Laser Cutting Job Work: How to Prepare DXF Files for Accurate Parts

A laser cutting machine follows your drawing exactly, mistakes included. For laser cutting job work, the quality of the DXF or DWG file you send decides how accurate the parts are, how quickly they can be quoted and how much material ends up as scrap. This guide explains what a clean, cut-ready drawing looks like and which details help a job shop price your parts correctly.

Why the drawing decides accuracy and cost

When you outsource laser cutting, the programmer imports your file into CAM software, assigns cutting paths, adds lead-ins and nests the parts on a sheet. Every problem in the file, such as an open contour, a duplicated line or a wrong scale, has to be found and fixed by hand before cutting starts. A missed problem shows up as a scrapped sheet or a part that does not fit.

The cost of a laser cut part is driven mainly by three things: the material used, including the skeleton left after nesting; the total cutting length; and the number of pierces. A clean, correctly scaled drawing lets the programmer optimise all three. Our laser cutting services page shows the kind of flat parts that are typically cut from sheet.

Clean geometry: closed contours, true scale and units

The laser cuts along continuous paths, so every outline and every internal cut-out must be a single closed contour. Even a tiny gap between two line ends can make the software skip the feature or treat it as an open line.

• Draw at 1:1 scale in millimetres and state the units in the title block or file name. A part drawn in inches but read as millimetres comes out about 25 times smaller.
• Join outline segments into polylines, or at least make sure endpoints meet exactly.
• Delete duplicate and overlapping lines. Two lines on top of each other are cut twice, which burns the edge and wastes machine time.
• Use true arcs and circles instead of splines or many short segments. Splines often convert into thousands of tiny moves that slow the machine and leave a faceted edge.

Export the part flat, in its unbent state. An older ASCII DXF version is the safest choice.

Layers, line types and what should not be cut

Drawings usually carry title blocks, dimensions, notes and bend lines as well as cut geometry. If these share a layer with the outline, the programmer must separate them by hand. A simple layer structure avoids this.

Bend lines need special attention. If the part will be bent after cutting, note the bend direction (up or down) and the inside radius, or better, send the 3D model. Parts that move on to CNC press brake bending need a flat pattern developed for the actual material and tooling, not a generic one.

Kerf allowance and feature size versus thickness

The laser beam removes a narrow strip of material called the kerf. Its width is a fraction of a millimetre and varies with material and thickness. The CAM software offsets the cutting path by half the kerf so that the finished part matches the drawn size. This is why you should always draw parts to their final nominal dimensions. Do not add or subtract kerf yourself; the compensation would be applied twice and parts would come out undersized or oversized.

If two parts must fit together, such as a tab into a slot, describe the required fit in a note rather than adjusting the geometry by eye. The shop can then set the clearance to suit its cutting parameters.

Small holes and narrow webs

Very small holes and thin webs cause the most trouble. As a hole diameter approaches the sheet thickness, heat builds up, the hole may taper or fail to clear, and thin bridges between features can warp. The table below gives general rule-of-thumb guidance; real limits depend on the material, the machine and the assist gas.

Where a precise hole is needed for a bearing, dowel or tapped thread, it is often better to laser cut an undersized pilot and finish it by drilling or reaming.

Nesting, material and quantity information

Nesting is the arrangement of parts on a standard sheet to use as much material as possible. On a 2500 x 1250 mm bed, many small parts can be nested together, while larger panels may be cut one or two to a sheet. You can help the shop nest well and quote accurately by giving:

• The exact material and condition, for example CRCA, HR, stainless steel 304 or 316, aluminium grade, or galvanised (GI) sheet.
• The thickness of every part, ideally in the file name, such as bracket-A_2mm_SS304_qty50.dxf.
• Quantity per part and expected repeat orders. Larger batches nest better and cost less per part.
• Surface requirements: protective film, brushed side up, or no scratches on visible faces.
• Whether grain or finish direction matters, so parts are not rotated during nesting.
• Whether common-line cutting or small micro-joints are acceptable, since both save cutting time.

Common mistakes in laser cutting drawings

1. Sending only a scanned PDF. A PDF can be redrawn, but that adds time and a chance of error. Send DXF, DWG or STEP where available and keep the dimensioned PDF as a reference.
2. Leaving text as TEXT objects. Convert it to outlines and say whether it should be engraved or cut through.
3. Cutting letters such as O, A and B without bridges, so the centres fall out.
4. Putting parts of different thickness in one file without labels.
5. Sending assembly drawings with overlapping parts instead of individual flat parts.
6. Leaving sharp internal corners on parts that will be bent, without bend reliefs.
7. Copying tight tolerances from machined parts onto every dimension. Apply them only where function needs them.

Working with Vidhee Eng. Works

Vidhee Eng. Works has been in sheet metal work at New GIDC, Kabilpore, Navsari since 2004 and runs CNC fiber laser cutting in-house under an ISO 9001:2015 certified quality management system, with dispatch across India by road. Send us your drawing in DXF, DWG, STEP or PDF with material, thickness and quantity, and we will come back with any questions and a quote.