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
The most forgiving material to be used as spoilboard i found its Extruded PVC. At least in my country it is priced to match 18mm mdf so its well worth it because you dont have the worries of humidity!
A blast from the past… BuildYourCNC, early needle cutter, bluecore foamboard, and LinuxCNC! Styrofoam insulation panels made for perfect spoilboard for cutting RC planes/parts with needle cutter…
I was using 0.8mm router bit. I built a needle cutter, but never got it to work right. I was frustrated enough that I just tried with the 0.8mm bit, and it worked fine. The edges were slightly fuzzy, but other than that, no issues. The needle cutter is in my pile of “someday” projects. If I end up with a stack of foamboard to cut, I’ll revisit it.
Also built a needle cutter, but wasnt happy with my results. Ended up cutting black foam with a laser. Re-trying the needle cutter is on the list, I also have 0.6mm cutters for the CNC that I may end up trying. I think I bought those for PCB milling…
A needle cutter certainly can be fiddly to set up… but they usually can be made to work reliably once that’s done. My earlier ones were actually the simplest and cut “miles” of bluecore and DT foam with just a DC motor from a junked HP printer, a small disc of aluminum, and a ball-inflation needle for a guide…
The later introduction of brushless RC motors, 3d printed frames/parts, and various bearing guides introduced a bit more complexity (though they’re still quite simple) and made them a bit more fiddly and less robust than those early ones. But those early all-wooden and metal ones were most forgiving and almost immune to construction issues often seen with later versions. Longer needles with shallow bend angles and lower RPM’s and feedrates let them run longer and with less stress.
