Really big dust collector - do I keep it or sell it?

[John Vigants]

I recently acquired a 4 hp Grizzly dust collector as part of a lot purchase (failed business disposing of assets). I'm a (new) hobby woodworker - so I will not be running multiple machines at the same time. Currently my 'shop' is a 2 car garage but I am about to expand to a third bay - I'll be building a wall interior to the new exterior side wall so that the dust collector will be in a 'bay' that opens to the outdoors, not the shop. Because of this I am not really worried about how perfectly it filters, since the fines will be ejected outside of my work space (at 3,560 cfm it should suck all the air out of the garage every 2 minutes J). I’m in Houston, so not planning to heat the space in the winter and too poor to cool it in the summer, otherwise I’d be looking at a canister or cyclone system for better exit air quality. I also plan to frame in an inlet vent with a furnace filter on the opposite wall so that if the wind blows the wrong way I’m not sucking in my own dust. Make sense so far?

Since I’ll be sharing the space with cars from time to time (during hurricanes and hail storms) I will have the larger stationary tools on mobile bases. My thought is to pour a couple of 4” runs in the floor from the dust collector to the space between garage bays 2 and 3 so that I have available outlets there and then plumb in 2 or 3 more runs through the attic to locations around the perimeter of the (new) third bay. Each of these 4 or 5 runs will be gated, so that at any given time I can connect whichever machine I am using to whichever port is most convenient, and leave the other ports closed.

My first question is whether I will derive any value from having this monster collector if normally I’ll have all but one port closed off. Should I plumb in the ducting as described but buy a smaller (say 2HP) collector? I could sell the big DC and buy a smaller one, then use the extra cash for another tool . . . I can probably get around $800 for the big one and find a smaller unit for $300, so that would liberate $500. If there will only ever be one machine running and none of the conduit runs longer that 15’ – 20’, how many cfm should I need in a DC? Some of the reading I've done seems to suggest that if you are using only one machine at a time that anything > 800 cfm should suffice, but seems like lots of hobbiests (who also presumeably only use one machine at a time) have significantly larger units. Why? Am I missing something?

Also, will it hurt the big dust collector to run it this way (with only one machine connected and the rest of the ducting closed off)? Seems like it would be running 'choked', but is that a problem? I don't know. Anyone?

I am also trying to make sure I understand operating costs. I put an amp clamp on one of the live wires today and found that with all 4 of the ports open it drew 16 amps, with one blocked off it drew 14 amps, with 2 of the 4 blocked it drew 12 amps and with 3 of the 4 blocked it drew 10 amps. I think that I need to double these figures to account for the second pole of the 220V circuit, so the effective 110V draw will be somewhere between 20 and 32 amps. Taking the average of 26 amps x 110V = 2860 watts, every hour of use will consume 2.86 KWH which (at 15¢/KWH) is 43¢ per hour of use. Over the course of a year I cannot imagine averaging more than, say, 2.5 hours per week of use, or <$60 per year. Dropping down to a unit that is half as big will save maybe $25 - $30 per year. Not a big deal.

Final question – I also lucked into a deal on a 30” louvered fan. I plan to install this in the same wall behind which the dust collector will sit, so that when I am in the shop it can suck clean air in through the filtered intake on the opposite wall and eject that shop air outside. My thought is that dust which escapes the dust collection system at the machine and floats in the sir will be removed, and the 30” fan will draw much less current than the dust collector. So I could run the fan the whole time I am in the shop and run the dust collector only when actually running a machine. Suppose I spend 10x more time in the shop measuring, jigging, fitting, etc. than actively making sawdust, then the annual cost of running the big dust collector climbs up to the $500 range. I am thinking that I could save several hundred dollars a year running the louvered fan rather than the dust collector.

So should I keep the big collector and install the wall fan? Should I keep the big collector and use it for both machine dust collection and venting the room air – and sell the louvered wall fan (and not bother having to install it)? Or should I sell the big dust collector to someone that needs to run multiple machines simultaneously and get a smaller dust collector (and install the fan to cycle room air)?

[J.R. Rutter]

1. If I were you, I would keep it. As you noticed, a blower motor draws less current when flow is restricted, so it would be fine to run it with just one port open at a time.

2. Run larger diameter duct lines. 5 or 6 inches to each machine. Your bigger than average blower will give you nice dust and chip collection this way. 4 inch lines are too small. Alter your machine ports if you can to the larger size.

3. As for the 30" fan, that would be an added bonus, but wouldn't replace the dust collector. Your machines will function better, and work will be much more enjoyable with the chips and dust going away rather than collecting on the work area and floor.

[Mickey Elam]

I'm not too sure there's any such thing as a dust collector that's too big, unless your electrical system won't support it. The key reason to use a dust collector is to protect yourself from the fine dust that results from machining wood. The best way to do this is to collect the dust at the source and this requires airflow into the dust collection system. The higher the airflow, the better off you are.

I'd also strongly advise you to run 6" ducting rather than 4". The amount of air that the smaller ducting will flow is MUCH lower than the 6" and, as mentioned above, airflow is key to collecting the dust at the source.

I assume that this collector uses bags to capture the chips that come through is and some of the dust. Since you plan to exhaust the dust outside, that should be fine, but give some thought to where the dust will go if someone opens the garage door or there is an air leak into the house.

Running the collector with all ducts closed would not hurt it. Since the motor on the collector doesn't depend on airflow through the colllector impeller to cool it, sealing off airflow has no harmful effect on the machine. A dust collector does the most work when the most air is flowing through it; you observed this when you put the ammeter on it a saw the diminished amp draw when closing off some of the ports.

Finally, I'd recommend reading Bill Pentz' site. It's a wealth of information and will almost certainly be eye-opening for you. Link below:

http://www.billpentz.com/

However, if you decide to get rid of the collector, let me know, as I might be interested in it.

Mickey

[John Vigants]

Now educated. No such thing as a too big DC. Thanks, folks.