Autofocus on thin foil material

Hi there!

I recently bought a second-handed MK4 fabkit (Smoothieboard), which I am controlling with lightburn. So far, after some realigning and cleaning, the system is performing according to specs.

One of the challenges I’m currently facing, is cutting of very thin foil, which has a thickness between 100 and 200 µm. I noticed that the auto-focus Z-switch of the machine requires quite a bit of force to activate. I’m afraid that I will force the ball switch through the foil when I perform auto-focusing.

One thing I tried is focusing on a sheet of 1 mm PMMA, offsetting the z-axis by 1 mm (raise bed by 1 mm) and try to cut. However, the machine is always returning to the auto-focus z-height before starting the cut.

Does anyone has some advice or some tips and tricks on how to approach this challenge?

Thank you for your response! :slight_smile:


In Lightburn you can set a Z offset for each layer to adjust for that, which should allow you to do what you want to achieve…


Thanks, I will give it a try!

Has it worked with the tip of CescoAiel?
BTW: wouldn’t you want to have a layer of 1mm material underneath anyway to have it lay down flat enough?

Hi there,

Sorry for the very late reply! Yes, the tip of CescoAiel helped out!

I use a 1 mm sheat of PMMA for the autofocusing (the thin material will not trigger the Z limit sensor). Subsequently, I offset the Z-axis with 1 mm, so the laser focuses directly on the bed itself (where the thin foil will be positioned). Usually, I place the foil in between a couple of have books to straighten it out before laser cutting.



Nice to know. And no worry about the reply time. So you just have an special layer/color for the tinfoil material now, which defines the z offset?