Sorry I missed this the first time...Originally Posted by mike wallis
For one thing, non-ferrous metals like brass, copper and bronze don't respond well to a fiber, if at all. And because they don't respond well, they, and copper in particular, become mirrors able to reflect the beam back up into the lens. Personally, I'm of the opinion that while this is true, what would normally reach the lens would be so out of focus as to be insignificant. I accidentally put my arm right thru the beam one day to open my exhaust's blast gate while engraving black anodized at 100% power. The only reason I knew I'd done it is the laser's 'music' stopped playing-- didn't feel a thing. Not a smart move, but it did tell me that an out of focus fiber beam had no effect on my skin. Counter point-- twice with the fiber and many times with the LS900 I've been hit with beam reflections (engraving curved items) and in all cases, I was a good 2' from the source of the reflection, and in all cases I felt a very pronounced amount of heat. SO-- it's definitely possible an errant reflect could damage the machines- and your eyes if you're not wearing glasses.
More on not responding well, I have a piece of solid copper, and some copper plated cups I've tested. Solid copper just won't mark. Occasionally I hit a speed/power/freq setting that worked somewhat, but it wouldn't repeat. Same with the cup, once in awhile I'd get a dark brown burn, but right next to it a faint mark. The burn was simply that the laser found its way thru the coating and was burning the stainless base metal.
As for engraving stainless--
On mirrored or otherwise shiny SS, setting the laser at lower power and a higher freq results in a nice bright mark that is very high contrast to the shiny surface. How bright depends on settings, and also hatch spacing. Too much power and the result starts to go yellow. Too tight a hatch and the result is 'flat', but in certain cases this is a good thing. Black Cermark on shiny SS is counter productive because whatever is reflected from the background surroundings washes out the marking. If there's nothing but blue sky or white walls reflecting (rare in real life
For mill finish or #4 or other non-shiny finish, you simply can't beat Cermark. It's main pain is the extra steps involved, but the results can't be beat. I do a LOT of stainless, I just bought my 3rd 500 gram bottle this YEAR. Black via Cermark simply works, and is very popular with my customers. Give up spraying it and start brushing it, it's easier, no overspray to worry about, in my testing I use half as much brushing as spraying (I'm taking 1 to 4+ square foot operator panels)...
Even for small plates, a fiber isn't the best option for black. For deep engraving to keep some engineers happy, the fiber works okay. It's actually slower than tool engraving, but that extra time is more than evened out by NOT having to sharpen the laser beam
I could keep going but that's the jist of it, based on my experiences. Been using Cermark for 15 years, and for all it's cost and PIA factor, until something else that actually works comes along, I'll keep using it
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