Shopvac pressure release valve?


I built a router table extension for my table saw. Upon using it, I noticed that non-though dados were a problem as far as dust collection was concerned. And I want to do a lot of non-through dados in the middle of panels. So... I found a web site:
http://www.oak-park.com/usa12.html
where they had a vac-plate with a couple of holes in the plate for dust extraction. I decided to drill a 1.25" hole in my top, about 10" to the left of my bit, and put a Rockler dust port on the bottom of the table. Now, non-through cuts toss the dust right at the hole in the top and the dust is extracted. The problem is, when the material covers the hole, the vac starts working pretty hard (because the port is mostly obstructed), and begins to work as a very effective hold-down.
Any ideas on a way to add a vac pressure release somehow? Is there anything made for something like this that doesn't cost an arm and a leg?
I thought of actually adding yet another hole and dust port, and some sort of Y- or T-fitting. So when one hole is covered, the other is open. Problem is, that would start to add quite a bit of "crap" under the table that I don't know if I have room for.
Any ideas appreciated.
Thanks! Phil
Thanks! Phil
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Actually, when the airflow is blocked, the vac is not "working hard," it's freewheeling. The sound you hear is the motor speeding up because there's no load on it. However, the potential problem is that some vacs rely on the exhaust airflow to cool the motor. Restricting the airflow will cause overheating.
You might try cutting a dado in the router table top, intersecting the dust collection hole, to provide some airflow relief. Basically the same as the "T" idea, without taking up any extra space.
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You are a wealth of information, I think I will probably implement your suggestion. I'm still considering a down-draft enclosure as a possible alternative. I think I can squeeze one underneath, but I have doubts about how well it would work, and I'm not sure how I would mount it.
Thanks! Phil
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snipped-for-privacy@gmail.com wrote:

I currently only have dust collection in the fence. It seems to me that the best of both worlds would be to use a "Y" fitting and combine the two--I can't think of a scenario where both ports would be blocked simultaneously.
Chris
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WRT your "non-through" dado, I've never heard of a "through dado"(insert smiley-face here). One would think that there's a route for air to flow along the newly cut dado, though. Tom
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Certainly the larger the dado the less hold-down I get. I like the idea of routing a T to the edge of the table (above). And I'm still pondering a down-draft table.
Thanks! Phil
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Just a WAG, but maybe it's a dado that doesn't reach the edges of the stock?
Maybe it would be a "blind dado"?? *lol* Mac
https://home.comcast.net/~mac.davis https://home.comcast.net/~mac.davis/wood_stuff.htm
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I wrote:>WRT your "non-through" dado, I've never heard of a "through

So Mac wrote:Just a WAG, but maybe it's a dado that doesn't reach the edges of the stock? Maybe it would be a "blind dado"?? *lol*
Ahh, or a "stopped" dado? Tom
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On 1 Mar 2006 14:22:30 -0800, snipped-for-privacy@gmail.com wrote: <snip>

In plumbing, there is a device called an "air admittance" valve, designed to vent fixtures when they can't be vented to the outside. They are designed to open when there is suction on one side, and stay closed otherwise. Might work, but I have a feeling it may open just under normal operation in this case. But it's only a few dollars, might be worth a try. Search for "Oatey air admittance valve". (Oatey is a common brand name.)
But why not make your own? All you need is a little hinged flap closing a vacuum port with a spring holding it closed. You could adjust the spring tension so it only opens when the other port is blocked.... The spring would have to pull away from the vacuum and hold the flap against a seat of some sort, but it would be easy and quick to make something up...
Paul
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Rather than a fitting to each hole, consider boxing in the router with a vac connected to the box. Also you may want to make the holes into a rectangles. Mine are 1 5/8 x 1 3/16 and I have never had a problem with them blocking up. See pics at:
http://www.woodworking.org/photo/displayimage.php?album 311&pos=6
http://www.woodworking.org/photo/displayimage.php?album 311&pos=7
http://www.woodworking.org/photo/displayimage.php?album 311&pos=8

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Ridgid makes a connector/handle that has an adjustable port on it. You twist a sleeve to progressively open the port to adjust vacuum level. It should ft any 2 1/2" hose. You can get them at Home Depot for ten bucks, here is a link to the Ridgid web site that shows the part:
http://www.ridgidparts.com/accessories/VT2505.phtml
Dennis
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Have you considered drilling another hole in the top of the table, directly left of the router bit. Keeping the centerlines matched up. Once the board with the dado passes over it that should allow air to flow thru, thus releasing the
One note though, I've noticed that when cutting dados with a 1/4 straight bit it does tend to leave the saw dust packed in pretty, usually need a screwdriver to clean it out. Maybe, consider a spiral cut bit also.
Ron
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