any top tips for reverse engraving clear acrylic

[Graham Taylor]

I need to reverse engrave a logo and some text onto some clear cast acrylic and was wondering if there is a 'best practice' method?

I would like to get a bit of depth to it so there is a bit of contrast when it is placed on top of a black background so,


is it better to take several passes with lower power and high speed/
one pass at higher power and lower speed?
set the focus so the acrylic is slightly further from the lens than normal?


I would like the engraved area to be as smooth as possible so you dont see the lines produced during the engraving process so is it best to use the 3rd point above to achieve this?

I am going to do some test pieces later today and see what happens but just wondered what the experts do

Thanks again for all the help and advice you guys give beginners like me - we all appreciate it (enough of the love fest, its time to make another cup of tea :D )

[Keith Colson]

Hi Graham, I find that most solid fill (no greyscale) engraves are much better done out of focus like you suggest, they can also be done in lower resolution which is faster. They come out much smoother with minimal raster lines. When engraving out of focus you may need to shrink the widths in the graphics to compensate.

The catch is the dirty raster lines are what would make it stand out from the background. I personally like to engrave the wrapping off the plastic sheet and then spray paint the engraved area for contrast. After that is complete I do the cut out and peel the protective layer to expose the finished result.

I think you are best to do a bit of characterization and write down the settings numbers on the bits of plastic you test on, I keep these for samples for the next job.

Cheers
Keith

[Mike Null]

If you are using cast acrylic you will get a good contrast with your first pass. You may want to try out of focus effects or more than one pass to minimize the engraving striations.

When color filling cast acrylic better results can be obtained by filling from the front as the frosted white of the engraved area diffuses the color when filling from the back.

[Graham Taylor]

Thanks for the replies - I didnt get a chance to test this out today so will try it over the weekend

[John Noell]

If you use two passes, the 2nd out of focus by about 1 cm, the striations are not very noticeable (to me). All three colours were reverse engraved like that.312543
(The scuff marks are because this was a duplicate that got left laying around the shop.)

[Kev Williams]

since you have a Trotec, you might try what I've found works wonders with my Gravo LS900--

Be it anodized, glass or plastic, whenever doing large expanses of 'black', you are going to get banding
in one way or another. When trying to steer a local wine restaurant away from sandblasting or
acid etching their glasses, I spent a whole day trying to figure out how to eliminate the visible
lines, and the larger glass fractures that are inherent.

What works for me, is 'photo mode' and 'less than black'...

With glass I found that 70 to 80% black, and equal but lower resolution gives me nearly perfect results.
By equal resolution I mean X and W are set the same, and on glass, usually 300 DPI-x and 300 LPI-y.
Different jobs & materials means tweaking res, speed and shades of gray, but 80% and 400 dots is
usually a good starting point.

Simply put, it seems to me that the dithering effect created by the software trying to create a gray
almost completely eliminates banding issues. Once I'm dialed inI can engrave a square foot of glass
and it truly looks sandblasted, with very minimal large fracturing.

Same for anodized, which I do a LOT of.

Here's the results of some testing & tweaking I did recently, the logo is about an inch wide-

312546

The #1 version engraved 'normally' is exactly how I engraved a test piece for my customer's customer.
My customer didn't notice the banding. But I did, and so did HIS customer. With a few tests & tweaks,
it came out near perfect, and everyone was pleased :)