Quick Engrave Cutting Too Deep

I also ran into this problem.

Solution: level the board with a 20mm end mill. This will set your height uniformly across the board.

After that, my Z values were perfect.

Try using another part of the board and check the results. Another way would be setting your end mill to Z0 and let it run from Y0 to Y800 or whatever size is yours. If your board is not leveled, it will cut it at some point.

Thanks, unfortunately I won't be able to face off the surface as I'm hoping to engrave on a gift box.
I doubt the workpiece is deflecting that much but with the original stepcraft clamping it might be
possible. I think it is time to invest in a dial indicator and new worktop with a better clamping system.
In the mean time I might break up my engraving into multiple toolpath sections and zero the Z above each
section to minimise the impact of any deflection.

I've run into this exact issue before with V-Carve and UCCNC. The preview showing 1mm but the machine cutting 2-3mm deeper usually comes down to your Z-zero reference point. Double-check that you're setting Z-zero from the material surface in both the software and at the machine. Also, verify your tool geometry settings, if the tool definition doesn't match what you're actually using, UCCNC can misinterpret the depth.

What bit are you using? Some engraving bits have a flat tip that affects depth calculations. I found that resetting the Z-axis home position and recalibrating helped me solve it. You can find more troubleshooting tips here if you need additional guidance. Hope this gets you sorted out.