A common complaint about most of the K40 laser cutter/engraver machines sold on eBay and Amazon is that the fan is basically useless. They are correct. The provided fan doesn't mount correctly to the machine, leaves large air gaps, and doesn't even move a decent amount of air.

Instead of throwing the fan out, I decided to take it apart and found, much to my surprise, that the fan motor is actually of decent quality! So, based solely on the provided motor, I decided that I could salvage it by creating an enclosure for it with new fan blades to use as a fume extraction solution.

I use this fan at the end of my exhaust system so that air is being sucked away from the laser, not pushed. This creates negative pressure inside the exhaust duct so that if there are any leaks it will be sucking air in from the workspace, and not pushing fumes out into the workspace.

Performance video

Monoprice

Maker Select Plus

No

Yes

0.3mm

20%

I used 0.3mm to speed up the prints, as well as provide a slightly stronger print (compared to 0.2mm). For the "Fan housing", supports are needed everywhere, whereas all other models only require supports touching the build plate.

To finish putting the housing together you will need to take the parts you salvaged from the stock fan (see photo above), screw the motor down to the motor housing, insert the new blades onto the motor shaft, secure the blades with the clip and knob from the stock fan, and then secure the rest of the fan housing to the motor housing.

I used hot-glue to secure the housing together. I know it's not the best solution, but I didn't design any screw holes on the fan housing. Maybe I will later.

I decided to go with a simple centrifugal fan design, as they are compact and efficient. The inlet and outlet are both 4" (102mm) in diameter to fit with common ducting.

I designed the fan blades to be a similar style to the ones that came on the K40 fan, but made them larger (15mm instead of ~10mm) so they could push a little more air. I also simplified the mounting point of the blades to the motor shaft so make printing simpler.

Stock K40 fan: 117 CFM
Upgraded fan: 151 CFM
195CFM (rated) fan: 158 CFM

You can see how these were measured in the provided video, but I'll also document my procedure here.

Each fan was turned on and measured directly at the air outlet with an anemometer (air flow meter) in feet per minute. The obtained number was then multiplied by the surface area of the air outlet opening in square feet, which resulted in the cubic feet per minute measurement.

In the case of the stock K40 fan, the air outlet opening was not a complete 4 inch opening, because it was partially blocked by part of the fan housing. The surface area was multiplied by 0.75 since the blocked portion takes up about 1/4 of the total outlet opening.

The "195 CFM" fan was purchased on Amazon for $25 before I decided to see if I could improve the stock K40 fan. As the results show, that fan only provides a slight volume boost compared to the upgraded fan. With better fans claiming to provide higher CFM being over $45, you're better off just upgrading your K40 fan that you already have, rather than shelling out the money to buy an off-the-shelf fan which may or may not perform as it claims.