Should stainless steel be drilled fast or slow?

Stainless steel should normally be drilled at lower speed with firm feed and cutting fluid. Too much speed causes heat and work hardening.

Can aluminum be drilled at high speed?

Aluminum can usually run faster than steel, but lubrication is important because aluminum chips may stick to the cutting edge.

Is RPM the only drilling parameter that matters?

No. Feed pressure, coolant, workholding, bit material, point angle and hole depth also affect tool life and hole quality.

Drill Speed Chart for Steel, Stainless Steel and Aluminum

Drill speed is one of the easiest settings to get wrong. Too fast, and the drill bit burns. Too slow, and productivity drops. Too little feed, and the bit rubs instead of cutting.

Drill Speed Chart - industrial drill bit selection guide cover image — Drill Speed Chart – industrial drill bit selection guide cover image

The chart below is a practical starting point for common metal drilling. Real conditions still depend on bit material, machine rigidity, coolant and hole depth.

Practical RPM Starting Chart

Drill diameter	Mild steel with HSS	Stainless steel with cobalt	Aluminum with HSS	Cast iron with carbide/HSS
3 mm	2,000–3,000 RPM	800–1,500 RPM	4,000–6,000 RPM	1,500–2,500 RPM
6 mm	1,000–1,500 RPM	400–800 RPM	2,000–3,500 RPM	700–1,200 RPM
10 mm	600–900 RPM	250–500 RPM	1,200–2,000 RPM	400–800 RPM
13 mm	400–700 RPM	180–350 RPM	900–1,500 RPM	300–600 RPM
20 mm	250–450 RPM	120–250 RPM	500–900 RPM	180–350 RPM

Note: These are starting ranges, not fixed rules. Use lower speed for deeper holes, poor rigidity, harder material or larger diameters. Increase cautiously only when chips, heat and tool life are stable.

Why Larger Bits Need Lower RPM

The outside edge of a large drill bit travels farther per revolution than a small bit. At the same RPM, a 20mm drill has much higher cutting speed at the edge than a 3mm drill. That is why bigger bits need lower RPM.

Mild Steel

Mild steel is relatively forgiving. Standard HSS works for many jobs if the speed is reasonable and the bit is sharp. Use cutting fluid for cleaner holes and longer tool life, especially above 6mm.

Stainless Steel

Stainless steel is the material where speed mistakes are most expensive. It conducts heat poorly and can work-harden when the bit rubs. Use lower speed, steady feed and cutting fluid. M35 cobalt is a good starting point for many workshop users.

Aluminum

Aluminum can be drilled faster than steel, but it can stick to the cutting edge. Use sharp geometry, good chip clearance and lubrication. If chips weld onto the bit, the hole finish gets worse and the bit may grab.

Cast Iron

Cast iron is abrasive and creates powder-like chips. Coolant is often not used in the same way as steel drilling, but dust control and tool material matter. Carbide can perform well in rigid machines.

Buyer Takeaway

When customers say a drill bit burns, ask for RPM and drill diameter. Many failures are not caused by the bit itself; they happen because a large bit is run like a small bit, or stainless steel is drilled like wood.