Downdraft design questions

Not sure if this is the right place, but I suspect someone here has experience with this.

I am trying to find the best type and size fan to exhaust the smoke/fumes/dust from my table. The table is 6x12 and has a v-shaped basin. Suspended halfway between the basin bottom and the cutting surface is a 7" ID steel pipe with 8ea 4" square 'ports'. There is only one outlet on the table located at one end. The table will be situated in my shop in such a way that the outlet of this pipe is 8' from the exterior wall, at 90 degrees from where I need to vent.

I have read good things about backward incline blowers. Any input on what size and type fan as well as connection methods will be much appreciated.

Thanks

That looks like a really nice design.

This article suggests 3200-3600 CFM for a 4' x 4' table
www.hypertherm.com/learn/spark-the-blog/fume-control/
So for a table that size you would need a LOT of air. 16000 cfm.
Most commercial tables are zoned

Assuming you are going to use Linuxcnc's Plasmac, I would suggest you add an air activated shutter on each of the 8 outlets that is triggered based on the position of the x & y axis. You don't need seperate compartments to contain the air. Better that you don't
so by using 8 zones, you would reduce the air flow requirement to a much more reasonable 2000 CFM

Here is a bit of a rough demo of mine showing how this can be done


You could use two lincurve components with axis.x.pos-cmd and axis.y.pos-cmd as respective inputs but you would need a bit of hal trickery to merge these into a zone. I think it would be a lot easier to write a custom component which is the path I took for the demo.

I am planning to use LinuxCNC. The PC is built and I am about to begin hurting my head learning about how to connect the Mesa cards and all the other electronics. I have one hobby in the queue that I am nearing completion on, so I should be ready to start in earnest on the electronics this week, or early next week. I think I have everything from the original list you made for me. To get the table running in the meantime I connected my CandCNC setup.

So you are saying if I can manage to add automated vents controls then I do NOT need to add zones or baffles?

What type of fan/blower would you recommend? Should I be looking for 2000 CFM at 0 SP?

Lastly, would you be willing to write the custom component for a fee?

Your setup is top shelf! I like the cabinet, very tidy work.

As always, thanks for taking the time to help!

I had in mind something like a pneumatic slide gate valve www.acsvalves.com/options/view/maintenan...-valves-air-operated

I'm not sure if baffles would be needed. I did see one big commercial table that just had a central duct with air ram activated flaps that was not baffled hence my idea. The air rams were inside the duct and they used copper tubing to the rams. I guess so it did not melt from sparks.

You would have to do your own airflow engineering.

I'd start with one of the cheap axial workshop blowers to prove the idea.

I have a cheap tube axial fan now. It might be worth a try, I would have to price the air rams and associated actuators. If it worked I would still be facing the software challenge. How challenging would the software be to configure to operate 8 devices based on the location of the torch?

txtrone wrote: I have a cheap tube axial fan now. It might be worth a try, I would have to price the air rams and associated actuators. If it worked I would still be facing the software challenge. How challenging would the software be to configure to operate 8 devices based on the location of the torch?

The software would be easy. The software for my example was 4 lines of code but it could be done in 1 line

I'll have a look at it.