Dust collection hood?

Kevin McGovern

Kevin McGovern

Joined
Jul 31, 2015
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I have a brand new gable vent fan that I have no use for. It's 1600 CFM. I am thinking of making a hood that would be above my grinder (maybe 2'x2') with a filter on it. This would be attached by ductwork (maybe 6") to the fan mounted on the outside wall blowing out. Any input on the effectiveness of something like this? I have considered partitioning off my grinding area, but with a 10'x13' shop, it would be difficult. My shop is also not heated, or cooled so being in and enclosed space would be less than comfortable. Currently, I have a large catch funnel under my platen going into a cyclone on a spark bong then to my shop vac. This catches most of the dust, but I would like to catch the really fine stuff in the air before it migrates to the entire shop. Again, any advice would be greatly appreciated. Thanks.
 
If you're venting it straight outside, I wouldn't use a filter. The filter will cut down on your air flow substantially, and the more flow the better.
 
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i had considered that. It may be too much dust to pass the wife's inspection. How about a catch bag outside, like one that would go on a dust collector?
 
On mine I've sat a garbage can full of water under the vent (downwards pointing dryer vent) and it seems to catch the vast majority of what flys out, without cutting back on airflow any.
I think if you had it just pulling dust out of the air from above, you wouldn't run into much in the way of volume of dust though. I'd imagine anything fine enough to stay airborne would be carried far enough away by the breeze for it not to be noticable
 
Thanks,

it would be pointing right at my grape arbor. I don't actually use the grapes for anything anyway. I've thought about making wine, but i have enough hobbies already.
 
Ahh yes I know what that's like.... The water bucket seems to do a good job.
A big and cheap (the largest micron size you can find) furnace filter would be another good option. It wouldn't cut down on flow too much, but should trap most of the visable dust. I'd still want it on the exhaust side rather than in the hood though. I know at least in my shop if I had that setup, I'd accidentally bump something into the hood when it's not running and take a dust shower
 
Geoff Flato said:
Ahh yes I know what that's like.... The water bucket seems to do a good job.
A big and cheap (the largest micron size you can find) furnace filter would be another good option. It wouldn't cut down on flow too much, but should trap most of the visable dust. I'd still want it on the exhaust side rather than in the hood though. I know at least in my shop if I had that setup, I'd accidentally bump something into the hood when it's not running and take a dust shower
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I just remembered something. I don't think the motor is sealed. So should i use a large micron filter for sure in that case? The fan is such that it would be drawing dust past the motor. (motor is inline with the fan in a tubular housing)
 
I'm not exactly a motor expert, so I couldn't say anything for sure. My gut says probably yes, but I've had a few open frame motors in my shop for years without a problem yet. I'm sure it wouldn't be good for it, but how long it would last is hard to say
 
I have looked at some airflow charts online, and 6" diameter round HVAC duct (if you are thinking of using that size) might be too small for 1600 CFM. I bought a fan that is rated for somewhere around 750 or 900 CFM, and I think I may need 8" diameter round duct to get maximum airflow from the fan. I am not an HVAC expert, though, so anyone who knows better can jump in with better information.

Another consideration is how you will get fresh air into the workshop to replace the 1600 CFM air being exhausted out of the grinder area. I am thinking of cutting a hole in my cinder block basement wall for exhausting dusty air, and another hole in another wall for fresh air intake, with duct work leading from each hole to the dust containment box around the grinder.

A third issue is condensation. Where I live, hot and humid air in the summer might condense on the inside of the ducts, since the basement is always somewhat cool. I will probably insulate the ductwork and also slant it slightly so that any condensed water will run outside the workshop instead of dripping from the end of the duct inside the workshop, near the grinder.
 
Oh make-up air won't be a problem. My shop is the original, uninsulated, former well house of my 115 year old home.
 
Assuming an 8' ceiling, a 1600 CFM fan will change all the air in the 10' X 13' shop every 45 seconds. If you think it's drafty in there now, just wait

Most gable vent fans I've seen are not designed to work against much back pressure or friction. I could be a bit more definitive if you have a picture of the fan, or a make and model, but in general to get the full airflow out of a fan like that, you want a duct about the diameter of the fan blade. And the intake "ventilation holes" in your drafty building will to have to be slightly more in total area. Otherwise you'll get much less airflow. The idea of the overhead hood is better than nothing, but you might be better served selling the gable end fan and buying a good 2 or 3 Hp material handling (dust collector) blower and catch the dust down at the grinder, before it drifts past your face on the way to the hood. You could move about half as much air and get better dust collection, with 6" duct too. With a good cyclone in line very little visible dust will be vented outdoors. But beware where you vent, how much of the makeup air will be drawing the fine dust right back in to the shop?
 
So I built an air cleaner using this motor. It's basically a square box with an open bottom (with an HVAC filter on it) and the motor in the top blowing up. Mounted a single pole switch to turn it on/ off on front of box. I mounted it above my grinder. Using this last night sanding some G-10, there was much less dust in the air, and on surrounding benches. I did notice that my VFD right next to the grinder seemed to have more dust on it. I think the air cleaner may be working against my vacuum spark bong that has a funnel under the platen. The dust is less over all, but immediately adjacent to the grinder it seems like a bit more settles. The motor is a permanent split capacitor motor of 1/5 hp. Can I install a speed control (I'm thinking a dimmer may work at this low power) so I can turn it down while grinding and then crank it up to clear the shop after wards. I will say the air circulation in my unconditioned shop is much improved when it runs, and it is very quiet. Any help appreciated. thanks.
 
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