Fan for down draft, opinions please

[dichdoc]

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

[jmsrbrt]

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.
Bob

[abmagrum]

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

[_Ogre]

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.

[tnbndr]

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.

[planetxfred]

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.
Fred

[abmagrum]

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 .

[dichdoc]

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.