Exhaust System - 8'x4' Laser Cutter

[Ash Bentley]

Hey Guys,

Firstly, I've been scouring these forums for years. It has been a terrific resource with amazing contribution from the whole community. So a big "thank you" to you all!

Now, I'm in need of some help for my new laser cutter. I've had a 4'x3' (1200x900mm) enclosed Chinese laser cutter for a few years now and it's been great. The exhaust on it hasn't been brilliant, as I can still smell MDF or acrylic when cutting, but overall, I can't complain. I just got a new 8'x4' (2500x1300mm) Chinese laser cutter and the exhaust system I have isn't doing a good job at all. I've been reading up as much as I can but I'm still a bit lost.

The current extraction system:

• 3 vents under the laser cutter bed that have ducts leading to 2 x 6"(150mm) outlets. These 2 ducts run to their own 500w Chinese Fan. Ducts would be 6' (1.8m) from the laser cutter to the fan
• A single 4"(100mm) duct from the top of the gantry. This runs to it's own 500w chinese fan(no idea on CFM). Flexible Duct would be around 6' (1.8m) from the gantry to the fan.
• Ducting from the fans is 4" (100mm) and runs 6' (1.8m) to a custom adapter (dodgy, yes) then into 6" (150mm) ducting that travel around 33' (8m) to the roof. There is a standard metal roof cowl to stop rain getting back into the ducts. There is also a y-join along this section of the duct where the ducting from the smaller laser cutter hooks up.

I've taken a few pics as my explanation is probably really hard to follow. Haha.

In essence, it's really bad. It's loud. It struggles to pull any smoke, especially when cutting and the laser head & gantry is moving around. There is always a lot of smoke on top of the material that just doesn't get picked up.

I know it looks like a bit of a mess, I literally set it up with what was provided with the laser cutter and what I had available to ensure the laser cutter worked as required. The laser cutter is now all dialled in and it's time to get the exhaust figured out.

It's a fairly large workshop with roller doors always open, so makeup air shouldn't be an issue.

One idea I was thinking of was to run semi-rigid or rigid ducting where possible and replacing the fans.

What would everyone recommend? What fans? Also, does anybody do something different on top of the gantry for better extraction of smoke from the top of the material? I'm open to any ideas!

Any help would be greatly appreciated!

Cheers,
Ash

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[Bill George]

#1. Get rid of the flex, extreme loss of flow. Hard pipe all the way.

#2. Complete re-design of the entire system, smoke rises I see nothing over the carriage where the cut is taking place. You will need some sort of hood over the table.

#3. You can not combine exhaust from separate fans into one common duct. Needs to be a common fan pulling from different duct with shut offs or dampers on each to balance.

[Dave Sheldrake]

You need 2 x 1hp+ squirrel cage fans

I have 3 open bed machines but I have no idea how you get away with a class IV machine layout like that...I'd get murdered by the factory inspector if I tried

[Ash Bentley]

#1. Get rid of the flex, extreme loss of flow. Hard pipe all the way.

Will do!

#2. Complete re-design of the entire system, smoke rises I see nothing over the carriage where the cut is taking place. You will need some sort of hood over the table.

Good point. Do you happen to have any images or links that shows a good hood design? I'm trying to figure out the best approach.

#3. You can not combine exhaust from separate fans into one common duct. Needs to be a common fan pulling from different duct with shut offs or dampers on each to balance.

Does this mean if I have multiple fans for the laser cutter that each one will need their own duct to the roof?

Also, what fans would you recommend Bill?

Thanks so much for taking the time to reply. I really appreciate it!

Cheers,
Ash

[Ash Bentley]

You need 2 x 1hp+ squirrel cage fans

Thanks Dave. Do squirrel cage fans go under any other names? I'm struggling to find any in Australia. Do you have any links or brands you'd recommend?

[Bill George]

Thanks Dave. Do squirrel cage fans go under any other names? I'm struggling to find any in Australia. Do you have any links or brands you'd recommend?

Does this mean if I have multiple fans for the laser cutter that each one will need their own duct to the roof? Yes


Look at the Harbor Freight website under dusk collectors or exhaust fans. You need someone to design and install a proper ventilation system. If I was still in the business I would do so, but not for free.
Find a local HVAC company that specializes in industrial ventilation design, build and install.

[Mike Null]

I agree with Bill on going to a HVAC company. I don't agree on Harbor Freight for your application. I would look at in-line blowers or the squirrel cage as Dave suggested.

Here is an example of a squirrel cage blower. https://www.zoro.com/dayton-blower-4...g&gclsrc=aw.ds

[Dave Sheldrake]

Two of those Mike posted will do it, the gantry flow is axial extraction and is normal on bigger machines but you may want to enclose the laser head area with panels to help with the airflow and protect against risk of injury.

To echo what others are saying...smooth wall pipe, minimum bends, short run distance and you will win

[Kev Williams]

How about a BIG blower...
carwashblower.jpg

[Keith Winter]

Those chinese fans are junk + you are cutting down their efficiency dramatically by forcing them into a small common pipe on the exhaust end + it looks like your run is quite long. Bill, Dave, Mike gave you excellent recommendations. I second everything they said. If the exhaust pipe is say 6" and you combine them, then you need a 12", or two exhausts. Looks like you are forcing two 6" into one 6" or 8" pipe currently, that's killing you.

Only thing I would change is either go with 2 - 2hp units or 3 3hp units. Because your end exhaust is so long and also you table is so big the extra horsepower will be helpful. Bigger blower will pull more of that smoke in. Dave's ideas for the side panels is great as well.

[Bill George]

You can not combine two fan/blower exhausts into one pipe. One fan will always be stronger than the other restrictng the flow. IF you put another Exhaust Fan = or greater than the two in series after it might work ok. But most people just run the one larger fan/blower and install a Y with shut offs to balance it out.

[Gary Hair]

You can not combine two fan/blower exhausts into one pipe.

I have two in series and even though I don't get twice the volume of air, it is noticeably more than a single blower by at least 50%.

[Neville Stewart]

You can not combine two fan/blower exhausts into one pipe. One fan will always be stronger than the other restrictng the flow. IF you put another Exhaust Fan = or greater than the two in series after it might work ok. But most people just run the one larger fan/blower and install a Y with shut offs to balance it out.

I've seen some vacuum lines in an industrial setting with a booster pump inserted in the line, not disagreeing with you but isn't that two pumps/ 1 line?

[Bill George]

Yes you can put two or more pumps/fans in series. What the OP had was two fans blowing into a common pipe and that pipe headed to the roof (without a booster fan), that will not work very well.

[Neville Stewart]

Yes you can put two or more pumps/fans in series. What the OP had was two fans blowing into a common pipe and that pipe headed to the roof (without a booster fan), that will not work very well.

Thank you Bill, obviously you know what youre talking about, whereas I...