Tried a DC to empty a shop vac bin?

Planning my next router table and thinking about dust collection. My shop vac works great in my current router table, which is an open stand.
The next router table will have an enclosure for the router, and I want to add a DC hookup to the bottom of the enclosure to also pick up dust/chips that come through the bit opening. This made me think of one possible configuration to use both a shop vac and the DC: Connect the shop vac 2 1/2" hose to the fence dust collection port. Have a 4" Y fitting built in so that one branch picks up at the bottom of the router enclosure (build something of a slope into the sides to help funnel chips down to the opening) and the other branch cobbled into the bottom of the shop vac's bin to empty it.
My big question is - what would this configuration do to the shop vac? The normal air flow is coming in the inlet hose, into the bin, through the filter, and out the outlet vent. With a shop vac connection in the bottom of the tank, the flow would branch - some going through the filter and out the outlet, and some going out the DC connection.
Wondering if someone on the wreck has tried something like this. How would it actually work in practice? Would the DC flow starve the shop vac blower for air? And if that was the case, would it basically end up being no different than having the DC connected to the fence pickup through a reducer? I've read that a shop vac has higher suction, but a DC moves more air, so it seems that a shop vac would be better suited to pulling chips out by the fence opening.
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Keith Carlson wrote: > Planning my next router table and thinking about dust collection. My shop > vac works great in my current router table, which is an open stand. > > The next router table will have an enclosure for the router, and I want to > add a DC hookup to the bottom of the enclosure to also pick up dust/chips > that come through the bit opening. <snip>
Check out the NYW design.
Norm solved this issue with his design.
Lew
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On Oct 30, 11:52 pm, "Keith Carlson"

I certainly haven't tried it, but my initial response is that your idea sounds far more complicated than necessary. If a shop vac in the fence has worked well so far, stick with it unless/until you have problems. Once you make the router enclosure, you could always vacuum it out once in a while, or hook up a straight 4" DC port there if you like. It seems like the hassle and potential useless-ness of an automatically-emptying-shopvac would be a lot more trouble than it's worth. How long does it take to empty your shop vac? I probably spend 3 minutes every 3 weeks on that (at most), so I definitely couldn't justify spending an hour or several rigging up something that might or might not save that time. Also, what if you turned your shop vac on when your DC was off - wouldn't it start pulling dust from your DC bag?
My advice, for what it's worth: keep it simple, and don't fix what ain't broke. On the other hand, I'd be sort of curious to hear what happens when someone hooks up a DC to a shopvac bin and turns them both on, so if you have the time, go for it and let us know what happens. Andy, whose shopvac-thru-fence chip collection has been more than sufficient for his router table work
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But that is the beauty of this system! Whichever is full, you just turn on the other to empty it, so you never have to worry with manual emptying of either! Right? That would work, right? <g>
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Beautiful! I guess I just wasn't thinking about the "big picture"... On a similar topic, on my way in to work this morning, I saw a lawnmower with a "dust collector" on it - not just a bag for clippings/leaves, but a full 50gal barrel right on top of the mower deck, with a DC-type fan on top of that, connected by a large hose coming up from the mower. Hey - sure is faster than raking. Andy
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Yeah, it definitely would be more complicated than necessary, but part of the fun of a shop is experimenting and trying things out! Seems like it could be ideal - combine the suction of the SV at the bit, but the high volume of the DC moving dust and chips out of the inside. And of course, if you had a shop vac on there, and a DC hose right there, who wouldn't think "Hmm... why am I empyting this tank?"
If I find a cheap SV on craigslist or even on freecycle I'll play around with it and see what happens.
Another way of getting past the question would just be to connect the DC line to the shop vac tank with a blast gate. Leave it closed while using the router table, then shut off the shop vac (wired to the same switch as the router), open the gate and let it clean out the tank.
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Keith Carlson wrote:

I suspect that the shop-vac will end up sucking the air out of the DC hose rather than the other way round. It's got way more suction power than the DC does.
Chris
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This is the one I'm currently building (with a few modifications):
http://www.delorie.com/wood/projects/router /
incorporating some of the dust collection ideas from here:
http://www.woodworking.org/WC/GArchive98/7_10johnsrtab1.html
I think it incorporates most of what you are wanting or, if not, can spark some ideas about how you might want to do it.
On Tue, 31 Oct 2006 04:52:07 GMT, "Keith Carlson"

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You've read correctly, and when you think about it, you sill see you have answered your own question. If the vac has more negative pressure, which way will the air flow at the DC/SV interface? If both are running, the shop vac will be sucking air out of the DC system, probably lowering the shop vac inlet suction to close to that of the DC.
An interesting variation on your idea would be to include a flap valve that allows flow from the SV to the DC but not reversed. Then when the DC is running but the SV is not, you would likely remove material from the SV's tank.
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