Air Assist & Fume Extraction
Last Updated: 20th January 2012
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
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
The image below shows my first experiment:
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've 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 to prove the point but not something I'd want to use extensively.
The next image shows my second experiment:
What I've 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.
My Penultimate Solution
The image to the right (and below) show my penultimate solution.
The first thing to observe is the new fan (poking out of the window), which is my partner's old hair dryer. I removed the heating element and attached a pond hose fitting to the back. This provides plenty of suction and allowed me to increase my feed rate.
The second thing to note 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 can now close the lid when it's in use.
Note that I've called this my penultimate solution because although everything works, I think I can improve upon it slightly by using my milling machine to manufacture my own parts instead of using the pond hose fittings. I might then offer them for sale as a kit of parts... so watch this space and let me know if you'd be interested.