Banding! Help

[Carlos Eduardo]

First, excuse my English, I'm using Google Translator.

I'm engraving pictures in black anodized aluminum and is showing horizontal and diagonal stripes with equal spacing between them . I am using the picture in grayscale and engraving in the option of 3D Advanced Driver. What may be happening?

Machine: Versalaser 25W

Thanks

Carlos

[Craig Hogarth]

Carlos, I recently went through this problem myself, although i did not have the diagonal banding. ULS has some upgraded bearings that they replaced free of charge for me (i had just purchased new bearings a month prior) that were designed to reduce banding. While it hasn't completely eliminated it, the bands are hardly noticeable only if you look for them. My wife doesn't see them and thinks I'm crazy.

[David Dustin]

I see thim on my ULS if I have the speed set too high.

Reducing the speed, reduces the banding.

David

[Rob Bosworth]

The pattern that you are seeing on your anodized aluminum parts are not what is known as banding. Banding is caused by fluctuations in the output of the laser. It is caused by fluctuations in the pulsing dynamics of the laser.

What you are seeing are probably caused by a mechanical inconsistency on your machine. Dirty or worn belts can cause this. Dirty or worn bearings can cause this. Debris build up in drive pulleys can cause this. Belt idlers wearing or dirty can cause this. I do not think you are seeing something that is caused by an electronic problem.

But I've been wrong before!

[Darren Null]

The horizontal banding is probably something to do with your machine. Usual suspects are dirty and/or worn belts/pulleys/bearings. Give the machine a serious clean, paying particular attention to the moving parts. Also, burn something else before going to your work piece- sometimes the first job of the day comes out with bands for me, seemingly just because it is the first job of the day. Also, try dropping the speed and the power and see what happens.

The diagonal bands are almost certainly something to do with the image. I'm guessing that it's a scan or photograph of a printed image, and the diagonal bands are the texture of the paper it's printed on. Have a close-up look at your image and see if the diagonal bands are there. It could be some sort of moire or interference effect caused between the image and the printer driver, but paper texture is more likely.

[David Dustin]

Hey everyone,
We have been out of the loop for quite a while. Our other business (animation) is doing really well, so we have to concentrate on the one that butters the bread best (try saying that fast).

We were trying to lase some aluminum business cards this morning for an upcoming business trip and found no matter what we tried, there were diagonal lines through the image.

The image is a rendered, grayscale logo for my animation company.
I lased this before perfectly using the HPDFO lens and 15% power, 60% speed before, now there are bands all across it.

Now every card has the diagonal lines, reducing the speed does reduce it but I am curious what has changed?

Thanks for any help.
David
(universal PLS-360)

[Doug Griffith]

Carlos and David,
I agree with Darren that the diagonal most likely caused by moire or interference effect. I'm curious if the diagonal banding is in the same position on all the pieces you engraved. Also if it is in the same position if you rotate the material 90 degrees (not the image).

Cheers,
Doug

[David Dustin]

Doug,
I did rotate the part, and the diagonal pattern was the same.
The most confusing part is this used to work just fine.

The machine has only been used 2 or 3 times since I made the originals.

Thanks,"
David

[Doug Griffith]

David,
since your image is rendered and not scanned, I don't see it being your typical moire problem. It is possible for moire to be caused by the image and the substrate it is printed on. An example would be printing a patterned fabric on top of the same patterned fabric rotated a few degrees off of alignment. That affects the print world where there is line screens. I doubt that translates to laser engraving. I've never seen it. My far fetched theory was that the dither pattern of your image was interfering with the brushed grain of the anodized aluminum. So if the dither is vertical and is a degree or so off of the vertical aluminum grain you may see interference as diagonal banding. Once again far fetched for lasers.

Cheers,
Doug

[Rodne Gold]

I solved banding in 2 ways , the primary cause was "dirty" power and now we use huge AC/DC/AC Ups's that smooth the power big time to a constant ripple free 220v.
The other way I solved some banding or moire issues was to inject a small amount of noise in the greyscale image.
Mechanical banding will normally exhibit itself on a far more frequent basis than on the original image.
Diagonal banding is unlikely to be mechanical in origin

[Dan Hintz]

Make sure your image is sampled and engraved at the same dpi. If you create a 2"x3" image at 150 dpi, but later resize it to 2"x2.95", you'll get banding.

[Scott Shepherd]

Banding can also the anodizing. No matter what, you won't get it out.