Electronics > Mechanical Engineering

Laser exhaust

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dunkemhigh:
(I suspect it would have been simpler and cheaper to buy a CO2 laser, but I thought that would take up too much space...)

Built a box for the laser so I can exhaust the fumes. As it happens, I am stuck on PLA for 3D printing because I don't have an exhaust system, so I took the opportunity to fix both of these by having a 110x55 ducting fixed behind the boxes which leads out via a 120mm mains fan.

The laser box is made from a wooden frame and hardboard sides, except the front which is red perspex. A single 80mm fan feeds out the back to a 100mm duct which leads to the main ducting. The front perspex has a row of holes at the bottom for inlet.

The problem is I get some fumes coming out. Nothing like what goes to outside, but it's enough to worry me. The box isn't airtight but I figured air would be going in rather than coming out. Or maybe there is a leak in the ducting.

How can I find where the fumes are leaking? There isn't sufficient (at least in a concentrated way) to feel anything by hand or waggle a piece of tissue.

(The ducting is open from the laser to the 3D printer, but the external fan is sufficient to stop anything doing down that route - I can put my head in the printer and not smell a thing.)

james_s:
It doesn't take much of a leak for fumes to get out. Do you have or know anyone who has a fog machine? If not, you can probably find a deal on one in a few weeks when the Halloween stuff goes on sale.

dunkemhigh:
I started this at just the right time, then!

Good idea. I think I might have a smokecloak around somewhere which could be resurrected. But I'd have to ensure it's not pumping in but being sucked in.

Ian.M:
Cut the power to the duct fan and block off the duct branch to the 3D printer so only the laser enclosure fan is running, which will give you slight positive pressure in the ducting.  You can now check for leaks using the smoke from a joss stick held below the duct at the joints.

If you don't find any leaks, its likely the 80mm fan isnt scavenging the fumes from the laser enclosure effectively.  A gate or cap to block off the printer duct while the laser is in use may help, but odds are the airflow within the enclosure  is causing eddies back out the vents, so you may need to add some baffles to get unidirectional flow rather than circulation.   Again investigate with a joss stick just outside it.

dunkemhigh:
Wouldn't a positive pressure in the duct prevent air being sucked into the box, so anything in there would leak out through the (intentional and otherwise) holes?


--- Quote ---likely the 80mm fan isnt scavenging the fumes from the laser enclosure effectively
--- End quote ---

Could be, yes. I can feel the air being sucked in at the front, but there might be a dead spot with no airflow in a corner, say.

Joss stick is a good idea  :-+

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