Fan for down draft, opinions please

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dichdoc
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Fan for down draft, opinions please

Post by dichdoc » Sun Nov 17, 2013 5:30 pm

So I'm new to the cnc plasma world I picked up a PlasmaCam 98z that had never been hooked up two weeks ago and have it cutting...and filling my 28x30 shop up with smoke in a matter of seconds. I have had a gable vent fan in the wall since I built and with a door cracked it will clear out the smoke in a few minutes but still covers everything in dust. So I built a water pan rolls under the table's original grate so water is 4"-5" below the metal grate. It was only a marginal success cut down on some but the smoke was still overwhelming so I'm on to a downdraft set up. My plan was to enclose the base of the table and run ducting out the back wall of the shop (into a hill and no neighbors). This would still allow me to run the water table if wanted but would I be better off to build the hopper style for increased suction?? I've sourced this used vent fan (I'm not really wanting to spend $500 on a fan right now) The cfm isn't listed on the fan and the web site has that model listed with different sizes and from 42cfm - 32,000cfm! My plan was to have a short duct run and use make up air from the door (goodbye heat) for now with thoughts of a make up vent near the table in the future. Thoughts & input?? Thanks Travis

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jmsrbrt
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Re: Fan for down draft, opinions please

Post by jmsrbrt » Sun Nov 17, 2013 5:42 pm

My 2 cents...get your water closer to the metal. 4-5 inches is a LONG way. I have my water close, and no more than 1-2 inches...pert near no smoke.
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abmagrum
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Re: Fan for down draft, opinions please

Post by abmagrum » Sun Nov 17, 2013 6:30 pm

you need the water 1/2 inch to a inch below the plate

or you need to build a plenum or what ever its called for the vent fan to work properly
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Re: Fan for down draft, opinions please

Post by _Ogre » Sun Nov 17, 2013 7:26 pm

without knowing the cfm of the fan it would be hard for anyone to voice an opinion.
if you heat your shop in a cold weather area of the country i would definitely move the water table up and try that first.
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Re: Fan for down draft, opinions please

Post by tnbndr » Mon Nov 18, 2013 9:48 am

Coming from an HVAC background and installing tons of those fans that fan looks pretty small (12x12 base?) I would venture to say it won't move more than 400 cfm. and they are made for roof mounting on a curb not sidewall. Mounted on a sidewall the bearing will fail pretty quick.
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Re: Fan for down draft, opinions please

Post by planetxfred » Mon Nov 18, 2013 1:50 pm

I would suggest enclosing the sides and making a downdraft system. Use a 1/2 hp belt drive blower from a home furnace, can often pick them up nearly free. Mount so that the fan is near to the wall or even outside (with a shelter),
With decent size duct, you can get near 2000 cfm of flow. That is what I have, I cover open areas of the table with Masonite sheets, You can see the dust being sucked down. The machine stays nice & clean, Same for shop and lungs. I'm in Minnesota and provide a fresh air makeup supply inlet above the table so the incoming COLD air is dropped on top of the table. Fan switches on and off with the torch cutting signal.
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Re: Fan for down draft, opinions please

Post by abmagrum » Mon Nov 18, 2013 8:05 pm

great ideal. its cold here in MI. and am debating on down draft or water heater

is there a special antifreeze for plasma cutters ?
I know you cant use regular antifreeze.
I have the winter off but no heat .
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dichdoc
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Re: Fan for down draft, opinions please

Post by dichdoc » Mon Nov 18, 2013 9:06 pm

That is all good input I appreciate it. The fan base is 18" still not sure on the cfm though. Fred what size ducts are you using. I like the air intake right over the table idea too.

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