Choice of support board materials
 

Just looking for opinions on the better option to go with. My MM is 5'x12'. I'm at the point of needing to purchase material for the support board. So far, I'm limited to 2 options,

1) Countertop particle board material 1.125" thick 30"x12' in size. This option would require 2 sheets being butted together.

2) MDF sheet 5'x12' in size and 1.25" thick (288 lbs).

Given the expertise out here, I figured I would ask for opinions on the better option.

Thanks
SteveE.

I would avoid any joints in the support board. It is surprising how heavy the forces can get on that board. If you screw down a thick sign blank and then proceed to carve out big letters, that sign cups/warps and drags the support board with it.

Steve put your particle board ( chip board )joined together on top of your support board it is cheaper to replace and it doesn`t warp as much as mdf once you start cutting into it

I may be able to get a 4'x8' x1/2" PVC plastic sheet for $95. I think this sheet normally retails for around $400. What do you think about using this PVC for the support board and then mdf for the sacrificial board. I am not sure I can glue the MDF to the PVC.

Chris, I think I'd buy that sheet and reserve it for other purposes, like surfacing jigs, cutting gears, making drawer slides, and the like.

No reason to create a complex situation in gluing the sac board to the support. Think forward to your first sac board replacement. How close are you going to get, and then what type of glue are you going to use? What about the second time?

I think that 1/2" thick PVC is much more flexible (less stiff) than a wood based board.

The PVC and will sag between the supports... I just built a cabinet for a fishing pier out of both .500 and .750 plastic. I had to support the countertop with a .750 thick layer of plywood underlayment after I noticed the top started to sag after only one week...

Thanks for the great information. I have not handle any sheet PVC in person so I assumed it would be stiffer than MDF.

Hi Guys.
I was thinking more like using 1" birch or phenolic faced ply for the base board.
What do you think?
Regards Charlie.

Phenolic faced Baltic Birch is great stuff, but it would be very hard to glue your spoil board to it.

If you call a real plywood wholesaler, you can get MDF in any giant size you want, including 5x12'.

http://www.allamericaplywood.com/stocklist.pdf

Just to give you an idea what is commonly available.

Clicked on your link.
unless I missed it,
only "Industrial Particleboard" is available in the 5'x12' size needed.
All the MDF was listed in 49x97 sizes.

You might have blown right past it.

Page 3 under "Standard MDF":

61x145"

You can use the Ultralight MDF (bottom of page 3) as the spoilboard of your vacuum system. You seal the edges and the air just pulls right through the entire sheet.

Right you are.
My apologies.