Laser Cut Stencils: Files, Materials and Settings

To make a laser cut stencil, you need a vector file (SVG or DXF) where every shape is a closed cut line, with bridges holding any loose pieces in place, and a laser-safe sheet such as polyester mylar or cast acrylic. Find your power and speed with a small test cut on the same material, because settings vary from machine to machine. And never put PVC or vinyl in a laser: it releases chlorine gas.

Why laser cut a stencil

A laser cuts the same stencil perfectly every time, gets into detail a knife can't, and doesn't tire out halfway through a big sheet. If you're making the same stencil more than once, or selling stencils, it pays for itself in hours saved.

The catch is that a laser does exactly what the file tells it. A messy file gives you a messy stencil, very quickly.

Which file to use: SVG or DXF

Lasers cut along vector paths (lines defined by maths, not pixels). A JPG or PNG of your design won't cut cleanly; the laser software can only engrave it or trace it, and tracing rarely gives clean edges.

LightBurn, which a lot of hobby laser owners use, imports both. If you're not sure, try SVG first. If your machine or workshop asks for DXF, use DXF. I go into more detail in the stencil export formats tutorial.

Whichever you use, check three things after importing:

1. Size. Measure one known dimension. If it's way off, the file has been read in the wrong units.
2. Closed shapes. Each cut should be one continuous loop. Gaps mean the piece won't drop out.
3. No doubled lines. Two identical paths on top of each other means the laser cuts twice and burns the edge.

What kerf is and why it matters

Kerf is the width of material the beam burns away as it cuts. On thin stencil sheet it's usually a fraction of a millimetre (roughly 0.1 to 0.3mm, depending on the machine, lens and material).

That sounds tiny, but it adds up on a stencil:

• Every opening gets slightly bigger by about the width of the kerf.
• Every bridge gets slightly thinner by the same amount.
• Fine detail can vanish completely if two cut lines sit closer together than the kerf.

You don't usually need to compensate for kerf on a stencil. You do need to design with it in mind: keep bridges and thin strips at least 1mm wide, and more on large stencils that'll be handled a lot.

Why bridges matter even more on a laser

Hand-cutters notice when a piece is about to fall out. A laser doesn't. It'll happily cut the centre out of every "O", "A" and "R" and leave you with a sheet of holes.

Any island (an enclosed shape with nothing attaching it to the rest of the sheet) needs a bridge connecting it back to the frame. Get these in before you cut. You can see how to add and adjust them in the bridge stencil islands tutorial.

Which materials to use

For a stencil you'll use with paint, mylar is the usual answer. For a template you trace round with a pencil or router, acrylic or plywood. If you're still choosing, my reusable stencil guide covers mylar thickness in detail.

Never laser cut PVC or vinyl

This is the one rule that isn't up for debate. PVC and most vinyl contain chlorine. When a laser cuts them, they release chlorine gas, which is harmful to breathe and turns into acid that corrodes the inside of your machine.

That catches people out because a lot of adhesive stencil vinyl is PVC, and some cheap plastic sheet sold as "stencil plastic" is PVC too. If you don't know exactly what a sheet is made from, don't cut it. Ask the supplier for the safety data sheet (a document listing what's in the material). If they can't give you one, use something else.

Polycarbonate is another one to avoid: it cuts badly, discolours and can catch fire.

How to find your laser settings

I can't give you one correct power and speed, because a 10W diode laser and an 80W CO2 laser behave completely differently, and two sheets of mylar from different suppliers do too. Here's how to find yours:

1. Cut a test grid. A grid of small squares, each at a different power and speed combination. LightBurn has a material test generator that builds one for you.
2. Start low. Begin with lower power and faster speed than you think you need, then step up.
3. Pick the gentlest setting that drops out cleanly. The square should fall out on its own or with a light push, with no melted beading or scorch marks.
4. Write it down. Note the machine, material, thickness and settings on a label on the sheet stack. You'll forget otherwise.
5. Cut a small piece of the real stencil next. A corner with fine detail tells you more than a square does.

A few habits that help on almost every machine:

• Use air assist if you have it. It blows smoke away from the cut and reduces flare-ups.
• Cut, don't engrave. In LightBurn, set your stencil layer to Line mode so it follows the paths. Fill mode engraves the shapes instead of cutting round them.
• Weigh the sheet down. Thin film lifts in the airflow. Use honeycomb bed pins, magnets on a steel bed, or a few weights outside the cut area.
• Cut inside shapes first. Most laser software lets you order cuts so inner details go before outer edges. If the outer edge goes first, the piece can shift and the inner cuts land in the wrong place.

Laser safety basics

• Never leave the laser running unattended. Stencil materials are thin and catch fast.
• Ventilate properly. Every material gives off fumes when lasered; vent them outside or through a proper filter.
• Keep a fire extinguisher suitable for your machine within reach.
• Wear the right eye protection for your laser's wavelength if the machine isn't fully enclosed.

Making multi-layer laser stencils

For a stencil with more than one paint shade, each layer is its own sheet. They need to line up perfectly when you spray. Registration marks (small alignment shapes in the same place on every layer) make that easy: cut them into every sheet and line them up before you paint.

Free Stencil Maker splits a photo into up to 6 layers, adds the bridges and registration marks, and exports SVG or DXF ready for your laser software (SVG and DXF need Pro or a one-off project unlock). See the DXF stencil maker if your workshop wants DXF.

FAQ

What is the best file format for laser cutting stencils?

SVG works with most hobby laser software. DXF is the safer choice for CAD software and some industrial machines. Both are vector formats; a PNG or JPG is not suitable for cutting.

Can you laser cut mylar?

Yes, as long as it's polyester (PET) mylar and not PVC film sold under a similar name. It tends to melt at the edges, so use lower power, faster speed and air assist, and test first.

Why didn't my laser cut stencil pieces fall out?

Usually the power is too low or the speed too fast for that material, the path isn't fully closed, or the sheet lifted during the cut. Check the file for gaps, weigh the sheet down, and run a test grid.

Is it safe to laser cut vinyl stencils?

No. Most vinyl is PVC, which releases chlorine gas when lasered. Cut vinyl with a blade cutter such as a Cricut instead.

Ready to cut? Upload your photo to the laser cutting stencil maker, check the bridges, and export a clean file for your machine.