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Thread: banding issue

  1. #1
    Join Date
    Jan 2012
    Location
    Christchurch, New Zealand (shakey town)
    Posts
    107

    banding issue

    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.
    Attached Images Attached Images
    Epilog Helix 50W, Epilog Fusion 40 75W, Tekcel Router, Taylor Hobson Model D & K
    Roland SP300, Dalgren 2516i

  2. #2
    Vertical banding, caused by beam overlap--

    band2.jpgband3.jpgbanding1.jpg << 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...
    Last edited by Kev Williams; 10-05-2017 at 11:04 PM.
    TEN CNC rotary tool engravers, 3- V3400's, 2- V5000XT's, 1- V5000, 1- V3200, 1- IS400, 1- IS7000, 1- C2000, all New Hermes
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    Mini lathe,Belt sander
    All at home...





  3. #3
    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.
    Lasers : Trotec Speedy 300 75W, Universal PLS4.60 with Rotary Attachment
    Printers : Mimaki UJF-6042 UV Flatbed Printer , HP Designjet L26500 61" Wide Format Latex Printer,
    Ricoh Dye Sublimation Printer, Summa S140-T 48" Vinyl Plotter
    Router : ShopBot 48" x 96" CNC Router Rotary Engravers : (2) Xenetech XOT 16 x 25 Rotary Engravers

    Real name Steve but that name was taken on the forum. Used Middle name. Call me Steve or Scott, doesn't matter.

  4. #4
    Join Date
    Jul 2005
    Location
    Sammamish, WA
    Posts
    7,529
    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.



    Sammamish, WA

    Epilog Legend 24TT 45W, had a sign business for 17 years, now just doing laser work on the side.

    "One only needs two tools in life: WD-40 to make things go, and duct tape to make them stop." G. Weilacher

    "The handyman's secret weapon - Duct Tape" R. Green

  5. #5
    Join Date
    Jan 2012
    Location
    Christchurch, New Zealand (shakey town)
    Posts
    107
    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.
    Epilog Helix 50W, Epilog Fusion 40 75W, Tekcel Router, Taylor Hobson Model D & K
    Roland SP300, Dalgren 2516i

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