Why Does a Nested Laser-Cut Part Come Out With a Heavier Taper on One Edge Than an Identical Part Cut Elsewhere on the Sheet?

Usually it's a focus or nozzle standoff drift across the sheet, not the nesting itself. A large sheet has enough flatness variation, thermal drift, and nozzle wear over the length of a run that a part cut early in the program can genuinely look different from one cut twenty minutes later on the same sheet.

What actually causes it

A laser beam that isn't perfectly perpendicular to the sheet, or a focus point that's slightly off from ideal, cuts a kerf that's wider at the top than the bottom, or vice versa. That's the taper. Several things push that around across a single sheet:

• Sheet flatness. Mill-finish sheet isn't perfectly flat. A slight bow means the standoff distance between nozzle and material changes as the head moves across the sheet, even with capacitive height sensing doing its best to track it. Faster tracking response helps, but on a wavy sheet some parts will sit at a slightly different standoff than others.
• Thermal drift in the cutting head. Lens and nozzle temperature rise over a long cutting run. A part cut near the start of the program, before the optics have warmed up, can cut cleaner than one cut later, or the reverse, depending on how the machine's assist gas is managing heat.
• Nozzle wear or contamination. A nozzle picking up spatter or losing its concentricity partway through a job changes the assist gas flow pattern non-uniformly, which shows up as inconsistent taper from part to part rather than a clean gradient across the sheet.

Cut order matters too. Parts cut later in a densely nested layout sit closer to material that's already absorbed heat from earlier cuts, and that local heat changes how cleanly the edges near it cut.

What to check

If the taper correlates with position on the sheet — worse toward one corner, consistent along one axis — that points at sheet flatness or a leveling issue on the cutting bed. If it correlates with cut order instead, regardless of position, that points at thermal drift in the optics or nozzle wear over the length of the run. Pull the nozzle and check it for spatter buildup or an out-of-round orifice; that's a five-minute check that rules out one whole category of cause.

What this means for tolerance

DigiForge holds ±0.13 mm on the cut for sheet metal work. That tolerance accounts for normal kerf and taper behavior on a well-maintained machine. It's not a promise that every edge across a large nested sheet looks identical under a microscope. If a specific edge condition matters more than the rest of the part (a mating edge, a visible cosmetic surface), calling that out on the drawing lets the shop prioritize orientation or cut order for that feature rather than treating every edge as equally critical.

The practical takeaway

One part cutting worse than its neighbors on the same sheet is a process variable, not a random defect. Chase it by position first, then by cut order. You'll usually land on either a flatness problem or a nozzle due for a swap.