Laser Cutting

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Help me to understand "focus" (lemmy.dbzer0.com)

submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]

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I am playing with a laser cutting/engraving machine. There is a small wedge with the machine, with 3 widths, each width having a text on it :

cutting 7mm wood (close to the surface)
cutting 5mm wood
engraving and cutting 3mm wood (far from the surface)

It allows you to set the height of the laser. I try to understand what would be the best setting to engrave rock. I understand that to etch on wood, you want a large laser to burn it instead of vaporizing it. There are even toturials on defocussing the laser to get better blacks (larger laser, more burning, less vaporizing). Random example : https://www.youtube.com/watch?v=Xcg1y2cQl-o

Now, I want to engrave rock. I don't want a larger laser. I want the hotter tinniest spot on the surface of the rock. I start to get great results on black rock (1000mm/s, 10W, 3 passes).

To get the more focused spot, should I go with the setting close to the surface "cutting 7mm wood" or with the seeing far from the surface "engraving and cutting 3mm wood" ?

Has any of you tried to engrave rock ? Do you have tips ?

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[–] [email protected] 2 points 1 year ago

I have not engraved rock on my current laser, but several years back at TechShop (still bitter they are gone) I did some slate tiles and they came out well. I don't know where they were sourced from because I found them lying around.

I didn't change the laser lens or do anything out of the ordinary for it. I think they had a little stick that was cut to the laser's focal distance, and I used that to focus it right on the surface of the stone.

It left a slightly rough, matte white surface where I had engraved. This was probably at maybe 30-50W with air assist on?

Not sure what results you would get from other kinds of rock, e.g. granite. My gut says you'd want to avoid rock with lots of reflective crystals in it, e.g. quartz or silica-bearing rock, but I don't have any solid evidence for that.

[–] [email protected] 1 points 11 months ago (1 children)

Did you ever find the answer to your question?

It will depend on your lenses and their corresponding focal length. Normally for cutting you want that focal point to hit halfway through the thickness of the material you are cutting. For etching slate I would put that focal length right at the surface.

The standard focal length for a k40, which is the laser I use, with the stock lenses is 50.8mm I believe.

[–] [email protected] 1 points 11 months ago

Thanks. Actually I tried mnémotechnique settings and the focus does barely nothing. At least compared to speed and power. And even to precisely etch wood, I can't distinguish any variations of focus. The laser beam is really thin.

[–] [email protected] 1 points 1 year ago

First, it's important to know what material you're cutting because you don't want to release any harmful gases or dust.

You usually want the focus to reflect an accurate distance for the height of the material you're cutting. You can test minor adjustments if you have sample material to get the best results at the same heigh before cutting the final material.