Full Version: Need Help With Banding Problem

From: Awardsguy [#1]
 21 Jan 2007
To: ALL

I need some help. I'm having a problem with vertical banding on acrylics that have a solid fill on about 40% of the engraving area. I was having a horizontal problem, too, and ULS sent me a new belt and focus carriage bearings. That fixed that problem. They sent me a replacement tube, but it didn't fix the problem. I've tried playing with the power and speed and different dpi. Sometimes that seems to work, but them the next piece has the bands. Any suggestions would be appreciated. I have to ship this Friday and it's for my biggest customer (of course!).

From: Carl (CSEWELL) [#2]
 21 Jan 2007
To: Awardsguy [#1] 21 Jan 2007

Garry;

Shot in the dark, any chance that what you are engraving is close to the left edge? If so, move it away and try it.

From: Awardsguy [#3]
 21 Jan 2007
To: ALL

I'm 1 inch from the left and top. My customer has me going clear to the edge on all 4 sides, so the image is 1/4 inch larger each way so the laser goes passed while still firing.

I used to etch the awards on glass but was having a problem with the centers of the Os and As blowing out because of the small font size and not enough glue underneath to hold the masking. I thought lasering on acrylic would solve the problem. Boy was I wrong!

From: Harvey only (HARVEY-ONLY) [#4]
 21 Jan 2007
To: Awardsguy [#1] 21 Jan 2007

When you say the next piece has the problem, is it an identical piece, or another image?

What software are you using, and the version?

Where are the lines? Are they consistently in the same place?

I know Corel 9 has a bug that can give a line down the center vertically, and two fixes.

From: Awardsguy [#5]
 21 Jan 2007
To: Harvey only (HARVEY-ONLY) [#4] 21 Jan 2007

Hi Harvey,

It's in the same place. I'm trying to do 5x7 acrylics right now. I'm using Corel X3. I've found if I make it about .040 out of focus that I pretty much eliminate it from the bottom of the piece, but I still get it on the section at the top that's solid fill. It's pretty consistent. I'm working on changing some of the image parameters in the ULS driver and see if that does any good.

From: Dave Jones (DAVERJ) [#6]
 21 Jan 2007
To: Awardsguy [#5] 21 Jan 2007

This may seem obvious, but have you tried a thorough cleaning of the rails? And if it has a linear encoder strip, a good cleaning of that?

From: Awardsguy [#7]
 21 Jan 2007
To: Dave Jones (DAVERJ) [#6] 21 Jan 2007

Yep, did a very thorough cleaning yesterday.

From: logojohn [#8]
 21 Jan 2007
To: Awardsguy [#1] 21 Jan 2007

On most acrylic I focus and then off focus 5 clicks on my knob which is about 1/16 inch.

If your driver has a photo mode you can use a medium shade of grey instead of solid black so it leaves a more smooth frosted look. The dithered dots leave less chance of banding You could convert to a bitmap and dither it with coreldraw or photograv if your driver can't do it.

Reduce the dpi to 300-400 instead of 600 at the laser driver settings.
For very large areas I sometimes create 2 vector hatch fill lines at 90 degree angles with a very tiny space in between. But it is still rastered and not vector lasered. Since you are rastering thin lines very close to each other you do not get the unwanted patterns. Its like the bottom left in this image but the lines are close enough that the space is not visible to the naked eye and you can apply a pen thickness to close it up. I even did one image that was over 12 inches by 17 inches on glass using that method and it looked perfectly smooth with no chipping.
xhatch example


Sometimes it also helps to just reduce the speed and power proportionally especially with older lasers.

former native Iowan (angel)

EDITED: 21 Jan 2007 by LOGOJOHN

From: Awardsguy [#9]
 21 Jan 2007
To: logojohn [#8] 21 Jan 2007

I will give this a try. I did try reducing the dpi, but not as low as you suggested. I moved it out of focus .060 (i guess that's about 1/16th of an inch) and it has made it so it's not too noticeable. I'll try the other stuff you suggested. Thanks for your input.

From: Harvey only (HARVEY-ONLY) [#10]
 21 Jan 2007
To: Awardsguy [#5] 22 Jan 2007

Vertical lines that show at the top and bottom only, or horizontal lines at the top and bottom? (It does make a big difference.)

EDITED: 21 Jan 2007 by HARVEY-ONLY

From: Awardsguy [#11]
 22 Jan 2007
To: Harvey only (HARVEY-ONLY) [#10] 22 Jan 2007

Vertical lines are at the top and bottom. There is some faint horizontal banding, too, but not as noticeable.

