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dust collector hood, another version

S

Steve Tiedman

Joined
Oct 25, 2020
Messages
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Location
Minneapolis, MN
Here is another dust collector hood idea. This is a somewhat updated version of hoods I built (and used since) over 20 years ago. They consist of lightweight plastic kichen mixing bowls (11" O.D. x 6" tall) and 4" HVAC duct "start collars" with crimp tab connection, found at Menard's, H.D. etc.

I'd tried a 4" dia. bell air inlet (black aluminum, shown for comparison) that was discussed here in the past. It works well but it has to be quite close to the spinning wood to be effective at grabbing all the dust (I don't vac chips). I use a 650cfm (1hp?) Jet 2-bag collector (5-micron cloth bags, recently cleaned, performance improved greatly!)

I chucked a 4" hole saw in my drill press to drill the bowls and used a bench chisel to trim the burr plastic from the holes. Insert the crimp tabs of the sheet metal start collar in from the bowl's exterior and firmly bend over the tabs flat against the inside bowl bottom. It helps by standing the duct collar on your bench and pressing against the tabs. That's it, it's ready to insert into your 4" exhaust duct/hose. (The same start collar comes in 6" and larger, too.)

I show it hanging from bungees at my Vicmarc and supported horizontally behind my Oneway. Both of these hood supports are loose- at the Vic, I can use my left hand to hold the placement of the hanging hood where I need it. At the Oneway I can move closer and further as needed. The 11" funnel effect of the bowl sure works well to direct air from the bowl rim area, a larger area than the aluminum bell hood.

The system will only allow 4 photos per message, I'll post as few messages to show them all.

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Interesting - from what I’ve read, the bowl appears to have very similar characteristics to the smaller air bell/inlet. I use a 4” air bell on my system and find that it does a good job overall on pulling air from a much wider area than that if the actual diameter of the bell itself. If you keep the basic character of the shape (similar parabolic shape with a rolled rim, just expand it out to a larger diameter, makes sense that it would be more efficient over a wider area.
I’ve been planning to turn a new inlet to experiment - my systems Achilles heel is the rim area and the exterior of larger bowls - this seems to be able to handle both. The adapter looks like it would work for a wood bell, too.
 
Yes, the bowls have a similar, but smaller, rolled outer opening like the smaller air intake bell. At 11" diameter, and a relatively small dust collector pulling in the air, I'm not sure if the rolled opening plays as much of a part on efficient air intake as it might with the smaller air bell, but it shouldn't hurt anything. It adds rigidity to the light weight of the bowls. And the 11"x6" dimensions help to create more of a collector/funnel in the area of the woodturning.

And these bowls are cheap. I found them (an unplanned find) on the same shelf as insulated water jugs at my local Menards. Saw them, at $1.99 each, grabbed 2, and then headed to the HVAC area for the duct connectors, which were about $5 each, I think.
 
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What a neat idea! I’ve turned a small bell opening for my dust collector hose, but I like the idea of a larger “bowl,” though it immediately makes me think “why not a turned wood bowl?” I realize $1.99 is pretty cheap, but I’m always thinking “how can I solve this problem with my lathe.” I can imagine using the HVAC collar with the tabs left straight out and glued into a groove cut in the bottom of the bowl with a thin parting tool. I realize the bowl would be quite a bit heavier than the plastic solution, but it creates a challenge to make a pretty thin wall, and a base thick enough to accommodate the flange tabs. Hmmm…
 
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Lou Jacobs said:
What a neat idea! I’ve turned a small bell opening for my dust collector hose, but I like the idea of a larger “bowl,” though it immediately makes me think “why not a turned wood bowl?” I realize $1.99 is pretty cheap, but I’m always thinking “how can I solve this problem with my lathe.” I can imagine using the HVAC collar with the tabs left straight out and glued into a groove cut in the bottom of the bowl with a thin parting tool. I realize the bowl would be quite a bit heavier than the plastic solution, but it creates a challenge to make a pretty thin wall, and a base thick enough to accommodate the flange tabs. Hmmm…
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I turned mine from a piece of dried 12/4 lumber with schedule 40 PVC drainage cap (Basically a cap with slots cut into it for floor drains) - cut out the slotted opening , turn your parabolic bowl inside dimensions to just the I.D. of the pipe fitting, (or a bit smaller) flip it over (jam chucked or whatever means) and shape your outside as you see fit and then cut recess into the bottom just to the O.D. of the fitting. just deep enough for the fitting to fit flush or a bit below, then cut the rest of the way through the bowl bottom at the I.D. of the fitting so it meets the inner bottom , then 5 minute epoxy the fitting into the "funnel" you just made. With Mine, I drilled pilot holes in a couple spots opposite each other just to the outside of the recess and drive in a couple screws, figuring it would add a bit of "wedging" effect as a hedge against wood movement letting the PVC & Epoxy pop out of the joint, but from my results so far, I doubt it'll ever come apart unless I whack it hard with something... (like a bowl coming off the lathe?)
 
