The gold TiN coating is a ceramic layer that is extremely hard and drastically reduces the coefficients of friction. This means that the drill bit slides better through the material, heats up less and has a service life up to 6 times longer than an uncoated HSS drill bit. Examples of drill bits with TiN coating: the HSS PZ Cobalt and the HSS Cobalt Grip from ALPEN.

The most common mistake and the big misunderstanding: the coating is only on the surface. As soon as you regrind this drill bit, you also remove the coating on the cutting lip and tip — exactly where it’s needed. The drill bit is then degraded to a normal HSS drill bit.

In addition, TiN is heat-sensitive at extreme temperatures. If you drill too aggressively without cooling and the tip turns blue, the coating loses its hardness. TiN drill bits are ideal for series drilling in steel, but only as long as they do not need to be reground.

A standard drill bit has a "chisel edge" at the centre of the tip. This chisel edge does not cut, but only pushes and scrapes away the material (similar to a chisel). That’s why a standard drill bit tends to "walk" on smooth surfaces without centre punching and requires high feed pressure (about 70% of the force is used just to push the chisel edge!).

With the split point, as used on most of ALPEN’s metal drill bits, this chisel edge is ground away ("pointed"), creating a sharper, self-centring tip. This creates two additional small cutting edges directly in the centre.

The effect: the drill immediately centres itself as soon as it touches the material. It grips more aggressively, requires about 30–40% less feed pressure and does not wander. This is especially valuable when drilling freehand into metal pipes or on curved surfaces, where using a centre punch would deform the pipe.

• Flat-bottom (spade) bit: the "rough" tool. Very cheap, very fast, but produces rough holes. Ideal for pass-throughs (cables/pipes) in beams, where appearance doesn’t matter. Tends to cause tear-out on the exit side.
   
• Forstner bit (e.g., Sharp Shark from ALPEN): the "precision tool". It is guided through the outer ring, not the tip. Produces extremely clean, smooth-walled blind holes with a flat bottom (e.g., for cup hinges). Disadvantage: it heats up quickly (friction on the outer ring), so take breaks!
   
• Spiral (auger) bit (e.g., Form Lewis from ALPEN): the "deep drilling tool". The threaded tip pulls itself into the wood (no pressure needed!). The large spiral ejects chips from deep holes (e.g., 20-40cm deep beam holes). It is indispensable for precise, deep through-holes in structural timber construction.

1. No catching: thanks to the straight flute geometry, it does not screw itself into the material.
    
2. Deburring included: the next step automatically engages (deburrs) the edge of the previous step.
    
3. Dimensional accuracy: a 10mm hole comes out exactly 10mm, not 10.2mm as often happens with a wobbling twist drill bit.
    
4. Centring: it centres itself and gradually expands the hole, which is gentle on the material.

This phenomenon occurs when the drill tip breaks through the material on the backside. In that moment, the axial resistance disappears. The chisel edge is no longer in contact with the material. The drill bit suddenly plunges deeper (like threading into a screw).

Since metal sheets are often thin, the sharp main cutting edges catch on the edges of the almost finished hole. Instead of cutting, the drill "screws" itself into the residual material through the slope of the spiral.

Solution:

1. Use a sheet metal drill bit or step drill bit (these have a straight flute and cannot screw themselves in).
    
2. For twist drill bits: just before breakthrough, drastically reduce the pressure and maintain a high speed.
    
3. Always clamp the workpiece securely ("vice effect" prevents injuries).

A classic 2-flute bit has a single carbide plate. If this drill bit hits a piece of rebar, the carbide plate can "catch" on the side of the steel. This immediately blocks the machine (the slip clutch engages or the wrist is twisted) and often breaks the carbide plate.

A 4-flute bit often has a main plate and two secondary plates, or a solid X-head (like the Force X from Alpen) that fills the drill cross-section almost completely.

If it hits rebar, it cannot catch or snag, because the 90° geometry prevents this. It "scrapes" over the rebar instead of digging in and jamming. Additionally, four flutes remove the drilling dust faster and produce a rounder hole (important for anchor holding strength), whereas 2-flute bits often create slightly oval holes.

Twist drill bits tend to create out-of-round, triangular holes ("chatter") in thin materials (sheet metal, cable ducts). The step drill bit works differently: it scrapes the material away in defined steps instead of cutting like a wedge.

Advantages:

1. No catching: thanks to the straight flute geometry, it does not screw itself into the material.
    
2. Deburring included: the next step automatically engages (deburrs) the edge of the previous step.
    
3. Dimensional accuracy: a 10mm hole comes out exactly 10mm, not 10.2mm as often happens with a wobbling twist drill bit.
    
4. Centring: it centres itself and gradually expands the hole, which is gentle on the material.

When looking at a drill from the side, the surface behind the cutting edge (the "back") must slope downward. This is the relief angle (usually about 8-12°).

Without this angle (0°), meaning the back is the same height as the cutting edge, the surface behind the edge presses on the workpiece before the cutting edge can penetrate.

The drill bit just rubs on the material, generating enormous heat from friction but not producing a single chip. This is the most common mistake when manually sharpening drill bits: the cutting edge looks sharp, but the back hasn’t been ground away enough. The drill bit "rides up" and physically cannot penetrate the material.

Plexiglass is brittle and sensitive to heat. A standard HSS drill bit has a positive rake angle (it pulls itself into the material). Upon exiting the plate, this almost always leads to "bouncing" or shell cracking in the glass.

Adaptation (technique):

You need to "blunt" the sharp cutting edge of the drill bit (grind a negative rake angle) by gently holding it against a sharpening stone. This makes the drill bit act more like a scraping tool than a cutting tool.

Alternatively: very high speed, but extremely low feed (pressure).

And importantly: cooling with a water/detergent mixture or compressed air, as melted acrylic will instantly stick to the drill bit and then, due to expansion, cause the workpiece to crack.

