How do I carve with the router and then laser the same piece so everything lines up? (Laser offset and registration)

Why it shifts

The laser is bolted beside the spindle, so its beam lands a fixed distance away from the bit in X and Y. If you run laser toolpaths from the router's zero without accounting for that distance, the burn lands off by exactly that amount.

Measure the offset once

1. Clamp a piece of scrap. With a pointed bit, make a small mark and note the position.
2. Without moving X or Y, fire the laser at very low power to burn a dot. Sienci's method fires the laser at low power and moves it until it sits on the mark. Onefinity's guide uses a very low power command (M3 S2) for positioning.
3. Measure from the bit mark to the laser dot in X and in Y. Those two numbers are the offset.

Apply it, three options

• In the sender: Sienci's gSender has Laser Axes Offset fields (one for X, one for Y) under the Spindle/Laser settings. You zero with the router as usual and the offsets apply when you switch to laser mode. Sienci's rule for signs: the offset value takes the opposite sign of the direction the laser needs to move.
• At the controller: Onefinity's guide either enters the offsets permanently on the offsets page or applies them by a typed command.
• By re-zeroing: jog until the low power dot sits on your reference point and zero X and Y there for the laser file.

Run order that works

1. Zero X, Y and Z with the bit and run the router toolpaths.
2. Leave the work clamped. Remove the bit and collet (Onefinity's guide) and the dust shoe (Sienci's warning about bristles).
3. Switch the controller to its laser configuration. On Grbl that means laser mode on, and off again before the next router job.
4. Set the laser focus height and zero Z there.
5. Run the laser toolpaths as their own file.

The official post-processor guide notes that one post can often serve both router and laser toolpaths, but the machine's physical setup still has to be changed between the two.

Pro tips

• Raise Z well clear before jogging between positions. Sienci's trial and error method raises the spindle to a safe height before moving the laser over the mark.
• Sienci notes that its published offset tables are theoretical and may not match your mount, so measure your own.
• See the entry on focus height and Z handling for the laser Z zero.