Banding on Alumamark

[Bill Jermyn]

I'm getting banding on satin silver Alumamark. The image is an RGB tiff bitmap. It appears fine on the screen. I imported it directly into Corel without running it through any other program such as Photograv. Text and graphics look fine. Any ideas on how I can eliminate it?

I'm using speed 21, power 10, 600dpi.

[Tom Bull]

Do you have image resolution and dpi of engraving in sync.? Can get strange results if for example one is at 300 and the other at 200.

[Scott Shepherd]

Bill, I'm afraid you won't like my answer. I went through that same thing. Got in touch with the alumamark people and they said "Oh, yeah, that color is really tough to do. It bands worse than anything else we offer".

In fact, the lady told me that some banding, depending on the direction is part of the manufacturing process and some times they have batches that really show that pattern more than other batches and they'd be happy to swap it out, but in the end, it's still a problem material for them.

[Steve Chalmers]

Bill,

I do 50 plus sheets of Alumamark every month. . .a fairly even mix of Satin Silver and Gold. What Scott told you in correct in that the Satin Silver is the toughest to work with of any of the colors.

I've virtually eliminated the banding by using 23 PWR 100 Speed 1000 DPI. . .this is on a 50 watt Universal. . .but I will still get an occasional sheet that gives me trouble.

If you can, switch your customer to gold. . .it's a bunch easier to work on.

Hope this helps

Steve

[Frank Corker]

I think the banding is caused by the dithering process for the Epilog drivers in this case. It is a form of halftoning. You might find that a slightly bigger or smaller size will illiminate this. I have to admit when it comes to this type of graphic on aluminium and stainless steel the photograv dithering does the trick.

[Bill Jermyn]

Well, I started with a tiff image. I re-drew it as vectors, same problem. I also increased the dpi from 600 to 1200 and adjusted the settings with little change in result, so I'm thinking that probably it is the Alumamark itself, as Scott and Steve suggested. Maybe I'll try Cermark on aluminum. Thanks for the feedback.

[Dan Hintz]

Redrawing as a vector file will have zero effect on the bitmap fills, which is where the banding is the most prominent, unless you replaced the bitmap fills with "true" fills (since Corel can now output at the laser's native resolution).

If there is a difference in sampled versus designed resolution, Moire effects will cause banding, as Tom was alluding to. Doubling the sampled resolution from 600 to 1200 dpi won't change the overall effect, only possibly change its frequency (depends on the designed resolution).

I've never used Alumamark, so it very well could have issues with banding (though I cannot come up with a valid reason why any substrate would exhibit such a highly-periodic pattern over such a short area), but the small image you posted screams "process issue" to me. One easy way to check that is to draw several 1" squares of varying shades of gray directly in Corel... no importation of bitmaps. Send it to the laser directly... if there's no banding, it's either a processing issue or a hardware issue. My bet would be no banding on such a test... though I was wrong once before, sometime back in 1983, I believe.

[Scott Shepherd]

though I was wrong once before, sometime back in 1983, I believe.

Dan, I think you got that mixed up. Your WIFE was wrong once :D

[Dan Hintz]

Dan, I think you got that mixed up. Your WIFE was wrong once :D
We sold our set of encyclopedias long ago... not needed, Amy's knows everything.

I tell her there's nothing better than me, and she tells me I'm better than nothing.

[Scott Shepherd]

Call Horizon's or whatever the name of the company is. They have tech support and are more than happy to help.

[Bill Cunningham]

600 dpi for phtos always seems to turn 'muddy' for me.. I use about 30/30 P/S at 150 dpi, and back off the focus about 1/8" and get great pictures even on the silver.. Give it a test on on a small piece.. I also use photograv with greyscale images.. Even if the old PG would use RGB I wouldn't

[Andy Joe]

I had this problem once before, i made a couple of adjustments and i dont end up with any banding now, im not sure which one fixed the issue so i will just tell you all of what i did. First the way i understand it is dpi is a translation for the printer dirver to know size and locations of your drawing in corlations to the papper size(or laser bed in this case). For example if you pic is 150dpi and the laser is set for 300 dpi it will shrink you pic to force it to show at 300 dpi. So rather then changing my dpi i made and adjustment to my ramp start and stop speed, then i processed through photo engrave, then i added a black box on both side the whole height of the picture. Just as tall but only 1/8' wide. Then adjusted when my laser speed up and slowed down at start and stop of pic to being off my pic and over that box. I also adjusted the air pressure at my nozzle to increase the air flow. Im not sure which helped, i have tried them all on acrylic to fix banding and depending on what type of banding i get each one fixes a difrent problem. Im not good at spelling or explaining so i hope you understand what im trying to say