The difference lies in the binding of the diamonds and the cooling technology.

• Wet-core bits: the diamonds are embedded in a relatively hard metal matrix (sintered). You need water to dissipate the heat and flush out the drilling mud. Without water, the segment overheats, the solder melts (loss of the segment), or the matrix "smears" and the diamonds do not become exposed.
• Dry-core bits (for angle grinders/drills): these often use vacuum-brazed technology or special soft solders and have integrated cooling wax fillings in the shaft (for small diameters). Extremely high speeds (e.g. 10,000 rpm on the angle grinder) create a draft of air that cools. The diamonds protrude further. Even so, you need to "wobble" the machine (move it in a circular motion) so that air reaches the cutting edge; otherwise, these bits will also burn out.

Left-handed drill bits are geometrically identical to normal drill bits, only helically reversed. You need to switch the machine to reverse (left-hand) mode in order for it to drill.

Their primary use is to drill out broken screws.

The ingenious physical effect: While drilling into the broken bolt, the friction and cutting force transfer a leftward rotational torque onto the remaining bolt fragment.

That's exactly the direction needed to loosen a right-handed thread! Often, the remaining part of the screw loosens by itself due to the heat and torque generated while drilling and turns out on its own, without the need to use a left-handed screw extractor (pig-tail).

Cheap chucks tighten purely by friction. High-quality keyless chucks have a clamping force lock and a re-tightening mechanism.

The "clicking" or "chattering" when tightening is a detent mechanism. This prevents the chuck from opening on its own due to vibrations (hammer drilling) or the sudden stopping of the machine (braking) because of rotational inertia.

During metal drilling with strong vibrations, a simple chuck would loosen. The click system ensures that under load, the jaws bite even more firmly into the drill shank instead of loosening.

Classic motors conduct electricity via sliding carbon brushes onto the rotating armature (commutator). This creates friction, heat and flying sparks – sheer waste of energy.

A brushless motor (EC motor) reverses the principle: the magnets rotate, while the coils remain stationary. The control is carried out electronically.

Advantages for drilling:

1. Compactness: The motor is shorter (better handling in corners).
    
2. Torque curve: brushless motors can maintain constant torque over a wider speed range.
    
3. No overheating: since there is no brush friction, the motor heats up less. This is crucial under continuous load (e.g., drilling many holes in hardwood), where conventional motors would "burn out."

An impact driver ("Impa") generates torque through rotational blows (tangential impact mechanism).

Problems when drilling:

1. Chuck: The ¼-inch hex shank inherently has "play". The drill bit wobbles ("runout inaccuracy"). Precise drilling is impossible.
    
2. Drill breakage: HSS drill bits are designed for continuous cutting. The hard impacts from the impact driver microscopically shatter the cutting edges or cause the drill bit to break.
    
3. Exception: flat spade bits or auger bits in wood. Here, the impact mechanism is actually helpful, as it eliminates reaction torque on the wrist. For metal or stone, however, the impact driver is a no-go.

Specifically for use in impact drivers, ALPEN developed the Impulzor line to avoid the problems that normally occur there.

The adjustment ring (numbers 1-20) on the cordless screwdriver controls a mechanical clutch. Balls are pressed into recesses by springs. If the torque exceeds the spring force, the balls slip over - the chuck stops while the motor keeps turning.

When drilling, however, we need maximum power transmission and, above all, continuity.

If the clutch triggers while drilling (e.g., set to 15 instead of the drill symbol), the drill bit gets stuck in the material. The chip removal stops immediately. If you don’t pull back immediately, the chip jams, friction increases, and the drill bit can break when you start again. The drill icon deactivates this mechanism (direct connection).

The quill is the movable steel tube in which the drill shaft is mounted, and it extends out of the housing during drilling.

On cheap machines, the quill has too much play in the cast housing ("slack").

In the retracted state, you will not notice anything. But as soon as you extend the quill 5-8 cm, the lever arm increases. The drill bit tip starts to "dance" (it deviates sideways).

The result: holes are not round, but triangular or oval, and drill bits break more quickly.

Good machines have an adjustable quill guide or tighter tolerances (a few hundredths of a millimetre of play, instead of tenths).

Drilling into steel generates high thrust forces. You push the drill bit down, and the workpiece pushes back.

In inexpensive drill presses or benchtop drills, the column (the vertical tube) is thin-walled and hollow. Under pressure, the entire column bends slightly backward (elastic deformation).

The result: the drill bit does not hit at a 90° angle, but slightly off-square. The hole "drifts" and becomes skewed as it goes deeper. In deep drilling of metal blocks, the drill bit emerges offset at the bottom.

Professional solution: solid, massive columns or extremely thick-walled tubes that do not twist.

Cordless machines have caught up, but in two areas, the wired device is physically superior:

1. Continuous load when mixing: those mixing mortar or tile adhesive need consistent, high torque over several minutes. Batteries overheat quickly here, as they have to deliver enormous currents. The corded machine uses the airflow of the fan wheel more effectively and has no limited energy reserves.
    
2. Drill stand use: a corded machine is usually slimmer and has a standard 43mm collar (Euro collar). Many cordless drills have a "pistol shape" due to the gearbox and battery, which either doesn't fit into drill stands or isn't axially aligned. Additionally, cordless drills often lack the lock button for continuous operation.

DIYers often think their machine is defective because the SDS drill bit "wobbles".

This is a system requirement. The SDS system doesn't hammer on the chuck (like with a hammer drill); instead, a striker inside hits directly on the end of the drill bit shank.

The drill bit (e.g., Force X from ALPEN) must be able to move freely axially (back and forth) in the chuck to absorb the impact and transfer it to the tip ("slip fit"). If it were clamped rigidly, the impact energy would shatter the chuck. Lateral guidance is provided by the hole itself once the drill has penetrated about 1 cm.

