Stainless steel reflecting laser.

[Mike Gaston]

I was just messing around with a piece of stainless that I had with a brushed finish(not polished like a mirror) and was getting good results.It was very slow 2% speed 100% power. The stainless was not coated with anything. All was going well the I noticed a light behind my #3 mirror.I paused the laser and found that I was burning a line across the #3 mirror access door. Apparently it was reflecting back through the lens and off the #4 mirror and just missing the #3 mirror.

Any suggestions on how I could stop this would be greatly appreciated.

[Dave Jones]

If a thin layer of the metal is melting, it becomes a perfect reflector. It doesn't matter if the surface looks shiny or not before lasering. I've read that this is a big problem in high power lasers when cutting aluminum and some other metals.

Guess 1 is that your mirrors are a little out of alignment, or the reflection might have made it all the way back to the laser tube, and possibly damaged it. You may be lucky.

Guess 2 is that possibly if the piece is on an angle then maybe less of it will reflect. (I don't know)

Guess 3 is maybe you shouldn't try this.

Guess 4 Cermark seems safe since it causes a black, non-reflective coating to be formed, rather than melting the metal.

Disclaimer: These are just guesses. I know nothing about this subject and have no idea what will cause or prevent damage to your laser.

[Richard Rumancik]

When I was first experimenting with my laser several years ago, I had heard that reflecting the laser light back into the laser itself could cause damage. I contacted Synrad about the risk and they did not give me the impression that engraving directly onto bare stainless could damage the laser. However, they did suggest that if I was concerned, I could incline the workpiece slightly so the reflected beam cannot re-enter the lens. I never actually tried the idea however.

The risk of angling the workpiece is that the reflected beam will hit somewhere else. It will be greatly out of focus and attentuated (since you won't get complete reflection) so it might not cause a problem, but be aware of the possibility of a stray beam. Maybe you would need a piece of black aluminum "target" around the carriage, or on the inside of the lid, to absorb any reflected beam.

You might do some experiments with a plain mirror and the red beam pointer, to test what angle is needed so that the return beam misses the lens. You don't want to use an angle greater than necessary, as a non-flat workpiece will reduce your depth of field. In other words, the beam will be in focus in some areas and not in others. If you are only doing a line or two of text, angling the workpiece might be an option, as you can focus coincident with the text line. I don't think it would work for any graphic of significant "y" dimension.

When you say you were getting "good results" did you mean that it was actually leaving a black mark? Or a frosted mark? I didn't expect that you could get much of a mark on bare stainless with only 30 watts. (Mine is 30 watts and it will make a slight frosted mark, but it is not particularly useful as a functional or decorative mark.)

I doubt that there is any possibility of melting of the stainless in this situation, but I am surprised that a brushed stainless would reflect that much back up the lens.

[Rodne Gold]

We can engrave Stainless with 25 watts , vector mode at VERY slow speeds , like .1% speed without any marking paste. It's worthlessly slow and the intensity of light generated is extremely high , very bright and white at the point of contact. We tried this once only.

[Bruce Boone]

I do titanium a lot, and once the reflected beam melted one of my X axis carriage wheels. I put some aluminum foil duct tape on the underside of my carriage, and it has prevented any further damage from reflected beams.

[Bill Cunningham]

Ahhh Duct tape to the rescue yet 'again'!!
Red Green would be proud:D