Air Assist & Fume Extraction

Last Updated: 19th October 2013

I've lumped air assist and fume extraction together on this page because, the way I see it, they're both about getting vapour/fumes away from where the work is being done.

At one point I had some info here about air assist and sub-bed extraction but there are now plenty of other places on the web where you can read about those... and if you search for them, you will find details of modifications that other people have made; ranging from the relatively simple attachment of a tiny fan to the head (a kit is actually being offered for sale), to quite highly engineered solutions for which you will need access to a lathe in order to make parts.

However I have gone down the route of attaching an extraction system to the cutting head, to suck the fumes away, rather than blowing (as with air assist), at the point that they are being created. More about that further down this page, but first, details of a simple modification that I made very soon after getting my laser cutter, and which I suggest everybody should make even if they do nothing else.

Fan Duct

Exhaust gaps sealed with duct tape.The fan unit supplied with the laser cutter is not a custom made unit and has a flap on the exhaust with hinge brackets - which mean that the ducting won't fit snugly and creates a gap.

So I removed the flap, cut off the plastic hinges (with a craft knife), trimmed a couple of centimetres off the end of the duct fitting, and fixed it in place with duct tape - no more gaps on the exhaust.

Easy to do and definitely recommended.

Head Mounted Fumes Extraction

The installed system works but there are a few issues:

1. It pulls the fumes away from the work area relatively slowly. If you've done any reading about air assist then you'll understand the benefits of getting them away quicker: more efficient cutting and less chance of the fumes igniting.

2. Fumes get pulled across the surface of the work piece and often leave marks which may, depending on what you're up to, need cleaning/polishing away later, and are thus a nuisance.

3. Fumes cycle around the inside of the cabinet, and the underside of the cutting head in particular, can end up getting very dirty.

While air assist systems tackle the first of these issues they do nothing about the others and I figured that it made more sense to think in terms extracting the fumes rather than just blowing them out of the way.

Head Mounted Fumes Extraction Experiments

I've tried, and am still trying, a number of methods and set ups for head mounted fume extraction on my laser cutter.

#1 Vacuum Cleaner

The image below shows my first experiment:

Fumes Extraction Experiment #1

What you see there is a length of 3/4" diameter flexible hose (sold for pond filtration system), attached to the cutting head with masking tape. I then fed the hose out of the cabinet and merely attached the other end to the vacuum cleaner that you see to the left...

...and it worked!

The down side was that the vacuum cleaner is noisy and of course we're not expelling the fumes outside so it's smelly too. Okay as a test of whether head mounted fume extraction was feasible, but not something I'd want to use extensively.

#2 Bathroom Fan

This image shows my second experiment:

Fumes Extraction Experiment #2

What I did here was to use the fan unit supplied with the laser cutter, and blanked it off, with the hose attached using some card and masking tape.

This didn't work as well as the vacuum cleaner but was a hell of a lot quieter... and of course expelled the fumes outside (by hanging the output hose out of an open window). I'd estimate that it managed to extract about 90% of the fumes with the laser running at the 800mm/min feed rate[1] that I'd been using with the vacuum cleaner. Slowing the feed rate to 400mm/min improved this to something like 98%.

Note that the ability to set a feed rate in mm/min is a feature of SheetCAM i.e. the CAM software that I am now using with Mach 3 since my conversion to using CNC software.

While I was happy that the fan is quiet and vents the fumes outside, I was not so happy about the 2% of fumes making my spare room smelly, or that I had to slow the feed rate to 400mm/min when I know that the cutter will happily run at much faster speeds.

Something else to observe (in the images above) is that the way I've run the hose: it needs a loop like this so it doesn't restrict movement of the head but it prevents the lid from closing.

#3 Hair Dryer

Fumes ExtractionThe first thing to observe in the image to the right is the new fan, poking out of the window... it's my partner's old hair dryer. I removed the heating element and attached a pond hose fitting to the back with epoxy glue. This provided plenty of suction and allowed me to increase my feed rate.

The second thing to note (image below) is that I made a new top plate for the cutting head. The hose attaches to this with a modified, pond hose, elbow fitting, thus allowing the hose to lie horizontally in the cutter... so I could close the lid when it's in use.

Fumes Extraction

Although the hairdryer was quite noisy, this set up worked well... for a while... because after a few months (not continuous use) the hair dryer started to rattle a bit and eventually died. Ultimately, a hairdryer is mean to suck in clean air for maybe 10 minutes a couple of times a week. Sucking on the crap coming out of a laser cutter for a couple of hours at a time... well it just wasn't up to the job.

#4 Spa Bath Blower

Spa Bath BlowerAround about the time the hairdryer started getting noisy I acquired some parts form a spa bath kit that were being discarded. The image below shows spa bath blower plus and how I connected it up.

You can probably just about make out that I was trying to take advantage of the venturi effect (Google it is you don't know what that is) to avoid drawing fumes through the blower itself. The main component of that was a sink waste pipe swept T junction.

It didn't work nearly so well as the hairdryer most probably because my pipework was far from perfect. Something to work on except that:

1. The blower is surprisingly noise. Not exactly conducive to having a relaxing bath I wouldn't have thought, and not what I was hoping for in my workroom either.

2. After my experience with the hair dryer I'm reluctant to put a lot of time and effort into developing something that relies on a component that I can't easily replace, namely the spa bath blower unit. Yes, I could buy a new one, but they're not cheap and again: aren't intended for prolonged use.

I figured that it made sense to do some research into other possibilities and while doing so I became aware of the existence of bilge blowers.

Before getting on to bilge blowers however:

Spa Bath Hose

The hose you see in that image came from the spa bath kit and it's MUCH more flexible than the pond hose that I was using previously. I've not yet found anywhere that I can buy it other than as part of a spa bath kit, but it's obviously out there, somewhere.

#5 Bilge Blower

I looked into available fan units on a number of occasions but of course it's hard to search the web for something if you don't know what it's called, or even whether such an animal exists. So it was purely by luck that I've stumbled on "bilge blowers".

Bilge blowers are extraction devices, a bit like shower fans, but with much higher throughput. They are intended for removing stale air from the bilges and engine rooms/compartments on boats; so they have to deal with salty air, diesel fumes, and other nasties. Thus the motor an other delicate bits are completely encapsulated to protect.

Because they are for use on boats they run on 12v or 24v but need quite a hefty power supply as they draw about 6 amps. Not cheap: I'm currently looking at about 70 UKP (on eBay) for a suitable fan and power supply.

I'm definitely in the market for one but am not currently sure how I'll connect it up.

Watch this space. :-)