[sjernigan]

I've recently purchased a K40 laser and cut my first acrylic. However, as shown in the photo, the clear acrylic turned cloudy near the cuts; I assume due to the heat. I took 3 passes at 15ma to cut this .22" acrylic at 7mm/s. I have a few questions.

Question 1: Does this power/speed/pass seem reasonable or is my focus off.

Question 2: How can I reduce the clouding near the cuts (e.g., more/less power, faster/slower, more/fewer cuts).

Question 3: I have some lettering that is raster engraved that I would like to stand out more. What techniques have you tried? I was thinking about painting with white or black acrylic paint and wiping it off the surface before it dries.

Thanks for the help

[robertk925]

I don't have a K40, I have a 50W eBay blue&white laser, but I can give you some general advice on your questions.

1. Your picture is really blurry, so I can't make a guess if your focus is off. However, with any laser, especially from China, it is a good idea to do a thorough beam alignment. Check out Youtube for various videos explaining the best ways to do this.

2a. Fewer cuts is always better. My 50W can cut through .25" thick acrylic in one pass at 65% power and 6mm/s. 65% power on my machine is approx. 18mA, so it seems like you should be able to cut through with 2 passes. I would also leave the paper on the rear of the acrylic to prevent backsplash/clouding. You could also try leaving the paper on the front as well.
2b. Are you using a honeycomb bed or something else? Honeycomb beds, although ubiquitous, are actually not that great for cutting, as the melted acrylic vapors get caught in the cells and more easily backsplash against the rear of the part. Also, the honeycomb can often restrict the exhaust airflow, which also worsens the backsplash.
2c. Are you using air assist? Sufficient air assist for cutting will help a lot to make a cleaner cut (and can also help you cut thicker materials by clearing away the acrylic vapors from obscuring the cut.)
2d. You can fairly easily polish out any clouding use a polish designed for plastic like from Novus.

3a. Yes, you can use paint, paintstik (paint in a crayon-like form), or even Sharpie markers to fill in engraved areas. I have tried all three and all work well. Sharpie only works for vector (thin) engravings. Paintstik seems to be the easiest to use and clean up.
3b. You will want to adjust the air assist (if you are using it) for engraving, as too much air-assist actually increases clouding on the surface.

Search for a user named SarbarMultimedia on Youtube for a lot of very useful videos on using a laser.

-robertk925

[coherent]

Use an air blower at the laser burn point to remove heat & smoke. It will likely solve clouding issue. If you have a 3d printer y9oucan print a nozzle.