How do you drill and tap each metal? Speeds, lubricant, and bits

What speed should you drill metal at?

One formula sets every drill speed: RPM = (cutting speed × 3.82) ÷ bit diameter in inches. Every metal has a published cutting speed in surface feet per minute (SFM): about 90 for mild steel, 30 for stainless, 250 for aluminum with a plain HSS bit. Small bits spin fast, big bits spin slow, and that's the whole science.

Worked example. Say you're putting 1/4″ bolt holes in brackets made from the 1018 flat bar on our carbon steel rack (a 12″ piece of 1/8″ × 1″ runs $5.34 CAD as of June 2026). Mild steel's cutting speed is about 90 SFM. So 90 × 3.82 = 344, divided by 0.25″ gives about 1,375 RPM. No press has exactly that speed, so set the belt to the closest speed below it and drill. The 3.82 isn't magic, it's 12 divided by pi: the unit math that turns feet per minute at the bit's edge into revolutions.

Two rules ride along with the formula. First, the chart numbers are ceilings, measured by bit makers on rigid machines with steady coolant, so the conservative end is where a home drill press lives. Second, the mistakes aren't symmetrical: too slow only costs you time, too fast burns the bit's edge off in seconds. When in doubt, halve it.

What drill speed does each metal want?

Mild steel wants about 1,375 RPM at 1/4″ and 690 at 1/2″, stainless wants a third of that, and aluminum and brass want all the speed a home press has. The table below assumes a plain HSS twist bit in a drill press, with the work clamped. RPMs compute from the conservative end of the published charts: Norseman and Viking print 80-110 SFM for mild steel, and we compute at 90. Round down to the nearest speed your press actually has.

Anything over about 3,000 reads "as fast as your press goes". Most benchtop presses top out a little over 3,000 RPM, and that's fine for small bits in aluminum and brass. Feed matters as much as speed: the old maker rule is .001″ per revolution for every 1/16″ of bit diameter, which at the bench means lean in until a real curl of chip comes out. Dust instead of chips means you're rubbing, and in 304 or 316 rubbing is fatal, because stainless work-hardens the moment the bit dwells. Keep the feed steady from first contact to breakthrough and don't stop halfway.

Three more table footnotes. Copper's published speeds scatter more than any other metal here, so we computed at 100 SFM, the cautious end, with oil and pecking. Holes deeper than 3-4 bit diameters want pecking too, plus speed and feed backed off up to half. And don't plan on drilling our chrome-plated 1045 rod: hard chrome plate measures at least as hard as the bit itself, so drill before plating or hand that hole to a machine shop.

Which drill bits do you actually need?

A sharp set of plain HSS twist bits covers steel, aluminum, brass, and copper. Add cobalt bits in your working sizes for stainless. Skip carbide at the bench, and don't pay extra for gold-coloured coatings on cheap bits.

HSS (high-speed steel) is the default for a reason: it's tough enough to forgive a hand-fed press, it resharpens, and at the speeds in the table above it handles everything on our rack. Cobalt bits (M35 has 5% cobalt, M42 has 8%) are the honest stainless upgrade, because the cobalt is alloyed through the whole bit, not painted on. It keeps its hardness when the cut runs hot, which is exactly what 304 and 316 do to a bit, and it survives resharpening since there's no coating to grind off. M35 tolerates a little handheld flex; M42 is harder but more brittle, so save it for the press.

Carbide runs 2-3 times faster, and in a production machine it earns its price. In a hand drill or a wobbly press it chips and snaps, because carbide trades toughness for hardness. The titanium-nitride question deserves a straight answer too: TiN is a coating a few microns thick over whatever steel sits underneath. On a quality HSS bit it cuts friction and stretches life; on a bargain-bin bit it's gold paint on soft steel, and the first resharpen removes it from the tip where the cutting happens. Buy the steel and the geometry first. One geometry worth paying for: a 135° split point, which starts on target with less push and barely walks.

How do you stop the bit wandering, grabbing, or biting you?

Centre punch every hole, clamp every piece, and keep gloves off while anything spins. Those three habits prevent most of what goes wrong at a drill press.

The punch matters because a twist bit's tip isn't a needle, it's a short chisel edge that skates across smooth metal. A centre-punch dimple gives that edge a home, so the hole lands where you laid it out. The chisel edge also explains pilot holes: the centre of the bit ploughs rather than cuts, and it generates most of the push you feel. A pilot hole just larger than the chisel edge (about 1/8″ for a typical 1/2″ bit) gives the centre nothing to plough, so big holes in steel suddenly need a fraction of the force. Use a pilot for holes 3/8″ and up in steel, and keep it near the chisel-edge width, not half the final size, or the big bit's corners take the whole load and chatter.

