CNC / machinist calculator
Drilling Feeds and Speeds Calculator
Drilling is not milling. A twist drill runs slower than an end mill in the same metal because the heat cannot escape from the bottom of the hole, and its feed is quoted per revolution, not per tooth. Enter the material and drill diameter and this calculator gives the spindle RPM and feed rate, the extra depth the conical point adds, and whether the hole is deep enough to need pecking, with a suggested feed reduction.
- Feed rate
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- Material removal rate
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- Point adds
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- Pecking
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How it works
Drill speed is set the same way as any cutting speed: RPM equals twelve times the surface speed over pi times the diameter. The catch is that the recommended surface speed for drilling is lower than for milling the same material, conventionally about three quarters, because a drill is buried in the work and cannot shed heat. This calculator takes the milling surface speed for the chosen material and derates it for drilling automatically.
Feed in drilling is a feed per revolution, and a good starting point is about one thousandth of an inch per revolution for every sixteenth of an inch of diameter. The table feed is that feed per revolution times the RPM. The conical point also adds depth: a 118 degree point reaches about three tenths of a diameter below the full-diameter shoulder, which you must add to a through hole.
Deep holes trap chips. Past about four diameters of depth you should peck, retracting to clear chips, and drop the feed and speed, more so in gummy metals like stainless and titanium where chips weld to the flutes. The calculator flags the depth-to-diameter ratio and suggests a strategy.
Worked example
A 1/4 in carbide drill in 1018 steel: milling speed is about 350 SFM, so drilling runs near 260 SFM, giving 4,011 RPM. Add about 0.075 in of depth for the 118 degree point on a through hole.
Frequently asked questions
Why is drilling slower than milling in the same material?
A drill is buried in the hole, so the heat generated at the cutting lips cannot escape into the air or coolant the way it can on a milling cutter. Running about three quarters of the milling surface speed keeps the drill from overheating.
What is a good drilling feed rate?
A common starting point is about 0.001 inch per revolution for each 1/16 inch of drill diameter, so a 1/4 inch drill starts near 0.004 inch per revolution. Multiply the feed per revolution by RPM for the table feed.
When do I need to peck drill?
Once a hole is deeper than about four times the drill diameter, chips struggle to clear and pack in the flutes. Peck by retracting to evacuate chips, and reduce feed and speed, especially in stainless and titanium where chips weld to the tool.
How much deeper do I drill for the point?
The conical point reaches below the full-diameter shoulder by half the diameter divided by the tangent of half the point angle. For a standard 118 degree point that is about three tenths of the diameter, which you add to a through hole.
Should I use a 118 or 135 degree drill point?
A 118 degree point suits softer materials, while a 135 degree split point centers better and resists walking in harder steels and stainless. The sharper 135 degree point also adds slightly less extra depth for a through hole.
Related calculators
Sources
Every formula on this page is shown and sourced. See how we verify.
These calculators are for planning and as a starting point. Recommended speeds and feeds are published starting values that vary with your specific tool, coating, machine rigidity, workholding and coolant. Always start conservative, listen to the cut, and follow your tool maker data sheet.