Drilling Techniques Reference
Why this matters
Service techs drill holes constantly: through wood + metal + concrete + tile. Wrong technique = scratched material, broken bit, wandered hole, broken bone. The tech who knows technique works fast + clean + safe. This is the field card.
Universal drilling principles
Sharp bit + right speed + steady feed: produces clean cuts.
Dull bit + wrong speed + forced feed: burns material + breaks bit + injures user.
Match bit to material: covered in common drill bits reference.
Match speed to bit + material: see RPM table below.
RPM by material + bit size
Wood: 1/16 - 1/4" bit 2,000 - 3,000 RPM; 1/2" 1,500 - 2,500; 1" spade 1,000 - 1,500; auger/hole saw per manufacturer.
Mild steel: 1/16 - 1/4" HSS 1,500 - 2,500 RPM; 1/2" HSS 600 - 1,000.
Stainless: 1/16 - 1/4" cobalt 500 - 1,000 RPM (slower than mild).
Aluminum: 1/16 - 1/4" 2,000 - 3,000 RPM with cutting oil.
Concrete (carbide masonry): 1/4 - 1/2" 1,500 - 3,000 RPM in hammer mode. SDS rotary hammer: per tool.
Tile (diamond bit): 300 - 600 RPM with water spray. Glass (spear-point carbide): 100 - 300 RPM with water spray.
Center punch first
Critical on metal: punch divot exactly where hole goes.
Bit nests in divot instead of walking across surface.
Tools: spring-loaded automatic center punch, OR hammer + punch.
Result: clean precise hole placement.
Start the hole
Wood: tap the bit lightly into wood; once gripped, start drilling.
Metal: bit in center-punch divot; press firmly; start slowly.
Tile / glass: low speed; create a small starter divot with corner of tile spear point; then drill through.
Concrete: hammer mode; bit perpendicular to surface; firm pressure.
Drilling holes step-by-step
- Identify hole location + diameter
- Center punch (metal) OR mark precisely
- Select bit + speed for material
- Apply lubricant (metal + tile + glass)
- Drill at marked location, perpendicular to surface
- Steady feed; don't force
- Withdraw bit at full speed (to flush chips)
- Deburr edges (round file, deburring tool, OR knife)
Lubrication + pilot holes
Metal: cutting oil, WD-40, OR Trefolex/Tap Magic; mandatory for stainless. Tile + glass: water spray OR sponge. Wood + concrete: no lubrication. Stainless: dedicated cutting fluid. Cast iron: dry (or minimal cutting oil).
Pilot holes: drill smaller pilot first for larger bits. Metal: pilot = drill bit point diameter (~ 1/8" pilot for 1/2" bit). Wood screws: pilot 60 - 70% of shank. Lag screws: pilot 1/16" smaller than shank. Prevents binding + breakage.
Drilling by material
Thin metal: slow speed (less chatter); firm pressure; wood backing block prevents tear-through; step bit (Unibit) for hole-size flexibility.
Thick metal: pilot hole required; cutting oil critical; slow + steady; annular cutter (rotabroach) for clean large holes.
Stainless steel: cobalt bit (not HSS); cutting fluid mandatory; half normal RPM; firm pressure (no slip + work-hardening). Blue/black hole = work-hardened; restart with new bit + better lube.
Tile + porcelain: diamond bit (solid OR hollow); water spray essential; very slow start; light pressure (let diamond cut + cool); wood/foam backing prevents chip-out.
Concrete: hammer mode (rotary + percussion); carbide bit; perpendicular to surface; withdraw periodically to clear dust; SDS rotary hammer > 1/2"; HEPA dust extraction (silica).
Drilling holes through walls
Locate studs + cavities: stud finder OR knock test.
Check for hidden infrastructure: electrical, plumbing, gas. NEVER drill blind into hot wall.
Through drywall + stud: long auger bit OR spade.
Through plate + sheathing: long bit OR through joists.
Sleeve insertion: when running cable / pipe through; protects from edges.
Caulk hole afterward: prevents air + bug + moisture infiltration.
Drilling overhead
Eye protection mandatory: dust + chips falling.
Hard hat: heavy debris (concrete).
Steady drill + supported arm position: harder than horizontal.
Multiple short drills rather than one long push.
Stop + clear dust more often.
Drilling glass
Diamond bit ESSENTIAL: regular carbide chips glass.
Slow speed (100 - 300 RPM).
Continuous water spray.
Light pressure: let diamond cut.
Bevel-side of glass facing you: if cut OR scored already, drill from outside.
Tape the spot: marker visible; bit doesn't slip.
Drilling in plaster + lath
Older homes: hard outer plaster + soft wood lath.
Standard wood OR multi-purpose bit: works.
Caution: plaster chips out if forced; slow speed + steady feed.
Behind plaster: 1×4 OR similar wood lath, then air gap, then back plaster.
Drilling holes in finished surface
Marking: light pencil mark.
Bit suited to finish material (wood, drywall, etc.).
Slow speed + light pressure: prevents tear-out.
Skim trim ring after: hides minor imperfection.
Caulk + paint: final finish.
Common drilling mistakes
Wrong bit for material (HSS in concrete; masonry bit in steel). Wrong RPM (too fast = burn; too slow = won't cut). No center punch (wandering on metal). No lubrication on stainless (work-hardens). No water on tile / glass (chips, cracks). Drilling blind into wall (hidden infrastructure). Forcing dull bit (broken bit, injury). No backing on thin metal (deformation). No PPE (eye injury).
Safety
Eye protection ALWAYS: chips fly in every direction.
Hearing protection: large drilling (hammer drill, rotary hammer).
Gloves: depends on task; gloves grab rotating bits (NOT for high-speed drilling).
Cut-resistant gloves OR bare hands: for material handling but not for actively drilling.
Hard hat overhead: concrete + brick chips.
Respirator: silica dust (concrete + brick), lead paint, asbestos.
Cordless drill clutch + brake: prevent over-tightening + reverse kick.
When to drill vs other method
Drill: round hole, specific diameter, through any material.
Punch / chisel: not for service work (slow + sloppy).
Saw: rectangular OR larger opening.
Hole saw: round opening 3/4" - 6".
Plasma cutter: very large metal hole.
Diamond core drill: large concrete OR masonry hole.
References
- Manufacturer technical data (Bosch, Milwaukee, DeWalt, Irwin)
- OSHA 1926.300 (Power Tools)
- ANSI B7.1 (drilling safety)
- Manuall internal: Common Drill Bits, PPE Selection by Task