Would these fans work for downdraft table

[Sampson Jones]

Thinking of converting my 4 ft x 8 ft water table to downdraft . I found theses at horrible freight for 77.00 each , with 20 percent coupon it's 64.00 . Would one work or hell for that price would two work mounted side by side ?

[weldor2005]

No,

For my 4x4 I have a 12" fan like that from northern, and even it needs to have entire table covered for good ventilation. If it is covered, it is nice, as holes get cut and parts start to drop, then you loose suction. Maybe a bank of like 10 of them.

edit: I think my 12" pulls about 2950 CFM.

[bigcreek]

I have the 2000cfm fan I bought off this website and use it on my 5x10 table and it works AWESOME, so long as you keep the table covered. It even draws the smoke from the opposite end of the table no problem, but you do have to keep the table top covered.

[Capstone]

I bought this HF unit and have used it generally to ventilate my garage from fumes as my table is still being constructed; slowly. It actually seems to grab smoke/dust/smells and expel them quickly but a plasma going full bore is a whole other matter.

three to four of these flipped on their ends, blowers down, in a mounting plate, which completely boxes off the bottom of the table I think would be good for a 4x4, but not a 4x8 table as others have said.

[jimcolt]

For best fume control on a 4 x 4 table you need a minimum of 3200 cfm airflow.

Jim Colt Hypertherm

[CNCCAJUN]

After many hours of research I have determined that your downdraft needs are somewhat dependent on how you will use the table. I have quizzed HVAC Engineers in my office to the point where they run and hide when they see me headed their way.

If you intend to simply drop a piece of 14 gauge sheet metal that is 24" X 24" on a 5'X10" table to cut a job without covering the remaining area of the table, your CFM requirements will be vastly different than if you were to use sections of welding curtain to cover the remaining areas.

For example, when speaking with one machine builder, they recommend covering the remaining areas of the table with pieces of welding curtain as general practice. I have seen this done and works quite well. The advantages are lower power blower required, potentially less noise, lower operating cost. . . . excellent result.

While speaking with another machine builder, they recommend 5?10 Table needs 4500 CFM @ 2? SP. Since most of their customers are industrial they realize they will not want to count on there employees covering unused portions of the table. They have to contend with OSHA, which most of us do not.

Below you will find downdraft exhaust requirements as posted one CNC Plasma Manufacturer's website.
I reference it because I know the engineer that determined the below worked for over a decade for a very large blower/fan manufacturer. Also, when selecting a blower, look at a "backward inclined blower". It can be direct driven or belt.

4?4 Table needs 2000 CFM @ 2? SP
4?8 Table needs 3500 CFM @ 2? SP
5?10 Table needs 4500 CFM @ 2? SP
6?12 Table needs 5500 CFM @ 2?SP

Based on this, for a 4X8 table, I would look for a backward inclined blower that would be as shown below:

GREENHECK - 16-BISW
16" Backward Inclined Single Width Centrifugal Fan
3720 CFM @ 2" static pressure
2 1/2 Horsepower Motor 230VAC

Hope this helps . . .
Steve

[jimcolt]

A little more info...

- When you cut thin materials at low power levels....the particles of molten material are smaller than if you were cutting on thicker materials. Larger particles tend to fall to the bottom of the table as they are heavier than air.....the smaller particles tend to rise (they are small and hot, and lighter than air) in the form of smoke.

To summarize the above statement...thinner materials often produce higher levels of smoke as compared to thicker materials. I can often cut 1/2" steel with my 3200 cfm blower off, with little or no smoke rising from my table. When I cut 18 gauge, the 3200 cfm blower barely keeps up with the smoke.

I am suggesting that 3200 cfm is the bare minimum for a 4 x 4 cnc plasma table if you need to cut smoke free. This is from my observations over 35 years of plasma cutting.

Jim Colt Hypertherm

[Capstone]

For best fume control on a 4 x 4 table you need a minimum of 3200 cfm airflow.

Jim Colt Hypertherm

That's a good number to keep handy. Thanks

[CNCCAJUN]

Just remember a CFM number alone is meaningless without taking into account "Inches of Water Column Static Pressure Number"

Most any blower will do the job if you are willing to block off all area on the table with stock to be cut and/or blocking material . . . i.e. squares of welding curtain and seal all around the table skirt.

Steve