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Gravity holds ours in place when the vacuum isn't running.
Attempting to adhere Mdf to Phenolic on on of the more foolish things I attempted, Ended up tapping nylon 1/4 x 20 screws to hold in place
We rely on gravity as well but there are times when Im doing odd work sliding heavy parts around and the spoilboard scooting gets annoying and my solution has been to use 1/2" SpeedTape from Fastcap around the perimeter. Its super thin and holds the spoilboard just fine, also acts as a bit of a perimeter gasket/sealant and the spoil board never slips.
I flip the spoil board every few times I resurface and the spoil board gets swapped often enough I'd never want it fastened with anything that wouldnt come of super easy/quick.
I run 24" x 48" spoil board quarters on my 4x8 table. One panel over each 24" x 48" vac zone. Having 4 small instead of one large spoil board makes for even more chance of movement.
I resolved the issue by cutting some ~1" lengths of 1" PVC angle (think plastic angle iron). I screwed these to the grid table at the corners. They stick up about 1/4" or so above the BOTTOM of the spoil board. This hold the outer corners in place.
Then I just made a few 1" high x ~1.5" long straight pieces for the four straight sides of the 4x8 table. Centered on the joints they keep the 24" x 48" panels from slipping outward.
The solution has been working well for about a year now. If I happen to hit one there is only a small chance of bit damage and the PVC piece is cheap and easy to replace.
You might consider putting in steel pins at the zero edges.
We have popup pins but when they are down or your shoving a large part (solid surface) in a direction away form the pins the spoil board will still slide.
We just ran a job that involved 200+ sheets of 1/4" thick 60" wide solid surface and then had to make about 100pcs of bullnose trim and the pins were out of the equation the bulk of the time. Having the spoil board taped down made all the difference in the world
i use industrial hot glue gun & just spot weld it around edges of spoilboard. when it gets thin & redy to replace i use putty knife to remove hot glue from table top.
If you do decide to drill and tap for screws to fix the spoilboard, program the position of the screw locations on the cnc. Then you can run another file to counterbore and pilot hole the spoilboard. This is how my cnc came (FMT) with canned spoilboard programs
Not sure of your table construction, but we have a gasket around the edge of the table that seals the spoilboard. It just lays on the matrix and is heavy enough 5x12 that gravity keeps it against the pins.
I backed out a couple of Screws that hold the phenolic grid table down and machine holes with counterbores when making a new spoilboard. I replace the steels crews in the corners with nylon 6mm bolts. That keeps the corners down and I don't have to flip the board with each mill. If by chance an operator does something dumb and a tool hits a nylon screw, no harm will come to the tool or machine.
The nylon screws work ok but are easily stripped, I prefer aluminum
Does Titebond III sick I know it sticks to PVC
Titebond may "stick" but it wont bond. And considering the holding of any spoil board to plenum is a shear situation I would never want to trust it. That said, in this scenario I'd guess the hope is only for the hold to be strong enough when the vac is off. When the vac is on, who cares?
Maybe Im lost but the only reason in my mind to adhere the SB to the machine is so it doesnt shift/scoot/slide when the vac is off.
The hot glue seemed like a good solution as its easily removed to me. For whatever reason my tape solution seems to stick to the MDF so a flip and the tape is all up top and gets surfaced off.
If you dont flip, stick it down however you can.
before i started hot gluing my spoilboard down i was constantly having the board raising around the edges when the vac was off. then when trying to remove cut parts the board would move all around. maybe my problem has to do with high humidity in the south . seems others dont have this problem.
Just an idea here.
I have to switch spoilboards between 4x8 on the locating pins ( plastic rods ) and the 5x10 ( full table ) when I go to 5x5 material and solid surface so being able to switch it up quickly helps.
The other thing I thought about was a vacuum lift to help load the sheets with no sliding required and eliminate the need to fix the spoilboard.
We have plastic "cleats" across the front of our spoilboard that only lip up about 3mm high. Those prevent the spoilboard from being pushed off the CNC.
Easy to make. We used 3/4" polyethylene plastic since we had it but there's no reason some maple or oak couldn't do the same thing.
On our configuration, they aren't in the way of anything. They just lip up enough to block the spoilboard from being pushed off.
I have a Biesse with autoload. The spoilboard is bolted to the phenolic with nylon bolts. The phenolic has several threaded inserts in it. We drill 8mm thru holes for the bolts. We drill a larger 30mm I think for a countersink. After board is bolted down we insert midfield plugs into the big holes and surface smooth. We start with a 1” thick midfield spoilboard and surface down to about 12mm. We surface at .2 mm increments. We wrote a program that drills through hole and surfaces bottom side, pauses, we flip board, it drills counter sink holes, pauses, we bolt down and plug and it surfaces top. All this is done in one program after we remove old spoilboard.