What is Kerf? Why Every Designer Should Care About Laser + CNC Tolerances

If you’ve ever designed something for laser cutting or CNC routing and found that parts don’t quite fit, chances are you’ve met kerf — even if you didn’t know its name.

Kerf is one of those technical details that separates a clean, professional build from a frustrating assembly. And if you’re designing for fabrication, you should care about it.

So, What is Kerf?

Kerf is the width of material removed by a cutting tool.

• On a laser cutter, kerf is the thin path burned away by the beam — often between 0.1–0.3 mm, depending on the material.

• On a CNC router, kerf is the diameter of the bit as it carves through wood, plastic, or composite — anything from 1/32″ (0.8 mm) for fine detail to 1/2″ (12.7 mm) for heavy clearing.

In both cases, the machine doesn’t just follow your line — it erases a path around it. That difference is the kerf.

Why Kerf Matters

1. Fit & Assembly

   Imagine designing slots for interlocking parts at exactly 6 mm wide because your plywood measures 6 mm thick. Once cut, the slots are too tight — or worse, too loose. That’s kerf in action.

2. Precision at Scale

   On small details, kerf can erase delicate geometry. A 0.25 mm laser kerf might not sound like much, but at 1:200 scale, it can eat an entire mullion.

3. Edge Quality

   On CNC jobs, using too large a bit means you’ll never get a sharp inside corner. Kerf defines the minimum radius every cut will have.

How to Design With Kerf in Mind

• Laser Cutting

  • Offset geometry by the beam width if precise fits are needed.

  • Test cut a small slot gauge in your material — it tells you the real kerf for that machine and that stock.

• CNC Routing

  • Always remember: the smallest inside corner radius = bit diameter ÷ 2.

  • For joints, add dogbones or teardrops so square parts can fit into rounded corners.

  • Allow clearance — typically +0.1–0.3 mm — so parts slide together without breaking.

• General Rule

  • If it must fit, design for kerf. If it’s only visual, kerf is still there — but less critical.

The Takeaway

Kerf isn’t a flaw — it’s a fact of fabrication. Knowing it, testing for it, and designing with it in mind is what separates a clean professional model from a pile of parts that don’t fit.

At BDR DSG LAB, we always check tolerances before running a job. For students, that means your laser-cut model assembles without endless sanding. For small businesses, it means your sign or product display comes together exactly as intended.

👉 Got a design that needs to fit perfectly? Send us your file — we’ll account for kerf, material thickness, and tolerances to make sure your project assembles cleanly and looks professional.