Skip the pilot where it backfires. In brass and copper, an open pilot hole lets the bit's sharp lips screw themselves in and grab; C360 is famous for it. Stone the cutting lips to zero rake first, the trick our metal cutting guide walks through, and drill brass in one pass where you can. Thin sheet is the other exception: stacked drill sizes leave lobed, triangular holes, so use a step bit instead.

On safety, we follow CCOHS's drill press rules and they're blunt: no gloves, rings, watches, or bracelets at the press, because anything a spindle can catch, it winds in. Clamp or vise the work, never hand-hold it; a 12″ bar that catches becomes a propeller at 1,000 RPM. Chuck key out before the power goes on, safety glasses on, and chips leave by brush, not by hand. Gloves go back on afterward for handling, since fresh burrs are razor-sharp.

What lubricant should you use on each metal?

Cutting oil for steel and stainless, WD-40 or another light kerosene-class oil for aluminum, nothing for brass, generous oil for copper. Tapping always gets lube, and thicker is better.

The why is different for each family. Steel and stainless use oil for cooling and edge life, and on stainless the oil is half of beating work-hardening. Aluminum isn't hard, it's sticky: dry chips weld onto the bit's edge and the welded lump does the cutting badly, so the kerosene-class lubricants are there to stop the sticking. That's been the shop standard for decades, and it's why a thin spray like WD-40 works well on 6061. Leaded brass machines dry because its 3% lead is a built-in lubricant that breaks the chip for you. One finish note: the dark sulphur oils can stain brass and copper, so keep them on the steels if the part's colour matters.

What size hole do you drill before tapping?

Smaller than the bolt, and always from a chart: each tap has one matching drill. A 1/4-20 thread takes a #7 bit (0.201″). Drill the "obvious" 1/4″ hole and the tap has nothing to cut, so you get zero thread. The chart targets about 75% thread height, the standard for hand tapping.

Metric is friendlier: tap drill = diameter minus pitch. M6 × 1.0 takes a 5.0mm bit, M8 × 1.25 takes 6.8mm, M10 × 1.5 takes 8.5mm. Number and letter bits like #7 and F come in a 115-piece index, and the chart lists nearest fractional substitutes if you don't own one. One honest nuance the chart itself prints: the 75% column is for aluminum, brass, and plastics, and a second column near 50% covers steel, stainless, and iron. Taller threads in tough metal cost far more torque than they add strength. Hand-tapping 304? Use the easier column.

Taps come in three grinds. A taper tap leads in over 8-10 shallow threads, so it starts square with the least effort. A plug tap leads over 3-5, the all-rounder to buy if you buy one. A bottoming tap leads over 1-1.5 threads, cuts to the bottom of a blind hole, and should never start a thread. Start dead square: with the work still in the drill-press vise, stand the tap in the chuck and turn the chuck by hand, power off, then finish with the wrench. Every half turn forward, back off a quarter turn to snap the chip. C360 brass is the classic first tapping project: cut a 12″ stick of 3/8″ hex ($9.11 CAD as of June 2026) into 1″ lengths, drill #21, tap 10-32, and you've made standoffs. Why leaded brass taps that sweetly is the story of our 360 vs 260 brass guide.

Why do taps snap, and what do you do about it?

Taps snap for five reasons: the hole's too small, the tap's crooked, it's running dry, the flutes are packed with chips, or it hit the bottom of a blind hole. All five are preventable, and none are cheap to fix after the crack.

The hole is the usual culprit. Drill 3/16″ instead of #7 for a 1/4-20 and you've asked the tap to cut nearly full-height threads; in steel it wedges and cracks before the third full turn. Crooked starts bind a little more every revolution, which is what the drill-press-chuck start prevents. Dry taps gall, especially in stainless and aluminum. And in blind holes, chips have nowhere to fall. Drill deeper than the thread you need where the part allows, back out to clear the flutes every few turns, and wrap tape on the tap as a depth flag. Stop the moment the feel goes soft. Run the taper or plug tap first and let the bottoming tap only finish the last few threads.

Stainless adds its own trap: a tap that stalls and rubs in 304 work-hardens the thread walls, the same logic as the drilling rule, and the next turn fights metal harder than the tap. Sharp taps, the 50% column, steady cutting, and tapping fluid keep you out of it; our cutting guide covers the same habit for saws and grinders. If a tap does snap, know what you're up against: hardened tap steel laughs at HSS bits. Extraction means a tap extractor on bigger sizes, carbide in a rigid setup, or honestly remaking the part. On a $9 stick of hex, remaking wins.

Drilling annealed O1 for a knife or punch project follows the table like everything else; the heat-treating that comes after is its own subject, and our O1 tool steel guide covers it start to finish. Want the metal to show up ready for the drill press? Type your length in inches on any bar on the store and that's what arrives, the cut free to ±1/8″, up to 96″ shipped anywhere in Canada. Got a job past the bench, production tapping, hardened material, or a few hundred holes? Send a quote request with a sketch and we'll price it; sourcing and odd work runs 2-21 days.