Designing parts for laser cutting

1. Understand the kerf

The laser removes a narrow strip of material as it cuts — the kerf. On our CNC fibre laser it's roughly 0.1–0.3 mm wide depending on material and thickness, and the cut sits centred on your drawn line. Two things follow:

• Holes come out slightly larger and pegs/posts slightly smaller than the nominal line, because half the kerf is taken from each side. For general fabrication this is well within tolerance; for a press-fit, call it out and we'll compensate.
• Two cut lines can't sit closer than about one kerf width or they merge into one — so very thin webs and slots have a practical minimum (below).

You don't need to offset for kerf yourself — draw the part at nominal size and tell us any critical dimensions. We set the cut compensation in the machine.

2. Minimum feature size scales with thickness

The most useful rule in laser design: the thicker the material, the larger the smallest feature it can hold. Fine detail that's effortless in 1 mm becomes marginal in 10 mm. Two guidelines cover most cases:

• Minimum hole diameter ≈ material thickness. A hole much smaller than the plate is thick pierces poorly and can come out tapered. In 5 mm steel, keep holes to about 5 mm and up.
• Minimum slot width / web thickness ≈ material thickness. A 6 mm slot in 6 mm plate is fine; a 1 mm slot in 6 mm plate is not. Same for the wall left between close features.

3. Give internal corners a radius

A laser beam is round, so it can't cut a perfectly sharp inside corner — there's always a small radius. Design it in rather than fighting it:

• Add a small fillet of at least 0.5× the material thickness to internal corners. It cuts cleaner and relieves stress.
• If a sharp corner is functionally needed (for a tab to seat fully), add a small relief / dog-bone notch rather than expecting a knife-edge.
• External corners can be sharp — break them only if you want them safe to handle.

4. Space holes and edges sensibly

• Keep a hole at least 1× thickness from any edge, ideally 2× near a bend or for a countersink, so the thin wall doesn't distort.
• Leave at least 1× thickness of material between adjacent holes.
• If the part will be folded, hold holes back from the bend line by at least 2.5× thickness plus the bend radius.

5. Use bridges and tabs to hold small parts

When a part or an internal feature is fully cut free, it can drop into the machine or tip up into the head. Most parts are fine, but two cases need bridges (micro-tabs):

• Very small or light parts — tiny washers, fine lettering, delicate filigree — that would fall through the bed or move and re-cut. A few small bridges hold each part in the sheet until you snap it out.
• Loose internal islands — the centre of a letter "O", a captured ring — which drop out without a bridge.

A bridge is a short un-cut segment, typically 0.3–1.0 mm wide. We add and place them during review, so you don't have to draw them — just flag any part where a clean, untabbed edge is critical and we'll hide them where they won't show.

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