Downdraft Questions

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teamXDR
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Downdraft Questions

Post by teamXDR »

Well I received my Hypertherm Powermax 45 yesterday and started on a 2x4 cut area table with 2x1/8" flat bar spaced at 2" intervals that will eventually host a GoTorch CNC. Now where I have the questions.. For downdraft design I plan on boxing in about 12" below the slats in a square, in the middle of that square I plan on using a J-Vent, https://www.famcomfg.com/roof-vents-1/j ... nized.html. Attaching to the bottom of that I'll use a 12" elbow that will be connected to this blower, http://www.northerntool.com/shop/tools/ ... _200007174. Then from there use some flexible 12" ducting to run outside the garage.

Do you guys see any issues without running a filter with the hood design on that vent? I know there are better fans/blowers but trying to keep the budget down and at 2905 CFM for a 2'x4' table, it seems like it would be adequate as long as most of the top is covered. I will also be building a hard mount for the blower to the table and use rubber feet to isolate vibrations.

Another option would be to run 2 of these blowers, http://www.harborfreight.com/8-inch-por ... 97762.html with the hood/vents spaced more evenly. It would just complicate it a little bit and have less space below the table with the additional duct work.

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East German
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Re: Downdraft Questions

Post by East German »

Hallo,
this is my Downdraft Table with Water.
See you:
http://www.plasmaspider.com/viewtopic.php?f=87&t=13136

Regards Peter
Sorry for my language! The last English class was in 1982.

Homemade CNC Plasma-Watertable
MyPlasmCNC
Hypertherm Powermax 85
Machine Torch
Hypertherm Powermax 1100
Machine Torch
teamXDR
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Re: Downdraft Questions

Post by teamXDR »

Thanks for the input East German, a little too complex for my small setup that will be somewhat mobile around my garage.

Some things I've found, not sure how accurate but it looks like you want to maintain at least 2.00 inH2O static pressure and cfm is dependent on table size. For a 4x8 that is at 3500 cfm. For my 2x4 the math says ~800 cfm.

The Q STANDARD 39012 12" blower is rated at 2905 cfm with a static pressure of 1.97 inH2O or 2.09 inH2O depending on where you're looking. So that would be more than enough movement for what I need and could still be used if I expand up to a 4x4.

So is what I'm researching correct? I could spend some extra and get a 16" blower that is rated at 3860 with a static pressure of 2.05 inH2O but I'd most likely have to run a reducer to 12" ducting to the table.
jimcolt
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Re: Downdraft Questions

Post by jimcolt »

The key is with blowers that can maintain the static pressure....they are generally more costly. You can get away with lower flow as long as the whole top of the slat bed is covered with metal. If cutting out of a piece that is smaller than 2 x 4 simply mask the rest of the table top off with sheetmetal.

I built two tables for trade show use a few months ago with built in fan / water trap / filtration units. These had to operate in trade show booths cutting steel without any external connections and no smoke. They both performed well. To get a good working blower at a reasonable price I had to build my own. Here are a few pics:
IMG_3692.JPG
IMG_3639.JPG
IMG_3495.JPG
IMG_3494.JPG

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