How to prepare a drawing for laser cutting

A file for a laser-cutting shop must contain closed shapes, no overlapping lines, true size in millimetres, holes no smaller than the sheet thickness, separate layers for cutting and engraving, and a DXF version the shop can read. Get these right and the shop can load your file straight into the machine. This guide explains each rule, then walks through an example and a checklist.

Why a file that looks right on screen can cut wrong

A laser cutter does not "see" a picture the way people do. Its software reads the lines one by one and turns them into a toolpath. Two lines lying exactly on top of each other look like one line on screen, but the machine cuts that edge twice — burning it and wasting time. A shape with a 0.01 mm gap at one corner is not closed as far as the software is concerned, so it cannot apply kerf compensation or decide the cutting order, and a part may drop out before its inner holes are finished.

Someone at the shop then has to repair the file. Some shops charge for that; others miss it and cut a whole sheet wrong. Preparing the file properly from the start saves money and days.

Six rules for a good laser-cutting file

1. Millimetres, true size, 1:1

Always draw at real size and never shrink or enlarge the drawing to fit a sheet of paper — the shop cuts exactly the numbers in the file. If a millimetre file is read as inches, the part comes out 25.4 times larger. DXF files exported from DXCAD2D Online are always in millimetres, but still write "units mm, scale 1:1" in your message to the shop.

2. Every cut shape must be closed

The outline and every hole must be a fully closed loop. The safest way is to draw with tools that make closed shapes to begin with — Rectangle (R) and Circle (C). For free shapes use Polyline (PL) and finish by clicking the first point again. If you draw with single lines, keep object snap on (F3) so the ends meet exactly.

3. No doubled lines and no stray bits

Doubled lines usually come from copy-and-paste or from drawing a rectangle over an edge that already exists. Before sending, select everything and check that the object count is what you expect. Click a line and delete it: if a line is still there, there were two. Also remove construction lines, centre lines, dimensions and the drawing frame from the file you send, or put them on clearly named layers that the shop will not cut.

4. Understand kerf (the width of the cut)

The beam has a width, so a narrow strip of material disappears along every cut. That strip is the kerf. It depends on the machine, the material and the thickness, and is usually a fraction of a millimetre. Most shops set kerf compensation on the machine, so draw the finished size and do not add or subtract kerf yourself unless the shop asks you to.

For press-fit parts — slots in wood or acrylic that must hold tight — kerf matters a lot. Ask the shop whether they compensate and how much clearance to allow, or order a small test piece first.

5. Hole and slot size must suit the thickness

A common rule of thumb in the trade: a hole diameter should not be smaller than the sheet thickness — no smaller than Ø3 in 3 mm steel — and the web between a hole and an edge should not be thinner than the sheet either. Smaller holes may come out out-of-round, burnt or plugged with dross. What a machine can really do depends on the machine and the material, so ask the shop.

This table is a starting point, not a standard. A shop with a high-power fibre laser may cut smaller holes; some materials need more.

6. Separate cut-through and engraving

If a job has both cutting and surface engraving or marking, put them on separate, clearly named layers such as CUT and ENGRAVE so the shop can assign different laser power straight away. In DXCAD2D Online, add layers in the layer panel on the right and move the selected lines to the right layer. Text to be engraved should be converted to outlines (select it and press XP, Explode), or ask whether the shop accepts TEXT entities.

Example: a 120 × 80 mm mounting plate with four corner holes

1. Open DXCAD2D Online, press R, click a start point, type 120,80 and press Enter. You get a rectangle 120 wide and 80 high.
2. For the hole positions, make construction lines with Offset (O) 10 mm inside the edges (remember to delete them before sending).
3. Press C, click the intersection of two construction lines (object snap shows a crossed square), type 3 for the radius and press Enter: a Ø6 hole. Repeat for the four corners, or draw one and use Array (AR).
4. Delete the construction lines, or Trim (X) anything that overlaps.
5. Add Dimensions (D) on a separate DIM layer so the shop can check sizes, and tell them that layer is not to be cut.
6. Export a DXF R12 (Export → DXF…), then open the file again to check that everything is there.

Checklist before you send the file

1. Units are mm and the size is real, 1:1 — at least one distance has been measured again.
2. The outline and every hole are closed shapes.
3. No doubled lines, duplicates or tiny stray dots outside the part.
4. Frame, title block, construction lines and centre lines are removed from the cut layer.
5. Holes and narrow slots are not smaller than the sheet thickness, or the shop has confirmed them.
6. CUT and ENGRAVE are on separate layers.
7. Text to be cut or engraved has been converted to outlines.
8. Saved as DXF R12 (or the version the shop asks for), with a file name that says material, thickness and quantity, e.g. plate_S275_t3_x10.dxf.
9. Your message states material, thickness, quantity and which layers are not to be cut.

Tick everything on this list and most shops can put your file on the machine without phoning you back — and your parts arrive sooner.