White dust with air assist

Hello,
I have a custom built laser, when I turn the air assist on, I get this white residue on the engraved areas. It looks like the smoke sticking to engraved parts. It comes off by touching it with your fingers or blasting it fairly hard with compressed air.

In this image, you can see right next to the T in Think, there is some of this white dusty stuff. the areas around it have been dabbed with my finger and you can see its come off.

What is the best way to avoid this? Some engravings are completely covered and it ruins the piece…

A few tips:

  1. While engraving reduce air assist to where it’s just enough to protect the lens. This prevents the air assist from forcing smoke residue back down onto the material
  2. Setup a method by which you have a current of air passing quickly over the top surface of the material and being quickly evacuated out of the laser chamber
  3. For the cut, ideally you’re getting through in a single pass. This should have most fumes coming out beneath the material. Also, elevate the material so that there’s good airflow underneath the part. Use a healthy amount of air assist to get the cleanest cut possible. Make sure you’re venting air out of the chamber at a good pace so it’s not lingering.

Side questions:

  1. What material are you burning to?
  2. How are you getting such a dark burn? Or has that photo been retouched?

As an additional clarification to @berainlb … the direction of the engraving has consequences.

If your machine draws air out the back, the engraving should start closest to the front. Air flow should move any debris towards areas of the material that have not been engraved and away… This helps a lot.

Good luck

:smile_cat:

As @jkwilborn pointed out, airflow is important and dynamic. Since you built it yourself, does it have a variable focus depth on the laser? If the laser enclosure allows it, if you could try to raise the laser optics up higher and adjust the focus downward to hit the correct depth. That might allow for better air movement to better evacuate the smoke. Hard to say without pictures of the setup but just a thought.

We all love diy here, so it seems it might help if we could see how your head/machine is physically configured… post a few photos :pray:

There are many tube/lens options depending on the type of head you have installed.

:smile_cat:

Currently I have the exhaust being pulled from the bottom of the machine so the exhaust fumes must be pulled down onto the surface of the work and then around the edges. I am working on the proposed solution to pull the exhaust fumes out of the back of the machine. When I get the solution implemented I will post some pictures.

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I designed a duct that brings the exhaust right up to the back of the bed. It appears to be extracting fairly well, but the smoke embedded on the burn is worse than ever before:

It seems you’re generating quite a bit of smoke. I didn’t realize how deeply you were engraving from the first photo.

What’s your air assist situation? Is it at a minimum? There’s a lot of turbulence in the smoke so want to make sure I understand where that’s coming from?

How is air entering the chamber? Ideally you’d have a way for air to enter the chamber from the front in this case. While it looks like smoke seems to be get pulled out once it reaches the back the smoke is lingering for some time above the surface.

On an unrelated note your laser makes the most peculiar noise when firing.

My air assist comes from an air compressor with a control valve. It is incredibly low. I can barely feel any air coming out. If I increase it, the situation worsens as the smoke is blasted straight into the burned area.

Temporarily, I have a rubber foot propping the front of the lid open so air can come in from the front and pull across the wood to the back.


I completely agree, my K40 has a very different sound and my friends big 100w Chinese laser also sounds very different.

It sounds like you’ve got all the basics covered. What do you see in how the smoke behaves that’s different than previous?

I could theorize that the smoke is getting brought down toward the wood as it’s exiting but not getting pulled away quickly enough to keep it from depositing on the wood.

What type of fan are you using for the venting? How much airflow can it manage?

A couple of things to try:

  1. Try placing the work piece closer to the front of the laser
  2. Try placing a fan at the opening of the laser to see if you can literally blow the smoke away before it gets evacuated

Can you cover the honeycomb so the air flow is ‘drawn’ where you want it and not ‘wasted’ going down through the honeycomb where there is no smoke to remove … ?

:smile_cat:

This is the blower that I have attached to the laser enclosure:
VIVOSUN 6-Inch 440 CFM Inline Duct Fan https://a.co/d/1pAulAm

So I put some wood over the bed material right in front of where the exhaust duct lines up with the bed. It didn’t seem to make much of a difference.

I also created some vent fins to try and “straighten” out the air, it made no difference. Here is a rendering of the duct as it’s hard to get a picture of it.

I’m not sure that 440cfm is enough air flow, and maybe some of the tubing is too long or constricting airflow. I don’t know what other people exhaust setups look like or how much their blowers can pull.

In principle that should be plenty but I suspect you’re onto something with the specific path that your air has to go through. I’m actually surprised this is the fan you have given the rate of evacuation. If you haven’t already, try sealing all potential areas where you’re losing pressure on the outfeed.

If you can straighten out the exit path might be worth explorting.

An auxiliary source of air blowing over the top of the surface might work around some of this as well.

If you covered the entire honeycomb that would be the best… anywhere it can go around the material it will…

:smile_cat: