STEM Builder
Log InSign Up
🔦
Unit 5 of 6 · about 18 min

How Laser Cutters Work

A beam of light as a blade — cut versus engrave, the kerf, nesting, and the safety rules
✋ 0/1 picture tasks
📖 Read🔤 Words to know🛠 Mini activity✅ Check

A blade made of light

A laser cutter is a drawing machine with a very hot pen. A laser — light squeezed into one color and one direction — bounces off mirrors, passes through a lens, and comes to a focus on the material about the width of a human hair. At that point there is enough energy to burn or vaporize wood, acrylic, cardboard and paper in a line thinner than a pencil mark. The head rides on rails and follows your drawing, so a laser cutter is really a plotter that burns instead of inks.

CUT — vector line, slow + strongthe beam goes through; the shape falls outENGRAVE — raster sweep, fast + gentleback and forth like a printer; only the surface darkens
Cut or engrave. A slow, high-power pass along a vector line takes the beam all the way through the sheet — a cut. A fast or gentle pass only marks the surface — an engrave. Filled areas and photos are engraved by sweeping back and forth like a printer.

Cutting and engraving are different jobs

Give the machine a vector line and it will drive the beam along it at a chosen power and speed: slow and strong goes all the way through the sheet — that is a cut. Fast and gentle just scorches the surface — that is a vector engrave, good for lettering and outlines. Give it a filled area or a photo and it switches to raster mode, sweeping back and forth line by line like a printer, darkening the surface where the picture is dark. Cut lines come from paths; engraved pictures come from fills or images. That is why the SVG file matters: the laser needs to know which is which.

The kerf: the line that is not there

A saw blade turns some wood into sawdust; a laser turns a thin stripe into smoke. That stripe — the width of material the beam removes — is the kerf, usually around a tenth to a quarter of a millimeter. It sounds like nothing, and it ruins parts that must fit together. Cut a slot exactly as wide as a tab and the slot ends up a kerf wider; cut the tab and it ends up a kerf narrower. Designers who make boxes with finger joints or slot-together stands plan for it: they shrink the holes or grow the tabs by about one kerf so the pieces snap together snugly instead of rattling.

✋ DO THIS ONE
☐ Task: Set a kerf of at least 0.2 mm and see what it does to the fit.
slot: drawn 40, cut 40tab: drawn 40, cut 40no kerf: perfect fit (never happens)
Kerf0.0 mm
Add a kerf. A real laser removes about 0.1–0.25 mm along every cut.
The kerf. The beam removes a thin stripe of material along every cut. A slot comes out one kerf wider than drawn and a tab one kerf narrower, so a tab drawn to fit its slot rattles. Designers shrink the slot or grow the tab by about a kerf so the joint is snug.

Flat parts, clever joints

A laser only cuts flat sheets, so laser designers think in two dimensions and assemble in three. Boxes are six flat panels with fingers along the edges that interlock. Shelves use tabs that pass through slots. A row of closely spaced cuts turns a stiff board into a bendable living hinge. The trick of the trade is nesting: arranging all the parts on the sheet as tightly as possible, like puzzle pieces, so that the fewest sheets are used and the least material is thrown away.

room for one morescattered: a second sheet needednested: same parts, one sheetnesting = packing the parts like a puzzle so little wood becomes scrap
Nesting the parts. A laser only cuts flat sheets, and sheets cost money. Nesting means arranging every part as tightly as possible, like puzzle pieces, so the job uses the fewest sheets and leaves the least scrap.

Materials: good, risky, never

Plywood, acrylic, cardboard and paper cut beautifully. Some things must never go in: PVC and vinyl release chlorine gas when burned, which poisons the operator and eats the machine; polycarbonate just catches fire; anything with a mirror finish bounces the beam back. If you do not know what a material is, you do not cut it.

The rules that keep fingers and buildings

Every laser has the same short list. The lid stays closed while it runs, because the beam that cuts wood also cuts eyes. Ventilation is on before the job starts, because smoke is the job's main product. Someone watches the whole cut, because a small flame becomes a big one in seconds. And the material gets a moment to clear before the lid opens. Follow those and a laser cutter is one of the friendliest machines in a shop.

The laser's big cousin: the CNC router

When the sheet is too thick for light — three-quarter-inch plywood, a slab of plastic, even aluminum — the shop reaches for a CNC router. It is the same idea with a different tool: a computer drives a spinning bit, called an end mill, along your vector lines, and the bit chews a path through the sheet instead of burning one. Everything you learned about flat parts carries over: nesting, tabs and slots, planning for the width of the cut. But the numbers get bigger. A router's kerf is the whole diameter of the bit, often a quarter of an inch, so a slot loses far more than a laser's hair-thin stripe. And a round bit can never cut a sharp inside corner. It leaves a radius the size of the bit, so designers add a small round dog-bone relief at each inside corner, or round the mating tab to match.

a square pocket for a square tabas drawnwhat a round bit leavesdog-bone relief: tab fits
A round bit cannot cut a sharp corner. Drawn square, a pocket cut by a router comes out with inside corners rounded to the bit's radius, and a square tab will not seat. A dog-bone relief scoops a little extra out at each corner so the tab drops in. Lasers do not have this problem; routers always do.

The work is held to the table with screws, clamps or a vacuum, and the router leaves thin tabs of material so finished pieces do not fly loose before the job ends. It makes chips and dust instead of smoke, so the rules change: safety glasses and ear protection, hands nowhere near the bit, and the dust collector running before the spindle starts.

A laser cutter does exactly what the drawing says, one kerf too wide. The drawing, the material and the person watching are what make the part come out right.

🔤 Words to know

Laser
Light squeezed into one color and one direction, focused to a tiny point hot enough to burn or vaporize material.
Focus
The exact height where the lens brings the beam to its smallest, hottest point on the material.
Cut
A slow, high-power pass that takes the beam all the way through the sheet along a vector line.
Engrave
A fast or low-power pass that marks only the surface — along a line, or sweeping a filled area like a printer.
Vector line
A path in the drawing that the laser follows exactly; cuts and line engravings come from these.
Kerf
The thin stripe of material the beam removes along a cut, which makes slots wider and tabs narrower than drawn.
Finger joint
Interlocking tabs along the edges of flat panels that let laser-cut pieces form a box.
Living hinge
A pattern of closely spaced cuts that lets a stiff flat board bend.
Nesting
Arranging all the parts tightly on a sheet so the fewest sheets are used and little is wasted.
Ventilation
The fan and ducting that pull smoke out of the machine and away from the people around it.
PVC
A plastic (also in vinyl) that must never be laser-cut because burning it releases chlorine gas.
CNC router
A computer-driven machine that cuts flat sheets with a spinning bit instead of a beam — thicker wood, plastic, even aluminum.
End mill
The spinning cutting bit of a CNC router. Its diameter is the width of the cut and the smallest inside corner it can leave.
Dog-bone
A small round relief cut at an inside corner so a square tab can fit where a round bit could not cut sharp.

🛠 Mini activity: Run the job safely

The class is laser-cutting a slot-together phone stand from 3 mm plywood with an engraved name on the front. Sort the drawing, the materials and the steps.

  1. 1
    Sort each part of the drawing: will the laser CUT it or ENGRAVE it?
    💡 Outlines and slots go through the wood. Names and pictures only mark the surface.
    For each card, tap the bin it belongs in.
    The student's name on the front
    The holes for the charging cable
    The outer outline of each panel
    The slot the back panel slides into
    A small photo of the student's dog
    Cut
    Engrave
  2. 2
    Which materials are safe to put in the laser cutter? Choose every one.
  3. 3
    Put the laser workflow in order.
  4. 4
    The back panel rattles loosely in its slot. Choose every explanation or fix that is correct.

✅ Check: How Laser Cutters Work

🔒
Finish the lesson first
  • Picture tasks in the lesson: 1 left — look for the ✋ DO THIS ONE badge.
  • Mini activity: every step needs its ✓.
The five-question check unlocks here as soon as the last one lands.
↑ Back to the lesson
← Unit 4: How 3D Printers WorkUnit 6: Made by Design →