Most drill press speed charts are posted in shops and ignored completely, or consulted once and never looked at again because they seemed to say something different every time someone read them. That's not because the charts are wrong — it's because a few key concepts about how to use them don't get explained clearly. This is a plain-language walkthrough.
Speed charts for drilling are based on Surface Feet per Minute (SFM) — a measurement of how fast the cutting edge of the drill moves across the material surface. This is what actually determines heat generation and tool life, not the RPM number on your drill press dial.
The chart gives you SFM recommendations by material. Your job is to convert that SFM recommendation into an RPM setting for the drill press, using the diameter of your specific drill bit.
The formula is: RPM = (SFM × 3.82) / Drill Diameter (in inches)
This is the only formula you need. Write it on a piece of tape on your drill press if you want.
| Material | SFM (starting point) |
|---|---|
| Aluminum (6061, cast) | 200–300 |
| Mild Steel (A36, 1018) | 80–100 |
| Alloy Steel (4140, 4340) | 50–70 |
| Stainless Steel (304, 316) | 30–50 |
| Cast Iron | 50–80 |
| Brass / Bronze | 150–250 |
| Titanium | 20–40 |
| Hardwood | 150–250 |
| Soft Plastic (Delrin, HDPE) | 150–300 |
These are starting points for sharp, standard HSS bits. Cobalt and carbide bits can run faster — generally 1.5–2× these values. Dull bits require lower SFM regardless of material.
You have a 3/8" drill bit and you're going into 1018 mild steel. Recommended SFM: 80–100. Start in the middle at 90 SFM.
RPM = (90 × 3.82) / 0.375 = 343.8 / 0.375 = 917 RPM
Find the closest speed setting on your drill press. Most machines have 5–16 speed steps — you won't hit exactly 917, so round to the nearest lower setting. Running slightly slow is almost always better than running too fast.
Too fast: Heat builds up at the cutting edge faster than the chip evacuation and cutting fluid can remove it. The bit gets hot, the temper comes out of the HSS at the point, and it dulls rapidly or fails completely. Blue or brown chips are the early warning.
Too slow: In soft materials, running slow mostly just means slower drilling. In hard materials like stainless, running too slow combined with light feed puts the bit into a rubbing situation rather than cutting, which generates friction heat without productive cutting and work-hardens the surface.
The general principle: it's better to run slightly slow than slightly fast. A bit running too slow will drill slowly. A bit running too fast will dull fast or burn.
Speed charts tell you RPM. Feed rate — how fast you push the bit into the workpiece — is equally important and often less discussed.
| Material | Feed rate (IPR) for standard HSS |
|---|---|
| Aluminum | 0.004–0.008 |
| Mild Steel | 0.003–0.006 |
| Hard Steel / Alloy | 0.002–0.004 |
| Stainless | 0.002–0.004 |
| Cast Iron | 0.003–0.005 |
| Brass | 0.004–0.007 |
On a manual drill press, you're applying feed by hand and can't measure it precisely. The practical translation: make sure you're producing a real chip, not dust. Steady, firm pressure that produces continuous spiral or curled chips is the target.
The chart assumes a sharp bit. A dull bit requires lower SFM (reduce RPM by 20–30%), more cutting fluid, and lighter feed in hard materials. The honest answer for a dull bit is: sharpen it or replace it. Trying to compensate for dull geometry by adjusting speed and feed is a losing game, especially in stainless or alloy steel.
Post a chart near the drill press or keep one folded in a drawer. Better yet, pre-calculate common combinations:
Put those on a laminated card. In actual production, you'll look at the same 6–8 combinations most of the time.
Surface feet per minute is the real variable — the chart gives you SFM by material, and you convert it to RPM using your drill diameter. Too fast means heat and dulling. Too slow means rubbing in hard materials. Feed hard enough to produce real chips. And a sharp bit makes all of this work — a dull bit defeats proper speed and feed both.
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