Rastering Acrylic

[Ross Lowry]

Ok I am having a look I dont like when engraving acrylic.
I have attached a picture.
Do you think the power is to high?

[Joe Pelonio]

Can you post a pic from farther away that shows more of it?

[Ross Lowry]

I could, but would rather not on this piece.
It is for a person who has a family member playing in a major game right now. So I am choosing to show only a portion of the piece.
Sorry, but I think that should be good enough for a person who has experienced this before.

Thanks

[Kim Vellore]

Hmmmm You dont like the deep groves or the raster lines that looks like bumps, what is the magnification of that picture, Cant make out much from that picture without any reference for size around it. Also cant make out how deep the engraving is to suggest DPI, speed or power.
Kim

[Ross Lowry]

Ok I will reveal more.
It was propped up on my wallet.

[Ross Lowry]

Forgot to add the dpi is 300, the speed 100, and power 50.

[Joe Pelonio]

What are the dimensions of the piece, what kind of acrylic is it, and how many watts is your laser?

That looks much like almost any laser engraved surface highly magnified.

Normally it would not be noticeable, but in the case of a reverse, where the background is engraved away, it becomes much more visible.

[Ross Lowry]

Hello Joe.

The piece size is 2.78 wide x 3.383 tall.
My machine is a 45 watt Epilog.
The picture was taken with the upclose option on my camera.
I then cropped out the rest of the photo.
The engraving isn't bad but normally I dont get those imperfections.
It is 1/8" cast acrylic.
I am wondering if it is focusing correctly?

[Scott Shepherd]

Not sure what's causing it either, but I'd start by dropping the speed into the 50-60% range, lowering the power down into the 20% range and try that.

It might just be traveling too fast for that level of detail, that small.

That's 100% a guess, and more of something to try, not so much an answer to your question.

[Frank Corker]

I think it would even out if you doubled your dpi, the dots would be overlapping, that unfortunately would double the time it takes to engrave it, the ridges on all acrylic is never even. Sometimes there are slightly deeper ridges but the paint is making it appear worse, especially viewed from the front where the clear acrylic is magnifying your engraving.

When I'm engraving acrylic, generally I will use the recommended settings of 100 power and 35 speed, virtually no visible marks from the front. Although this marks clearly, quite often it doesn't have that impressive look, so if I want a deeper engraving I will swop the two figures over, takes longer but much deeper noticeable engraving.

Increasing the speed will make the engraving look less bumpy but it will also loose quite a bit of the depth which in turn will make the infilling a lot harder to contain.

[Mike DeRegnaucourt]

I agree with Frank. I often use 600 dpi on my acrylic and never see the ridges. It's going to take a little longer but if this is a one-off piece or a few pieces, then it might be worth it to help improve the appearance.

[Bill Cunningham]

You can also take it out of focus (I back off the table about 1/8 inch) this makes the spot slightly bigger, and can smooth the surface somewhat.. Experiment on a scrap piece with focus distance until the striations smooth out.. It your running a sharp focus on plastic, you could basically just be cutting trenches

[Joe Pelonio]

There's also the issue of small size and return time on plastics, which do get warm with a reverse etch. You might get better results if doing a whole sheet of them, or by doing a vertical line a few inches on each side of it to allow more time between passes.

[Ross Lowry]

Frank there is no paint on this piece, just my black wallet behind it to prop it up for the picture.

[Frank Corker]

In that case I think, owing to the size of the piece, that it's a case of a 'Blind man on a galloping horse would be glad to see it'.

[Dave Johnson29]

When I'm engraving acrylic, generally I will use the recommended settings


Frank,

What if Ross mushed the focus a little so you get a blurry dot? Maybe max power and slow down the speed a little as well.

[Frank Corker]

It's possible Dave. The lines may appear to him to be too harsh. Only experimenting with what he has will get the optimum result. You suggestion is as good as any. However as I said in my last post, I think he is worrying too much about it, it doesn't appear too bad to me. If the item is small (and it is) the vast majority of people looking at it are going to be suffering some type of myopia anyway!

[Steven Wallace]

Being a baseball fan and the season is finally over we'll be seeing the whole piece soon... please:)

[Mike Null]

Frank

It looks like you had a make-over since this morning. I can't decide whether the old you was better or not.

[Frank Corker]

Thanks Mike :(

[Mike Mackenzie]

And I thought it was a Halloween thing.

[Rob Bosworth]

Ross, move the focus either into or higher up on the piece. If you move the piece up or down, try about 1/6" out of focus. It will generally smooth out the bottom of engraving on acrylic.

Good luck.

[Richard Rumancik]

If you have a beam size of .003" diameter and you are engraving at 300 dpi in both axes then there is no overlap between rows. In fact, at 300 dpi the pitch is .0033". So with a small well-focused beam I am not surprised to see some ridges. Some people have suggested going out of focus. This will increase the beam diameter a bit so it will overlap more. If you don't mind longer run time increase the dpi so you have overlap.

When doing recesses in acrylic even at high dpi I still see the parallel horizontal lines. In some cases this does not look that good. I have had some success in using texture fills or greyscale fills and then converting to a b/w using a Stuki conversion in PhotoPaint. It may look bad on the screen but lasers okay. It will generate a random background texture instead of straight raster lines (which you get with solid black fills).

It can also be done in two stages: use a regular raster to create the recess and then follow it with a light texture fill to even out the background.