Connecting shop vac suction to dust collector?
This has been annoying me for a while.
I have a decent central dust collection system, but some tools are just better done with the higher speed airflow of a shop vac.
Although you can sort of step down, periodically you still need a good blast to clear the ducting as the flow rate through narrow flexible tubing is a bit low.
For things like the chop saw, a 4 inch pipe is good enough – the dust is thrown back fast enough that there is no need to make a seal – just something to pick up the ejecta, but for routers and the 60mm dust port on my TS guard, that’s another thing.
I could of course use a shop-vac, but I don’t want to have to keep emptying several buckets.
Is it worth trying to make a suitable higher pressure impeller to suck from the table saw and eject its fine dust into the regular DC system? Has anyone done this? What are your solutions (if any) that do not include using multiple shop vac connections?
Replies
Most shop vacs have an exhaust port that fits the same size hose as the inlet. I suppose this is so that the vacuum can be used as a blower. Mechanically, the vacuum exhaust could be connected to the dust collector input with a 2 1/2 inch to 4 inch reducer (diffuser). In flow dynamics, what happens is the the pressure drop across the vacuum’s blower goes down and flow goes up. The operating point moves toward the maximum flow point on its pressure-flow curve. Interestingly, despite the assist from the dust collector, this vacuum’s motor current goes up. A blower with no back pressure might burn up the motor due to high current. You should never operate your dust collector without ductwork and cyclone/filter connected. With the vacuum and dust collector in series, it would depend on the pressure-flow curves of both dust collector and vacuum. If you maintain some negative pressure across the vacuum (inlet pressure lower than exhaust), it would probably be ok.
I have a 4" drop from my 5" main trunk behind my saw. It reduces to take a rockler hose to hook to the guard port on the tablesaw. I have a hook in the ceiling for when I pull the saw away from the wall. I use the same hose under the table on the router port.
Thanks - I suppose it needs only pick up the finest dust anyway.
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