How to Use This Table
This chart provides pre-calculated spindle RPM values for HSS drill bits based on the standard cutting-speed formula:
RPM = (Vc × 1000) / (π × D)
Where Vc = cutting speed (m/min) and D = drill diameter (mm)
Each column corresponds to a specific material and drill grade combination. The Vc values used are:
- Carbon / Mild Steel — Vc = 25 m/min (M2 HSS)
- Alloy / Tool Steel — Vc = 18 m/min (M2 HSS)
- Stainless Steel (M2) — Vc = 12 m/min (M2 HSS — conservative to avoid work hardening)
- Stainless Steel (M35) — Vc = 18 m/min (HSS-Co M35 cobalt — 50% higher than M2)
- Cast Iron — Vc = 25 m/min (M2 HSS)
- Aluminum — Vc = 80 m/min (M2 HSS — aluminum runs much faster than most machinists expect)
These are starting-point values for machine drilling with adequate clamping and cutting fluid. See the Adjustments section below for handheld and difficult-condition modifications.
Spindle RPM by Diameter and Material
All values assume a standard HSS-G (M2) drill unless the M35 cobalt column is specified. Use cutting fluid for all metal drilling.
| Diameter | Carbon Steel Vc=25, M2 |
Alloy/Tool Steel Vc=18, M2 |
Stainless (M2) Vc=12, M2 |
Stainless (M35) Vc=18, M35 |
Cast Iron Vc=25, M2 |
Aluminum Vc=80, M2 |
|---|---|---|---|---|---|---|
| 2 mm | 3,980 | 2,860 | 1,910 | 2,860 | 3,980 | 12,730 |
| 3 mm | 2,650 | 1,910 | 1,270 | 1,910 | 2,650 | 8,490 |
| 4 mm | 1,990 | 1,430 | 950 | 1,430 | 1,990 | 6,370 |
| 5 mm | 1,590 | 1,150 | 760 | 1,150 | 1,590 | 5,090 |
| 6 mm | 1,330 | 950 | 640 | 950 | 1,330 | 4,240 |
| 8 mm | 990 | 720 | 480 | 720 | 990 | 3,180 |
| 10 mm | 800 | 570 | 380 | 570 | 800 | 2,550 |
| 12 mm | 660 | 480 | 320 | 480 | 660 | 2,120 |
| 16 mm | 500 | 360 | 240 | 360 | 500 | 1,590 |
| 20 mm | 400 | 290 | 190 | 290 | 400 | 1,270 |
All values in RPM. Apply cutting fluid for all metal columns. Stainless (M35) column requires an HSS-Co M35 cobalt drill bit.
Feed per Revolution (fn)
Feed rate (fn) defines how far the drill advances per spindle revolution, in mm/rev. Correct feed rate is as important as correct RPM: too light a feed causes rubbing and heat; too heavy a feed can chip the cutting edge or stall the spindle.
| Diameter Range | fn (mm/rev) — Starting Range | Notes |
|---|---|---|
| 2–3 mm | 0.04–0.07 | Minimum pressure; let the drill cut — don't force |
| 4–6 mm | 0.07–0.12 | Steady feed; peck every 2–3× diameter in deep holes |
| 8–10 mm | 0.12–0.20 | Use cutting fluid; maintain consistent pressure |
| 12–16 mm | 0.15–0.25 | Machine setup recommended; rigid clamping essential |
| 20 mm | 0.20–0.35 | Drill press or machining center; pilot hole recommended |
For stainless steel, use the lower end of each range. For aluminum, the upper end or beyond is acceptable. Use the interactive drill calculator to compute exact feed rates for your spindle RPM.
Why Stainless Steel Needs Lower Speed
One of the most common mistakes machinists make is drilling stainless steel at the same RPM as mild steel. The table above shows that stainless requires roughly half the RPM of mild steel for the same diameter. Here is why:
Work hardening is the key mechanism. Austenitic stainless steels (304, 316) harden at the cutting zone under heat and pressure. If the drill is moving too fast, the thin layer of material ahead of the cutting edge hardens faster than the bit can cut through it. The result is that the bit stops cutting and starts rubbing — generating more heat, hardening the material further, and dulling the drill in seconds.
