My design for a MPCNC work table top works in theory – time will tell if it does so in practice.
Here is a picture of my design. The light blue shows the entire MPCNC work table top. It will be made of 1/2 inch plywood sized 32” deep and 38” long. It is attached to a frame made from two by fours. The steel rails for the MPCNC will be sized 29” by 35”. This will leave me with an 18” by 24” work area – that is a rectangle where the tool can reach while moving about on the X and Y axis.
As discussed previously, the MPCNC frame will attach to the table using 5/16” bolts through the plywood surface.
Two questions then remained. First, how would I attach a spoil board, also called a waste board? Second, how would I hold down the material onto the surface of the spoil board?
Having a spoil board is important, because you don’t want to damage the table top when you are cutting material. The spoil board has to be secured to the table top. It cannot move around. Similarly, you need to be able to attach clamps or hold downs to secure work material.
The spoil board will likely be a piece of MDF sized 24” long and 20” deep. There will be holes spaced 3/4 inches from the upper and lower edges to hold the spoil board to the MPCNC work table top. My plan is to use nylon bolts to attach the spoil board. The advantage of nylon bolts is that if things go terribly wrong while cutting, the tool won’t be damaged if it hits the bolt head. (I will also 3D print a hole jig so I can drill these holes accurately and easily.)
MPCNC Work Table Top – T-Nuts to the Rescue
One of the ideas I have seen on the web is to use T-Nuts in the table surface for attaching small bolts for the spoil board and clamps. This link describes the idea. I found a good selection of these at Lee Valley Tools in Calgary.
Using bolts with a 1/4-20 thread seems to be an almost standard for spoil boards and work hold downs. So, when the MPCNC work table top is assembled, the orange and yellow dots will become 5/16” diameter holes. The T-nuts will be inserted and attached from the bottom. Then the 1/4-20 bolts will be used to attach the spoil board and work hold downs through the top of the MPCNC work table.
I think I will also 3D print some caps to cover any unused holes and keep the threads clear of debris. There are many designs for plastic hold down clamps on Thingiverse that I can try.