Some time ago we ordered a K40 style laser cutter like the one here: Getting Control over a 50 Watt CO2 Laser Cutter from China | MCU on Eclipse
We replaced the Nano M2 with a Mini Gerbil, which works fine.
What we couldn’t manage was the kerf. We get the following values:
Is the huge L inlet caused by a cheap lens? I appreciate any hints 
If your goal is to get a more even cut profile, there are a couple of things you can try.
Try setting your focal point half way into the thickness of what you are cutting. This will give more of a half hour glass shape where the widest part is in the middle.
A longer focal length would also help.
Up your power some to get more power through the cut so the bottom becomes a bit wider. This may also make the top a bit wider, so it’s a bit of a trade off.
Also make sure your lens is installed with the curved side up.
Thank you for your help. We’ll try and report back.
What lens are you using and with what material/thickness? … this is seriously poor optically, to cause this…
I’d expect a kerf of ~0.20mm or Loutlet, from one of these…
Where is your point of focus?
Have you tried a ramp test?
Set a sample piece at an angle and cut along it. If you know the height at each end of the cut, you can find the height with the best cut and then set that as your height for future cuts, using a depth gauge (as simple as a laser cut piece between the nozzle and the work piece).
Thank you for your help. Flipping the lens improved the quality. Not perfect, but better.
The fact that the lens was orientated wrong is a bit embarrasing… 
If this is the last time, you’re doing great… If I got a nickel for every time I’ve done something stupid, I’d be in the multi millionaire club
Hop on the boat with the rest of us and just enjoy your machine…
