Looking for extraction hood spec

**marbles** · 19-09-2017

Hi,

I've recently moved to smaller premise and i'm instantly noticing the plasma fumes, much more noticable that mig fumes, even though I have a water table on my cnc table.

I'm wondering where is the best place to extract from, the width of hood and fan size. I can either add a hood at the cutter or make a larger hood to cover the whole 4x 4 table and extract from a single apex point. Currently have a lot of 6" 150mm hose should that be a good diameter.

Any ideas or links welcome.

Thanks

**philgrady** · 21-01-2018

Hi,

I suggest the following

Face area of table 2.5M x 1.25M x 0.75 = 2.34m3/s or 8437.5 m3/hr

That would give a fan and ducting size of 630mm diameter.

The 0.75 m/s comes from the HSE recommendation for venting of plasma tables.

I went for something smaller as I did not want to cut that size hole in the wall, so I went for 500mm diameter and uprated the fan to move more pressure. It's louder but I can vary the speed as required.

I vented from under the table, to prevent the finish face from discolouring etc.

**magicniner** · 22-01-2018

How does your table work?
Industrial tables usually have water baths which significantly reduce emissions to the workspace.

**marbles** · 22-01-2018

That's great advice, thanks.

I currently use a water table, which is a 100% necessity with plasma. TBH I use the plasma infrequently but when its on it runs on and off all day. i'll probably have to use a standard 300mm dia hose because thats the max exhaust size I can use to the outside. Will extend the hood and fan power accordingly.

**Bladevane** · 19-07-2019

On my 4' x 2' table I boxed in 3 sides and created a duct for the 4th side fitted with a 6" flexible hose connected to a 1.5 HP 3000 rpm centrifugal fan exhausting outside the workshop. I drape fireproof blanket over the gap between the workpiece and the table edges so most of the smoke and fumes are extracted downwards.

**marbles** · 19-07-2019

Originally Posted by Bladevane

On my 4' x 2' table I boxed in 3 sides and created a duct for the 4th side fitted with a 6" flexible hose connected to a 1.5 HP 3000 rpm centrifugal fan exhausting outside the workshop. I drape fireproof blanket over the gap between the workpiece and the table edges so most of the smoke and fumes are extracted downwards.

Nice 1, fire blankets a good way forward