Drilling Brass — The Tricky Material That Grabs and What to Do About It

Brass has a reputation for being a beginner material. It's soft, it machines cleanly, it doesn't work-harden. And then a machinist drills their first brass piece with a standard jobber drill and the bit grabs, digs in, and either spins the part off the vise or snaps the drill. Sometimes both.

The self-feeding behavior in brass is real, predictable, and completely preventable if you understand what's driving it.

Why Brass Grabs

Standard HSS jobber drills are ground with positive rake angles on the cutting lips. That positive rake is what lets the drill cut aggressively into steel and cast iron without excessive thrust. In hard materials, it's an asset. In brass, it's a problem.

Brass is non-work-hardening and has very low shear strength. When a positively-raked edge enters brass, it doesn't just cut — it digs in and accelerates. The material in front of the cutting edge fails so easily that the drill wants to corkscrew deeper with each revolution rather than feeding at a controlled rate. This is called self-feeding or dig-in, and it happens even at controlled feed rates because the edge geometry itself is driving it.

The result is a spiral of increasing bite: the drill advances too fast, the chip load spikes, and if the workpiece isn't clamped absolutely rigid, it lifts off and spins. In thin brass sheet work, this is nearly unavoidable with standard geometry unless you address the drill.

The Fix: Scrape, Don't Cut

The solution is to reduce or eliminate the positive rake on the cutting lips — specifically, to modify the relief angle so the bit scrapes the brass rather than biting into it.

This is done by stoning or grinding a small flat on the rake face of each cutting lip, parallel to the drill axis. What you're doing is reducing the effective cutting angle from something aggressive to something near zero or slightly negative. With neutral-to-negative rake, the drill can't self-feed. It removes material at exactly the rate you control with your feed, and it produces a smooth, round hole.

The geometry change is subtle — you're talking about a few thousandths of an inch of flat on each lip. But the behavioral difference is dramatic. A drill modified this way feels completely different in brass: controlled, smooth, no grab.

The Right Tool for the Job

If you're drilling brass regularly, the cleanest solution is dedicated drills ground specifically for the material. Several manufacturers offer "brass drills" or "non-ferrous drills" with zero-rake geometry from the factory. Norseman, Precision Twist, and a few others have these in their catalogs. They're not a specialty item — just ask for drills ground for brass or non-ferrous.

For small shops doing occasional brass work, the hand-stoning modification on standard HSS bits is perfectly practical. It takes about two minutes per bit and you don't need a grinder.

On Carbide: Not Always the Upgrade You Think

A common instinct is to reach for carbide when a material gives trouble. Carbide's hardness and wear resistance are real advantages in the right applications. But in brass, carbide doesn't solve the self-feeding problem — it just makes it more violent. The geometry issue is still there. And carbide drills are brittle; the sudden torque spike from a dig-in event in brass is exactly the kind of shock loading that snaps a carbide bit.

In brass, use HSS with correct geometry. Save the carbide for abrasive materials, interrupted cuts in hardened steel, and high-volume production where wear life matters.

Speeds and Feeds in Brass

Brass cuts best at high surface speed — faster than steel for the same diameter. Typical HSS speeds for brass run 200–300 SFM, where steel might be 80–120 SFM for the same bit. Use a cutting oil or no lubricant at all; water-based coolant can leave staining on brass that shows up in jewelry and instrument parts.

Chip formation in brass should be short and broken, almost powdery at higher speeds. Long stringy chips mean the rake is still positive — the dig-in risk is still present.

Applications Where This Really Matters

Brass drilling comes up frequently in three areas: jewelry making (small-diameter brass stock, often hand-held), instrument repair and manufacturing (brass tubing and plates, often thin-walled), and plumbing fittings (yellow brass, thicker sections, usually on a drill press or mill).

In all three, the consequences of self-feeding are different but consistently bad. Jewelry and thin-wall tubing get torn or deformed. Fittings get pulled off the table. The geometry fix applies uniformly across all of them.