Laser starts fire while cutting

Community Laser Talk
1

Hey everyone,
Can anyone tell me what is happening with my laser. Its just 2 months old, I didnt work much with it.

I have Sculpfun S30 33w. I use same material all the time. On begining it worked very well, there were almost no burns at all.
2 weeks ago I dont know what happened but laser starts fire while cutting material.

So, long story short:
Material - mdf 3mm coated (material is same all the time so material is not problem)
Focus - checked with metal tube that comes with laser
Lens - changed, new one
Cutting speed - 450mm/min
Power - 80% (never went above that)
Passes- 1 pass
Air-assist - original sculpfun… its always on or it would be real fire

Engraving is great, no problems with that… I engrave on 5000mm/min speed and 70% power… If making sufrace lines I set 2000 mm/min and 70% power and then there is no trace of any burn…

(same result is when I put higher speed and more passes, for example 1250mm/min and 4 passes)

Link of 3 videos below

Thank you in advance

2

One more video

3

No material is the same. They can have changed the glue type, the coating type etc. The material still can be the reason.

Too slow. Never cut below 600 mm/min, for the 33W I recommend never cutting below 1000 mm/min.

Increase according to speed increasement, e.g. 1200 mm/min - 3 passes.

4

What I saw in the video looked like turbulence from the laser cooling fan. It did not look like the nozzle was ejecting air.

Reduce power to 0.5%, run a test, and pull the air assist off the nozzle and check for air pressure.

5

It worked well for 2 months at that speed…
Even 2500mm/min and 7 passes leave huge burns…

6

Yes, true… When I put my hand near laser its like I put hand through car window (very windy)… What is solution for that… ??? On burns I can see air direction… sometimes its inside burn, sometimes outside…

7

Are you sure your laser is focused correctly?

8

By focus you mean distance from material ?

9

Yes. You can get some burning because the laser is out of focus.

10

Yes, focus is ok. I have metal tube from sculpfun that i put under laser for measure so it cant be wrong…

11

Have you cleaned your lens?

12

yes. I clean lens before every start… this is new lens actualy… i dont use machine often… maybe 3 times per week, total 5 hours… small projects mostly