I have built a flat-ish table for my full sheet LR3 using 2x4 frame and 3/4" plywood as the top surface.
I was thinking about using a sheet (well actually two 24" x 96" pieces) of 1/2" styrofoam as a replaceable spoil board, with a couple of 10’ sections of 1/2" x 3" trim board to elevate the Y Rail and Y Rollers to the same elevation as the top of the styrofoam.
I found a couple of threads that mention foam spoil boards by searching the forums, but they don’t really have any discussion of how it held up over the long term, or what any drawbacks might be.
(example: LowRider CNC- Full sheeter - #53 by vicious1 )
Any thought on the pros and cons of this approach? I was wondering if the styrofoam might bow up, or get compressed/dented in some areas leaving the surface uneven. Also what would be the best way to secure it to the plywood so that it stays put but can be easily removed/replaced (double sided tape?)
If maintaining ‘flat’ from piece to piece isn’t an issue it would work I guess. Cutting into a small piece with a soft support is going to allow it to tip/dip as you cut. If you’re cutting BIG pieces, probably less of an issue.
I guess if you could figure out a good way to hold your work pieces down it’d be ok. My only concern would be if if the foam gets compressed when the work is clamped down and you cut something out, the foam decompresses and your Z0 is now off.
For my Primo, I recently created a foam topper for my spoil board. I’m using it to cut foamboard for RC planes, not for wood projects. Since I only use foam topper occasionally, I cannot address longivity.
To attach the foam, I 3D printed large washers. Then I had the CNC cut wells for the washers at regular intervals, and screwed the washers to the spoil board. In my case, I already had inserts in my table base, so I set up the wells to match the inserts and used machine screws. Sheet metal screws directly screwed into the spoil board should work well.
If all you are using your machine for is contour cutting, then, with a foam spoil board, flatness might not matter as much.
As an alternate method to attach the foam panels, there are a couple of spray gules that work with foam (most spray glues melt the foam). I use Permatex Automotive Headliner Adhesive for gluing foam. I’ve read that 3M Super 77 also works with foam.
I bought a sheet of R3.9 foam core board, I think it’s about 3/4-in thick to do exactly what you’re talking about but when I got it home, I laid it flat and i was compressed about 3/16-in different from corner to corner, so decided not to use it for a spoil board.
Once I finish cutting the permanent aluminum flat parts for the LR3, I will mostly be cutting full sheets of 3/4" plywood (or at least that’s the plan ATM).
I tried the foam as a spoilboard on my full sheet LR3 and like others have said it would compress as I screwed down my material so I decided against it and went with 3/4” MDF and surfaced it after leveling the X gantry to make it perfectly flat with the LR3