Newbie- Laser engraving, burns acrylic (plexiglass)

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Wood-Smoke
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Newbie- Laser engraving, burns acrylic (plexiglass)

Post by Wood-Smoke »

Howdy,
I've had the SD110 for about 5 months and it's been damn cold in the shed, so I've not been out there as much as I wanted to. I do have a heater so I've braved many days to take a shot at engraving on plexiglass.
I've searched these many posts, for information about tips and hints to be successful in getting a reasonable engraved name in 1/8" thick plexiglass but haven't found the information that solves my dilemma.
I have the SD110 with the 2W Next Wave laser module and created jobs using VCarve desktop 11.09. I don't have the laser software add-on yet, I'm working with Nextwave to get the trial version first.
I've used tips learned in posts but haven't found the sweet spot to etch the plexiglass without burning either the top layer or the sacraficial board underneath. I've attached an image of the burn. The image is text that was turned into a tool path using the "Quick engrave" tool. I've adjusted the RPM from 400 to 800 (laser power out where 1000RPM is max). At 400 RPM which I presume is 40% laser power, the top of the plexiglass is burned unevenly ( some letters don't even burn/etch the top of the plexi) and the sacraficial board underneath is also burnt.
Here are the settings:
Quick engrave
tool chosen: Engraving (15 degree)
tool settings: Pass depth .01, Stepover .001, spindle speed(laser power) 800, feed rate 15 mm/sec,
Text Fill chosen with Hatch at 22.5 degrees, cross hatch selected.
Depth / pressure .001
My Machine SD110 is in the machine area
PP is Next Wave Laser (inch)(.tap)
here is the image
here is the image
Am I not moving the laser fast enough (feed rate)? Would the laser software add-on help with this? Am I expecting too much from the 2W laser module?
I was hoping for a deeper cleaner cut, but it looks like the laser is just going through the plexiglass. Using alcohol on the burn areas lightens the carbon burn a little but it doesn't go away.
I tried putting some painters tape on the top side of the plexiglass, in hopes it would just burn through the tape and etch the plexi, but it just made a mess of the tape.
I'm sure this is something simple that I've over looked.
I'm attempting to capture my results (both good and bad) in an excel sheet so I can keep track of the variables.
Thanks for your time in reading this far.
Constructive tips, hints and suggestions are very welcome.
Cheers
FB
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FixitMike
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Re: Newbie- Laser engraving, burns acrylic (plexiglass)

Post by FixitMike »

I've successfully engraved acrylic with a diamond drag tool. The diamond point is spring loaded to compensate for varying material thickness. The exact amount of pressure doesn't make much difference.
No laser experience.
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Jellyfish plaque (Medium) (2016_04_03 23_57_58 UTC).JPG
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Tex_Lawrence
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Re: Newbie- Laser engraving, burns acrylic (plexiglass)

Post by Tex_Lawrence »

Wood-Smoke wrote:
Mon Jan 10, 2022 4:15 am
At 400 RPM which I presume is 40% laser power, the top of the plexiglass is burned unevenly ( some letters don't even burn/etch the top of the plexi) and the sacraficial board underneath is also burnt.
FB, the problem is that the plexiglass is really transparent to the diode laser. It has to do with wavelengths.

I haven't had a chance to try this on plexiglass, but ceramic tiles are easily burned by spray painting white Rustoleum paint on it (let it dry.) After burning, use mineral spirits to wipe away the paint, you have your etched tile. Now, there are many variations to this technique that allow grayscale burning of images and even some color.

The paint basically has titanium oxide (a metal) in it to aid the color characteristics. The laser heats this metal to do the burning.

Experiment with that paint on plexiglass, but don't let the paint dry so much that you can't get it off with mineral spirits.

Good luck!
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Leo
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Re: Newbie- Laser engraving, burns acrylic (plexiglass)

Post by Leo »

It looks like you are using PolyCarbonate (plexiglas) NOT acrylic. Big difference. Polycarbonate is bad to be lasered as the fumes are really not healthy.

Acrylic is a bad smell but not bad like polycarbonate.

Polycarbonate burns, Acrylic kinda melts to a clear finish.

There are 2 kinds of acrylic - cast and extruded. Cast is better but extruded is ok.
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Re: Newbie- Laser engraving, burns acrylic (plexiglass)

Post by BDM »

If all you're doing is names, I would consider not using a laser at all since there are much better options. But if you insist, the tricks I've seen that seem to work is to spray the surface with Rustoleum Peel Coat (black) which is a rubberized product. It works similar to the paint trick on ceramic, but in this case you can peel off the rubber that isn't burnt off by the laser. Another neat trick is spraying a piece of sheet steel (not galvanized) with gray primer and then using that as your sacrificial board. The laser will heat up the paint on the steel enough to melt/etch the acrylic. I also remember seeing some youtube videos using black contact paper, but I don't remember if you put it on top or on the bottom?

I have a similar power laser as you do and I'm slowing working my way through wood, then ceramic and next will be glass and acrylic, so I'm having fun experimenting. However, from what I've seen with acrylic, unless I'm doing a photograph, I'll stick with my diamond drag engraver for everything else. Much more consistent and I don't have to worry about fumes and ventilation. Keep us informed about what you try and the results.

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Wood-Smoke
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Re: Newbie- Laser engraving, burns acrylic (plexiglass)

Post by Wood-Smoke »

Thanks for the quick replies!!
So, it's completely possible that this is polycarbonate instead of acrylic plexiglass. It was some scrap pieces I picked up from the scrap bin at work.
Perhaps using the laser for names in plexiglass isn't the best tool for the task. I'll do some more studying about the diamond drag tool. I recall reading in one of the blog posts, that the 60 degree is great and you can get good detail, but easily broken if care in set up is not observed. After further study, I'll consider a 90 degree drag tool and pay attention to my set up.

I just ordered a 1/32" ball nose bit that I'm also planning to experiment with in the plastic.
I'm sort of volunteering at the local Model Train club, to install/fix things but not run trains. It seems I'm one of a few that knows the difference between the hot and cold end of a soldering iron and how to make it work... Now that I have the CNC, there is a need to mark the switch turn outs with names and switch position, so this is why I'm even experimenting with plexiglass.
I do appreciate the advice.

It's becoming obvious that the more I learn,
I realize there is more to learn....
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Re: Newbie- Laser engraving, burns acrylic (plexiglass)

Post by FixitMike »

And, cast acrylic is definitely preferable to extruded for cutting.
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Experience comes from bad judgement.

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