How is RPM calculated from cutting speed?

For inch tooling, RPM equals (cutting speed in SFM times 3.82) divided by the drill diameter in inches. For metric, RPM equals (cutting speed in m/min times 318.31) divided by the diameter in millimeters. Larger drills must spin slower to keep the rim speed within the material's limit.

What cutting speeds does it use?

It uses common shop values: roughly 100 SFM for mild steel, 50 SFM for stainless, 300 SFM for aluminum, and 80 SFM for cast iron with HSS drills. Carbide drills run two to three times faster. These are starting points to refine by sound, chip color, and finish.

Why does feed depend on drill diameter?

Feed per revolution scales with drill size because a bigger drill removes more material per turn without overloading. A rule of thumb is about 0.001 inch per revolution per 1/16 inch of diameter for small drills, increasing for larger ones, which this tool applies.

When should I peck drill?

Peck when the hole depth exceeds roughly three to four times the drill diameter, so chips can clear and coolant can reach the tip. The tool suggests a peck increment of about one diameter per peck for deep holes; reduce it in gummy materials like stainless.

Should I slow down for hard or thin material?

Yes. Reduce speed for hardened or work-hardening alloys to avoid burning the edge, and reduce feed when breaking through thin sheet to prevent grabbing. Always start conservative and increase once the chip and finish look right.

Drill Feed & RPM per Material Calculator

Getting drill speed and feed right means clean holes, long tool life, and no burned edges or snapped bits. This calculator converts a material’s recommended cutting speed into spindle RPM for your drill diameter, derives a feed rate from feed per revolution, and suggests a peck depth for deep holes.

How it works

The core conversions from surface cutting speed to machine settings are:

RPM (inch)   = (SFM * 3.82) / diameter_in
RPM (metric) = (m/min * 318.31) / diameter_mm
feed rate    = feed_per_rev * RPM

Feed per revolution scales with drill diameter, and carbide tooling runs at two to three times the surface speed of HSS. For deep holes the tool recommends pecking in increments of roughly one drill diameter so chips evacuate and coolant reaches the cutting edge.

Example and tips

A 1/4-inch HSS drill in mild steel at 100 SFM spins at about 1,530 RPM, with a feed near 0.004 inch per revolution, or roughly 6 inches per minute of feed. Watch the chips: long, silvery, curling chips mean good settings, while blue chips or a squeal mean too much speed. Always clamp the work, peck deep holes, and add cutting fluid for steel and stainless to keep the edge cool.