Compressed Air & Exhaust Volume Guides?

[Mikah Barnett]

I've been cutting 1.5" Polyurethane foam recently with great results. The only disappointment I have is that the smoke lingers in the machine around the head longer than I'd like to see it be there. I also know my "came free with the machine" compressor is weak and I need a bigger, drier air supply.

So - for a 1200x900mm table size, what is the right amount of exhaust CFM, compressed air pressure and compressed air CFM? I typically subscribe to the "more is better" on this kind of deal, but thought I'd see if somebody's got a setup they are in love with already.

[Dave Sheldrake]

7 to 9 cfm for a compressor @ 25psi plus a drier, (remember FAD is different to CFM displacement)

Exhaust, 550+ M^3 and hour would be good if fitted directly at the back of the machine if an inline, bigger centrifugals can be sited further away without having static pressure problems.

More is better doesn't always work in this scenario, efficiency is the key not brute power.

cheers

Dave

[Mikah Barnett]

7 to 9 cfm for a compressor @ 25psi plus a drier, (remember FAD is different to CFM displacement)

Exhaust, 550+ M^3 and hour would be good if fitted directly at the back of the machine if an inline, bigger centrifugals can be sited further away without having static pressure problems.

More is better doesn't always work in this scenario, efficiency is the key not brute power.

cheers

Dave

Thanks, Dave. That sounds easily doable, and that's higher than what I've got now (about 450M^3/hr), so fits with my feeling that I'm lacking.

Apprecaite it!

[Brian R Cain]

Thanks, Dave. That sounds easily doable, and that's higher than what I've got now (about 450M^3/hr), so fits with my feeling that I'm lacking.

Apprecaite it!
Nowhere near enough. In my experience, and I've seen a lot of set ups, inadequate extraction causes more problems than enough. Get it right, and you'll have few issues. Universal is one of the few companies that specify the exhaust requirement in their advertising blurb. They make a 1200 x 600 machine for which they specify 1000 CFM @ 6" static pressure (1700 m3/hr at 1.5 kPa)

[Mikah Barnett]

Nowhere near enough. In my experience, and I've seen a lot of set ups, inadequate extraction causes more problems than enough. Get it right, and you'll have few issues. Universal is one of the few companies that specify the exhaust requirement in their advertising blurb. They make a 1200 x 600 machine for which they specify 1000 CFM @ 6" static pressure (1700 m3/hr at 1.5 kPa)

Interesting - thanks for that, Brian. The exhaust outlet on my machine is 6" diameter - I do not believe I've seen any 6" fan that will move that kind of air. I'll do some more poking around.

[Joe Hillmann]

In the manual for my Universal, with a 18"x32" bed, it says the minimum requirements for the exhaust is 500 cfm (850 cubic meters/hour) and 6inches of static pressure. The measurements are to be taken right before where it connects to the laser, not measured at the blower. Which means that the longer your exhaust duct work is the bigger the blower has to be to make up for the loss of suction.

When I used to just engrave glass with the lasers I had a much smaller blower and it was enough but when I started engraving on items that smoke my old blower wasn't near enough.

Of course your machine is designed different than mine so it may require more or less air but that gives you a place to start.

[Mikah Barnett]

Thanks Joe - both yours and Brian's figures work out to about 1500CFM requirement for my machine. That just seems like way too much air to be able to move through a 6" hole.

The way my machine is set up, the exhaust outlet is connected to a manifold so that it pulls air from slots at the back of the machine (see attached picture). The total area of those slots adds up to almost exactly the same as a 6" circle.

So, do I need to add some holes at the back near the slots, replace the 6" exhaust outlet with something bigger (probably 6x8" rectangular) and then buy a big ol' 1500CFM fan? Or, should I simply add a secondary 6" outlet to the back that evacuates through the whole machine (rather than through the manifold) and use both fans when I'm cutting smoky stuff?

