ASVAB Shop Information — Power Tools and Workshop Safety Questions

Hand plane: removes thin shavings of wood to smooth, flatten, and shape surfaces. Operation: blade (IRON) extends slightly below the sole (bottom); push or pull plane along wood; blade shaves curls of wood; depth of cut adjusted by tightening or loosening blade; angle of approach is critical (with grain for smooth cuts, across or angled for stubborn grain). PARTS: IRON (BLADE) is sharpened steel cutter, honed to razor sharp; CHIP BREAKER (CAP IRON) sits just above the cutting edge to break the shaving and reduce tear-out; FROG holds iron at correct angle with adjustment screw that moves frog forward/back to change mouth opening; SOLE is the flat bottom that must be flat for accurate planing; MOUTH is the opening in sole where blade emerges; HANDLE/KNOB for two-handed operation; DEPTH ADJUSTMENT (Y-lever and brass wheel) fine adjusts blade depth; LATERAL ADJUSTMENT lever adjusts blade left-right for even shaving width. PLANE TYPES (Stanley/Bailey numbering system): #1, #2 are small and rare; #3, #4 are smoothing planes (9-10 inches) for fine finish work; #5 is jack plane (14 inches) for general purpose; #6 is fore plane (18 inches) intermediate; #7, #8 are jointer planes (22-24 inches) for flattening long boards and jointing edges; BLOCK PLANE is small (4-6 inches), one-handed, low-angle blade (12-20 degree bed) for end grain, chamfering, small adjustments; RABBET PLANE for cutting rabbets (step cuts on edges); SHOULDER PLANE for fine adjustment of shoulder cuts in joinery; SPOKESHAVE is short plane for curved surfaces. SHARPENING the iron is essential because dull plane equals poor results, tear-out, hard to push. Sharpening methods: waterstones (Japanese style, 800-8000 grit progression), oilstones, diamond plates, sandpaper on glass; HONING GUIDE for consistent angle. Final polishing/stropping creates razor edge. ADJUSTMENT: minimal blade exposure first, then advance until paper-thin shaving appears; very small adjustments. PUSH plane with body weight, not just arms; keep pressure on FRONT knob at start of stroke, EVEN pressure in middle, REAR handle at end of stroke. PLANES vs SANDERS: planes leave a polished surface (cut, not scratched); sanders leave scratch pattern (even very fine grits); hand-planed surfaces are aesthetically preferred for high-end furniture. MODERN POWER alternatives: electric planer (handheld) quickly removes material; useful for trim adjustments, door fitting; doesn't replace hand plane for fine work; JOINTER (machine) flattens one face, squares one edge; THICKNESS PLANER (machine) for uniform thickness; DRUM SANDER (machine) thicknessing alternative with sanding rather than knives. Hand planing remains popular: quiet, no dust, can correct issues machines can't, satisfying.

