banding issue

[vic casware]

Hi fellow engravers,
My Fusion seems to be suffering from a banding issue that i must admit
has been happening for a few months now, it doesn't affect every job
just those with large areas of black or large ares on acrylic that i fill.
Epilog are of course having me check the belt tension, alignment etc
but those are all fine, the picture is a 1/2 inch high engraved strip
on Rowmark silver, at 300dpi.
It is less obvious when you get to 600 dpi but still there.

[Kev Williams]

Vertical banding, caused by beam overlap--

369179369180369181 << the top of this one, look familiar? ;)

These I did on my LS900 (50 lines per inch, different speeds) while still under warranty 12-1/2 years ago, and it still does it. Run yours at 50 lines, it'll likely look just like these...

As is easy to see, the beam wobbles, and it's not mechanical. Proof of that is the bottom line, which was a simple vector hatch I drew manually at 50 lines per inch. My vector at 100% speed is pretty slow, about the same as 20% speed in raster, however, the line above the vector was rastered at the same speed; the raster wobbled, the vector is dead straight. Slower speeds helped, and varying the lines per inch would help. Sometimes. The reason for the bands, is when the line-above's lower wobbles overlap the line below's upper wobble- in plastic, the overlaps cause slightly more melting than where there's little or no overlap. Similar results can happen with anodized aluminum... But what to do about it?

I had a factory repair guy here for 2 days trying to 'fix' it. He did manage to get the banding reduced a ton, but it required loosening the belt so much you couldn't run it above 25% speed. It WAS a workaround if I HAD to eliminate the banding. His boss told him the wobble was something to do, or necessary for, photo engraving. I believe his boss had no more clue than I do as to this issue and just came up with a BS reason for it... this is part of the reason why Gravograph has such a bad CS reputation...

Anyway- Over the years I've found that a great number of 'western' lasers do this. Not sure if it's a Synrad thing, or an RF-laser-in-general thing or a controller thing. My little 25w ULS absolutely did not do this, and when inspecting its engraving with a loupe, the engraving has a knurled look to it, I've always assumed it did this by splitting the spacing of the laser's pulses of each sweep direction. Whatever, that thing always made everything look sandblasted, and still does...

The only fix I've found, and it's not perfect, is to engrave in photo mode at 70 to 80% black, as the dithering randomly breaks up the beam pulsing, which reduces the effects of overlap a ton.

what also may help is to reduce the raster pulses per inch, way down to 250 or even 150 dpi, but I've never really tested that theory...

[Scott Shepherd]

That's pretty excessive banding. As Kev suggests, getting away from 100% black can help. That, and take it out of focus. I had an in depth conversation about 6-7 years ago with a guy at ULS who was in the know. He said banding is a function of the tube and you just have to deal with it. He also told me they had developed a tube that didn't have any banding, but the process was so expensive that it was cost prohibitive.

[Joe Pelonio]

When I had some of that about 8 years ago it was a bad encoder strip, though I clean it regularly. I replaced it with a new one from Epilog and never had a problem since. Not a fusion, though, so I don’t know if you even have that part on yours.

[vic casware]

Hi all,
Just a quick update, Thanks Joe and Scott for the suggestions, the change to off black made a small difference,
Epilog got in touch suggesting tightening the X belt, that was a mission but got it done, has made a difference
but not eliminated the issue, but the engraving is more glossy now which kind of hides the banding,
I will keep working at it.

[Chris M Jones]

Were you able to completely resolve your issue? I have the same symptoms on my Universal.