Air curtains?

[Deadeye]

There's a steady flow of dust extraction discussion on here - focused (almost?) exclusively on sucking HPLV/HVLP and cyclones/filters.

We seem to hook up the port and the air travels to it in whatever way it can; I don't think I've seen any discussion of, or attempts to, combine targeted air blowing with the sucking. Is there a reason that air curtains aren't combined to prevent leakage and funnel dust towards the extraction point? I could see them being quite effective on table and band saws; also for steering shavings out from thicknessers, or creating an air cage around lathe sanding.

Has anyone tried this? Laminar flow cabinets are based on the idea of managing *both* the inflow (sterile air sheets) and outflow. I thought particle velocity might be an issue but I did a couple of cheap and cheerful experiments with table saw and lathe and it's not hard to stop the particles being thrown out.

Perhaps it's just down to the fact that extraction seems to be an afterthought in almost all machine design?

 

[TheTiddles]

Because if you get it even slightly wrong you’re going to be blowing the dust everywhere and making the problem worse and getting it perfectly right is pretty well impossible
Aidan

 

[Deadeye]

Because if you get it even slightly wrong you’re going to be blowing the dust everywhere and making the problem worse and getting it perfectly right is pretty well impossible
Aidan

Thanks for the relpy - is that from trying it? I agree about the possibility of blowing it around, but a curtain delivering a smallish fraction of the air being extracted is unlikely to do anythign other than reduce the escape that's happening anyway. Ideally you'd set up laminar flow across the work and into the extractor. I'm not talking about high pressure air being blown at the blade!

 

[SimonStevensCanes]

I've often wondered the same specifically for mitre saw stations where the dust extraction is more challenging

 

[TheTiddles]

Thanks for the relpy - is that from trying it? I agree about the possibility of blowing it around, but a curtain delivering a smallish fraction of the air being extracted is unlikely to do anythign other than reduce the escape that's happening anyway. Ideally you'd set up laminar flow across the work and into the extractor. I'm not talking about high pressure air being blown at the blade!

I’ve not tried it, I wouldn’t based on my general experience of design things for clean rooms and operating theatres. In general you want to reduce the pressure somewhere you want the waste to go and let the atmosphere push it in. Trying to blow it will fire it all over the place. We’d use an air curtain on an entrance to a box (like over the conveyor) with an extractor reducing the pressure in that box to make sure the pressure from the curtain went into the box and was taken away along with whatever we were doing in the box, such a a spray deposition, solder fumes etc... Alternatively we’d place one in between two rooms, effectively making them the boxes. Trying to do it locally in an open space would be novel. The closest I could think of would be Venturi nozzles but those are inside a funnel so the entrained air is s

 

[Ollie78]

I have not tried it directly but I sometimes employ an extra fan in the workshop to make more circulation of the air, to encourage all the fine dust into my ceiling mounted air cleaner.

Also I have thought about employing something like it for my cnc machine, like a cross draught.

There are a couple of problems I see using it for mitre saws and things. The wood itself and your arms etc is going to deflect the airflow all over the place when putting it in and taking it out etc.
Also the amount of airflow required is not trivial and needs to be created and paid for.
Perhaps putting the mitre saw on a downdraught table would be enough.

I think the idea has merit but thinking it through what you will end up with is a workshop built like a spray booth. So the entire room is a downdraught table, or positively pressurised with filtered airflow in and out.
Could be great to have but would need to be built specially and not cheap.

Ollie

 

[Inspector]

The last company I worked for had an assortment of downdraft tables and booths to capture the sanding dust from the parts we made. They did have one downdraft unit that had an air curtain across the front to help contain the grinding dust. The metal finishers tended to grind at the edge or in front of it so its effectiveness was limited. The air was drawn down from the table through a churning water bath, up through water impinging filters, through the 5hp impeller, and blown over the booth where it exited as an air curtain across the front of the working table. When the finisher had the part in the middle of the table the air curtain helped turn the dust down into the water below. They were a great device when use properly but not practical for a home shop. Here is a link to them. Hydrotron Wet Dust Collector Downdraft Tables

If you were to make a downdraft sanding table enclosed on all but the front and direct the air down across the front it would go a long way to contain the dust and direct it into the table. You would have to make sure the filters were very good and maintained or you will be breathing a lot of fine dust. It isn't a new idea but difficult to execute properly.

As for using one to enclose a machine I have not seen anything like it and see a lot of hurdles to overcome unless it was in a booth and the air curtain was across the entrance. That would take up a lot of space.

There are commercial air curtain units to mount in doorways to contain dust. They are basically squirrel cage fans in a row above the door. A search for Air Curtain Dust Control will give you lots of examples and might lead to other information.

You can also search Air Knives and find a bunch of info (don't forget to look at the images). They provide a concentrated high pressure air stream across a surface like a sanding belt to strip off the dust and direct it into the dust collection system. Unfortunately the beasties use a lot of compressed air. I once thought an air nozzle set up to blow off the teeth a table saw blade could keep dust from coming back up the back of the blade but have never played with it. Have at it if you like. Exair is a US company with a lot of compressed air devices including air knives you might glean some ideas from. Super Air Knife Systems and Accessories

Pete