Get Results with Little to No Burning or Charring
While scrolling through some Reddit posts. I came across a post asking for assistance in laser cutting MDF. When you see the picture below, it becomes obvious that this Redditor needed urgent assistance in learning how to laser cut MDF.
So, What Were They Doing Wrong?
From the original posting, the Redditor indicated that they had been trying to laser cut 1/4 mdf (6.35mm) thick MDF with an 80W CO2 laser machine. The settings they were using were 2 passes at 40% power and 15mm/s. The issue they were having is that by the time the laser beam had cut through the MDF, the surface had started “turning into charcoal!”
Based on previous experience of cutting MDF, I knew that it wasn’t the easiest material to work with. Especially, as it gives of toxic fumes when laser cut. (See What can a Laser Cutter Cut for details.) However it shouldn’t be anywhere as bad as the Redditors photo indicated.
So I decided to do a quick check to remind myself how difficult it was. Luckily I had a Piece of 6mm thick MDF available, while slightly thinner than the 1/4″ MDF used, it would be close enough.
My Laser Cutting MDF Settings
I have a 50W CO2 laser machine, so I was already at a disadvantage compared to the 80W the Redditor had. Checking my LightBurn Material Library, I already had some settings for 3mm MDF (22mm/s and 59% power) so I just halved the speed and went for it. NB: 59% power on my laser machine equates to around 48 watts at the work surface.
I used a 2″ lens and achieved a clean cut, with just a little smoke marking the top surface. Since I had the lid open to take a video, the extraction performance was compromised. This was probably the reason for the smoke marks. Air assist was at my normal setting and I was using the standard aquarium pump supplied with the machine.
Because this was the lens and nozzle that came with the laser, the distance of the nozzle from the work surface was 16.4mm. This is considered a bit far for laser cutting but it still works. If I was using a setup that was focussed approximately 5mm from the surface, I may have been able to run at 12~13mm/s. There was no soot residue on the edge of the cut. This is usually a good indication that the Laser power / Cut Speed settings are correct for the material thickness.
PS: I would probably run this job in the future at 10mm/s as there were a few tags left on the cut.
How to Laser Cut MDF – Important Considerations
Here are some real world considerations to take into account:
- When cutting any organics, you need to run at the safe maximum operating current for your tube.
- Then you carry out some cutting trials starting at high speeds, gradually decreasing the speed until you are consistently cutting through the material.
- I normally decrease the speed by an additional couple of mm/s to take into account any variance in the thickness of the material.
- Air assist is needed to protect the lens and to blow smoke out of the kerf (the thickness of the laser cut). This is because the smoke will disperse the laser beam. You do not need excessive air pressure, an aquarium pump is more than sufficient.
- The air assist becomes more effective the closer the nozzle is to the surface of the material.
- The closer the air assist to the material, the higher the chance of contaminating the surface of the material with smoke debris.
- When air assist is too low, it is possible for the laser beam to ignite the smoke.
- This video on Relief engraving and Air Assist gives a good overview of how air assist works in laser cutting and engraving.
- Pro Tip: For acrylic, a high air assist can decrease cutting performance as it cools the cut down.
- Masking is only really useful when used to protect the surface from debris falling onto the surface. To minimise contamination, you need to get your airflow across the top and bottom work surfaces optimised. So that the smoke is whisked away as soon as it is generated. Masking offers minimal protection against an excessive Heat Affected Zone (HAZ).
- Good effective extraction is needed, you need to be able to see the smoke being pulled away from the work piece.
- This video on Incised Engraving and Air Flow Management gives a good overview of how to improve the air flow over and under your work piece.
- Lenses play a big part in laser cutting. Make sure that they are clean and seated correctly in the lens tube / nozzle assembly. The best cutting lens is a 2.5″ GaAs lens. But you should be able to cut up to 9mm with a 2″ lens. I only use a 4″ lens for thick foams (>20mm thick) because of the longer focal depth.
- This video on Lens Performance Comparison Data gives you all the real world data you could want regarding the cutting performance of different lenses with a variety of materials.
As the Redditor was clearly having problems with cutting MDF with an 80W laser, there must be other factors in play that were causing the issues.
How to Laser Cut MDF – Possible Performance Issues
Things to check for cutting performance issues:
- Clean the optical path, mirrors and lenses. Check for any damage to mirrors and lens surface.
- Ensure the beam alignment is ok, especially that the laser beam passes vertically through the centre of the lens.
- Check out The Ultimate A to Z Tutorial of Beam Setting for more assistance
- Make sure you are cutting at the correct focal height, a good indicator is the thickness of the kerf at different focal distances. You want to be cutting at the distance where the kerf is the thinnest. Don’t assume that a 2″ lens will focus at exactly 2″ there is always some variance. This is why you need to do checks every time you use a new lens.
- Is your laser bed level with your nozzle across the width of your bed?
- Check out Setting The Work Table Level for more assistance
- Do you have a blunt laser beam? You need to carry out a mode burn test. This is to determine if the beam coming out of the tube is sharp (a tall thin cone) or blunt (a short fat cone). If it’s blunt, then you will need to get a new tube for laser cutting, although you could still use the blunt tube for engraving.
- Check out How Laser Cutting happens – this video shows how to do a mode burn test.
- Is your laser tube underperforming? I.e. is it only outputting 40 watts instead of the expected 80 watts? The only way to check this is by getting yourself a laser power meter and checking for yourself.
How to Laser Cut MDF – Additional Resources
You may wish to check out this video by Russ Sadler called Poor Laser Cutting Is Rarely Beam Alignment. Where Russ explains a number of reasons why a laser s cutting performance may be less than optimal.
Frequently Asked Questions
How to Laser Cut MDF
Set your laser to it’s maximum safe operating power with air assist on high. Use a 2″ lens for MDF thicknesses up to about 6mm and a 2.5″ lens for thicker than 6mm. Cut some test 25mm squares, starting at a high speed and gradually decrease the speed. When you are cutting through the MDF consistently, take a speed 2~3mm slower to take into account variations in the material. Ensure you have good extraction and a decent airflow across the top and bottom work surfaces. A good cut should give very little soot on the cut surface.
Best MDF for Laser Cutting
MDF is an engineering wood product held together by adhesives. It has the same issue as plywood with the potential to form formaldehyde gas. However, there are now some “laser friendly” low formaldehyde mix MDF sheets on the market. Engraving is easier on MDF as it has a more consistent surface, although the results can be quite bland. You can also get MDF veneers that offer the benefit of a consistent cutting performance, with the beauty of a finished surface.
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Last updated August 26, 2021
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