS Rotary Files: 150–300 SFM
  • Carbide Rotary Files: 300–600 SFM
  • HSS Countersinks: 80–200 SFM
  • Carbide Countersinks: 200–400 SFM

HSS Rotary File RPM Chart

Recommended RPM ranges for HSS (M2 High Speed Steel, Rc 63–65) Midget Mills, Junior Mills, and Lab Mills. Values calculated at 150–300 SFM.

Tool Diameter Low (150 SFM) Medium (225 SFM) High (300 SFM) Typical Product Line
3/32" (0.094") 6,096 9,143 12,191 Lab Mills
1/8" (0.125") 4,584 6,876 9,168 Junior Mills, Lab Mills
3/16" (0.1875") 3,056 4,584 6,112 Junior Mills
1/4" (0.250") 2,292 3,438 4,584 Midget Mills
3/8" (0.375") 1,528 2,292 3,056 Midget Mills
1/2" (0.500") 1,146 1,719 2,292 Midget Mills
5/8" (0.625") 917 1,375 1,834 Midget Mills
3/4" (0.750") 764 1,146 1,528 Midget Mills

Carbide Rotary File RPM Chart

Recommended RPM ranges for Carbide Midget Mills, Carbo-Mills, and Sever-Cuts. Values calculated at 300–600 SFM. Carbide tools run at roughly double the speed of HSS.

Tool Diameter Low (300 SFM) Medium (450 SFM) High (600 SFM) Typical Product Line
1/8" (0.125") 9,168 13,752 18,336 Carbide Junior Mills
3/16" (0.1875") 6,112 9,168 12,224 Carbide Junior Mills
1/4" (0.250") 4,584 6,876 9,168 Carbide Midget Mills, Carbo-Mills, Sever-Cuts
3/8" (0.375") 3,056 4,584 6,112 Carbide Midget Mills, Carbo-Mills
1/2" (0.500") 2,292 3,438 4,584 Carbide Midget Mills, Carbo-Mills
5/8" (0.625") 1,834 2,750 3,667 Carbide Midget Mills
3/4" (0.750") 1,528 2,292 3,056 Carbide Midget Mills

Material-Specific Recommendations

The workpiece material has a significant impact on the optimal speed and pressure. Use this table as a starting point and adjust based on your results.

Workpiece Material HSS SFM Carbide SFM Pressure Notes
Aluminum (6061, 7075, cast) 300 600 Light Use sharp tools; chips can load flutes. Wax stick or cutting fluid helps prevent loading.
Mild Steel (1018, 1045, A36) 200 400 Moderate Good general-purpose starting point. Cutting fluid recommended for extended runs.
Stainless Steel (304, 316, 17-4) 100 250 Light Work hardens quickly. Use cutting fluid. Maintain consistent feed—do not dwell. Carbide strongly recommended.
Cast Iron (gray, ductile) 150 350 Moderate Produces abrasive dust. Carbide significantly outlasts HSS. No cutting fluid needed (dry cutting preferred).
Brass / Bronze 250 500 Light Machines freely. Use light pressure to avoid grabbing. Single-cut tools preferred for finish work.
Copper 200 400 Light Soft and gummy. Use sharp tools. Cutting fluid or wax stick prevents loading.
Tool Steel (D2, H13, A2) 80 200 Light to Moderate Carbide required for hardened stock. Reduce speed if tool chatters. Use cutting fluid.
Titanium (Ti-6Al-4V) 60 150 Light Low thermal conductivity—heat builds at the cut. Use flood coolant. Carbide required.
Plastics (Nylon, Delrin, ABS) 200 400 Light Avoid heat buildup which causes melting. Use low RPM and light pressure. No cutting fluid needed.
Composites / Fiberglass 100 300 Light Extremely abrasive. Carbide strongly recommended. Use dust extraction. No cutting fluid.

Countersink Speed Recommendations

Countersinks require lower speeds than rotary files to maintain control and produce clean, chatter-free chamfers. The Chatterless Countersink design allows higher speeds than conventional countersinks.

Countersink Body Diameter Mild Steel (RPM) Aluminum (RPM) Stainless Steel (RPM) Cast Iron (RPM)
1/4" (0.250") 1,200–2,400 2,400–3,600 600–1,200 900–1,800
3/8" (0.375") 800–1,600 1,600–2,400 400–800 600–1,200
1/2" (0.500") 600–1,200 1,200–1,800 300–600 450–900
5/8" (0.625") 480–960 960–1,440 240–480 360–720
3/4" (0.750") 400–800 800–1,200 200–400 300–600
1" (1.000") 300–600 600–900 150–300 225–450

Feed Rate Guidelines

Rotary Files (Hand-Held / Die Grinder)

When using rotary files in a hand-held die grinder or flexible shaft tool, feed is controlled by the operator's hand pressure. Follow these principles:

  • Let the tool do the work. Excessive pressure causes premature dulling, overheating, and poor finish.
  • Use a brushing motion. Move the tool across the workpiece rather than pressing it into one spot.
  • Maintain consistent movement. Dwelling in one area causes localized overheating and uneven stock removal.
  • Listen to the tool. A high-pitched whine means too much pressure. A smooth, consistent hum indicates proper feed.

Countersinks (Machine / Drill Press)

When using countersinks in a drill press or CNC machine, use these feed rate starting points:

  • Hand feed (drill press): Slow, steady advancement. Let the tool cut without forcing.
  • CNC feed: 0.001–0.003" per revolution for steel, 0.002–0.005" per revolution for aluminum.
  • Peck cycle: For deep countersinks, use a peck cycle to clear chips and reduce heat.
  • Chatterless advantage: Severance Chatterless Countersinks can run at higher feeds than conventional countersinks due to their 6-flute unequal-spacing design.

Tips for Maximum Tool Life

Do
  • Run at the recommended RPM for your tool diameter and material.
  • Use cutting fluid on steel, stainless, and titanium.
  • Keep the tool moving across the work surface.
  • Select the right tool material (HSS or Carbide) for the job.
  • Inspect tools regularly for wear, chipping, or loading.
  • Store tools properly to protect cutting edges.
  • Send worn tools for regrinding rather than discarding them.
Don't
  • Don't exceed the maximum recommended RPM—it generates excessive heat.
  • Don't use excessive pressure—it dulls tools prematurely.
  • Don't dwell in one spot—it causes overheating and work hardening.
  • Don't use HSS on hardened steels above Rc 45—switch to Carbide.
  • Don't run Carbide at low speeds with interrupted cuts—it causes chipping.
  • Don't use water-based coolant on cast iron (use dry or air blast).
  • Don't use a worn tool thinking you'll save money—it produces poor results and damages workpieces.

When to Use Cutting Fluid

Material Cutting Fluid? Recommended Type
Aluminum Optional (helps prevent loading) Wax stick, light oil, or WD-40
Mild Steel Recommended Soluble oil, cutting oil, or sulfurized oil
Stainless Steel Required Heavy-duty cutting oil or sulfurized/chlorinated oil
Cast Iron Not recommended Dry cutting or air blast preferred
Brass / Bronze Optional Light oil or dry
Tool Steel Required Heavy-duty cutting oil
Titanium Required (flood) Water-soluble coolant at high flow
Plastics Not recommended Dry or air blast (fluid may damage some plastics)

Need Application-Specific Advice?

Our application engineers can recommend the optimal speed, feed, and tool selection for your specific operation.

Contact Us 989-777-5500