Choosing the wrong coolant ruins the tool or workpiece:

• Steel/stainless steel: here, you need drilling emulsion or cutting oil. Water cools well, but it doesn’t lubricate. Without lubrication, the oil film breaks, and the cutting edge and material microscopically weld together. Moreover, pure water immediately causes rust.
   
• Aluminium: aluminium is soft and "lubricates" (it sticks). It clogs the flutes of the drill bit (built-up edge). Alcohol (ethanol) is ideal because it cools extremely well (evaporative cooling) and prevents the chips from sticking to the drill bit. Oil would often be too viscous here and would cause the chips to stick.
   
• Brass: It is usually drilled dry (short-chipping chips), as lubricants can cause the drill bit to suction itself in ("pull in").

When drilling in concrete, fine drilling dust remains in the hole and settles in the pores of the wall. If you now insert a wall plug, this fine dust acts like ball bearings. The friction between the plug and the wall is drastically reduced.

With conventional expansion plugs, this can reduce the holding force by up to 50%. With injection mortar (chemical anchors), it is even fatal: the mortar then bonds only to the dust, not to the masonry. If you pull on the screw, you pull out the entire mortar plug along with the dust layer ("sausage-skin effect").

Therefore, the mandatory order applies: 1. Drill the hole, 2. Blow out the hole (at least 2x), 3. Brush out the hole (mechanically!), 4. Blow it out again. Only then insert the plug.

This labour-intensive process of cleaning holes for anchors in concrete can be simplified or even partially eliminated by using the Alpen Dust Extractor. With this suction drill bit, the drilling dust is extracted directly from the hole while drilling.

An expansion wall plug holds by pressure: it presses against the wall of the drilled hole. This expansion pressure can cause the concrete edge to chip in edge-near holes (e.g., railing mounting close to the concrete edge).

Injection mortar works without expansion pressure. It bonds the threaded rod to the concrete chemically. The load is distributed evenly over the entire bonding depth.

This makes it indispensable for:

1. Edge-near fastenings: because no expansive force occurs.
    
2. Porous or crumbling substrates: the mortar flows into cracks and cavities, solidifying the surrounding material.
    
3. Dynamic loads: awnings or heavy gates that shake. A plastic wall plug can "work loose" from vibration, but hardened mortar cannot.

Aerated concrete is very soft and consists largely of air pores. A standard expansion wall plug compresses the material only slightly when expanding; when you tighten the screw, the wall plug "pulverises" the soft surrounding material and strips out. No counter-pressure is generated.

Solution:

1. Special wall plugs (GB anchors): These have wing-like ribs that don’t expand but actually cut into the soft material (form fit instead of friction fit).
    
2. Undersize drilling: In aerated concrete, you often drill 1 mm smaller than specified (no hammering!) so that the wall plug fits extremely tight as soon as it’s inserted.
    
3. Tapered drill bit: For heavy loads, the hole is widened conically at the back (relief cut) and filled with mortar, forming a "plug".

A plasterboard panel itself holds very little weight (the gypsum crumbles). The load must be distributed to the back of the panel.

• Knotted wall plugs (plastic): When you tighten the screw, the wall plug shaft contracts and knots behind the panel into a bundle. Important: This only works if the screw is long enough to fully pass through the front of the wall plug and the torque is applied correctly.
   
• Toggle wall plugs / spring toggle bolts (metal): These are pushed through the hole and open up in the cavity behind (like an anchor). They distribute the force over a larger area and are mandatory for ceiling installations (lamps) on plasterboard, as they withstand far higher tensile loads than plastic knotted wall plugs.

The problem: The outer 10-20cm of the wall is only soft polystyrene/wool. If you screw into it, you push the facade in, and water can penetrate. If you screw a long screw all the way into the masonry, the metal conducts the cold inside (thermal bridge risk & risk of mould inside).

The solution is thermally separated mounting systems (e.g., Thermax).

These consist of a threaded rod (for anchoring in the masonry) and a head made of fibreglass-reinforced plastic (GRP). The plastic cone sits in the insulation and interrupts the flow of cold ("thermal separation"). Additionally, it automatically cuts through the plaster and seals the hole.

Brass is a soft, short-chip-forming alloy. Standard HSS drill bits have a positive rake angle (the spiral is sharply twisted, causing the bit to pull itself into the material).

In the case of brass, this results in the drill bit being "grabbed" greedily. It does not cut in a controlled manner, but suddenly screws itself into the workpiece. On a drill press, it pulls the workpiece upward; when hand drilling, it can wrench the machine out of your hands.

Solution:

You need to "de-sharpen" the main cutting edge of the drill bit (grind it to a 0° rake angle, i.e., slightly flatten the sharp front edge of the lip). As a result, the drill bit scrapes the brass in a controlled manner instead of eating into it.

Stainless steel does not rust because it forms a passive chromium oxide layer. However, if you use a tool (bit or drill bit) that has previously worked on "mild steel" (construction steel) on stainless steel, you transfer microscopic iron particles onto the stainless surface.

These iron particles begin to rust when exposed to moisture. This rust "infects" the stainless steel (contact corrosion) and eats its way through the passive layer.

Rule: use strictly separate tools! Bits and drill bits for stainless steel ("Inox") must never touch normal steel. If in doubt, use diamond-coated bits or special stainless steel bits (torsion).

The rattling is caused by resonance. When a countersink with 3 cutting edges (symmetrical) hits the material and one cutting edge "bounces," the others follow in the same rhythm. It starts to oscillate ("polygon effect").

Good countersinks use two tricks:

1. Unequal spacing: The cutting edges are not exactly arranged at 120°, but rather at angles like 118°, 122°, etc. This breaks the resonance frequency.
    
2. Speed: Rattling is almost always a sign of too high a speed. Countersinking must be done extremely slowly (a few hundred rpm), but with high pressure, so the countersink cuts and doesn’t vibrate.