Washer functions: DISTRIBUTE LOAD (spreads clamping force over larger area; prevents bolt head/nut from sinking into softer materials like wood, plastic, aluminum, painted steel; without washer, point loading can crush material); PREVENT SURFACE DAMAGE (protects finish from being marred by rotation of bolt/nut during tightening); PROVIDE BEARING SURFACE (clean smooth surface for nut to bear against; especially important on rough surfaces); PREVENT LOOSENING (lock washers add vibration resistance); FILL SPACE (when bolt is too long, washers or spacers take up the difference); ELECTRICAL ISOLATION (special washers like nylon, fiber electrically isolate parts). WASHER TYPES: FLAT WASHER is standard, round, flat, for general load distribution. FENDER WASHER has large outer diameter for soft materials, thin sheet metal, distributing load over wide area; common in automotive body panels. LOCK WASHER prevents nut loosening from vibration; types: SPLIT-RING (helical spring, most common; one end of split twists creating friction and bite into surface), STAR (TOOTH, external or internal teeth bite into surfaces), DOUBLE-COIL; modern bolted joints often use Nord-Lock washers (wedge-locking, very effective), prevailing-torque nuts (Nyloc with nylon insert), or thread-locking compound (Loctite). BELLEVILLE WASHER (conical spring) provides constant spring force for high-vibration applications. SHOULDER or DOUBLE-D WASHER has special shape for specific applications. SEALING WASHER has bonded rubber to seal against fluid leaks; common in plumbing, hoses, oil drain plugs. WAVE or CRESCENT WASHER has wavy form with mild spring tension. WASHER MATERIALS: zinc-plated steel (common, rust-resistant for indoor use); stainless steel (corrosion-resistant for outdoor, marine); brass (non-magnetic, decorative); nylon/plastic (non-conductive, light); rubber (sealing, vibration damping); bonded (rubber-to-metal for sealing under pressure); copper (sealing on certain mating surfaces). INSTALLATION ORDER (typical): bolt head, flat washer, material, material, flat washer, lock washer, nut. Lock washer goes against the nut (or rotating element); flat washer between material and lock washer to protect material. CRITICAL applications use torque wrench to apply specified torque; under-tight equals clamping force insufficient; over-tight equals bolt stretches or breaks. Some assemblies use STRETCH BOLTS or TORQUE-TO-YIELD (TTY) bolts where measured rotation past initial torque deliberately stretches bolt to a specific clamp load; one-time-use, must be replaced. THREAD ENGAGEMENT rule of thumb: 1.5 times bolt diameter of thread engagement for normal applications; 2 times or more for aluminum or other softer materials; thread engagement past full threads of nut doesn't add strength.

Drill types: HANDHELD DRILL is battery-powered (cordless) or corded; portable; for general drilling, driving screws, light tasks; less precise (depends on operator steadiness); chuck typically 3/8 or 1/2 inch; variable speed; reversible; clutch (cordless) prevents over-driving screws. DRILL PRESS is stationary; mounted on bench or floor; precise vertical alignment; depth stop for repeatable depth; chuck holds bit; quill extends bit down via lever; adjustable table for workpiece; speeds changeable via pulleys (typically 5-12 speed steps); advantages: perfectly perpendicular holes; consistent depth (multiple holes same depth); much more powerful for hole saws, Forstner bits, large bits; better for difficult materials like metal. IMPACT DRIVER provides high-impact torque for driving screws and lag bolts; not a precision drill. HAMMER DRILL is handheld drill with hammering action for masonry; impact mechanism vibrates as it rotates; for concrete, brick, stone. ROTARY HAMMER is larger, more aggressive hammer drill; uses pneumatic piston for stronger impact; for harder concrete, drilling holes for anchors. RIGHT-ANGLE DRILL has 90 degree head for tight spaces. MAGNETIC DRILL (mag drill) for drilling holes in steel beams; magnetic base. CORE DRILL for very large holes. DRILL BIT TYPES: TWIST DRILL is most common; for wood, metal, plastic; HSS (high speed steel) for most materials; cobalt or titanium-coated for harder metals; carbide for very hard materials. BRAD-POINT has center point and outer cutters; for wood; clean entry hole, no walking. FORSTNER BIT for flat-bottom holes; wood; large diameter holes; very clean. SPADE BIT (PADDLE) for fast wood drilling; rough holes. AUGER BIT is long wood drilling bit with screw lead. HOLE SAW is cup-shaped saw with pilot bit; for large diameter holes (1-6 inches). MASONRY BIT is carbide-tipped for stone, brick, concrete. STEP DRILL (UNIBIT) has multiple stepped diameters; for thin metal/sheet metal. COUNTERSINK is angled bit for countersinking screw heads flush. PLUG CUTTER cuts wooden plugs to fill counterbored screw holes. DRILL OPERATION: PILOT HOLE is small hole drilled first as a guide for the main hole, especially in metal, hardwood, or near edges; prevents drift, splitting. MATERIAL CLAMPING: clamp workpiece, especially metal; bit grabbing and spinning the workpiece is dangerous. DRILL SPEED matches material — wood: high speed for small bits, lower for large; metal: slower for harder/larger; high-speed steel bits dull when overheated; oil/coolant for metalwork. BREAKING THROUGH: slow down at the breakthrough point; otherwise bit grabs and damages workpiece. SAFETY: clamp work; remove jewelry; tie back hair; safety glasses always; chuck key removed before starting; never reach across spinning bit. DRILL POWER ratings: cordless by battery voltage (12V light duty, 18/20V general, 36/40V heavy); brushless motors more efficient and longer-lasting than brushed; corded by amperage (5-10 A typical).

