Smoke assist on your k40 laser machine

This page is work in progress, suggest changes or addons to it in the comments.

I personally coined the expressions “smoke assist” a year ago when i was trying to explain to new users what the difference is on air assist and smoke assist, and what the two different techniques should be used for 🙂

What is smoke assist?

Smoke assist is a helping hand to keep your mirror or/and lens clean of the smoke generated by the lasing work.
The exhaust should only do the work of transporting the smoke from the exit to the end of the hose, nothing else.
The smoke assist helps moving the smoke from the cut area to the exit where the exhaust fan takes over.

With the smoke assist you can use less powerful exhaust fans, as the exhaust doesnt need to put the machine casing under negative pressure to clean out the smoke, the smoke assist helps with this.
Common airflow and air dynamics, what you want is a flow trough the machine with air, from the smoke assist fans -> exhaust fan.

Easiest solution for a smoke assist

Add fans, doesn´t matter what fans, i used my daughters hair dryer the first weeks and later changed to two 50mm 12v DC fans mounted in the front of the machine blowing air over the bed.
Later on i added more fans inside the machine on my laser head to keep the lens clear.
For bigger machines you need bigger fans, like 120mm computer fans.


This laser head is custom made by me, not a original product.


Here is the intake fans in my lid. You can mount them in the bottom or front piece, just add fans to help out with the input of air.

Comments (14)

  • Cody Reply

    I am considering putting 2 smaller computer fans, maybe 50-80mm in the front of my machine with holes cut for air intake, along with a 150cfm squirrel cage fan at the exit from my building, will this work well?

    My thinking is if I seal the lid better and have a larger exhaust fan that having the two little ones sucking in fresh air to blow over work piece would move the smoke out fast with less escaping into my house.

    6 September, 2017 at 16:49
    • HP Persson Reply

      Yes, anything that helps the exhaust will do better than no fans at all. Pushing air in will increase the pressure a bit so the exhaust has less negative pressure to make (to pull the air out).
      The best ratio is somewhere about 1:0.9 where the intake is a bit less than output, to prevent smoke from being pushed out trough cracks in the case.
      If you already have the squirrel fan, use it. If you going to buy one check out the inline fans instead, and keep it at the end of the hose, not back of the laser.

      6 September, 2017 at 22:11
      • Cody Reply

        Thanks I already have the fan, it was off a Pellet stove that failed, so its free. I was going to mount it right at my window exhausting outside through a dryer vent type setup. It has flaps that close so rain doesn’t come in etc.

        7 September, 2017 at 16:43
  • Renee Reply

    Hi There,
    Any ideas as to why all of a sudden our exhaust is blowing more smoke than usual when cutting timber / MDF. Never used to exhaust so much before but all of a sudden it seems to look like the side of house is on fire when we have the machine cutting. Having to cut at night as to not be so noticeable to neighbors.

    4 October, 2017 at 03:14
    • HP Persson Reply

      Most probably it´s because outside temperatures drops now, colder air outside and you exhaust hot air will be more visible. Similar to breathing in cold air, or boiling water. The bigger temperature difference – the more it will be visible. And the humidity plays a big role too i beleive.

      4 October, 2017 at 03:16
      • Renee Reply

        thanks for your reply. Our temps are actually increasing as we are in southern hemisphere. Think this would still be same issue.

        4 October, 2017 at 03:58
  • Jon Reply

    Looking at your picture, it would appear you have “something other than a stock K40″…your x-axis looks much larger than typical. To that point, I would not recommend anyone add any significant mass to K40 head (such as a fan)…the stepper motors/drivers cannot handle it and would start skipping steps quickly (especially while engraving at high speeds)

    10 October, 2017 at 03:16
    • HP Persson Reply

      Correct, this is the newer design of the K40, often named K40D but its beefier both on the steppers and controller boards so no problem with the movements. I have the older style too but never tried adding anything to the head on that one though 🙂
      The picture was mostly a example of air assist, the best solution is if the fans are in the case itself creating turbulence, eliminating the need for a big fan.

      10 October, 2017 at 10:18
      • Baldrick Reply

        on the subject of motors, what is the current k40 motors rating? I`m looking to build a rotary and presume that ideally the motors should be the same so not to complicate the job.

        20 November, 2018 at 18:50
        • HP Persson Reply

          Less than 1A power and 0.9 degree per step is what the original have. If you have upgraded the controller you can use bigger motors. The original board will burn sooner or later with 1,5 or 2A steppers.

          21 November, 2018 at 00:02
  • Jon Reply

    I was going to comment on your “air assist” (that is why I ended up on the site), but no comment section.
    I agree with your assessment. I actually have “that” air-assist, and it is much better than not having it. Without the air-assist, my lenses would require constant cleaning and wood would often catch fire. With this assist, I have had none of these problems (I don’t see any venturi effect as the lens itself blocks the path).
    However, I was on a search because my newly purchased 25mm focal distance lens does work with this assist (the geometry of that system cannot bring the work piece close enough without interfering the x-axis). Having a fixed air-stream driving the smoke toward my exhaust path as your “brake line” assist makes a lot of sense (rather than blowing everywhere, then trying to exhaust it)…thanks

    10 October, 2017 at 03:48
    • HP Persson Reply

      Yeah, any kind of air assist is better than none for sure 🙂

      10 October, 2017 at 11:48
  • Marv Reply

    Hi HP, great info.
    So how and where do you connect the pc fans to? I saw a schematic somewhere that the power supply only has a 5v and a 24v out?

    I read a lot about people adding all sorts of stuff like laser pointers, fans, lights etc. but no one seems to talk about how they connect everything. I can solder, but I’m not well versed in the arts of volts, watts and ohms.

    14 November, 2018 at 22:11
    • HP Persson Reply

      I always suggest adding a extra power source for fans and other stuff to the machine. If you get a problem further ahead, you will know for sure the stuff you added is not a reason for the problems. 12v and 2A can be found everywhere and very cheap, enough for some fans and lights. You might have a old wall plug somewhere from a screw driver charger or similar, just check the volts and amp output.

      17 November, 2018 at 12:12

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