Solutions for a Curling Spoilboard

You can flip the spoilboard when it curls and flycut the other side, or you can fasten it down at the perimeter with nylon screws. March 28, 2010

What is the best way to keep a spoilboard flat? Our spoilboard tends to curl up on its ends. Generally it's not a problem because putting a sheet of melamine on it lays it down. However, when we are running a smaller sheet, it sometimes won't vacuum down. Is fastening the spoilboard down an option - maybe with nylon screws?

Forum Responses
(CNC Forum)
From contributor J:
Without actually fastening it down, the best way I've found is to flip it over and fly cut the other side when it starts to curl. It'll stay flat for a while, then when it starts to curl again, flip and fly cut again.

From contributor M:
I have a phenolic grid table under my spoilboard that is fastened to the aluminum vacuum plenum by 6mm cap screws. I removed the screws in the corners and in the middle of each table. When dressing my spoilboard, I drill and counter-bore holes in my spoilboard where the bolt holes are. When finished machining my spoilboard, I attach the MDF to the grid table with 6mm plastic screws. This keeps the board in place 24/7 and I never have to flip it to machine the other side.

From contributor D:
I'm with contributor J. Simple and works every time for me.

From contributor B:
I do what contributor J does, but if I had my choice I'd do what contributor M does. I bet his vacuum filter stays pretty clean. Spoilboard never lifts, so no chance of fine chips getting underneath and sucked into the vacuum filter when you turn it on.

From contributor K:
Spoilboard, the million question topic. I got a spoilboard with my router. It came from Uni-Board, is an ultra light MDF, and works great. I'm having a hard time locating this product or any other ultra light MDF. There are other suppliers such as Trupan ultra light and Weyerhaeuser Premiere. I have tried Plum Creek light MDF, fly cut the bottom 2mm, fly cut the top 6mm, but am still not having the holding power of the ultra light MDF. I had 6"-8" of mercury with the Uni-Board ultra light with table open, no sheet on it. Lots of air volume passing through the sheet. I put a sheet on it and I get 27" of mercury, excellent holding power. With the Plum Creek light, after machining the shit out of it, I still have 19" of mercury with the table open, no sheets on it. Very restrictive on air passage. I put a melamine sheet on it, and I can lift the corner with one finger. With the ultra light, I grab with two hands and can't lift the corner! A lot more holding power. More air is passing through the spoilboard and making contact with the sheet I want to hold! I have 2-10HP pumps, 27" mercury on my 5x12 table. Lots of vacuum. Regular MDF or light MDF just do not work for me. For me ultra light is the answer. Let the arguments begin!

From contributor M:
Not really an area for argument. I have a 40hp oil ring pump, you have two 10hp carbon vane pumps, others use different types of systems, and horsepower on 3' x 8' tables all the way up to 5' x 22'. Differing methods to plumb the vacuum will give different results. Some folks never cut out small parts, others never cut out big stuff with lots of surface area. I have used carbon vane pumps, the same type in series, and oil ring pumps from 20-40hp. I've also used both LDF and MDF spoilboards on lots of different equipment.

The correct board is based on available vacuum, the plumbing of the flow on the machine, and the parts being held. All I can say is if you are not happy with the current holding ability, try a different board. When using LDF, I found the thicker the panel, the better holding ability I had. As the board thinned, it bled like cheese cloth and everything moved around. As previously stated, it's also hard to find in small quantities. I am not an expert on how it actually works from a textbook sense, but I know what I like now. Either way, good cutting and have fun doing it.

From contributor R:
As a CNC installer/trainer back in the day, I always showed my customers how to fasten the spoilboard, and yes, nylon screws are the best choice.

Write a program to drill and counter-bore a 5/16" hole with a 3/4 CB. (Make sure the 5/16 hole does not quite go all the way to the sub table.) Lay the holes out around the perimeter of your spoilboard, 12" to 18" apart. Run the program, then go in with a 7/32" drill, and drill into the sub table at each location.

Tap the sub table holes 1/4-20, replace the spoil board, and screw it down with the nylon screws. When you change out the spoilboard next, simply run your program again, and all the holes will line right up. McMaster-Carr is a great source for nylon screws.

From contributor U:
I have been told by operators that CNC routers will have a max (at a particular thickness) suction when using either MDF or LDF depending on their own vacuum system. You do not pick up more suction the thinner the bleed through sheet. Make sure the gasketing in the table consistently reaches up and touches the bottom surface of the bleeder board.

From contributor V:
Twisting and cupping of the spoil board is solved easily. Surface both sides of the MDF so the sheet is balanced. Doing only one side leaves a wax coating on one side and will allow moisture to enter only one side, hence the cupping. When you are done with the machine, cover the spoil board with a cover sheet. Our spoil board receives the same treatment that any panel in our shop gets. Our relative humidity varies a lot, but we never have problems with our spoil board.