Lumber categories: SOFTWOODS come from coniferous (cone-bearing) trees; faster-growing; generally less dense; less expensive; used primarily for construction (framing, sheathing) and some furniture; common species: PINE (yellow pine for framing, white pine for trim/furniture), FIR (Douglas fir is primary framing lumber in West; very strong relative to weight), SPRUCE (SPF is Spruce-Pine-Fir generic framing grade; also for musical instruments), CEDAR (red cedar, white cedar; naturally rot-resistant; siding, outdoor furniture, fence posts), REDWOOD (rot/insect resistant; outdoor use; less available). HARDWOODS come from deciduous (leaf-shedding) trees; slower-growing; generally denser; more expensive; used for FURNITURE, FLOORING, CABINETRY; common species: OAK (red oak, white oak; strong, common; white oak is rot-resistant; flooring, furniture), MAPLE (hard maple, soft maple; flooring, cabinets), CHERRY (rich color, ages well; furniture), WALNUT (dark, fine grain; high-end furniture), BIRCH (cabinets, plywood); EXOTIC tropical hardwoods like teak, mahogany, ipe, ebony are very expensive. ENGINEERED LUMBER AND SHEET GOODS: PLYWOOD is multiple thin wood veneers glued with grains alternating perpendicular (cross-grain); very stable, strong relative to weight, available in 4 by 8 foot sheets, thicknesses 1/8 inch to 1 inch plus; grades: A (best, smooth, sanded), B, C, D (rough, knots); face/back grades combined like A-B, A-C, C-D (construction grade). OSB (Oriented Strand Board) is wood strands compressed with adhesive; structural sheathing for floors, walls, roofs; cheaper than plywood. MDF (Medium-Density Fiberboard) is finely ground wood plus adhesive; smooth flat surface; great for painted projects; no grain, won't warp, but heavy and creates dangerous dust when cut. PARTICLEBOARD is coarser version of MDF; cheap cabinet construction. HARDBOARD (MASONITE) is thin smooth panels. LVL (Laminated Veneer Lumber) is for headers and beams; very strong. PSL (Parallel Strand Lumber, like Parallam) is similar to LVL but using strands. GLUE-LAM (Glued Laminated Timber) is beams made by laminating layers. I-JOISTS (TJI) for floor joists; engineered shape (top and bottom flanges with OSB or plywood web). LUMBER DIMENSIONS nominal vs actual: construction lumber sold by NOMINAL size (e.g., 2 by 4) which is BEFORE drying and planing; actual dimensions are SMALLER. Standard examples: 2 by 4 equals 1-1/2 by 3-1/2 inch; 2 by 6 equals 1-1/2 by 5-1/2 inch; 2 by 8 equals 1-1/2 by 7-1/4 inch; 2 by 10 equals 1-1/2 by 9-1/4 inch; 2 by 12 equals 1-1/2 by 11-1/4 inch; 4 by 4 equals 3-1/2 by 3-1/2 inch; 1 by 6 equals 3/4 by 5-1/2 inch. Important: design and measure with ACTUAL dimensions, not nominal. Hardwood lumber sold by quarter-inch thickness: 4/4 equals 1 inch (about 7/8 inch finished); 8/4 equals 2 inches (1-3/4 inch finished). MOISTURE CONTENT: wood swells when wet, shrinks when dry; KILN-DRIED LUMBER (KD) has been dried to 10-19 percent moisture (construction grade) or 6-8 percent (furniture grade). Pressure-treated for ground contact (chemicals like ACQ resist rot, insects) has green/brown tint; required for deck framing, fence posts. NEVER USE PRESSURE-TREATED indoors (off-gassing of chemicals); never burn it (toxic smoke).

