Drill Bits in Kenya: Matching Bit to Material So the Drill You Bought Actually Works

A customer walks into our Ngara branch holding a three-month-old drill and announces it is weak. It will not go through a wall. It smokes in steel. It tears wood. He wants a bigger, more expensive machine. Then we look at the chuck and find a shiny metal bit, ground down to a blunt shine, that has been asked to drill steel, concrete, and mahogany in the same week.

The drill was never the problem. A drill supplies rotation and, in some models, hammering. The cutting happens at the tip of the bit, and a bit costing a fraction of the machine decides whether the machine performs. Put the wrong bit in the best drill in the shop and it will disappoint you; put the right bit in a modest one and it will surprise you.

This guide teaches you to read a bit the way a toolmaker does: what the steel and the tip tell you, what each material demands, how the SDS system works, why bits burn and turn blue, what can be sharpened, when a hole saw or forstner is the honest answer, and how to build a bit kit without buying counterfeits.

Your Drill Does Not Cut Anything. The Bit Does

Most "my drill is weak" complaints trace to one of two bit problems. Either the bit is the wrong type for the material, so its edge cannot cut at all, or the bit is dead: the cutting edges have rounded over and the tip is rubbing instead of slicing. Rubbing generates heat, heat destroys what is left of the edge, and the operator responds by pressing harder, which makes more heat. The drill takes the blame for a five-shilling piece of worn steel.

The test is simple. Fit a fresh, correct bit and try the same hole. A sharp HSS bit in mild steel produces two continuous curls of swarf, like ribbons. A sharp masonry bit with hammer on produces a steady stream of dust and walks into block work without leaning. If a new bit transforms the machine, you have your diagnosis. We cover the machines themselves in our cordless drill guide and the wider power tools buying guide; this article is about the part that touches the work.

Reading a Bit: What the Steel, the Tip and the Shank Tell You

HSS twist bits are the metal-drilling standard. HSS stands for high-speed steel, an alloy that keeps its hardness at the temperatures metal drilling creates. The whole bit is one piece of hardened steel, ground to a conical point, commonly at a 118 degree angle, with two cutting lips that shave the metal. Finishes vary: bright ground, black oxide, or a gold titanium nitride coating that reduces friction. HSS will also drill wood and plastic, though it leaves a rougher hole than a wood bit.

Carbide-tipped masonry bits attack concrete, stone, brick, and block by a different principle. Concrete cannot be shaved; it must be crushed. So a masonry bit carries a wedge of tungsten carbide brazed into a slot at the tip, visibly wider than the steel body behind it. The carbide chisels and pulverises while the flutes lift dust out. The steel body is softer than an HSS bit because it never does the cutting.

Wood brad point bits have a centre spur that anchors the bit exactly where you place it, plus two outer spurs that score the wood fibres before the lips lift the waste. The result is a clean, round, splinter-free hole that starts precisely, which matters in furniture and door work far more than raw speed.

SDS-plus bits are masonry bits with a special shank for rotary hammers: a round 10 mm shaft with grooves. We explain the system fully below, because it is the most misunderstood item in the drawer. Multi-material bits carry a specially ground carbide tip that copes with tile, brick, timber, and light metal in rotary-only mode: the right choice when one fixing passes through several materials, a compromise everywhere else.

The SDS System, and Why SDS Bits Do Not Belong in a Keyed Chuck

SDS-plus is a shank system for rotary hammers. Look at the shank and you will see four grooves: two closed oval slots and two open channels. The open channels transmit rotation from the machine; the closed slots hold the bit captive while letting it slide back and forth about a centimetre. That slide is the whole point. Inside a rotary hammer, a piston fires an air cushion against the bit thousands of times a minute, and the bit itself hammers forward into the concrete while spinning relatively slowly. The machine barely vibrates; the bit does the pounding.

Now put that same bit in an ordinary keyed chuck. The three jaws clamp a smooth round shank that was never designed to be gripped by friction, so under load the bit spins in the jaws, glazing the shank and scoring the chuck. And even where it grips, an ordinary hammer drill cannot use it properly: its cam-type hammer action is a fast, shallow rattle produced by two ridged discs, a fraction of the impact energy of a piston. You get a damaged bit, a worn chuck, and a slow hole. The pairing runs one way only: SDS bits in SDS machines, straight-shank bits in chucks. Adaptor chucks that let an SDS machine drive straight-shank bits exist and are useful for occasional wood or metal work, but they add wobble, so keep precision drilling on a proper chuck or a bench machine like our industrial drill press.

Speed and Pressure: Metal Slow and Oiled, Masonry Hammered, Wood Fast and Clean

Every material has a cutting speed its edge can survive, and the rule of thumb runs opposite to instinct. Metal wants low speed and firm, steady feed. The larger the bit, the slower the spindle, because the outer edge of a big bit travels much faster than the centre at the same rpm. Add a drop of cutting oil, or any clean oil in a pinch: it carries heat away and lubricates the cut. Watch the swarf: ribbons mean the feed is right, dust means you are rubbing, and a squeal means the edge is dying. Centre punch the hole first so the point cannot wander, and step up through a pilot hole for anything large.

