Air Exhaust and Smoke Filter System for Laser Cutters

The K40 and similar laser cutters have provided access to laser etching and cutting to many hobbyists like me. Instead of venting the fumes produced during laser cutting to the outside atmosphere it would be better to clean up as much of the toxic materials from the fumes before ejecting it outside. The fan that comes with the K40 is substantially underpowered and would not be able to push the fumes through even the most basic filters. So I decided to make a system that would provide enough suction to clear the cutting deck of a laser cutter as well as filter as much of the toxic materials from the air. The system needed to be easy to build and flexible so that I can adapt to positioning it in different locations and to modify later as I came up up with better ideas. As you can see in the images and the video, the system met the requirements.

The concept is shown in this diagram. Starting from the bottom, smoke and fumes enter a bottom chamber though a circular vent, large particles drop to the bottom by gravity. A second chamber rests on top of this bottom chamber, the air is drawn though a series of filters in this chamber based on the suction generated by the strong blower fan in the top chamber where a centrifugal blower pulls the air from the laser cutter, through the filters and then ejects it out into the external atmosphere.

Step 1: Making the Blower Compartment

The first step was to make a box for the blower. I had

acquired a couple of blowers from an auction which would form the heart of this unit. If I were to buy these new, each would cost about $500. The motor on these was marked at 200V and the wiring had UK wire code colors. The fans did run on 110V AC but for the full output I would need 200V AC. The fan was about 12 inches wide so A 15 inch cube would hold the fan with space for the air to enter and for the electrics to be attached.

I used white melamine 15.75 in wide shelving boards remnants. The 4 sides of the boxes were assembled by butt joints held with glue and screws to create a rectangular cylinder. The output vents of the fan would be two plastic toilet flanges that were 4 inches outside diameter and cost about $4 each. I drilled a hole and then used a jigsaw to cut out the 5 inch diameter circles.

I had attached the drawer handles too and you can see the washers on the two sides.

I then used scrap pieces of wood to attach the fan to the enclosure with screws and glue. The blower would eject the air through the two large holes or rather the two toilet flanges attached over the holes.

The top of this fan as seen here would be covered with a 15 inch square piece of the melamine shelving (shown being cut in one of the images) which forms the top of the the whole air filter system. The top was held with glue and screws. Three metal screws were used to attach the top of the fan to the top panel (last image).

Step 2: Adding the Power Switch and AC Input Socket

I cut holes in the sides of the blower fan chamber to attach the power switch on one side and then an IEC AC input socket on the opposite side. Had to look up the UK color code, blue is for neutral , brown is for live, and green for earth. The recycled socket that I had seemed miswired.

The fan came with a power cord so I reused sections of it to complete the wiring.

Step 3: Wiring the Blower Fan

As the fan was a 200V unit I had to extract a 110V to 200V transformer to jump up the 110V to 200V AC.

Have summarized the wiring in this diagram.

The live and neutral wires were connected to the two pole power switch. The brown live from the power switch was connected to the transformers black 110V input and the blue neutral from the switch was connected to the white neutral wire on the transformer. The blue neutral was also connected to the fan neutral. The transformer I had had different outputs from 200V to 240 volts. Decided to use the 200V output, so connected the 200V output to the live of the fan.

All the earth connections were tied to a single point on the transformer as shown here.

In the image the IEC AC input is on the left. The transformer is on the right with the power switch just below it. The transformer was attached to the wood panel with nuts and bolts. Wiring to the power switch is shown on the left.

Once the wiring on the blower box was completed, I tested it to make sure it works.

Step 4: Making the Bottom-most Compartment That Connects to the Laser Cutter

Then moved on the making the bottotm most chamber in my stack of three chambers. This would be where the fumes come in from the laser cutter.

The box was assembled from the melamine shelving, 4 sides and a bottom. With the same side wall dimensions and bottom dimensions as the blower box but only 7 inches in height.

A hole was cut for the smoke-and-fume inlet into a side. Used the toilet flange as the inlet vent, which was attached with caulking and screws. Added the drawer handles.

Glued a wooden lip to the top edge (in brown) to keep the enclosure that would rest on top from sliding off and to create an air-tight seal.

Added caster wheels to the bottom.

Step 5: Design for the Smoke Filter Chamber

I used a 3 stage filtration approach. First to remove large particles with a matted filter pad and remove chemicals with a mixture of activated charcoal and regular charcoal. 2nd stage to remove smaller particles with regular home air furnace filters and and the last stage to remove micron level particles with a HEPA filter. This staged approach also extend the life of the more expensive HEPA filter.

I had 14 inch square air filters that I decided to use instaed of 15 in square filters which would be better suited for this system. I also had a few 5 inch by 15 inch HEPA filters from a cleanair system that I will use.

Step 6: Making the Middle Filter-holder Chamber

I made the enclosure that would hold the filters. The box was 12 inches tall and would be open to the top and bottom. Bridging the bottom input vent chamber and the top blower chamber.

I added the wooden lip to the top of this filter chamber to create an air-tight seal with the blower chamber.

I joined the 5 inch wide HEPA filters together with air tight joins to create a larger HEPA filter. The HEPA was then wedged into the top of the filter against the wooden lip.

Below the HEPA would be the regular furnace air filters. These were attached to a frame from white wood, to bridge the gap betwwen the 14 inch filters and the 15 inch internal spacing of the chamber.

I used strips of double-sided foam tape to form a barrier and attached two air filters that had been glued together before to this frame. The logic of using two filters is that you get a major improvement if you stagger two filters. The frame with the two filters was pushed against the HEPA filter and held in place with tape.

The bottom most filter stage, with the filter pad and carbon filter, were a box made out of 3.5 inch wide MDF that slides into the filter enclosure cube. The bottom of this box is covered with fiberglass window mesh and metal grid used for stucco walls. The mesh and grid were held in place with screws.

A blue filter mat was wedged into the bottom of this box against the mesh.

I had prepared a cloth rectangular bag slightly larger that the inside of the box (from a cushion cover) and filled it with a mixture of regular crushed charcoal that had been autoclaved and commercial activated charcoal granules. Sorry did not take images for the carbon filter. The top of the filter box was covered with another piece of metal grid held with screws.

Also attached eyelets to the bottom of the MDF sides of the box and a nylon tape to serve as a handle for the box to pull out. The assembled box was slid inside and attached to the sides of the filter chamber with a screw from each side of the enclosure.

Step 7: Making the Window Vent

Finally, made a window vent to attach the air filter to, to exhaust out into the atmosphere.

I bought two clothes dryer vents for about $10 each which would make it easier to attach the flex tubes and also look nicer from the outside. I trimmed the metal cylinders attached to the vent to a shorter length.

I measured the size of the opening in the window and then cut a white plywood shelf panel to size, cut two 4.25 inch holes in the panel for the vent tubes and attached the two vents to the holes with caulk and screws.

Then attached rubber window seals to the edges of the panel to prevent rain water intrusion, placed the panel in place and attached two 4 inch diameter flex tubes.

Step 8: Putting the Three Modules Together and Testing for Suction

Stacked the three chambers on top of each other, plugged it in and did a test with an anemometer. Was surprised at the amount of air this system moved and was also a bit surprised at how relatively quiet the system is.

Overall pretty happy.

If was to do this again, I would make it like a cabinet with a door in the front so that filters and fan can be easily accessed. May be a challenge to make sure that air seals are tight in this configuration but still doable.