Chisels and punches look similar but have different purposes. CHISELS for SHAPING by REMOVING MATERIAL: WOOD CHISELS are most common; flat steel blade with sharp beveled cutting edge; wooden or plastic handle; struck with mallet or hand-pushed; sizes by blade width (1/8 inch to 2 inches plus); types: BENCH CHISELS (general purpose, beveled-edge), MORTISE CHISELS (thick, for chopping mortises), PARING CHISELS (long, thin, for delicate hand work), CORNER/SKEW CHISELS (specialty). METAL/COLD CHISELS are heavy hardened steel; struck with hammer; for cutting bolts, rivets, sheet metal, cold-shearing steel; various shapes — FLAT (general), DIAMOND-POINT, CAPE, ROUND-NOSE for different cuts. MASONRY/BRICK CHISELS have wide blade for splitting bricks/stones. JAPANESE CHISELS (NOMI) have laminated steel construction; very hard; struck on the hooped end; pulled or pushed; renowned for joinery. CARVING CHISELS / GOUGES have curved blades for sculptural work; many profiles. WOOD CHISEL USE: bevel side up for paring (push by hand); bevel side down for chopping (struck with mallet) where bevel acts as ramp lifting chips; KEEP BLADE SHARP like a plane iron; honed to razor; sharpening with stones or sandpaper progression; strop for final polish. Work FROM EDGES INWARD when cleaning out waste. NEVER chisel toward yourself or your hand; always away from body. Cuts should be SLICING (angled) rather than push straight ahead; easier and cleaner. KEEP BLADE SHARP because dull chisel requires more force, slips more, and is more dangerous than sharp chisel. PUNCHES for DRIVING or MARKING: CENTER PUNCH has sharp point; makes small dimple in metal to start drill bits (prevents drill from walking). PRICK PUNCH has finer point than center punch for marking layout lines. DRIVE/PIN PUNCH has flat or shaped end; drives out pins, rivets, bolts; sizes match pin diameter. STARTING PUNCH (TAPER PUNCH) is slightly tapered, larger end; gets stubborn pins started. NAIL SET for driving finish nails below wood surface so head can be filled with putty; various sizes. HOLLOW PUNCH has circular cutting edge; punches holes in leather, gasket material, sheet metal. AUTOMATIC CENTER PUNCH is spring-loaded; press downward, internal spring releases striking blow; doesn't require hammer; convenient for repetitive marking. STRIKING CHISELS AND PUNCHES: use STEEL HAMMER for cold chisels and steel punches; WOOD MALLET for wood chisels (steel hammer mushrooms wooden chisel handles); wear EYE PROTECTION because chips and shards fly from struck metal; STRIKING ENDS may mushroom (deform) with use; grind off mushroom periodically to prevent chunks from flying off. STORE chisels safely with edge protected; rolling a sharp blade across a hand can cause severe cuts; keep them sheathed or in chisel rolls/blocks.

