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Dust Collection; Another Question

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Forum topic by NedG posted 01-26-2012 07:09 PM 2042 views 0 times favorited 11 replies Add to Favorites Watch
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NedG

56 posts in 1779 days


01-26-2012 07:09 PM

First, thanks for the responses to my question a moment ago regarding dust collection for a Unisaw.
It occurs to me a separator between the saw and the collector would be a good idea. Any thoughts? Brands? Size?


11 replies so far

View Scot's profile

Scot

344 posts in 2861 days


#1 posted 01-26-2012 08:13 PM

there is a seller on ebay That makes and sells cyclone separators, I have one and it works fantastic. I have used it with as low as 750 cfm blower and now have it set up with a Grizzy 3 HP dust collector with canister filters. So far NOTHING has gone past the separator and into the bags on the dust collector. Except of course the one time I let the catch drum over fill !

-- If the old masters had power tools, they would have used them. So get off your damn High Horse.

View Gene Howe's profile

Gene Howe

8254 posts in 2893 days


#2 posted 01-26-2012 08:18 PM

I bought a plastic cyclone lid from Lee Valley (I think) and put it on a 35 gal. trash can. Like Scot, I’ve not seen any debris get past it.
One can be made easily with a piece of plywood and a couple 4” PVC elbows and connectors. I’d use DWV pipe. It’s thinner and cheaper.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View brtech's profile

brtech

903 posts in 2387 days


#3 posted 01-26-2012 09:21 PM

A cyclone is a great idea if you can get one sized correctly for your DC. It’s the most efficient way to separate. The next best thing seems to be a “Thien baffle” in a trash can separator (or mounted right inside the DC). A trash can separator without the baffle robs a lot of CFM from the DC.

The number one thing with a DC is adequate filtration. You want a .5 micron filter. If you don’t have that, upgrade that first.

View Fred Hargis's profile

Fred Hargis

3942 posts in 1958 days


#4 posted 01-26-2012 09:39 PM

The Thein separator will be cheaper and is a very effective separator….and I also agree that adequate filtration will be more important. You will certainly want at least 1 micron, and smaller is better.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Gene Howe's profile

Gene Howe

8254 posts in 2893 days


#5 posted 01-27-2012 12:23 AM

brtech, If the lid fits tight on the container, How does it rob the CFM? I’ve never checked it to see if it’s got more suck without the collector in line. Seems to work ok for me, though.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View NBeener's profile

NBeener

4808 posts in 2639 days


#6 posted 01-27-2012 12:46 AM

Gene: it increases static pressure, thereby decreasing CFM. I’m not SURE that a Thien baffle eliminates this effect.

It’s like running your ductwork through a 12’ x 10’ bedroom, instead of just running it through standard HVAC ducting.

If you’re interested, I can find (since I know I’ve seen it) the Static Pressure increase. I think they referenced a 30gal trash can, but … not sure. From that figure, you can use either the fan curve, for your DC, or … just guesstimate by looking at other fan curves, to guess how much CFM you’d lose…..

-- -- Neil

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NBeener

4808 posts in 2639 days


#7 posted 01-27-2012 12:48 AM

Okay. I checked.

A chip separator will typically add about two to three inches of static pressure.

Here are a few DC fan curves. From them, you can get an idea of the decreased CFM that a chip separator will impart:

-- -- Neil

View brtech's profile

brtech

903 posts in 2387 days


#8 posted 01-27-2012 12:53 AM

I’m no DC design engineer, but I believe the problem is that the trash can separator creates a vortex which allows the heavier material to drop out of the airstream. That vortex uses up some of the energy in the stream. The more efficient the vortex, the less impact on CFM. A cyclone creates a very efficient vortex due to its shape. The Thien baffle does much better than the trash can by itself.

A tight lid helps, but clearly, if you had a really airtight connection, but put a panel with a pinhole in front of the inlet or outlet, you would get less CFM, right? The basic trashcan separator isn’t a pinhole, but it has resistance.
With the baffle, it’s much less resistance.

There is a video around that shows the baffle inside the ring of a DC. When it works properly, there is virtually no cyclonic airflow in the bag – the chips just drop out of the airflow.

View Scot's profile

Scot

344 posts in 2861 days


#9 posted 01-27-2012 01:27 AM

You are right brtech about the drop off in air flow, other things that add to the drop off are 90’s and undersized piping. The cyclone separator I have was tested with a rotometer ( I was fortunate to know an AC&R tech that had access to one), He had a blower rated at 1500 cfm (1.5 HP I believe), We first tested just the blower and got just over 1400 cfm, after adding the cyclone the drop was down to around 1250 cfm. After installing the complete system in my old shop with A 1.5 HP blower and all main headers made with 6” snap lock ducting, I was right at 1200 cfm. Later I used duct seal on all 90’s, 45’s and joints I had a very noticeable increase in cfm ( never checked with a rotometer to see how much. I now have a 3 HP Grizzly dust collector with canister filters and I sometimes worry that that it will collapse the snap lock ducting if I close all the blast gates LOL. Another thing about the cyclone is that if there are any leaks at all between the cyclone and the dust hopper you will get carry over, I didn’t have the gasket seated properly once and blew saw dust and chips all over yard, at that time my system vented directly outside, but I guess the up side was is that I didn’t need to empty the hopper that day !

-- If the old masters had power tools, they would have used them. So get off your damn High Horse.

View Gene Howe's profile

Gene Howe

8254 posts in 2893 days


#10 posted 01-27-2012 04:27 PM

Thanks for the info Scot, brtech and *Neil.
Luckily, my DC only serves one machine at a time. As I stated earlier, it does the job I want it to do. That is, make my shop clean up easier and less often. Neil, your HVAC analogy is great. Made me smile and now, I understand.
Thanks again, guys.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View Scot's profile

Scot

344 posts in 2861 days


#11 posted 01-27-2012 06:44 PM

I finally got my new shop pics posted. I put a couple of my DC sys in so you could see and maybe get a few ideas that may work for you. It is still under construction but it is complete to the table saw.

-- If the old masters had power tools, they would have used them. So get off your damn High Horse.

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