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Cast iron drilling RPM

Estimate drill RPM for cast iron using diameter, a general cutting-speed reference, and an adjustable machine limit.

Calculate

Starting estimates only. Use the cutter supplier’s data and your machine’s limits for the actual operation.

Result

Enter your values, then calculate.

Calculation method

RPM = 1000Vc/(πD). Feed = RPM × feed/rev; milling multiplies chip load by flute count.

LittleMachineShop cutting speed tablesMethod 2026-10-05.1. Independent review pending.

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Applying a general cast-iron speed reference

Reference preset: Cast iron drilling RPM. These notes describe the original preset, not changes made in the calculator above.

The supported cast-iron reference is 80 ft/min, or 24.384 m/min. With a 10 mm drill, the equation gives approximately 776 RPM before limiting. The selection is a general starting basis; it does not distinguish every cast-iron grade, hardness, casting surface, or tool design.

Keep the drill diameter and cutting speed separate. If supplier guidance changes the surface speed, edit that input rather than changing a measured dimension to obtain a desired RPM. Check a proposed machine setting in the reverse surface-speed mode when the available spindle speeds are discrete.

A speed estimate does not select coolant, extraction, tool geometry, or a safe workholding method. Feed and travel must be supplied separately for a time estimate. Use the material and tool specifications for the actual operation, particularly where a casting has varying sections or an interrupted entry.

Calculating drill RPM from diameter and material

For a drill diameter D in millimeters and cutting speed V in meters per minute, RPM is 1000 × V ÷ (π × D). A larger drill needs a lower RPM to keep the same speed at its outer edge. Choose the work material, enter the drill diameter, and check the calculated speed against the speeds available on your machine.

When to enter your own cutting speed

The material presets are starting values for the stated tool basis, not recommendations for every drill. Use the tool manufacturer's data for a coated, carbide, indexable, or otherwise specialized drill. Deep holes, interrupted cuts, poor support, and limited coolant may need a different process.

Feed and drilling time

Feed per revolution describes how far the drill advances in one turn. Multiplying it by RPM gives feed per minute. The drilling-time estimate covers the entered cutting travel; pecking, retracts, approach moves, and handling add time. Do not treat that estimate as a complete production cycle.

Moving from a calculated speed to a machine setting

For a 10 mm drill and a chosen cutting speed of 20 m/min, the equation gives about 637 RPM. At the same cutting speed, a 20 mm drill requires about 318 RPM. Diameter is in the denominator, so doubling diameter halves RPM. These examples use an assumed cutting speed to illustrate the relationship, not a material-specific recommendation.

A stepped-speed drill press may not offer the exact calculated RPM. Choose a setting using the tool and machine guidance, then use the surface-speed mode to see what that setting actually produces. If a drilling feed of 0.1 mm per revolution is used at 600 RPM, feed is 60 mm/min. A 30 mm cutting travel would take half a minute at that steady feed. The drill point, breakthrough, peck cycles, and approach allowance can change the travel or elapsed time needed. Record the selected machine speed rather than retaining an unattainable theoretical RPM in a job setup sheet.

Formula

RPM = 1000Vc/(πD). Feed = RPM × feed/rev; milling multiplies chip load by flute count.

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