In deep blind holes, the flutes quickly fill completely with chips.

Once the flutes are full, the chips are pressed against the hole wall. Friction rises exponentially, the drill bit jams, and can break.

Technique: you have to "vent" (remove the chips). This means that after each drilling depth of about three times the diameter (e.g., with a 5mm drill every 15mm deep), you have to pull the drill bit completely out of the hole while the machine is running. The chips fly out, the coolant can flow in. Without venting, drill breakage in deep holes is inevitable.

An old DIY tip says: "Stick masking tape on the tile, then the drill bit won’t slip."

Physically speaking, that's only half the truth. The masking tape does give the drill bit tip some grip, but it doesn’t prevent drifting if the tip is dull.

The professional method for hard tiles: you must never use a hammer and centre punch (risk of breaking the tile!). Instead, use a sharp centre punch with hand pressure only: place it on the tile and twist/press it firmly into the glaze until a tiny indentation forms. The drill bit tip will sit securely in this tiny indentation. For porcelain tiles, only a drilling template helps (e.g., a piece of wood with a matching hole that you press or stick onto the tile).

You can completely skip centre punching with the ALPEN C-Protector Gen2, the top product for drilling in tiles and porcelain. When drilling into regular ceramic tiles, however, it is recommended to use the ALPEN MultiCut, with prior centre punching.

If there is no depth stop, many paint a line with a felt-tip pen on the drill bit.

Problem: during rotation, the line is often barely visible ("blurred"), and the drill dust/friction wipes it off.

Better solution: wrap a piece of coloured insulating tape ("tab") around the drill bit.

Hot tip: let the end of the tape stick out a little. When this little protruding tab sweeps the drill dust aside on the surface, you don’t just know visually that the depth has been reached, you can also tell acoustically and visually from the movement of the dust. In addition, it acts as a "fan", improving visibility of the drilled hole.

Many tenants drill into the joint to avoid damaging the tile ("easy to reverse" installation).

Technically, this is usually disastrous for load-bearing capacity. Joint mortar is porous, crumbly, and often has cavities behind it. A wall plug cannot develop any defined expansion pressure there. It is more likely to blow the mortar out.

In addition, joints are often narrower than the wall plug. If the wall plug then presses upwards and downwards against the edges of the tile when expanding, the tiles can crack or chip under the wall plug head.

Exception: only acceptable for very light loads (e.g., towel hooks). Anything over 1-2 kg should be anchored in the centre of the tile (or the stone).

A classic beginner’s mistake: you’ve drilled the hole, release the switch, and then try to pull the stationary machine out of the hole.

This often doesn’t work because chips or concrete fragments jam between the flute and the wall of the hole ("wedge effect"). If you pull by force, the drill bit can detach from the chuck and get stuck.

Correct method: always withdraw the machine while the motor is running (at high speed). The rotation actively conveys the drill dust outward like a screw conveyor and cuts through any jammed fragments.

Drilling into the ceiling is pure agony. The fine concrete dust doesn’t just fall into your eyes (safety goggles are a must!), it is also sucked in by the drill’s fan (usually at the front) directly into the motor and the chuck. This ruins chuck threads and bearings.

The trick: take half a tennis ball or a yoghurt cup, drill a hole in the bottom, and slide it over the drill bit (opening facing the ceiling). The cup collects 90% of the dust before it can reach the machine or your face.

You protect yourself and the machine even better from drilling dust by using a dust-collecting drill bit, such as the Dust Extractor from ALPEN.

This is the most important safety rule in machining: no gloves!

When a smooth drill bit rotates, the danger seems low. But as soon as a chip forms or the drill bit has a spiral, the material of the glove can be caught.

The glove does not simply tear. It is tough. The machine wraps the glove (and the finger/hand inside it) around the spindle in a fraction of a second. This can result in severe crush injuries, broken bones, and even the amputation of fingers. The human response time is not enough to press the "emergency stop" before the hand gets wrapped.

There are installation zones, but in older buildings you should never rely on them.

The theory: pipes and cables run vertically and horizontally, usually 30cm below the ceiling or 30cm above the floor. They also run vertically directly above switches/sockets.

The reality (older buildings): pipes and cables were often laid diagonally ("shortest route").

Therefore, never drill without a locating device. Areas directly next to door frames (often electrical wires) and walls behind bathrooms or kitchens (water pipes) are particularly dangerous. An RCD (residual current device) can save lives from electric shock, but drilling into a water pipe can cause damage costing thousands of euros.

A hammer drill produces sound pressure levels of over 100 dB(A). What many underestimate is that it’s not just the volume, but also the frequency and the pulsed nature of the sound.

Hammering metal on stone generates extremely high-frequency peaks. These high frequencies damage the hair cells in the inner ear faster than dull thudding. A single hole in reinforced concrete without hearing protection can, especially in small, echoing rooms like bathrooms, cause permanent tinnitus ("acoustic trauma").

Many windowsills from the 60s/70s are made of composite stone/fibre cement, which often contains asbestos (to make it shatterproof).

DIYers often drill into these to attach cladding or cable channels.

The grey dust looks harmless, like concrete dust. Asbestos fibres do not break down in the lungs and can cause cancer years later, so drilling into unknown composite stone slabs without testing is a major risk. If in doubt, stick instead of drilling!

50. The "ladder trap": Why do so many falls occur when drilling on ladders due to "counter-pressure loss"?

Anyone standing on a ladder and drilling into concrete with a hammer drill often has to lean their entire body weight against the machine ("push into it").

Here we have two potentially dangerous situations:

1. Breakthrough: the drill bit suddenly breaks through the wall. The counter-pressure suddenly disappears. The person lunges forward and falls from the ladder.
    