M35 Cobalt vs M2 in Stainless Steel
Our HSS-Co M35 cobalt drills allow a cutting speed of 18 m/min in stainless steel — compared to only 12 m/min for standard M2. That is a 50% increase in Vc, which translates directly to 50% higher RPM for the same diameter. The cobalt alloying raises the red hardness of the steel: the cutting edge retains its hardness at higher temperatures, resisting the work-hardening effect.
Example for 10 mm: M2 → 380 RPM | M35 → 570 RPM
Practical rules for stainless drilling:
- Use consistent, firm feed pressure — never dwell at the same depth; keep the drill advancing
- Apply cutting oil or sulfurized coolant — not just water or compressed air
- Use a 118° or 135° split-point geometry to reduce the chisel edge force and center the drill cleanly
- If the drill squeals or the hole surface turns blue, you are running too fast — reduce RPM immediately
Adjusting for Real-World Conditions
The RPM values in the table above are reference starting points calibrated for machine drilling under controlled conditions. Apply the following adjustments for your setup:
- Handheld drilling: Reduce RPM by 20–30%. A handheld drill cannot hold the bit as rigidly as a press, so the cutting edge flexes and rubs more. Lower speed compensates.
- Poor workpiece fixturing: Reduce by 20%. An unsecured workpiece vibrates and causes chatter, which creates micro-chipping on the cutting edges. Clamp before drilling.
- Deep holes (depth > 3× diameter): Reduce RPM by 20% and use a peck-drilling cycle — retract the drill every 5–10mm to clear chips. Chip packing in deep holes causes heat spikes and drill breakage.
- Dry drilling (no cutting fluid): Reduce RPM by 30%. Cutting fluid removes heat and reduces friction. Without it, heat accumulates rapidly, especially in stainless and alloy steel.
- Aluminum: Most machinists under-speed aluminum. A 10mm HSS drill in aluminum can run at 2,550 RPM — significantly higher than steel. Use a lubricant (WD-40 or a dedicated aluminum cutting fluid) to prevent built-up edge on the flutes.
Use the Interactive Calculator
The table above covers the most common combinations, but every job has variables — material grade, coating, coolant type, machine rigidity. For a custom RPM and feed rate calculation, use our interactive tool:
Drill Speed & Feed Calculator
Enter drill diameter, material type, and drill grade (M2 or M35) to receive instant RPM, surface speed, and feed rate recommendations — including adjustments for handheld use and hole depth.
Drill Grade and These Values
The RPM values in this chart are calibrated to the cutting speed capabilities of specific HSS grades:
- The Carbon Steel, Alloy/Tool Steel, and Cast Iron columns reflect the performance of our standard M2 HSS fully-ground drill bits. These are manufactured to DIN 338 / ISO 235 tolerances with a 118° or 135° split-point geometry and are suitable for all ferrous metals within their Vc range.
- The Stainless Steel (M35) column reflects the performance of our HSS-Co M35 cobalt drill bits. The 5% cobalt content raises red hardness, enabling the higher Vc of 18 m/min in stainless — and delivering significantly longer tool life compared to M2 in any difficult alloy.
- The Aluminum column is achievable with either M2 or M35 drills. A sharp, freshly ground split-point and a lubricant are more important than grade selection for aluminum.
If you are sourcing HSS twist drills for production or OEM use, contact our team for grade specifications, custom diameter ranges, and packaging options.
Related Procurement Programs
If you are sourcing this product line for a distributor, importer, or private-label channel, these OEM and wholesale programs cover the procurement questions buyers usually ask next.
- HSS Twist Drill Bits Wholesale & OEM Supply for Metalworking Channels — HSS twist drill bit wholesale and OEM supply for importers, industrial distributors, and private-label brands: M2, M35 cobalt, DIN 338, DIN 345, black oxide…
- HSS Drill Bits OEM & Private Label Program for Industrial Distributors — Build an OEM HSS drill bit range with documented M2/M35 options, DIN 338 and DIN 345 standards, private-label packaging, sample support, and factory-direct supp…
- HSS Drill Bit Sets OEM Packaging Program for Tool Brands — OEM HSS drill bit set program for private-label tool brands, distributors, and retailers: 19pc, 25pc, 29pc, and 115pc sets with M2/M35 options, metal index case…
