Today I added a waste board to my Mostly Printed CNC.
A waste board – also known as a spoiler board or sacrifice sheet – is a piece of material placed on top of the machine bed, to protect the table top. There are two good reasons to use one. First, it protects the table. You can let your cutting tool cut into the spoiler if necessary. Second, you can route your waste board to create a perfectly flat surface to work on.
As designed, my MPCNC has a work area of 18 inches high by 24 inches wide. I laid some paper on the work table, and marked the exact workspace – in particular, the four corners where my tool can reach.
To keep things simple, I picked up a 24” by 24” sheet of MDF from Home Depot. I attached this with four 1/4 inch screws, two near each of the upper and lower edges. They were spaced 12 inches apart, and six inches in from each side. The method of attachment was with a T-nut underneath the table top.
This was definitely a case of “measure many times, drill once”. I marked out the drilling template on the MDF with a pencil, including measuring the diagonals to make sure that the four holes were square. I drilled the holes in the MDF first. Then I used the MDF as a stencil on the table top, and drilled some 1/4 inch started holes through the spoiler into the table. Finally, I finished off the table holes with a 5/16 inch bit – the diameter required for the T-nut inserts.
How thick a waste board?
I chose a piece of 3/4 inch thick MDF. This is because I want to use some more T-nut inserts spaced along lines in the waste board to secure hold down clamps. Drilling these holes in the waste board for the clamp holders will be my first real CNC work project, once my end mills arrive. But first, I need to learn how design a graphic for the clamping holes and use that to create the G-code for the CNC milling.
By the way, I am using 1.5” 1/4-20 bolts to secure the waste board. The thickness of the waste board (0.75) plus the thickness of the table top (0.5) is 1.25 inches. Later, I will try to find some nylon threaded bolts to replace the metal ones. I think a lot of people use nylon bolts to prevent any damage to their tools in case they stray to far outside the work area.