Acrylic: CNC and Laser engraving?

Does anyone have recommended settings for CNC and laser engraving acrylic?

I have a few small pieces I’d like to experiment with, but they’re far more expensive than paper or wood, so I’m extremely hesitant to just throw it in and hope for the best.

For CNC engraving, I’ve heard horror stories that acrylic can cause problems if you run the bit too fast, as well as too slow, so I’m not sure if the max bit speed would cause problems or if it’s fine, and whether you need to keep the work speed lower than the default 600mm/min.
(I do know that I’ll want to have a vacuum cleaner right next to it with the nozzle in my hand as it runs to keep the dust and crumbs down)

For laser engraving, I only have the engraving head (and not the more powerful cutting head), and I know that laser cutting or engraving acrylic will give off a poisonous gas that needs to be vented outside as quickly as possible, which is not something I yet have, but do have vague plans to make.

So, suggestions? Recommendations? Experience?

acrylic does not absorb the 450nm light well, so you will need to put something on the plexiglass to get it to engrave. i hear black dry erase marker works… though my recommendation is don’t engrave/laser anything you cant afford to replace :slight_smile:

Depends on the color of the acrylic. I ran tests on some extra amber acrylic I had from my enclosure and it had no problem engraving. Clear I used black sharpie on.
-S

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you are correct, the acrylic for the enclosure is designed (with additives) to make it absorb light (like laser safety googles) but most acrylic you buy in a store wont do that. also color alone is not a good indicator, granted that colored acrylic will likely absorb light better then clear, but simply being colored does not mean it is designed to absorb the 450nm wavelength that is emitted by the laser like the acrylic included with the enclosure.

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It’s actually a 445nm wavelength. But close enough for practical terms.

There is nothing special about the acrylic that is used and sold as laser safety glass. It just has been tested to insure that it falls within certain specifications and is consistently manufactured. The key is the proper match of color to the laser being used. For the SM laser at wavelength of 445nm, amber acrylic #2422 is the proper color. It’s basic physics and the reason why an acrylic looks what color it does is because of what spectrum it filters out. BTW, all acrylic, including clear will filter UV wavelength.

The acrylic used with the SM enclosure is not certified and has not actually been tested either. It’s up to the buyer to decide whether that is important to them. (whether they build their own or go with the SM). Either way an enclosure should only be considered secondary protection and proper eye protection should always be worn.

As far as acrylic for cutting and engraving, there are two types. Cast and extruded. Cast works much better for engraving, either by laser or cnc. Generally what you’ll find at your local hardware place is cheaper quality extruded.

You’ll need to do tests with various colors to see if they work with the laser. For cutting, generally you’re going to have more success using CNC than the laser.

As far as venting, acrylic isn’t highly toxic like pvc or abs (which should never be lasered) it can be mildly irritating or just plain smelly and I would highly recommend it to be well vented.

-S

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the colors are created by including additives to the Acrylic. the amount and type of additives effects how much light is filtered. your right about the basic physics aspect but the chemistry aspect is a bit more complicated. as different additives can create the same color, and because 445nm is very close the UV it does not correspond directly to visible light. or in other words, amber is amber because it absorbs blue light, most things that absorb blue light will absorb UV light. they are different frequencies tough so its not a guarantee. clear acrylic filters very little UV light see this document for more information: https://www.plexiglas.com/export/sites/plexiglas/.content/medias/downloads/sheet-docs/plexiglas-optical-and-transmission-characteristics.pdf

though as a rule of thumb you are correct, but there are always exceptions :slight_smile:

Any advice on feeds and speeds for CNC engraving acrylic then?

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I think there are a few threads on here about that.
Try a search.
-S

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