Banding in logo fills using Cermark LMM6000 Paste

[Bernie Fraser]

Hi ,
I am new to lasers having bought my second hand Rayjet 30W earlier this year. I have engraved 80 SS bottle openers with text and a line graphic using Cermark LMM6000 paste brushed on using a foam brush and I was very pleased with the results. The mark is durable and the detail is good. Recently I have tried marking SS using Cermark on logos with fills and I have noticed banding in the final product. I carried out a power grid test looking for the best result with power and speed and it was close to the default setting. The process I have used is vector graphic in coreldrawX6 fill 100% RGB black, Power 100% speed 14% ordered dithered and I use either 600 or 1000dpi. Have also tried black and white instead of ordered dithered using the Rayjet commander software. Ran another test last night at higher speed as it still shows the banding and I am not concerned with the durability on this test piece as I would like to identify the banding issue. I tried plugging the Rayjet 30 into a different power point separate from the Atmos unit, banding still present. I then rotated the piece of stainless 90 degrees and engraved the flag logo and the banding appears to have gone from the bottom RH flag ( this flag was engraved with test piece rotated 90 degrees counter clockwise ). I do not know why the banding is very noticeable if I engrave in landscape but be seem to disappear if the flag is engraved in portrait mode ?. The flag size on this test piece is small just under 1.5 inches wide. . Have engraved durablack and granite using photographs and there is no banding evident when engraving these. Any ideas what I can try ?. Thanks for your input, Bernie

300330

[Richard Rumancik]

It can be difficult to track down the cause of banding and sometimes it seems it just can't be eliminated with certain settings. You have said you tried both dithered and B/w settings and both produce banding. As a long shot, try changing the color from 100% black to say 90% black and see it it hides the banding at all. I am a bit skeptical because dithering didn't help but might as well try. The 90% black will cause you to lose some dots so you don't want to go too low. In many cases a ~90% black will improve the appearance of solid fill backgrounds but hard to say if it can hide the banding you have.

Another option would be to convert the vector art to a bitmap and use a filter. If you are using CorelDraw - something like this: set color fill to 90% black, convert to bitmap (greyscale/xxxdpi) -> edit bitmap -> PhotoPaint opens -> image ->convert to black& white -> select "conversion method" eg Stuki, -> adjust intensity slider as required -> save -> Photo Paint closes, and image is transferred back into CorelDraw. Other people might have a different process.

Note that the preview image won't be that representative of what you get out of the laser. You need to develop a feel by experimenting. Just a few dots of white in the background is sometimes enough to break up a mechanical-looking background pattern.

Save a master vector image before experimenting/converting so you can revert, and keep good notes.

I am not sure what options the Rayjet permits but if you can select a Stuki filter some other way, it might be worth a try. I don't know what "Rayjet Commander" is.

Normally you shouldn't have to be using 1000 dpi unless the image is very small. For a 1.50" logo 600 dpi should be more than adequate. I don't have a good explanation why it looks better rotated 90 degrees. Sometimes the length of sweep of the laser carriage can have an effect on an engraved image. On a short stroke the speed might not achieve maximum and that can sometimes change image appearance.

[Bernie Fraser]

Thank you for the reply Richard. I had already tried the 90% fill and it eliminated the banding. When I placed the 90% fill logo next to the 100% fill I could notice how it looked more Gray. So the banding may be physically in the 90% fill but the banding is the same colour so at least I can get that. I may increase from the 90% and see where the banding becomes evident again. Have not tried the Bitmap conversion, will try it out and post the results. Appreciate you posting the information on the dpi settings and giving me your thoughts on this issue as it really had me scratching my head as to why the logo would engrave so differently when rotated.

[Mark Sipes]

I have on occasion re-lasered the object after taking the object to the edge of focal length. In short I lowered the table a hair to get a wider laser beam. Seems to fill in the gaps of banding.

[Bernie Fraser]

Thanks Mark, I will try that out also and report back how it goes.

[Dan Kozakewycz]

I have this problem quite a lot, though I do seem to have gotten it to acceptable levels now. If I am doing a file with a lot of black fill, I will now move the table down by 3mm and increase the power/slow it down to get the exposure up to the focussed levels. Can give a slightly fuzzy edge on some details, but it's about finding the right balance.

[Chris DeGerolamo]

As others have stated, lowering your table to increase the spot size [provided you can find a Goldilocks zone] should reduce/eliminate banding.

[Bernie Fraser]

Thanks Dan and Chris,
I did not get a chance to run the tests yesterday, but will do it this afternoon. It is reassuring to know that others have experienced it and found a way to engrave the fills to an acceptable level.

[Bernie Fraser]

So I did some testing this afternoon. The first test was to convert a 90% RGB black into a bitmap and use the Stuki filter as Richard had suggested in a post above. The result with the engraved file is that the banding was still present.

Second test was to engrave the image twice without adjusting the table height, just to see the difference between this test and lowering the table for the second run. Appears to be a similar end result as if I had lasered just once. Except I have a little bit of a sheen on a portion of the cermark on the LH side. This may be because my test pieces of stainless are thin and start to curve with the heat.

Third test I lasered once and then lowered the table by 2mm, no banding present but once again I have a sheen on part of my engraved image. These three tests were run on the same piece of thin metal, so the heat may be effecting the final outcome.

Fourth test I get one of the stainless bottle openers and run the engraving twice lowering the table by 2mm on the second run. The banding is not evident but it is not a great looking end product either. The engraving is not smooth when you rub your finger over it. Unsure if this is a result of the finish of the stainless bottle opener with its brushed surface.

I have been extremely happy engraving these same bottle openers with text and a side plan of a helicopter. The detail is excellent and I am happy with the cermark as well as the customer being happy with the result.

For now I think I will stick with engraving things where I can get a good end product, so may just steer clear of large areas of fill on stainless.Thank you for the information on this forum I am very happy with the way my Rayjet engraves photos onto granite and Durablack. The other information that I read here was to reduce my power when engraving anodised aluminium. Soon after I got the engraver I engraved a dog tag and then over the next few days there appeared to be a discolouration in some of the letters of the text and soon all the letters that I had engraved had corroded. Did the testing to see where I can get a good mark on anodised aluminium and the power has gone from the default 80 with a speed of 100 to a power setting of 50.

Thank you all for your suggestions in helping me out here, it is a great forum.

Bernie