Shop vac question

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dave

New User
Dave
How long of a period can you run a little shop vac? Could you run one continuously for 4-6 hours? More??
 

dlrion

New User
Dan
I use(d) mine as a dust collector for my scrollsaw, my drillpress, and my bandsaw...

I have run it (almost) continuously for hours....

but 4-6 I would start to worry about a fire hazard.

1-2 is possible though.
 

cpw

Charles
Corporate Member
Dave,

I'm not sure that you will be able to get a solid answer on that. Too many variables. The ones that leap to mind right off the bat are 1) the quality of the vac, 2) what kind of filter you use, 3) what you are vacuuming up.

Example: I have a 6 HP molded plastic Rigid model - not a pro machine by any stretch. I have used an old piece of pantyhose over the filter for years to catch the larger stuff, so only the fine dust gets trapped in the folds of the filter. When the pantyhose gets clogged the vac does not "breathe" very well and the motor starts to heat up, so I have to stop periodically, open the vac, and brush all that stuff off the pantyhose. Then once and a while the filter gets so clogged with dust that I have to take the whole thing outside, take it apart and beat and blow out the filter. Recently I've been using the vac to collect the shavings from the Festool TS55 and I was having to clean the pantyhose every fourth or fifth cut.

If I had a good separator like a Thien or a Dust Deputy it would eliminate that problem and I could run it a lot longer.

That said, continuous running may not be necessary. When I had my previous shop I used a couple of i-Socket switches. You plug your vac into the lower outlet and your tool into the upper outlet and when you turn the tool on the vac starts up too. When you shut the tool off the vac continues to run for several seconds to clear the hose of any last debris. It works pretty well and you don't have to listen to the whine of the motor continuously.

Hope this helps with whatever you are trying to do.
 

dave

New User
Dave
Thanks guys! I actually plan on hooking this up to a dust deputy (which I should have mentioned) and the DD will be connected to a CNC machine. It'll be pulling the dust/shavings from right around the cutting tool. Since some jobs could easily take 4 hours or more, I'll need to have something running for the entire time.

I have a 1.5hp DC as well, but with the small dust port size on the CNC, I expect it would not be able to move enough volume of air to be practical.
 

Joe Scharle

New User
Joe
Charles, I used to use a panty hose 'pre-filter', but then I started using an old, almost transparent sheet stretched across the vac 'tub'. When I noticed a suction loss, I'd just bounce one end of the vac to shake the dust into the tub.
Then I made a Thein and now I can't find the old sheet!
 

jhreed

New User
james
Dave, use your dust collector, its volume is far greater than the shop vac and probably has a 100% duty cycle.
James
 

CarvedTones

Board of Directors, Vice President
Andy
My gift for oversimplification is about to go on display again...

The draw in power translates almost directly into heat generated with the strain on the motor compounding that. If you can't disappate the heat quickly enough, it will burn up after a while. With all due respect to Dan, I would say if it will run continously for over an hour then it probably won't get any hotter if you run it for one more or ten more. I asked a similar question about using my router speed control on a big vac some time back and one of the folks who responded was running one for days on end at a slow speed. I am not recommending that. :)
 

dave

New User
Dave
Dave, use your dust collector, its volume is far greater than the shop vac and probably has a 100% duty cycle.
James

Someone correct me if I am wrong here, but I was under the impression that if the DC cannot move enough air, it could overheat or is just working harder than it should be. The dust port on this machine it 1.25in, so going from a 4" hose down to 1.25" seems like it wouldn't be able to move enough air and would be overkill. Is that right or am I way off??
 

gdoebs

New User
Geoff
I'd use the DC and either make the port larger on the CNC to match the DC or connect it to the 1.25" port and build some sort of "vent" so you don't starve the DC of air.
 

Alan in Little Washington

Alan Schaffter
Corporate Member
OK, a number of issues going on in this thread.

First, dust collection from small machines- for good dust collection with ANY machine you need to both move a lot of air (CFM) and have suction (static pressure). If the machine has a small port (<2.5") you are limited to mainly static pressure suction like that provided by a shopvac. A small port (low cross-section) can not pass much CFM and also has a lot of static pressure resistance. So, unless you open up the port to 4" - 6" you are pretty much stuck using a shopvac. It will have good static pressure suction but not be very good collecting much of the escaping dust- think of it this way- a shopvac can pick up a bowling ball, but hold the nozzle a few inches away from a pile of dust- it doesn't pick up anything. To do that you need to move a lot of air with a DC.

If you have a DC connected to a small port there is little reason to open another blast gate to provide more air- the motor certainly doesn't need it and it will have a negative impact on dust collection. The only reason is to improve separation in a true cyclone.

Reducing a 4" or 6" pipe from a DC to something small like 1.25" or 2.5" port severely restricts CFM and gains almost nothing in static pressure suction- a waste of time.

Dust collection through pipe in sized from 2" to about 4" is kind of a gray area to make generalizations- but, depending on the equipment, is best handled by a good shopvac.

Another point - centrifugal fans and blowers (DC, shopvac, etc.) will run faster (possible premature bearing failure) and make more noise when the intake or exhaust are severely restricted or blocked. However, contrary to what is often assumed, it does not make the motor work harder and does not cause it to draw more current- both are less.

However, opening up the intake and exhaust with no restrictions can cause the motor to move a maximum amount of air and cause it to work harder- and draw max current. A DC should never be run with no restriction or pipe on the intake side and/or resistance on the exhaust. The motor will try to work too hard, overheat, draw too much current, and likely cause the breaker to pop in just a few seconds.
 

Glennbear

Moderator
Glenn
" If you have a DC connected to a small port there is little reason to open another blast gate to provide more air- the motor certainly doesn't need it and it will have a negative impact on dust collection. The only reason is to improve separation in a true cyclone."

I do not know the physics or aerodynamics involved but I can say that when I connect a smaller diameter hose via a reducer to my 4" DC system the smaller hose has limited suction until I open another 4" gate in addition to the gate the smaller hose is connected to. :wsmile:


 

jhreed

New User
james
I defer to the comments by Alan at Little Washington. I asked for his comments in case my opinion was in error. I would advise you to follow his lead.
James
 
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