I realized I had not yet experimented with 3D engraves. I grabbed some 1/2" acrylic thinking I might try to go really deep, but I ended up pulling them to examine before getting too crazy.
Here are the two images I engraved.
Here are the results. I also found that a final pass with a de-focused beam did a pretty good job of polishing the engraved surface.
Super cool
I like that swirl thing…and think it would make a neat leather press. 
Can you describe how you did the de-focused pass?
Holy wow. All I’ve done is 1/4 and I thought that was amazing enough.
Those turned out awesome! looks like 3/4" acrylic?
Also interested in the de-focused pass, I’ve ran them on acrylic but havent reached a polished effect yet.
When you use manual settings, the focus depth is one of the user defined variables. In my case I set the final engrave from the surface of the acrylic (current max, 0.433 in this case) down to the bed at 0.01. Because most of the top surface was well above that, the portion of the beam hitting the acrylic was larger. That larger beam is what produced the smoother finish.
Seriously Amazing. Once again my mind is blown. Thank you.
I assume you just repeat the same piece? Would it be feasible to use a different lpi on the polish pass to save time? Could the same effect be achieved in less time with a small torch?
I did several passes on both, playing with settings as I went deeper and deeper.
I would say yes to both different lpi and torch, however I have not tested either. After seeing recent activity with the 3D settings I decided to give it a try. There is lots of potential for sure.
You can actually use a heat gun to polish acrylic but flame polishing with a torch is the more common (and likely faster) method.
Ooh. Another justification for the rarely used oxy-acetylene torch set that I “absolutely needed”.
“Never glue a flame polished edge,” they say. Isn’t every laser cut edge essentially flame polished?
Just scuff it first with some 120 grit sandpaper before applying the glue.
I believe so. I didn’t watch that video, but saying “polished edges may give undesired results” would have been more informative than “never do that”.
IIRC, extruded acrylic has more of a tendency to craze than cast, but it’s possible with both. And a polished surface might not be as conducive to the capillary action that some gluing techniques rely on.
People say annealing the acrylic helps/solves the crazing problem.
The issue is not the roughness, but that the flame induces residual stresses into the plastic that cause small cracks (crazing) when in contact with glue.
Never experienced that, and I’ve flame polished tons of plexi/acrylic.
You just haven’t run across it yet. The video above shows clearly what happens, but the issue is a “can happen” thing, not necessarily a “will happen” thing. The time that the acrylic is exposed to liquid solvent plays into it as well. Faster evaporating solvents tend to have less impact on crazing.
@Scott.Burns is correct about the roughness not being the issue. The smooth faces of acrylic weld/bond just fine.
Very cool. The spiral cut is really interesting.
