Horizontal banding on my Universal

[Keith Colson]

I did a job today and I am getting banding when engraving acrylic. Note there are two engraves in this image.

315830

The settings were 100% speed 50% power and density 1. The engraving was done in Coreldraw using 30% black. I used the universal dithering "error diffusion".

Any ideas? I have seen this happen with temperature cycling as the laser warms up and cools down with the fans. Its almost like these settings are sensitive to error. I am probably going to try a coarse stucki pattern and see if it hides it.

Cheers
Keith

[Dan Hintz]

I'm going to guess your image resolution was not the same as (or an integer multiple of) your engrave resolution.

[Keith Colson]

There was no resolution, it was a vector file with filled with 30% black. I used the universal dithering "error diffusion" which means it is all totally native resolution. I have been thinking about this and the density of "1" looks to be a poor choice on my part.

[Scott Shepherd]

There was no resolution, it was a vector file with filled with 30% black. I used the universal dithering "error diffusion" which means it is all totally native resolution. I have been thinking about this and the density of "1" looks to be a poor choice on my part.

I wondered what you were engraving with an image density of 1. I figured it was just giant letters :)

[Dan Hintz]

There was no resolution, it was a vector file with filled with 30% black. I used the universal dithering "error diffusion" which means it is all totally native resolution. I have been thinking about this and the density of "1" looks to be a poor choice on my part.

A 30% fill means at some point the image was dithered... nature of the beast. Being a vector file means nothing at that point. Combine that with a density of 1 and you have an immediate difference in image versus engraving resolution.

[Keith Colson]

It turns out my Z axis was 2mm or so out and just re-homing it was all that was needed. I guess this is a trap if you never manual focus.

I will try to remember to check my focus every so often from now on.

Between my out of focus, grinding bearings in my extraction and the USB stopping intermittently, it was an awful week last week. This week is looking good with all three issues solved. Positivity is on the rise.

Cheers
Keith

[Dan Hintz]

It turns out my Z axis was 2mm or so out and just re-homing it was all that was needed. I guess this is a trap if you never manual focus.

This doesn't follow for me. An out of focus beam does not cause banding. A mismatch in resolution can have its banding masked by an out of focus beam, but that just means you're not getting as good of an engraving as you could get.

[Keith Colson]

Before I posted my fixed result I tested my machine in and out of focus. I think what happens is with density 1 and error diffusion you get an optical harmonic called a Moiré pattern. It is the harmonic between the density 1 line resolution and the out of focus dot size of the the laser.

316035