2. Slipping: the drill bit slips.

Safety: always work with your arms extended on ladders, never press with your body weight. If high pressure is needed (hard concrete), a ladder is the wrong choice (use scaffolding), or the wrong drill bit and machine are being used. When drilling into hard concrete or stone and no pressure should be applied, it’s recommended to switch to a good hammer drill in combination with the Force X from ALPEN.

Adjustable hole cutters for the drill consist of a bar with a rotating blade.

Physically, this is an enormous imbalance. Even at low speeds (400rpm), enormous centrifugal forces develop at the outer radius.

The risk:

1. If the blade catches, the arm swings violently with tremendous force. Hands nearby can be seriously injured.
2. If the machine is not securely mounted in a stand, it can smash the user’s wrist.
3. The blades often come loose due to the vibration.

Classic Forstner bits have a continuous cutting rim. This generates a lot of frictional heat because it constantly rubs against the edge of the wood.

Modern Forstner bits (like the Sharp Shark from ALPEN) are also called Wave Cutters because of their toothed wavy rim.

The physical trick: the wavy shape reduces the contact area (less friction = less heat). At the same time, the "tooth tips" cut the wood fibres cleaner than a pressing, smooth edge. This allows higher speeds without scorch marks in the wood, which is especially important for hardwoods (oak/beech).

When installing flush-mount boxes (for sockets) in sand-lime brick or masonry, you use core drill bits with a pilot drill bit.

The mistake: Many leave the pilot drill bit in until the end.

The problem: the pilot drill bit absorbs energy from the machine’s hammering action (it dampens it). Even worse: when the core drill penetrates deeply, the pilot drill bit can get jammed in the material or break, as the leverage of the core bit is enormous.

Correct procedure:

1. Start drilling (about 5-10mm deep) until the circle of the core bit is "guided" in the stone.
    
2. Remove the pilot drill bit (core bits often have a wedge ejector for this).
    
3. Finish drilling the hole without the pilot drill bit. This is faster and protects the material.

If you need a 16mm hole, you tend to work your way up: 4, 6, 8, 10, 12, 14, 16mm.

This is inefficient and harmful to the drill bits.

A bit drill cuts with the main cutting edges. However, if you, for example, enlarge a 10mm hole with a 12mm drill bit, the main cutting edges barely engage - instead, mostly the delicate corners (chamfers) do the cutting. The drill bit catches ("chatters"), and the hole becomes irregular (polygonal).

Correct method:

You only pre-drill with the dimension of the chisel edge of the large drill bit.

Example for a 16mm hole: the chisel edge (tip) of the 16mm drill bit is approx. 4-5mm wide. So you pre-drill with 5mm.

Then you take the 16mm drill bit directly. Since the tip (chisel edge) now engages nothing (no pressure needed), only the main cutting edges do the cutting. This is faster and the hole becomes rounder.

Glass is an amorphous, solidified liquid with high internal stress. When drilling (with a spear-point or diamond drill bit), microcracks form.

Water does cool, but turpentine or paraffin have a higher viscosity. They bind the fine glass dust into a paste, which supports the grinding process instead of washing it away. In addition, they dampen vibrations.

Drilling all the way through: if glass is drilled completely from one side, a chip almost always breaks out on the exit side.

Technique: drill from one side until you see a minimal crack or point on the back. Then turn over the pane and finish the hole from the opposite side. his way, the holes meet in the middle, and both surfaces remain perfect.

Granite is made of quartz, feldspar, and mica. These minerals are extremely hard, but brittle.

Hammer drilling (mechanical hammering) leads to micro-cracks in the structure. With a thin granite slab (e.g., windowsill, kitchen countertop), the vibration often leads to the complete cracking of the slab – often only days later due to stresses.

In granite, you drill by rotating (without hammering) using special granite drill bits (with a carbide insert that is extremely hard soldered) or, preferably, with diamond core drill bits.

Important: Diamond requires high speed and water. Carbide stone drill bits require a lot of pressure and low speed. Patience is more important here than strength.

Cast iron contains a high proportion of carbon in the form of graphite flakes.

When drilling, this graphite is released. Graphite is an excellent lubricant (self-lubrication).

If you add oil, it mixes with the fine graphite dust to form a thick abrasive paste ("grit"). This paste wears the drill bit at the edge (guide chamfers) faster than when drilling dry.

In addition, cast iron produces "short chips" (crumbs) that fall out easily. Only for very deep holes or cast steel is an emulsion used for cooling; with standard grey cast iron, dry drilling is often the better choice for tool life.

Hardox (wear plate, e.g. excavator buckets) or reamed screws often have a hardness of 50-60 HRC. A standard HSS drill bit (including cobalt) has a similar hardness. It only scratches.

The only solution here is solid carbide (SC) or special drill bits with carbide inserts (all-purpose drills like ALPEN Profi Multicut work surprisingly well with hardened material when turned slowly).

Solid carbide drill bits are extremely heat-resistant and harder than any steel. The downside: they are as brittle as glass. You must not wobble or tilt them under any circumstances, otherwise the expensive drill bits will break immediately.

When you drill into the end of a beam (parallel to the grain), the bit encounters growth rings of varying hardness (soft earlywood, hard latewood).

The drill tip follows the path of least resistance and deflects into the softer earlywood. It wanders severely.

Solution:

1. Use of drills bits with a very long centring tip.
    
2. Better: Pre-drill with a smaller diameter so the larger bit is properly guided.
    
3. For larger diameters: use a Forstner bit, since its outer rim guides the cut before the centre can wander.

The best solution for drilling in end grain is certainly the Timber Twist from ALPEN. Thanks to its long centring point, unique geometry, and the grind of its pre-cutting edges, it delivers precise results, especially in this repeatedly challenging task.

A punch creates a dent in the material. This displaces material, creating a small crater wall around the hole. This wall interferes with precision work. Additionally, the impact compacts the material at the tip, making it more difficult to start drilling with small bits (<2mm) (the drill bit deviates on the hard tip).

