Not exactly a board but a waste layer to avoid wrecking up your original waste board. I’ve clocked in almost 24 hrs on the Carvey and the waste board is in pristine condition.
I used some thick card stock/craft paper to shim it up a bit. About 2-3 coloured craft paper is enough. I used different colours because it would allow me to monitor how low the bit is going kind of like tree rings. If I see a red colour coming out from the bit then I know it is going too low. You can use whatever colours you want.
I created another version which is a printable paper grid to project the grid reference to the top and expose any mounting holes. This will allow me to use the same paper waste board for smaller materials.
Another plus is it corrects the difference between inches 3, 4 and 5. As you can see with the ruler it is slightly off. If you prefer mm you can make one specifically for mm and covert the waste board to mm.