acrylic banding

[Bert Kemp]

I'm engraving acrylic and I'm getting banding will increasing my scan gap/dpi reduce the banding?
Well I tried going form 390 to 600 didn't work .

[Keith Downing]

Different types of acrylic can be tricky.

If you're rastering, try doing it ever so slightly out of focus at a tab bit more power. This worked wonders for me last time I did a logo on acrylic.

[Kev Williams]

Banding, nearly all machines do it...

Bert, do you have "X-swing / X-Uniliateralism " in the engraving settings? Or whatever they may be called in your software?

X-swing means the laser engraves in both directions, left to right and right to left,
X-unilateralism means the laser only fires left-to-right, but NOT right to left (or vice versa is possible I suppose)

Anyway, it takes twice as long to engrave this way, but it may eliminate the banding. I believe that's its purpose... If it does, twice as long and decent results beats crappy results in half the time! ;)

[Bert Kemp]

I don't think I have that on my machine darn:D



Banding, nearly all machines do it...

Bert, do you have "X-swing / X-Uniliateralism " in the engraving settings? Or whatever they may be called in your software?

X-swing means the laser engraves in both directions, left to right and right to left,
X-unilateralism means the laser only fires left-to-right, but NOT right to left (or vice versa is possible I suppose)

Anyway, it takes twice as long to engrave this way, but it may eliminate the banding. I believe that's its purpose... If it does, twice as long and decent results beats crappy results in half the time! ;)

[Bert Kemp]

It cast , I lowered my pwr from 70 to 40 increased speed from 300 to 325 and scan gap of .065 and that helped. Not gone but less noticeable. If I lower power more I loose detail in raster.


Different types of acrylic can be tricky.

If you're rastering, try doing it ever so slightly out of focus at a tab bit more power. This worked wonders for me last time I did a logo on acrylic.

[Dave Sheldrake]

Yea you do Bert, it's in the engraving dialog box, Unidirectional - Bi-Directional

[Bert Kemp]

341332This is what I have and the Bi dir box is always checked but it only engraves on the x axis. Is there another box some place?

[Keith Downing]

It cast , I lowered my pwr from 70 to 40 increased speed from 300 to 325 and scan gap of .065 and that helped. Not gone but less noticeable. If I lower power more I loose detail in raster.

Did you try doing is slightly out of focus? For me, it helps get a little melt in the raster that prevents the noticeable banding. You do have to play with it some though.

[Bert Kemp]

Yes I did take it out about an 1/8" it helps a little also.



Did you try doing is slightly out of focus? For me, it helps get a little melt in the raster that prevents the noticeable banding. You do have to play with it some though.

[Kev Williams]

Bert, UNcheck the bi-dir box-- it will still run on the X axis, but the laser should only fire in one direction--

here's mine with the drop down menu opened, X-swing is my default. It will raster on the Y axis too, but it's limited to 300mm/sec...

341333

[Gary Hair]

You might have uni-directional or bi-directional, try looking for that.

[Bert Kemp]

Kev you have screen shots of everything I have do you see were I might have x and Y engraving ?



Bert, UNcheck the bi-dir box-- it will still run on the X axis, but the laser should only fire in one direction--

here's mine with the drop down menu opened, X-swing is my default. It will raster on the Y axis too, but it's limited to 300mm/sec...

341333

[Jerome Stanek]

341332This is what I have and the Bi dir box is always checked but it only engraves on the x axis. Is there another box some place?


Your Bi-dir is checked uncheck it

[Rodne Gold]

Banding often arises cos the laser puts a lot of heat into the materials and they expand and contract
Try a teeny bit out of focus and reduce your scan gap ..ie a little more gap tween y axis scan lines

[Kev Williams]

Bert-
I don't see a Y engraving option in your software. Just the "bi-dir" which is for the X.

Banding is the Achilles heel of most lasers. The one laser I had that didn't do it was the old ULS. Under high magnification the finished burn path always resembled a diamond-knurl pattern. That machine also was the best machine I've owned for reproducing photos. I got stunning halftone results in leather with that machine, which I've never been able to re-create with any of my other machines. Whoever is responsible for programming the way that machined fired the laser has my utmost respect.

My LS900, for all it's positives, it's HORRIBLE for banding. Much of the reason for its banding is the laser beam 'wobbles'. According to Gravo this is on purpose, as it's supposed to aid with dithering when engraving photos. Can't argue that it's BS because for one, the wobble perfectly repeats over itself on subsequent passes, eliminating mechanical issues as the reason for the wobble. And it DOES do photos quite well, and it's phenomenal at glass engraving when running dithered gray in photo mode. Running glass on my other machines renders ridiculously bad results no matter what I've tried.
This is some plex I did awhile back on my LS900, different speeds, 50 lines per inch I believe. Note that this plate was engraved twice- every line perfectly repeated.
Also not the 3rd and 4th lines were done at the same relatively slow speed, the difference being line 3 was rastered, line 4 was vectored.
The vector is dead straight, which also eliminates mechanical issues causing the wobble...

