Hello. I have an Omtech 80W laser using light burn 1.7 with a Ruida controller. I have been asked about engraving bricks for a Veteran’s memorial. They already have the bricks so purchasing bricks specifically designed for laser engraving is not an option. The bricks are actually granite. I did a couple of samples for them and they love the look but they want the engraving to be deeper. The lenses and mirrors I have are the ones that came in the laser when I bought it, but I have read and watched several videos that mention using bigger lenses and mirrors. Is that accurate? If so, what size/type should I use and how much would you charge per brick? Each brick has 3 lines of text up to 20 characters per line. Thanks in advance for the help!
To get deeper engrave, have you tried running multiple passes and or slowing down the laser travel?
Less SPEED -and/or-
MORE Passes
= more laser energy put into the engraving, which should yield deeper results
Can’ comment on mirrors but they just reflect the beam, so I can’t see what they are referring.
bigger lens, probably meaning a longer lens, focal length wise.
You left out a couple parts here… what lens you are using. How deep did you go and how more is deeper?
Most of these come with a 1.5" or 2.0", with the two inch seemingly more popular. You should know which you have…
Approximate spot size and dof for different lenses. Based on a 6mm input beam size.
| Length | spot size microns | dof mm |
|---|---|---|
| 38.1 - 1.5" | 154 | 1.54 |
| 50.8 - 2.0" | 205 | 2.75 |
| 101.6 - 4.0" | 410 | 10.92 |
| 177.8 - 7.0" | 718 | 33.5 |
If you use a longer lens, you could go deeper and remain in focus. You will need some type of air assist to blow out the debris. Best application is to focus in the middle of the material.
Good luck… pretty tough stuff… can you show us a photo?
How much wear and tear is that going to put on my machine doing so many bricks though? Going high power and slow speed for multiple passed on 900+ granite bricks seems like it will burn out my laser pretty quick. Not disagreeing with you, just hoping for the safest option.
I will post a picture soon. I currently have a 2" focal length lens that is 0.71in in diameter. I am a newbie and not 100% sure how I can accurately measure the depth on this, but I believe I went about 0.8mm and I am guessing I will need to go about 1.6 - 2.4mm deep to meet their desired look. As for the mirrors, does a higher quality mirror provide a deeper/cleaner cut/engrave? Or is that mainly based on the lens focal length?
You’re kinda-sorta stuffed in a box:
- A CO₂ laser is not the best for engraving stone: fiber laser example
- The “bricks” aren’t particularly well-suited for laser engraving
- You (or they) want a specific result / appearance / depth that requires more energy than your laser can deliver in a single pass
AFAICT, you have several unpleasant alternatives:
- Get the right laser for the job, cost what it may
- Abuse your laser to do the job, cost what it may
- Talk them down on the engraving depth, which may affect how long the engraving lasts outdoors
- No bid = turn down a job that will lose money
If you decide to just abuse your laser and get it done, then set the price to cover buying at least a new tube & power supply.
Also, add enough labor + time to justify handling that many stones, because you’re gonna hurt after the first hundred or so. 
What is the right laser for this job? Does anyone know anything about this laser? Seems awful cheap for what it is…
It’s an 80W glass tube co2 machine, with a huge work area. As you can see with your example they do work…
I think you can do it, just add some more power and focus down about 2.5mm into the surface…
Might want to do one, and see where all that rock goes… might have to do maintenance of the basic machine surfaces more often.
I’ve done this on my 40W, really not excellent results…
I have a fiber, so I use that.
Good luck