NAIL SIZES are designated by 'd' (penny). The 'd' abbreviation comes from the Latin DENARIUS (a Roman coin) because early nails were sold by their cost in pennies per hundred. Common nail sizes (length in inches): 2d equals 1 inch; 3d equals 1.25 inch; 4d equals 1.5 inch; 6d equals 2 inches; 8d equals 2.5 inches; 10d equals 3 inches; 12d equals 3.25 inches; 16d equals 3.5 inches; 20d equals 4 inches; 30d equals 4.5 inches; 40d equals 5 inches; 50d equals 5.5 inches; 60d equals 6 inches. Most commonly used in framing: 8d for sheathing, 16d for framing studs to plates. The penny designation is for length only. NAIL TYPES AND APPLICATIONS: COMMON NAILS have full-diameter shaft and flat head; for framing and general construction; sturdy, hold well. BOX NAILS are thinner than common nails of same length; less likely to split wood; for siding, fencing, sheathing. FINISH NAILS have small unobtrusive head (cup-shaped); for trim, cabinets where you don't want the head to show; head countersunk slightly below surface, filled with putty. CASING NAILS are larger than finish nails with slightly larger head; for window/door casing. BRADS are very small finish nails (18 or 23 gauge); for small trim, picture frames; usually shot from brad nailer (pneumatic). ROOFING NAILS have wide flat head; galvanized for rust resistance; for shingles, felt paper; sized 7/8, 1, 1-1/4 inch; head pulls into shingle to hold. DRYWALL NAILS have bugle head, ringed shank for grip in framing through drywall; alternative to drywall screws. MASONRY NAILS are hardened steel for nailing into concrete/brick. DECK NAILS are galvanized or stainless for outdoor use; corrosion-resistant; ringed or spiral shanks for better grip. SPIRAL/RINGED SHANK NAILS are twisted or with rings; better holding power; especially for siding, decking, framing in seismic/wind zones (resist withdrawal). MATERIALS: STEEL is bright (uncoated, indoor only — rust), galvanized (zinc-coated, outdoor/treated wood), stainless steel (premium outdoor); ALUMINUM is for aluminum siding (no galvanic corrosion); COPPER for copper roofing; BRASS decorative. NAIL HEADS: full-size flat heads hold larger area (for plywood, sheathing); checked heads (cross-hatching) for grip; bugle head for drywall; convex/cup heads for finish nails; no head for double-headed nails (for temporary construction; pull out easily). NAIL GUNS (PNEUMATIC NAILERS): use compressed air to drive nails; types: FRAMING NAILER (driving 16d framing nails), FINISH NAILER (15 or 16 gauge for trim), BRAD NAILER (18 or 23 gauge for small trim), ROOFING NAILER (coil-fed for roofing nails), SIDING NAILER (galvanized box nails for siding). Battery-powered cordless options also available. SAFETY: never point at people; never carry with finger on trigger; wear safety glasses (ricochet hazard); use SEQUENTIAL TRIP (not bump-fire) for accuracy; bump-fire can cause double-fires when accidentally striking. NAIL vs SCREW: nails install faster (especially with nail gun); better in shear (sideways forces) which makes them good for framing; cheaper; screws have superior pull-out resistance, slower installation, more secure for things expected to be disassembled.

BAND SAW is a stationary woodworking machine with a continuous loop of toothed steel blade running over two or three wheels; cuts as the loop passes through the workpiece; relatively narrow blade (1/8 to 1 inch plus); blade tension and tracking adjustable. ADVANTAGES: CURVES (narrow blade can cut tight curves; smaller blade equals tighter radius); RESAWING (cuts thick boards into thinner ones; large band saws with wide blades and tall throat can convert an expensive 8/4 (2-inch) board into two 4/4 (1-inch) boards; saves material costs and creates book-matched panels); IRREGULAR SHAPES (follows pencil lines; great for furniture parts, sculpture, art); SAFETY (much less kickback risk than table saw; single-direction motion, not just throwing wood back; injuries less common than table saw); DEEP CUTS (depth limited only by throat height; 12-inch resaw capacity not unusual on mid-size band saws); CONSISTENT cut quality through varying thicknesses; METALS (slow-speed band saws cut metal as well as wood with different blades). DISADVANTAGES: blade can drift (cut not perfectly straight); requires tuning and good blade tension; slower than table saw for straight cross-cuts and rips; can't make square dado cuts. PARTS: WHEELS (upper and lower; 14 to 24 inch plus diameter common); BLADE (continuous loop, various tooth counts and widths); GUIDES (block or bearing guides hold blade in proper position above and below table); THRUST BEARING (behind blade, prevents blade from pushing back when work pushes against teeth); TENSION ADJUSTMENT (spring-loaded mechanism, must be properly set for blade size); TABLE (tilts up to 45 degrees for angled cuts); FENCE (for straight cuts parallel to blade); MITER GAUGE (for crosscuts at various angles). BLADE SELECTION: WIDTH determines minimum cutting radius (1/8 inch blade can cut very tight curves; 1/2 inch blade about 2-1/2 inch minimum radius; 1 inch blade for resawing); TPI (teeth per inch) — fewer teeth for thicker wood (4-6 TPI), more for thinner/precise (10-14 TPI); special METAL CUTTING blades have very fine teeth and slow blade speed. SETUP: mount blade with teeth pointing down (toward table); TRACKING (blade should run in middle of upper wheel; adjust with tracking knob); TENSION (too loose equals blade flexes and won't cut accurately; too tight equals blade breakage and bearing wear); GUIDES (set just touching blade body, just above and below cut path); THRUST BEARING (just barely behind blade). SAFE OPERATION: BLADE GUARD lowered to just above workpiece (exposes only the cutting portion); PUSH STICKS / push pads for small or narrow workpieces; STEADY feed rate; don't force wood through; keep fingers AWAY from blade path; even when blade isn't visible above table, blade is still in motion just below; allow blade to fully STOP before adjusting or removing material; BACK OUT carefully on curves to avoid pulling blade out of guides. SCROLL SAW has similar concept but reciprocating (up-down) blade; smaller, very fine blades; great for intricate decorative cuts; pierce cuts (through holes) where blade can be threaded through a drilled hole. Both band saw and scroll saw great for non-straight cuts, but scroll saw is for finer intricate work, band saw is for thicker/larger work and resawing.

SANDPAPER GRIT indicates abrasive particle size. HIGHER number equals SMALLER particles equals SMOOTHER finish; LOWER number equals LARGER particles equals FASTER material removal but rougher surface. COMMON GRIT GRADES and APPLICATIONS: 40-60 GRIT (extra coarse) for heavy material removal; stripping paint; removing finishes; rough shaping. 80-100 GRIT (coarse) for flattening rough wood; removing minor finishing; preparing for next grit. 120-150 GRIT (medium) for general smoothing; preparing for finer grits; first sanding step for most projects. 180-220 GRIT (fine) for final sanding before staining/finishing; reasonable smoothness. 240-320 GRIT (very fine) between coats of finish; fine sanding. 400-600 GRIT (extra fine) between coats of varnish/lacquer; preparing metal for polishing. 800-1000 plus GRIT for polishing; very smooth surfaces; metal polishing; auto body work between coats. 1500-3000 plus GRIT for automotive paint polishing; mirror finishes. SANDING TECHNIQUE: progress through grits sequentially because skipping grits leaves deeper scratches not removed by the finer grits; typical progression: 80, 120, 180, 220 for wood projects, sometimes finer for finishing. SAND WITH the GRAIN of wood because cross-grain scratches are very visible after staining (oil and stain emphasize scratches). Apply EVEN PRESSURE. Use a SANDING BLOCK (cork, foam, hard rubber) for flat surfaces because it keeps sandpaper flat and removes material evenly; using bare hands creates uneven pressure. Use a SANDING SPONGE for curves and details; flexes to follow contours. CLEAN dust between grits because leftover coarse grit will scratch the new finer-grit surface; vacuum or tack cloth. Final sanding with finest grit, then thoroughly clean. On end grain, sand to FINER grit than face grain because end grain absorbs more stain. ABRASIVE MATERIALS: ALUMINUM OXIDE is most common general-purpose; brown/red; for wood and metal. SILICON CARBIDE has sharp friable particles that renew themselves; black; for wet sanding, finish sanding, metal, glass. GARNET is natural mineral; orange/brown; for wood, especially hardwoods. CERAMIC is high-end; durable; for power sanding heavy work, hardwoods, metal. SANDPAPER FORMATS: SHEETS (9 by 11 inch) cut to size for hand sanding or sanding block. BELTS for belt sanders. DISKS for random orbit sanders (5 inch and 6 inch common, hook-and-loop