Plasma Cutting Kerf Compensation: Settings, Calculation, and Common Mistakes

Plasma Cutting Kerf Compensation: Settings, Calculation, and Common Mistakes

Kerf compensation offsets the torch path to account for the metal removed during cutting. Applied correctly, it helps external profiles, holes, and slots match the dimensions in the drawing.

The key is to keep the cut on the waste side of the finished edge. For an external profile, the torch centerline moves outside the part boundary. For a hole, it moves inside the hole boundary, into the material being removed.

1. What Is Kerf Width?

Kerf width is the width of material removed by the plasma arc. It is not a fixed value for every job: current, speed, torch height, gas conditions, and nozzle condition can change it.

Start with the recommended kerf width in the cutting chart for the selected material, thickness, and process. Treat it as a starting value and confirm the result by trial cutting.

2. Kerf Width and Offset Are Different

For a simplified, symmetric cut, the torch centerline offset is half the kerf width.

For example, if the measured kerf is 2.0 mm, the geometric offset is 1.0 mm toward the scrap side. This is an illustration, not a recommended setting for every machine.

Check what the input field means before entering a value. A field may require the full kerf width, a compensation radius, or a wear correction. These values are not interchangeable.

3. Choose Where Compensation Is Applied

CAM or nesting software compensation

The software offsets the drawing contours and exports an already compensated torch path. Select the appropriate inside or outside cutting operation and inspect the generated toolpath.

CNC controller compensation

A compatible controller offsets the nominal contour during execution. On systems that support these commands, G41 applies left compensation, G42 applies right compensation, and G40 cancels compensation.

Left and right are relative to the direction of travel. G41 does not always mean an outside cut, and G42 does not always mean an inside cut. Follow the controller manual and use a suitable postprocessor.

Avoid applying the full compensation twice. If CAM has already offset the path, adding full compensation at the controller can produce incorrect dimensions. Combined CAM compensation and controller wear adjustment should be used only when the workflow is specifically configured for it.

4. Determine Compensation Through a Test Cut

Use the same material, thickness, consumables, and process settings intended for production.

1. Inspect the torch consumables and confirm the cutting settings.

2. Cut a rectangular test piece with known programmed dimensions.

3. Allow it to cool and remove loose dross without grinding away the measuring edges.

4. Measure both dimensions consistently, noting any edge taper.

5. Adjust the compensation, cut another sample, and verify the result.

Example: correcting an undersized external rectangle

Suppose an external rectangle is programmed at 100.0 mm wide but measures 99.6 mm. If the error is caused entirely by insufficient kerf compensation, the total dimensional error is 0.4 mm across two opposite edges.

The required additional outward offset is therefore 0.2 mm per side.

A field representing full kerf width would need an increase of 0.4 mm; a field representing single-side offset would need an increase of 0.2 mm. Confirm the field definition and retest.

This example assumes a stable, symmetric cut. Do not use compensation to hide machine calibration errors, backlash, or excessive bevel.

5. Check Holes, Slots, and Small Arcs

An external rectangle alone cannot prove that every feature will meet tolerance. Include representative holes and slots in your trial part.

For an inward offset, an internal arc can become too small to produce a valid path. Narrow features may also leave insufficient space for the plasma arc and the required entry motion.

Preview the compensated geometry before cutting. Check small radii, narrow slots, lead-ins, and contour intersections. Modify the design or use a secondary operation when the required feature exceeds the process capability.

For critical bolt holes, evaluate diameter, roundness, and taper. Some applications require drilling or reaming after plasma cutting.

6. Keep the Cutting Process Consistent

Compensation is most useful when kerf width remains repeatable. A worn nozzle or a change in speed, current, height, or gas conditions can change the result.

Recheck sample dimensions after changing the cutting process or replacing consumables. Record the material, thickness, consumable set, cutting settings, compensation mode, and accepted measurements.

There is no universal 1 mm compensation setting. Each process needs its own verified value.

Practical Applications of Kerf Compensation

Flange blanks and mounting plates

These parts combine external profiles with internal openings. Correct compensation helps establish suitable blank dimensions before any specified machining.

Tab-and-slot fabrication

Slot width and tab width affect assembly fit. Test both features together, allowing for edge taper, cleanup, and any later coating.

Repeat production parts

Saved and verified settings provide a starting point for recurring work. Confirm a first-off part before releasing the batch.

Frequently Asked Questions

Can software and controller compensation be used together?

Only through a deliberately configured workflow. Applying the full kerf allowance at both stages can double the offset.

Can compensation remove bevel or dross?

No. It changes the path position. Bevel and dross require attention to the cutting process and equipment condition.

Should I use the same value for every thickness?

No. Use the relevant cutting chart and confirm the value with test pieces.

What should I send Eastrise when discussing a CNC plasma cutting application?

Provide the material grade, thickness range, part drawings, required tolerances, and production volume. Include details of critical holes and slots so the proposed process can be evaluated through representative sample cutting.