Weak laser power during auto-calibration / Understanding laser calibration

[brent113]

@SabinSnorlax

Reason #1 is to understand what’s going wrong with my laser auto focus calibration.

Only thing I can think of is the power is too low or the speed is too fast for the material you’re trying to calibrate on. You could investigate further with M1028 S6

@SabinSnorlax

What is the physical meaning of the “laser height”

It is the Z coordinate where the laser is in focus with a material thickness of 0.

@SabinSnorlax

• What is the connection between laser height, thickness of the material, the Z-coordinate after calibration, and the actual distance between lens hood and material?

Z coordinate = laser height + thickness of material. Lens hood will have to be adjusted by you to have a few mm clearance above the material, enough that with Z steps down into the material it won’t hit. Or just remove it like I did, it’s only purpose is as a ‘shield’ against stray laser light - just wear your goggles.

@SabinSnorlax

• Why do I keep seeing different values of the laser height tossed around, say 21mm or 25mm etc.?

There is a slotted lens holder up in the toolhead - by changing that you can change the laser focal length. Not every laser module comes with it assembled the exact same way.

@SabinSnorlax

Shouldn’t there be a “universally correct laser height”

Yes, and it’s when the beam waist is in the middle of the kerf you are cutting. There is not a fixed distance, however, it’s a functional definition.

@SabinSnorlax

Or to put it another way, shouldn’t there be a “universally correct distance between the lens hood and the material”?

Since this is something the instructions (at least the online ones) instruct you to adjust to a few mm, I’d say yes, and it needs to be adjusted manually (if you’re using a lens hood at all).

@SabinSnorlax

• What’s up with the lens hood, does it serve any role beyond added safety?

No, other than additionally possibly funnel dust and soot up into the lens area.

@SabinSnorlax

I saw this hood being mentioned as not strictly necessary, but is it “better” or “worse” to keep it on? (again, talking not just about safety, but also lasering quality etc.)

No functional improvement to keeping or removing that I’m aware of.

Section 6.5 from here: https://support.snapmaker.com/hc/en-us/articles/360041254874-Snapmaker-2-0-Laser-V1-0-0

6.5 Adjust Lens Hood

During the laser engraving / cutting process, if you feel that the lens hood is too far from the surface of the material to have the best light-blocking effect, you can follow the steps below to adjust the settings for the lens hood:

Sounds pretty subjective to me.

I’ll also add I changed my laser focus length to 37mm (by adjusting the slotted lens holder). Has some advantages and disadvantages, but it’s better for me. Advantages include more clearance to the material, less smoke gets drafted up into the lens, deeper depth of focus (which means less variability when engraving surfaces that aren’t perfectly flat). The main disadvantage is the longer focal length will reduce peak beam intensity, making cutting harder. I only use it for engraving though, so that’s not an issue for me.