attachment). ROLLS for hand sanding or industrial. MESH/SCREEN for drywall sanding (allows dust to pass through). SPONGES for curves and edges. POWER SANDERS: RANDOM ORBIT SANDER has disk that rotates and orbits with minimal swirl marks; most versatile general sander. BELT SANDER uses sanding belt for aggressive material removal. ORBITAL FINISHING SANDER (1/4 sheet) has rectangular pad with vibration only (no rotation) for fine sanding. DETAIL SANDER (mouse) has triangular pad for corners/tight spaces. DRUM SANDER (large stationary) for thicknessing or smoothing large panels. DISK SANDER (bench-mounted) for shaping edges. SPINDLE SANDER has vertical spinning drum for inside curves. SANDING SAFETY: DUST MASK or RESPIRATOR (wood dust is a carcinogen, especially hardwoods like walnut, cherry; MDF/particleboard contains formaldehyde adhesives; pressure-treated wood contains toxic chemicals); EYE PROTECTION (particles fly); DUST COLLECTION on power sanders is important; gloves not necessary for hand sanding because they can interfere with power sander dust collection. WET SANDING (for finishes and automotive paint) uses water or oil as lubricant; minimizes clogging; produces ultra-smooth surface; silicon carbide sandpaper.

Reference directions in construction: LEVEL equals HORIZONTAL (perpendicular to gravity, parallel to ground when ground is flat); PLUMB equals VERTICAL (parallel to gravity, perpendicular to a true horizontal); SQUARE equals at 90 degrees to another reference (often a corner or edge). Tools for each: SPIRIT LEVEL (BUBBLE LEVEL) is sealed glass vial partially filled with liquid (originally alcohol/spirit, hence the name) with a bubble; level when bubble is centered between marks; LEVELS have horizontal and vertical (plumb) vials; many also have a 45 degree vial; sizes from 9 inch torpedo to 8 foot levels; longer lengths give greater accuracy over distance. PLUMB BOB is pointed weight suspended from a string; gravity holds string vertical; for very accurate vertical reference over long distances (multiple stories); used by surveyors, masons. LASER LEVEL projects a laser beam or line; self-leveling (with pendulum mechanism) projects truly level/plumb lines; very accurate; modern construction standard; types include rotary (rotating point making horizontal plane), line lasers (projecting visible lines), cross-line (horizontal AND vertical at once). WATER LEVEL is clear hose filled with water; water surface in two ends will be at the same height (basic physics); used for establishing level over distances or around obstacles. SQUARENESS checks: TRY SQUARE has fixed 90 degree angle for small work; COMBINATION SQUARE is adjustable, multi-purpose (90 and 45 degrees, depth measurement); FRAMING SQUARE is large L-shape for layouts; tongue and blade; SPEED SQUARE is triangular layout for framing; SQUARENESS OF A RECTANGLE measured by both diagonals; if they're equal, the rectangle is square (geometric proof). For building a wall, deck, or any structure: mark and set corners by location (measurements); check PLUMB on uprights with level; check LEVEL on horizontal members with level; check SQUARE of overall structure with diagonal measurements or with 3-4-5 method (a triangle with sides 3, 4, and 5 units has a 90 degree angle between the 3 and 4 sides; mark 3 ft on one wall, 4 ft on adjacent wall; if distance between marks is 5 ft, it's square; multiples like 6-8-10 work for larger). LEVEL ACCURACY: check level on a known surface (set on table, mark position, flip 180 degrees; should read the same; if not, level is out of calibration). Modern quality levels are accurate; cheap ones often aren't. Digital levels show degrees precisely with a number. Check periodically; bumps and drops can affect accuracy. PLUMB BOB USE: suspend from high point; allow to settle (oscillation can take time); string is plumb when motionless; mark plumb point at base; for high accuracy, allow plenty of settle time; wind affects outdoor use. ESTABLISHING LEVEL: from a known reference point (existing foundation, established benchmark); use water level or laser for long distances; check periodically as work progresses. SPECIAL situations: when a floor slopes intentionally (drainage), level reference may not be horizontal but rather should match desired slope; when measuring from non-horizontal datum, use that reference; grounds out of level need shimming/leveling first.