[Joe Hillmann]

I wouldn't modify anything inside of your machine. It is set up so that air comes in at the front of the table at about the focus height and exits at about the same height at the back. That way the area with the fastest moving area is at or just above the focus area which makes it the most efficient. If you are looking at buying a new blower, rather than finding something second hand I would take a look at harbor freight dust collectors. They may not be super high quality but they are rated at 1550 cfm and are under $200

[Dave Sheldrake]

They make a 1200 x 600 machine for which they specify 1000 CFM @ 6" static pressure (1700 m3/hr at 1.5 kPa)

Do that on an LC1290 and the top window will be on its way in as soon as you close the lid :) Weikes are designed to use crossflow dynamics and not downdraft, big difference.

cheers

Dave

[Katie Browning]

Hi,

This thread is exactly what Ive been looking for! I also have a G.Weike LC1290 (1200x900mm-80w) and Ive been smelling smoke quite abit lately. Im not sure if its always been this bad or Ive just become paranoid and Im noticing it more and more. The fan that came with the laser has a label on it, but its in Chinese...very helpful :P

I was going to go buy a new fan, and since I read your comments above I was looking at 550 m3/hr + but Im wondering what the exhaust Im using now is. Maybe its already powerful enough and there is some other problem Im unaware of. Anyway can anybody make any sense of this label? Is it strong enough... which number represent the air capacity (m3/hr)

Any help would be fantastic!!
Cheers
Katie

320269

[Katie Browning]

Actually Ive found another label on the fan that is more relevant...(attached)

Strangely it says it is 870 m3/h but I wonder why im getting smoke coming out of the machine... I would have thought this would be strong enough

320272

[Matt McCoy]

If you did not have smoke and now you do, chances are the intake on the blower or somewhere downstream has become restricted due to build-up. Check any filters, hose/pipe, and the impeller/fan on the blower for junk and clean that out.

[Keith Winter]

Take the rating on your blower with a grain of salt, the chinese equipment could be much lower or higher than it's actually listed, likely lower. For instance the cpm listed by my harbor freight blower is really overrated compared to what my shopfox does. They list best case on the harbor freight not what you're really going to get day in and day out, it's still good but lower than they list; on a direct from China blower it is probably even more exaggerated. Not much quality control over there. First thing I'd do is measure and then throw away the Chinese blower if it doesn't pull enough. They very likely send the same blower with all the Chinese lasers regardless of size, it's likely insufficiency for the size of your laser.

Here is how to measure:

1) Buy a cheap Anemometer I have this one
http://www.amazon.com/gp/product/B00J2SNQOS?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

2) Measure the airflow inside your laser at the vents.

3) For my Speedy 300 I've observed airflow at the vents needs to be above 600 fpm in order to remove all smoke immediately. Your surface area of your laser is larger so you may need a bigger fpm/cfm but that at least gives you somewhere to start from before you start tearing down your system.

4) Plan your new system. Here is the post I did, in it I talk about 3 different blowers I've tried and how I engineered my system I hope it is helpful to you:
http://www.sawmillcreek.org/showthread.php?232398-Laser-Exhaust-Version-3

[Dave Sheldrake]

Just remember what goes out has to come in....

Calculate the internal volume of the cabinet
Work out how many air swaps per minute you need
Check that the extraction hole is less area than the combined inlets (by around 2%)
Calculate losses for length of tube

Or...simply fit an air powered screamer valve at the head and let it do point extraction for you :)

[Bill George]

Keith has done a great job of engineering. I just want to add please use sheet metal screws (at least 3) to hold the pipe together and then for pressure side connections either aluminum foil tape or hard cast to seal the joint either one work much better than "duct" tape. You sheet metal workers or tinners know what hard cast is.

[Rich Harman]

I use a Harbor Freight dust collector blower that is rated at 660 cfm. In addition I almost always run my laser with the lid wide open. Effectively making the "cabinet" the size of my shop. My setup falls short only when I am cutting something near the front of the machine, then the smoke starts to escape. This is when I shut the lid - then it is all drawn to the back of the machine.

The volume of my cabinet is a little more than 40 cubic feet. That makes for about 12 air changes per minute with the lid closed (after de-rating the blower by 25%).

I've noticed that at least a couple model of Universal lasers use 4" exhausts. That would explain the 6" static pressure requirement. A larger exhaust pipe can move the same volume of air at a lower pressure.

[Gary Hair]

and then for pressure side connections either aluminum foil tape or hard cast to seal the joint either one work much better than "duct" tape. You sheet metal workers or tinners know what hard cast is.

That's great advice but I would advise against having a pressure side if possible. No matter how well you seal it, it won't be sealed and some of the nasty exhaust you are trying so hard to evacuate will end up being forced through those leaks and into the air you are breathing. Granted, it will be a lot less than if you didn't at least try to seal it, but if you didn't have any pressure side connections in your airspace then you have one less thing to worry about.