In precision engineering, NC spotting drill bits are used. These are extremely short, thick, and rigid (they don't bend). They cut a small, clean 90° chamfer.

The twist drill bit finds perfect guidance in it, without any material being displaced.

A twist drill bit is a roughing tool. Due to its geometry (two cutting edges), it tends to vibrate and physically produces an almost "constant thickness" shape (a rounded triangle) rather than a perfect circular hole. A 10mm hole is often 10.1mm in size and slightly out of round.

If you want to insert a ball bearing or a dowel pin with a snug fit (H7 tolerance), you must:

1. Drill smaller (e.g. 9.8mm).
2. Use a reamer.

The reamer has many cutting edges (6, 8, or more) and removes only a microscopic amount of material from the sides. It guides itself in the hole and only produces the perfect cylindrical shape and dimensional accuracy.

If you drill 10cm deep into metal, the exit point at the bottom can be offset by several millimetres, even though you were "perfectly aligned" at the top.

Reason: The drill bit bends in the hole due to uneven grinding of the cutting edges. If one side ("lip") cuts even just 0.05mm more than the other, a lateral force is generated. The drill bit acts like a spring and bends in an arc through the material.

Remedy:

1. Perfectly ground drill bits (machine-ground).
    
2. Pilot hole (short and rigid).
    
3. For deep holes: reduce speed, reduce feed, ventilate often.

A 90° conical countersink is for countersunk screws (the ones with a flat head).

On the other hand, socket-head cap screws (hex/Allen) require a cylindrical "hole within a hole" so that the head sits flush or below the surface.

For this, a flat-bottom counterbore is used. These have a fixed or rotating pilot pin at the bottom (e.g., 6.4mm for an M6 clearance hole). This pilot pin guides the countersink perfectly concentrically in the drilled hole, while the cutting edges above it mill the flat bottom for the screw head. Without a pilot pin, a counterbore would immediately chatter and break out.

When drilling thin sheets or flat steel on a drill press, many people lazily hold the workpiece by hand.

The fatal scenario: the drill bit breaks through, catches (see question 14), and suddenly rips the sheet metal along with it. The sheet metal becomes a rotating blade (helicopter), which can break the user's fingers or sever tendons.

Safety rule: every workpiece on the drill press must be secured with a machine vice or clamping jaws. Alternatively: a stop (steel block) to the left of the workpiece to prevent it from rotating.

Left-handed extractors have a conical left-hand thread. You drill into the broken screw, insert the extractor counterclockwise, and it is supposed to loosen the screw.

The problem: Due to its tapered shape, the extractor pushes the remaining bolt apart (spreading effect). The threads of the bolt are now pressed even tighter against the nut threads. Often, the hardened extractor then breaks off in the hole. Drilling out a hardened extractor is nearly impossible (only achievable with EDM or diamond).

Better alternative: straight-slotted extractors (which don't spread) or welding a nut onto the stub.

If a thread in an aluminium engine block or steel has been stripped, re-threading won’t help (material is missing).

The solution is wire thread inserts (Helicoil).

1. You drill the hole with a special oversized drill bit.
    
2. You cut a special receiving thread.
    
3. You screw in a spiral made of diamond-shaped stainless steel wire.

And the funny part: the repaired thread is stronger than the original! The stainless steel insert is harder and distributes the forces better in the soft aluminium than the screw alone could. For this reason, Helicoils are often used preventively in motorsports and aerospace construction.

If you’ve drilled extremely hard (hammer drilling), a keyless chuck can seize so tightly ("galling") that you can no longer open it by hand.

Mistake: Using a pipe wrench (destroys the plastic sleeve).

Solution:

1. Clamp the longest Allen key or a piece of round steel across the chuck (if there’s still space) or place it against the jaws.
    
2. Give a sharp, dry blow with a piece of wood on the key (in the opening direction).

The short impulse (shock) releases the self-locking of the thread more effectively than slow forcing. Applying penetrating oil (WD-40) from the front into the jaws helps as well.

Aluminium is soft and tends to stick under heat. Without cooling (methylated spirits/oil), aluminium effectively "welds" itself to the cutting edge and the drill margin.

This is called a built-up edge. This lump of aluminium at the tip alters the geometry. It is irregular and acts like an eccentric. The drill bit begins to wobble and tears the hole open beyond size. The surface of the hole looks "ploughed."

Once aluminium has "welded" onto the drill bit, it must be painstakingly removed chemically (with caustic soda) or mechanically before the drill can cut accurately again.

The shank end of an SDS bit is struck thousands of times per minute by the hammer piston during operation.

Over time, the steel deforms at the end ("burr formation" or "mushrooming").

If you continue to use this drill bit, this burr will ruin the SDS chuck of the machine (the locking balls will wear out). In the worst case, you can't get the drill out of the machine.

Maintenance: Regularly check and grease the shank end (!). If a burr forms, remove it immediately with a file or on a grinding wheel and chamfer the edge. Drill grease is not a luxury, but life insurance for the drill chuck.

Carbon fibre-reinforced plastic (CFRP) is extremely abrasive (gritty). The carbon fibres act on the cutting edge of an HSS drill bit like sandpaper. A standard drill bit becomes rounded and blunt after just a few holes.

CFRP also tends to delaminate: the layers separate when the drill bit pulls on exit (positive rake angle).

Solution:

1. Material: solid carbide (VHM) or diamond-coated drill bits are essential.
    
2. Geometry: special "sickle" drill bits or drill bits with double-point geometry, which cut the fibres at the edge before piercing the centre (similar to a wood bit, but for hard materials).

Not every twist drill has the same spiral (helix angle). DIN 1412 distinguishes between:

• Type N (Normal): Helix angle approx. 30°. For normal steel and cast iron. The standard.
   