Masonry wants the hammer switched on and only moderate pressure. The carbide crushes on each impact; your job is to keep the tip against fresh material and pull back every few seconds so the flutes can clear dust, because packed dust is an insulator that cooks the tip. Wood wants speed and a light feed. High rpm lets the spurs slice fibres cleanly; back the workpiece with scrap timber and the exit side will not blow out. And in all three materials, ease off just before breakthrough, the moment when bits grab, holes tear, and wrists get hurt.

Why Bits Burn: the Blue Tip Is a Death Certificate

Heat is the enemy of every cutting edge, and three habits generate it. Running metal too fast is the biggest: the edge rubs faster than it can cut, friction climbs, and temperature soars in seconds. Drilling dry is the second: without oil, all the friction heat stays in the tip. The third is persisting with a dull bit, because a dull edge rubs by definition, and rubbing plus pressing is a blowtorch.

The evidence is the colour. When an HSS bit overheats badly, the steel loses its hardening (a change metallurgists call tempering back) and the tip turns straw, then purple, then blue. A blue tip is a death sign: that steel is now soft, and it will blunt again within seconds of touching work, no matter how carefully you sharpen it. Grind back past the blued zone into bright steel, or retire the bit. Stainless steel deserves its own warning: it work hardens, meaning the metal itself becomes harder wherever a rubbing bit polishes it. Drill stainless slowly, with firm feed and oil, and never let the bit spin without cutting.

Hole Saws and Forstners: For Holes Twist Bits Cannot Make

Twist bits run out of sense beyond about 13 mm in most chucks. For big holes, cutting the whole face is wasted effort; a hole saw cuts only the rim. It is a cylinder with saw teeth mounted on an arbor with a pilot bit in the centre, and it makes the large holes fundis meet weekly: door lock bores, sink and basin pipe pass-throughs, downlight cut-outs in ceiling board, cable entries through cabinet backs. Run it slower than a twist bit, keep it square to the work, and withdraw often to clear the deep kerf, because a packed hole saw burns rather than cuts.

A forstner bit does what neither twist bit nor hole saw can: a flat-bottomed hole, guided by its rim rather than its centre point. That is why it can drill a partial hole overlapping the edge of a board, and why every cabinet fundi needs one: concealed hinge cups on cupboard doors are a forstner job, full stop. Forstners are happiest in a drill press, where feed and squareness are controlled. And for edge profiles, grooves, and joinery rather than holes, a router bit set takes over where drilling ends; ask at the counter and we will match the shank to your machine. All of these live in our workshop and industrial tools range.

A Starter Kit for a Fundi, or Buying Singles?

Buy the spread as sets and the workhorses as singles. A sensible starting bench is a metric HSS set from 1 to 10 mm, a masonry set from around 5 to 12 mm, a small brad point set for clean wood, and, if you run a rotary hammer, SDS-plus bits in the two or three fixing sizes your plugs actually use. Add one or two hole saws sized to the pipes and locks you fit, and a driver set such as the 9-piece screwdriver bit set so screws stop eating your drill bits' spotlight. That kit covers most site work.

Then watch which holes you drill for a living. Every trade has two or three sizes that do most of the work: the masonry size that fits your wall plugs, the pilot sizes for your screws. Those are the bits that die monthly, and those you buy as singles, in better quality than the set, several at a time. A set gives you range; singles give you endurance where you actually spend it. Pair the kit with the right machine, from a 450 W corded drill for bench work to the 20 V brushless cordless for site days, and check current pricing on our price list.

Spotting Counterfeit Bits Before They Waste Your Money

Kenya's tool market carries plenty of bits stamped HSS that are plain carbon steel, hard enough to demonstrate in the shop and soft enough to die in the first real hole. The tells are physical. On a quality twist bit the flutes are ground after hardening, leaving bright, crisp, sharp-edged spirals; cheap bits are rolled or roughly ground, with rounded flute edges and a painted-on finish that flakes at the tip. Check the masonry bit's brazing: the carbide insert should sit centred and symmetrical in its slot with a neat fillet of braze, not tilted with blobs and gaps.

Read the shank: genuine bits state size and material grade in clean engraving or etching; fakes have blurry stamps, or nothing. Compare a suspicious gold bit against a known coated one, because fake "titanium" is often just yellow paint that scratches off with a fingernail. Mind the packaging spelling and, above all, the price: real HSS and real carbide have a floor cost, and a set priced like sweets is telling you what is inside. The cheapest protection is buying from a dealer who has to face you again when the bit fails, which is precisely the after-sales trade our six branches live on.

Anatomy Worth Knowing

A little vocabulary makes every counter conversation faster. The shank is what the chuck grips. The flutes are the spiral channels that lift chips and dust out of the hole; when they pack full, cutting stops and heating starts. The cutting lips at the point do all the work, which is why sharpening is really just restoring two small edges. On a masonry bit, the brazed carbide insert replaces the lips. Know those four words and the diagram below, and you can describe any bit problem precisely.

Frequently Asked Questions