From: laserman (MIKEMAC) [#12]
 22 Jan 2007
To: Awardsguy [#11] 22 Jan 2007

Gary,

Right now what I would do is to use the Texture option in the driver. In the advanced tab ENABLE Image Enhancements and then put a check mark into the texture box.

The files will be larger but this should cure your striping problem in order to get this job done.

If this works then do the job and then we will address a couple of things to check that should correct the problem.

From: Harvey only (HARVEY-ONLY) [#13]
 22 Jan 2007
To: Awardsguy [#11] 22 Jan 2007

That is indeed a strange one. Every explanation I try to think of is negated by that. It may be that what is at the top and bottom are more prone to showing that problem.

Some general rules of (my) thumb that I had to use with Corel 9 and to prevent problems.

Be sure that the width and height, pixel wise). of the image are both divisible by 4, 'long word' in computerese. If not, changing the size of the width of the image by one pixel width, (as a decimal in the width box on the toolbar), usually solves the line down the middle problem.

Be sure that the image is an even multiple of the engraving DPI, or an even fraction like 1/2, 1/4, 1/8. This is after you have resized it. Do this by re-sampling it to the size you have made it and the proper resolution. This prevents misinterpretation in the driver. This usually solves any possible software glitch. If you still get it it will probably be a mechanical problem.

From: Awardsguy [#14]
 22 Jan 2007
To: laserman (MIKEMAC) [#12] 22 Jan 2007

I did check the texture box early on to see if that would help. It did a little. I have been putting the laser .070 out of focus and it's worked pretty well for getting rid of the vertical banding. There is faint horizontal banding, but it isn't too bad. It's allowing me to get the job done, however I do need to figure this out. My wife says that I'm prpbably the only one who will notice it.

I just had to engrave one twice because of some paper that I used for placement came loose and interfered with the laser. After the second lasering the vertical bands are very prominent.

Any advice is appreciated.

I'm going to try Harvey's suggestions and see what happens.

Also, I normally use the HPDFO lens. I switched to the standard lens that came with the unit and that seems to have helped some. (edit)

EDITED: 22 Jan 2007 by AWARDSGUY

From: laserman (MIKEMAC) [#15]
 22 Jan 2007
To: Awardsguy [#14] 22 Jan 2007

Gary,

you should use the standard lens and run the focus 0.030 to 0.040 out. The Hpdfo is made to stay in focus with very little tolerance. by running the Hpdfo Len's you are basically defeating the purpose of the lens.

I would check the X belt tension once the dust settles. This may be all that it is.

Have you tried to move the graphic into another area of the table?

Try running the graphic in question at 18 power 33 speed just as a test.

EDITED: 22 Jan 2007 by MIKEMAC

From: Awardsguy [#16]
 22 Jan 2007
To: laserman (MIKEMAC) [#15] 22 Jan 2007

Well, after trying several of the suggestions, I finally have acceptable (for me, and I'm picky) engraving. I owe you and Logojohn and Harvey and Carl a drink. If you're going to be in Vegas, I'll buy. It was a combination of several things that worked. I tried so many that I'm not sure what I did. I just saved the settings and I'm going with it. Thank you all very much for the help!

I hate the learning curve.

From: Dave Jones (DAVERJ) [#17]
 22 Jan 2007
To: Awardsguy [#16] 22 Jan 2007

I don't know if I missed this in your posts or not, but is the image you are engraving a vector image or raster (or combination)?

If it's a raster or combination, maybe do a test engrave using a simple vector image with a solid rectangle and see if it has any bands.

From: Awardsguy [#18]
 22 Jan 2007
To: Dave Jones (DAVERJ) [#17] 22 Jan 2007

It's a vector image with solid fill. The bottom 20% and top 20% are filled rectangles that goes from edge to edge with text , so the banding was noticeable. The center portion is a lion's head & mane that merges into the bottom part with text in the middle.

From: Harvey only (HARVEY-ONLY) [#19]
 22 Jan 2007
To: Awardsguy [#18] 28 Jan 2007

The answer appears.

The dithering in the filled rectangles is conflicting with the DPI of the laser. Convert those to bitmap at an even multiple of the laser's DPI and it is solved.

From: Awardsguy [#20]
 28 Jan 2007
To: Harvey only (HARVEY-ONLY) [#19] 28 Jan 2007

Thanks Harvey, I will give that a try.

As you know I had a problem getting to the EE site. I thought I'd try another computer. Haven't had time to try the fix from Computer Associates on the other 2 and I'm a little gun-shy about using my work computers until I've done all of the diagnostics.

I appreciate your help with everything.

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