341385

But the problem with the wobble in general engraving is that the beam paths overlap more in some areas than in others, and these under/overlaps are always in the same vertical plane. The heat soak Rodne mentions comes into play, and also simple light reflections. The results are very visible vertical bands. This plate, the bottom lines were done at 75 lines, the top at 500. The top and second line were done at the same speed, the third line was done a bit slower. The top line is showing bad banding-in the second line you can see the bands corresponding to LESS overlapped areas...

341386

Not sure about how other machines 'track', and I've never tested any of my other machines. I really should :)


Horizontal banding, far as I can tell, is more of a substrate issue, where certain areas of the material itself are more sensitive to heat. Similar results but more because of how the material reacts to the laser rather than the path of the laser...

Now, THAT all said, Bert, this is why you should try running the machine with the bi-dir OFF, the laser firing in only one direction may help with heat soak AND with how light reflects off the engraving. If you read my watch-back thread, you noted in the sample pics the very bad banding the fiber did, and it was strictly caused by the direction the laser was moving, the engraving moving down catches the light totally different than the engraving that moved up...
:)

[Rodne Gold]

If things are really bad , it's often largely cured by converting the fill to a bitmap of 90% black.. you can try adding some random noise to the bitmap..essentially you are decorrelating the fill.

[Bert Kemp]

Thanks Rodney I'll try that also


Banding often arises cos the laser puts a lot of heat into the materials and they expand and contract
Try a teeny bit out of focus and reduce your scan gap ..ie a little more gap tween y axis scan lines

[Keith Downing]

Yes I did take it out about an 1/8" it helps a little also.

I usually go a bit more out of focus than that to achieve the "melt" effect. About 1/4 to 1/2" depending on the acrylic and power settings.

Might be too much for your design, but can't hurt to try if you're already testing.

[Michele Welch]

OK, really stupid question, but I've asked it several times and never got a concrete answer. When you say take the lens "a bit out of focus", are you talking moving it up (away from the material) or down (towards the material)? I've never had a straight answer. Forgive the ignorance!!!

[Tony Lenkic]

Michele,

I prefer to move table down but it may be fine either way.

[Keith Downing]

OK, really stupid question, but I've asked it several times and never got a concrete answer. When you say take the lens "a bit out of focus", are you talking moving it up (away from the material) or down (towards the material)? I've never had a straight answer. Forgive the ignorance!!!

Technically you could do either and be lasering out of focus. However, I always move the table further when trying to melt the acrylic by manipulating the focus. And here's the reason.

When you move the material closer, you are actually moving the focal point into the material. So, if your power is too high, you could inadvertantly end up with a focused beam at a point near the bottom of the engraving. When I'm doing this, I want the opposite. I want the beam to kind of spread out and blur the lines ever so slightly as it burns into the acrylic.

But feel free to play with it and see what works best for each individual project. There are so many factors to consider (power, speed, interval, focus, material, air assist, ambient temperature, etc). It's never a bad idea to try different combinations for yourself.

[Gary Hair]

I think this is about the best reasoning I've read for which direction to focus! The other one is that it gives you more room between the substrate and the lens instead of less.


Technically you could do either and be lasering out of focus. However, I always move the table further when trying to melt the acrylic by manipulating the focus. And here's the reason.

When you move the material closer, you are actually moving the focal point into the material. So, if your power is too high, you could inadvertantly end up with a focused beam at a point near the bottom of the engraving. When I'm doing this, I want the opposite. I want the beam to kind of spread out and blur the lines ever so slightly as it burns into the acrylic.

But feel free to play with it and see what works best for each individual project. There are so many factors to consider (power, speed, interval, focus, material, air assist, ambient temperature, etc). It's never a bad idea to try different combinations for yourself.

[Bert Kemp]

After running about 7 different tests I found reducing the scan gap or DPI worked best. Final settings
325mmps speed
40% Power
Scan gap .0847 or 300 dpi
Banding hardly noticeable
Thanks for all the suggestions
This is how it came out341484

[Bert Kemp]

Thanks everybody its done see previous post

[billy fayo]

i do mostly acrylic work. i get banding about every 2 weeks. all i do is clean my mirrors and lens. works every time. i take the lens out and clean it. not just a quick clean with a qtip.

[Scott Marquez]

Thanks everybody its done see previous post
Wow!!
I missed your your final outcome, watch out Bert you may soon find yourself busier than you care to be.
Keep up the great work.
Scott

[Bert Kemp]

Thanks Scott,:) I already had someone inquire about doing something similar as a memorial for her father.

[Mike Null]

Bert
Nice work on the layout!