I'm flattening/leveling out my spoilboard prior to sticking a PCB against it with double sided Nitto tape.



The first spoilboard material I tried was plywood, but it turns out that the knots in the plywood don't smooth as well as the rest of the wood, so I'm rejecting plywood.

I'm presently, as I type this, leveling out some particle board, and it seems to be leveling out quite smooth. The only downside is that it's loaded with formaldehyde resin, so the dust probably isn't healthy. I presume MDF would have the same issue.

So, for that reason, I may also consider Advantech, which allegedly has no added urea formaldehyde in it. It's more of a chipboard, though, so I'm unsure how well it will mill flat.

What material are you all using?

Presently, as you can see from the photo, I'm using aluminum holddowns, but I think I may switch to plastic bolts so that I'm not blasted with metal shrapnel if the cutterhead should ever slam into it (Murphy's Law, right?). Even then I would sink the plastic bolt-heads below the surface of the spoilboard, to make a collision even less likely. Also, that way I could mill the entire surface flat.

What kind of hold-downs do you guys use?