FIRE CLASSES (US system): CLASS A is ordinary combustibles (wood, paper, cardboard, fabric, most plastics); CLASS B is flammable liquids and gases (gasoline, oil, grease, alcohol, propane); CLASS C is energized electrical equipment (electrical fires need non-conductive agent; once de-energized, the underlying fire is usually Class A or B); CLASS D is combustible METALS (magnesium, titanium, sodium, lithium; require special agents like sand, special powders); CLASS K is cooking oils and fats (commercial kitchens; special wet chemical agents). FIRE EXTINGUISHER TYPES: ABC DRY CHEMICAL (red, with ABC label) is multi-purpose; most common in homes, shops, vehicles, offices; uses monoammonium phosphate powder; effective on Class A, B, and C fires; leaves residue that can be corrosive and damage electronics. BC DRY CHEMICAL (sodium or potassium bicarbonate) is for B and C only; less residue than ABC. WATER (Class A only) — DON'T use on electrical (Class C) or grease (Class B); spreads flammable liquids; energized electrical creates shock hazard through stream. CO2 (carbon dioxide) is for Class B and C; gas displaces oxygen, smothers fire; LEAVES NO RESIDUE — good for electronics, lab equipment, server rooms; less effective on Class A; loud discharge; doesn't cool sufficiently to prevent re-ignition; cold can cause frostbite if directed at people. FOAM is for Class A and B; smothers and cools; good for flammable liquids; not for Class C electrical. WET CHEMICAL (Class K) is for cooking oils; converts hot fats to non-flammable soap (saponification); commercial kitchens. CLASS D extinguishers use sand, sodium chloride, copper powders for metal fires specifically. EXTINGUISHER USE — PASS technique: P — PULL the safety pin; A — AIM at the BASE of the fire (not the flames; the fuel is at the base); S — SQUEEZE the handle; S — SWEEP side to side, advancing toward the fire. EXTINGUISHER SIZES: rated for fire size (numerical rating before letter — e.g., 2A:10B:C means it can extinguish 2 units of Class A and 10 units of Class B). Home/shop minimum: 2A:10B:C; preferred 3A:40B:C; commercial larger. WHEN TO USE vs EVACUATE: use only on SMALL FIRES (one trash can-sized maximum); PEOPLE FIRST — evacuate everyone before considering firefighting; KNOW YOUR EXIT — never fight a fire with the fire between you and exit; CALL 911 first (or immediately while someone uses extinguisher); if fire is large, spreading fast, or blocking exit — evacuate and call fire department; most extinguishers discharge in 10-20 seconds — limited time; if fire not out after one extinguisher discharge, evacuate. Stay 6-10 feet from fire when using extinguisher. FIRE PREVENTION in shops: eliminate ignition sources; proper electrical (no overloaded circuits; quality cords/outlets; GFCI); store flammables properly (METAL CABINETS for solvents, paints, fuels; flame-resistant containers; ventilation); housekeeping (sweep sawdust regularly); SOLVENT-SOAKED RAGS spontaneously combust as oil oxidizes (store in self-closing metal containers; never pile in trash; dispose properly); no smoking in shop areas; working alarm systems (smoke and heat detectors); clear exits; flammable storage separated from main work area; welding/grinding (clear flammables 35 plus feet; fire watch in place). SMOKE DETECTORS: every shop should have working smoke detectors; CO detectors near combustion equipment; check batteries regularly.