I’ve recently finished a project creating a custom board game box as a gift for a friend. I had a pretty limited supply of plywood to hand to make it from, and the stuff that I had was pretty badly warped.
I knew I wanted to do some engraving on the top surface which presented a challenge.
The above test cube was cut and engraved from some decent quality laser grade plywood. Yet if you look at the engraving on the bottom left compared to the top right there’s an obvious difference in the depth of cut. This could’ve been caused by a multitude of factors:
- Warping in the wood.
- Uneven clamping to the CNC machine base
- Badly calibrated CNC machine.
For the board game box I needed a consistent depth of cut because I wanted fill the engraving with an iron powder inlay, and the surface I wanted to engrave was much larger so all of the above factors would be magnified over the distance.
One common way of solving this would be to take a surfacing cut with a flat bottomed end mill over the whole sheet of plywood to level the top surface. I didn’t want to risk this because I don’t have decent work-flow for doing this with my machine yet, and I was worried I’d end up milling through the top veneer.
Another way to solve this would’ve been to use the touch probe functionality of GRBL to build up a map of the surface and warp the engraving paths appropriately. Alas I haven’t gotten round to building a touch probe yet but fortunately I had routed the touch probe wires to near the spindle. This sparked the beginnings of a cunning plan.
I had a can of 3M Remount spray from a previous project (same glue as found on the back of post-it notes) which i figured i could spray onto some tin foil to create a conductive top surface for the plywood.
After smoothing the tinfoil to the plywood I attached crocodile clips from the tinfoil to one of the touch probe wires, and the tip of the spindle to the other touch probe wire. I could then use Candle’s (an open source G-Code sender) touch probe functionality to build a height map.
With the height map generated the engraving paths could be warped to match it (again using functionality built into Candle) and the top surface could be engraved.
The tin foil is easy to remove and leaves very little residue thanks to the 3M remount spray.
Iron powder was then brushed into the engraving, fixed into place with super glue, and then sanded flat.
The other parts of the box could then be assembled.
I used some corner pieces cut from thicker plywood to help hold the shape of the box and mitigate the warping of the thinner plywood.
Using the same technique as the top surface I engraved a name tag to put on the front of the box.
Finally the box was assembled, sanded, oiled using butchers block oil, and some brass corner protectors added.
In some lights it’s possible to make out the remnants of the super glue. If done again I’d probably look to seal the entire top surface using super glue, or spend more time sanding.
But otherwise I’m pretty chuffed with how this turned out.