• Type H (Hard): Helix angle approx. 10-13° (the spiral looks "elongated"). For brittle, short-chipping materials like brass, plexiglass, laminate. The shallow angle prevents the drill bit from digging in.
   
• Type W (Soft): Helix angle approx. 35-40° (the spiral is "tight"). For soft, long-chipping materials like aluminium or copper. The steep spiral quickly evacuates the large chips, ensuring nothing gets clogged.

Anyone drilling brass with type W will have the drill bit torn out of their hand (catching). Anyone drilling aluminium with type H will clog immediately.

Large drill presses use Morse taper (MT2, MT3, etc.) mountings. They are conical shanks that are simply inserted into the spindle.

The principle is frictional resistance through self-locking. The angle of the cone is calculated so flat that the friction is greater than any torque that could rotate the drill bit.

Important: This only works if the cone and spindle are absolutely grease-free and clean. A single metal chip or a film of grease can cause the taper to slip ("seizing"). This permanently damages the precision surfaces of the shank and spindle.

A drill bit consists not only of the grooves. In the centre is the "web" (the solid core material).

For stabilisation, this web becomes thicker toward the back (toward the shank); this is called the core rise. At the tip, the core is thin (for chip space), at the shaft thick (for stability).

In physical terms, this means that:

1. The deeper you drill, the less space there is in the flutes for chips, because the web gets thicker and the risk of clogging increases.
    
2. If a drill bit breaks off and you sharpen it far back, the chisel edge in the middle is suddenly huge. Without "point thinning" (reducing the chisel edge), this drill bit just pushes and no longer cuts.

HPL (High Pressure Laminate) façade panels consist of resin-impregnated paper that has been pressed under enormous pressure. Their surface is extremely hard and smooth.

Normal drill bits slide on the surface (scratch the decor) and become extremely hot due to the resin inside. Upon exit, the decorative surface flakes off over a large area.

Technique: You need special solid carbide (VHM) façade panel drill bits with a centring tip (to prevent slipping) and extremely sharp pre-cutting edges. Additionally, a hardwood block must be clamped behind the panel to simulate backpressure during exit; otherwise, the backside looks like it exploded.

Anyone who needs to drill a 50mm hole in a steel beam would take hours with twist drills (pre-drilling 10, 20, 30mm…).

Core drilling machines use hollow core drills (similar to a hole saw, but milled from solid HSS/carbide).

The physical advantage: only a ring approximately 4-5mm wide is being cut. The inner core (40mm of solid steel) remains and falls out at the end.

Since far less material has to be converted into chips (around 80% less energy required), this method is many times faster and quieter than drilling solid.

Many try to use a rotary burr or grinding bit in a regular drill to "cut" an elongated hole.

This ruins the machine. The bearings of a drill are designed for axial loads (pressure from top to bottom). They can hardly absorb lateral (radial) forces.

The spindle starts to wobble ("bearing damage"), and the chuck remains permanently off-centre afterward. Milling also requires much higher speeds (20,000+ RPM), which a drill (max. 3,000 RPM) cannot provide; the tool catches and vibrates violently.

When an HSS drill bit gets glowing hot while drilling, many quickly dip it in a cup of water.

That's a mistake! HSS is a high-performance steel. The sudden temperature shock (from 600°C to 20°C in 1 second) causes microcracks (stress cracks) in the structure of the cutting edge.

The cutting edge may still look fine, but it will chip immediately during the next use (brittle edge).

Correct course of action: allow the drill bit to cool in the air or cool it permanently during drilling. If it is already glowing hot: take a break, let it cool down slowly.

Answer:

A flat chisel has a specific orientation. When removing tiles, the cutting edge must be horizontal.

Many users strain their arms and hold the entire tool at an angle because the chisel is "misaligned" in the holder.

Almost all SDS machines have a switch position between "hammering" and "drilling" (often shown with a symbol of a rotating chisel). This is Vario-Lock.

In this position, the chisel can be turned by hand to the desired position. When you then switch to "hammering," it locks in place to prevent rotation.

The chuck is usually screwed onto the spindle (the thread is often ½"-20 UNF).

To prevent it from unscrewing when running in reverse, there is often a small set screw at the bottom inside the open chuck.

Warning: This screw almost always has a left-hand thread!

Anyone who tries to loosen this screw "normally" (counterclockwise) will snap the head off, as this will actually tighten it. To change the chuck, this screw must be unscrewed clockwise (to the right).

Tropical woods have an enormous density. If you screw in a stainless steel screw without pre-drilling, it becomes so hot that it softens and shears off (torsional fracture).

More importantly, the screw shank is thicker than the thread.

You have to work with a special step countersink. This drills:

1. The threaded hole in the lower beam (pilot hole).
    
2. The clearance hole in the upper decking board (shank diameter).
    
3. The countersink for the screw head.

All in one go. Only if the hole in the upper decking board is larger than the thread, can the screw head pull the decking board firmly against the beam ("pressing effect"). Otherwise, the screw threads into the decking board and a gap is created (see question 98).

In drywall construction, the screw must not tear the paper (loss of holding power) but must sit deep enough for joint compound application.

With a normal bit, it's a matter of luck.

A depth-stop bit holder has a "cage" or ring around the bit. As soon as the ring rests on the board, the bit is mechanically disengaged (slip clutch in the holder) or magnetically decoupled. Each of the 500 screws sits at exactly the same depth, no matter how hard you press.

Anyone who buys an expensive diamond core bit (for hard concrete) and leaves the hammer drill on "impact" out of habit will destroy the tool in seconds.

Diamond segments are hard, but extremely brittle when subjected to impacts. The impacts shatter the diamond matrix and tear the segments off the carrier tube.

Diamond cuts only through rotation and friction. It must be used at high speed without impact.

In contrast, carbide-tipped core bits (with teeth) require impact to break the stone.

