ZING LASER Banding

[Philip Little]

So I have this irritating "banding" going on, it shows up mostly on plastics. I have changed out the X belt and motor, and a new tube was done yesterday. I have also cleaned the machine very well lenses and mirror are all good. Alignment is fine also.
I have talked to epilog they say it is the belts "it's just that model". I have had this machine since new, and I am very sure it didn't do it when I got it, anyone else have this?
I can get by on most of the work I do , but on a large raster job it sure is annoying.
Attached is a pic of it on red cause it looks the worst..401367

[Kev Williams]

Banding happens with nearly all machines in one form or another. I say 'nearly all' because my old 1997 25w Universal (renamed New Hermes Optima) absolutely does not, has not and probably never will produce any banding! My BIL now owns that machine and he's never seen any banding. When looking at the Uni laser's cut path under high magnification, the results resemble a perfect diamond-shape pattern, it appears that each pulse dot fires perfectly between the 2 dots above it. This staggered firing, however it's done makes for absolutely perfect 'mass black' engraving, such as large areas on plex or glass. None of my other machines can do that without creating a dithered pattern to run.

All my other machines will leave bands. What causes it? Don't know, but every mfr. has their own excuse...err, reason ;)

Below left is the original photo that my Gravo LS900 quite nicely reproduced on the right (done on non-laserable black/white material):
401407401408
but nice tho it may be, check out the banding up in the clouds, and some banding is visble on the snow...

What to do about it? Don't know. Changing up the settings can help, or not. My LS900 will band horizontally or vertically, or not at all. My new-to-me LS100, which engraves phenomenally clean and nice, it bands diagonally..? I don't get it. My CCC and Triumph also leave bands...

My only suggestion is try a second pass at different resolution settings, and change up the speed and power a bit maybe.

If your Zing has a photo or grayscale mode, you can try going with 70 or 80% black. In pure photo mode, I've found basic green works well. Doing this creates dithering, which breaks up the laser's firing into a more random-type pattern, which can really help, as some banding is caused by the laser's cut path overlapping in places, which get more heat and show up as bands...

[Philip Little]

Hi Kev
Thanks for the input at least I'm not alone..
Gonna try more settings..

[Kev Williams]

below are pics of some plex I test engraved on my LS900, probably 12 years ago when I was having banding problems while engraving plex...

each of the 'strips' is about 3/8" tall, and ran at 50 lines per inch I think it was. The top 3 strips were run at different speeds, slower each time. Notice how the beam path 'wobbles'. Now, one might think that it's a mechanical issue, loose belt or bad rail bearing-- but 2 things: first, check out the bottom strip, note the beam path is near dead straight... That wasn't a raster pass, that strip I just drew lines at the same spacing and ran them in vector. My 100% vector speed is pretty slow, but the 3rd strip was rastered at nearly the same speed, and it wobbles. And the best proof it's not mechanical, is that each strip was engraved twice- if it was mechanical the beam path pattern would be random, and the second pass would've obliterated the first pass. Instead, the second pass on all 4 strips lined up perfectly...?
401442

So as the beam path wobbles, what happens is that in certain places across the X path the paths will overlap more than in other places. Depending on the heat-sensitivity of the material you're engraving, you may get banding. Plex is fairly heat sensitive, so as you can see in the top strip, which I ran at high resolution, the extra- or lesser- overlaps create hot spots that reflect more light than the not-so-hot spots. In this case it results in vertical banding...
401443

Gravograph's explanation for the wobble was 'necessary for photo engraving'. I find it fascinating that laser can dead-on repeat the wobble like that, but for the life of me I can't figure out why it would be necessary, for photos or anything else... ;)

so-- for fun you might try a similar experiment with your Zing-- clear plex, 3/8" or so wide rectangle, 50 lines per inch on the Y axis and see what you get :)

All this pertains to metal/RF lasers. Not sure this type of banding occurs with DC glass lasers. But I have had power-change (for lack of a better term) issues at times that cause a form of banding... No clue of the cause!