Good idea to use a lightweight bowl off the shelf. Another improvement would be to replace the coarse bag with a filter rated at 1 micron or less. As is your system recirculates the small particles that are most likely to get deep into your lungs.
 
Hi Kevin- when I bought my collector 20-some years ago, the 5 micron bags were the upgrade, I don't recall if finer was even available on the consumer market yet. When I cleaned them a few weeks ago (admittedly for the first time, but I'm a sporadic turner even as a hobbiest, creating small dust loads with small projects), I removed the thick dust cake but there is still plenty of dust within the cloth, making the fabric more effective at stopping small stuff (as the filter experts would have us believe). I have no idea how much dust is forced through this material, but I use the 5-micron felt-like filter bags on the top and bottom of my collector, so air pressure out of the fan is lower on any given square inch of my filter bags vs. collectors that use air-impermeable plastic bottom throw-away bags. My collector is also inside a dedicated closet that vents back into the shop and I've not seen a surface buildup of fine dust within that closet or at the return vent opening.
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My thought process with the larger 11" opening of the plastic bowl is that I'm able to have the hood (my bowl) as close to the spinning piece as necessary, but the natural throw of the dust stream coming off the turning is better caught and contained within the large bowl, then drawn by the suction of the dust collector. See my photos, overhead and side view, to see the difference between my plastic bowl and the 4" aluminum air intake bell. Once I got the new bowl hoods installed, I chucked a piece of maple, killed the shop lights, and shined a small flashlight perpendicular the the bowl opening as I sanded the piece of wood. The dust did exactly as I planned- it was thrown into the large bowl (which is almost 3x larger in diameter that the metal air bell hood) and pulled away in the suction stream. Is this the best, the most effective method to collect dust? I doubt it, but for the $15 in materials (2 bowls and 2 duct thingies for 2 lathes), it seems to do the trick.
 
This is a very Good discussion and the scope of ideas hopefully will continue. If there are any "motor heads" out there, they will recognize the term "velocity stack"; was lucky enough to have turning friends who are into 3-D printing and understand the math behind that term. Complaining about breathing latent dust in the air led to, "Let me make something for you." One more example of the selfless sharing of this artistic group of people without regard for proprietary baloney.
 

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Bill T Tucker said:
If there are any "motor heads" out there, they will recognize the term "velocity stack"
Click to expand...

Thank you! I knew there was another, proper term for that device.

(That thing gotta Hemi?)
 
Bill T Tucker said:
This is a very Good discussion and the scope of ideas hopefully will continue. If there are any "motor heads" out there, they will recognize the term "velocity stack"; was lucky enough to have turning friends who are into 3-D printing and understand the math behind that term. Complaining about breathing latent dust in the air led to, "Let me make something for you." One more example of the selfless sharing of this artistic group of people without regard for proprietary baloney.
Click to expand...
Regards to sharing, is this 3D printed ‘velocity stack’ model available on thingiverse, printables, or another sharing site?
 
Sorry...don't know any of those sites. We just happen to have an expert on 3D stuff in our club and he took pity on an old codger. I'll ask him if you want me to.
 
Karl Loeblein said:
Regards to sharing, is this 3D printed ‘velocity stack’ model available on thingiverse, printables, or another sharing site?
Click to expand...
This is a link to a 6” bell mouth. I had a friend print this out for me and it works great. I’m not familiar with 3d printing but the site says it can be scaled to different sizes if needed.

DUST COLLECTON 150MM (6 INCH) BELLMOUTH by Peter H | Download free STL model | Printables.com

A Bellmouth opening improves the efficiency of dust collection pickup by an enormous margin. This one suits 150mm PVC. | Download free 3D printable STL models
www.printables.com
 
Kent Jaffrey said:
This is a link to a 6” bell mouth. I had a friend print this out for me and it works great. I’m not familiar with 3d printing but the site says it can be scaled to different sizes if needed.

DUST COLLECTON 150MM (6 INCH) BELLMOUTH by Peter H | Download free STL model | Printables.com

A Bellmouth opening improves the efficiency of dust collection pickup by an enormous margin. This one suits 150mm PVC. | Download free 3D printable STL models
www.printables.com
Click to expand...
Depending on its outside diameter where it would insert into the next downstream component, that 6" may insert into a 6" to 4" sheet metal duct reducer to attach to 4" dust collector hose or duct.
 
I have the 6” going into a 6” hvac elbo, but my collector ha 6” hose drops. If you have a 4” hose you can find stacks available commercially I think with a little looking.
 
Kent Jaffrey said:
I have the 6” going into a 6” hvac elbo, but my collector ha 6” hose drops. If you have a 4” hose you can find stacks available commercially I think with a little looking.
Click to expand...
I have a 4" velocity stack for my 4" collector, black anodized aluminum from Amazon, less than $20.
 
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