Normal drill bits have a rake angle of about 20-30°. They aggressively pull into the material. With soft plastics (PVC), this often results in uneven holes.

A trick used by model builders: grind the sharp cutting edge at the front vertically (0° rake angle), similar to a brass drill bit. Or you can take an old, blunt drill bit.

In plastic, blunter cutting angles often produce cleaner, smoother holes than razor-sharp new HSS drill bits, as they don’t "cut" the material, but instead thermally "scrape" it.

Regular work with impact tools (hammer drills) damages the nerves and blood vessels in the hands due to the vibrations. The fingers turn white, go numb, and hurt in the cold (circulatory disorder).

How to prevent that:

1. Good machines with AVC (Active Vibration Control) use a decoupled handle.
    
2. Keep your hands warm.
    
3. Don’t grip tightly - let the machine do the work.

Cheap hammer drills transmit the impact energy 1:1 to the hand, while good machines absorb it internally with counterweights.

DIY enthusiasts often screw the plastic part of a wire connector onto the drill bit to limit the drilling depth.

Danger: the rotation makes the connector an imbalance. Since it is only held in place by a small screw on the sharp spiral, it often slips off or becomes misaligned when it contacts the wall. This damages the drill bit flutes.

Better method: use the machine's depth stop or the mentioned tape flag.

How big should the pilot hole be?

The rule is: core diameter of the screw.

If you hold the screw up to the light, the core is the solid pin in the middle, with the threads protruding on the outside.

If you drill as large as the outer threads, the screw has no grip.

If you don’t pre-drill at all, the core splits the wood.

The core is usually about 70% of the outer diameter (e.g., pre-drill 3mm for a 4.5mm screw).

Exception: In the part to be screwed (the upper board), you drill as large as the outer threads so the screw can pass through (see question 98).

An experienced craftsman can tell by ear whether the drilling parameters are correct.

• A rich, deep hum or crunch: good chip removal, correct load.
   
• High whistling or singing: speed too high or drill bit dull (friction vibration).
   
• Rattling or stuttering: vibration. Workpiece not clamped securely, guide unstable, or cutter too fast.
   
• Screeching: metal on metal without chip removal ("increased hardness"). Stop immediately, reduce speed, increase pressure!

If a masonry drill bit turns dark blue/black at the carbide tip, it is thermally dead. The carbide structure has changed or the solder has softened.

With HSS metal drill bits, temper colours (yellow/blue) in the chip flute are often a sign of heat, but as long as the tip hasn’t softened (annealed), it can still be used.

However, if the tip itself turns blue, the hardness is gone (loss of temper). Thus, the drill becomes softer than the workpiece and needs to be re-sharpened (until the blue material is gone).

When drilling freehand, people almost never hit exactly 90° - it's usually around 88° or 92°. With a wall plug in the wall, it doesn't matter.

For furniture joints or thick beams being drilled through, the deviation can be critical: over a 10cm thickness, a 2° angle error means the drill bit emerges 3-4mm off on the far side. Components no longer fit together.

Here, mobile drill stands (spring-loaded drill mobiles) or at least solid wooden blocks pre-drilled with a bench drill as a guide ("template") are indispensable as a positioning aid.

In wood, a conical metal punch works poorly; it just splinters the wood.

Carpenters use a starter awl (a sharp pointed tool). They drive it deep into the wood grain to cut the fibres and create a "guide hole".

Important: In highly grained wood (spruce), always check whether the awl has avoided the hard annual ring grain. Often you have to actively correct the grain.

Normal house dust is coarse. Drilling dust (especially concrete/quartz) is very fine and respirable (silicosis risk).

A standard DIY store vacuum (often without a class rating or class L) catches the larger particles but blows the dangerous fine dust out the back because the filter is too coarse. What they do is fill the room with quartz dust.

On construction sites, at least class M is required for mineral dust. These vacuums have filter cleaning (shaking) and finer pores that safely trap the dust.

98. The "clamping effect" principle: why you can never screw two pieces of wood together with a continuous thread.

Answer:

One of the most common mistakes: you lay two boards on top of each other and drill a small hole through both. Then you screw in a Spax with a continuous thread.

Result: the boards are not pulled together. There is a gap between them.

Reason: the thread locks into board A and board B ("screw-jack effect"). The screw fixes the gap.

Solution: the top board must always be drilled large enough for the screw to pass through (clearance hole). Only then will the head pull the top board against the bottom one, where the thread grips.

One of the most common mistakes: you lay two boards on top of each other and drill a small hole through both. Then you screw in a Spax with a continuous thread.

Result: the boards are not pulled together. There is a gap between them.

Reason: the thread locks into board A and board B ("screw-jack effect"). The screw fixes the gap.

Solution: the top board must always be drilled large enough for the screw to pass through (clearance hole). Only then will the head pull the top board against the bottom one, where the thread grips.

When it comes to machines, it’s debatable - if you’re only drilling three holes a year, a cheap drill will do.

But when it comes to drill bits, this rule applies absolutely.

A cheap bit or drill bit set (100 pieces for €20) is made of soft steel, poorly ground, and often bent.

A single high-quality drill bit (e.g., from Alpen, Heller, Keil, Gühring) may cost €5-10, but can drill 500 precise holes, whereas a cheap drill bit overheats or breaks by the third hole in steel.

The frustration over stripped screw heads (from soft drill bits) costs more nerves than the price difference.

Drilling is a machining process, not a punching process.

• In metal, it's the geometry (sharpness) of the tool that does the cutting. Pressure helps, but cooling and slow speed are key.
• In stone/concrete, it’s the energy that shatters. Pressure is unnecessary with good hammer drills, it is only a detriment.
• In wood, it's the speed that cuts. High speed, sharp cutting edge.

Anyone who understands how their tool removes material needs less force, destroys less equipment, and achieves the perfect result.