Another dust extraction/shop vac question

[cgallery]

I still use a shop vac for dust collection. Due to shop size constraints, I'll probably be sticking with that. On my previous (V1) router-table extension for my BT3K, I discovered that dust extraction for non-through dados was a problem. I sorta solved this by drilling a 1.25" hole in the table, about ten inches to the left of the bit. I installed a dust port to the bottom of the table and connected my shop vac. When cutting dados, the dust pretty much is thrown right at the hole and is sucked away. As the cut continues, the piece eventually covers the hole and dust extraction continues (nice clean dados when I'm done with the cut). However, due to less air flow, you can really hear the shop vac work harder when the piece covers the hole, and there is quite a hold-down effect on the piece I'm cutting. It works, but isn't perfect.

Can anyone suggest a method of making a pressure valve that would allow air into the hose when the piece of material is directly over the hole?

Thanks!
Phil

[LCHIEN]

Yeah, this'll work great:
Drill holes in the bottom of your dado groove

OK, I apologize.

you deserve a real answer.... um how about more holes? A 1.25" hole won't exactly overwhelm your vacuum, it could stand more holes the same size and still suck pretty good.

[just4funsies]

Or maybe a more linear hole, in line with the dado groove, and like 4" long?

[Wood_workur]

What you really want to do is drill a seris of holes that is parallel to the fence, in the smallest sizes dado you plan on cutting. Then the suction from the shop vac will suck the dust, and not the wood.