Still confused about the Brady Vac

[archis]

Santa Clause with a lift gate will be bringing my Buddy a little after Christmas. In preparation I've been reading up on the Brady Vac system and the are still a couple of things that I don't understand.

From the Brady's Tricks Blog:

"The foundation for the BradyVac I or II is a sheet of Trupan with a grid machined into it and flipped over with the smooth un-machined face pointing up"

Is the smooth side of the Trupan the spoiler board? What purpose do the machined grooves serve if they are facing the floor?

I'm very confused, any clarifications would be greatly appreciated.

Thanks,
Jim

[jimmya]

I am sure the machined side would be facing up.

[oddcoach]

The side with the grid faces down. it lets the vacuum be spread evenly to the whole board. you place it over a hole in your table. you plug your vacuum hose in the hole from the bottom side. the smooth side becomes the spoil board.
hope this helps

[blackhawk]

Jim - The machined grooves do face down and the smooth side serves as your spoil board. I will explain my setup and hopefully that will help. I have a 4x8 machine with a 3/4" plywood base and a 3/4" piece of regular MDF glued on top of that. This is my normal setup if I am clamping, screwing, or nailing down whatever I am cutting. When I need to use vacuum hold down, I use the Brady Vac. My Brady Vac board is only about 30" x 30" and is made from Trupan. I have a hole cut out through my plywood and MDF table top. The hole is tight fit to the plastic hose from a Fein Turbo III shop vac. I place my 30x30 Brady Vac board over top of this hole with the grooves facing down. The grooves being down allows the vacuum to be distributed evenly under the Brady Vac board. The Trupan is porous so the vacuum is able to pull through the smooth side of the board and hold the material in place.

[jimmya]

Brad You Are Right!!!!!

I understand what you are doing now, and I do thank you for setting me strait. I am glad you chime in to correct me, because that's what this forum is about, and I was giving him bad info. So I hope all is well.
Jimmy

[archis]

Blackhawk,

Thanks for your detailed response, I think I get it now.

You're saying that the grooved side go down over an air tight surface forming a plenum that only allows the vacuum to escape though the top of the Trupan. Please let me know if I got it.

Thanks!

[blackhawk]

Yes, you got it, Jim. On my Brady Vac board, I also attached a gasket along the perimeter on the grooved side to seal up any leaks in that area.