CRAZING / HAZING on BLACK ACRYLIC

[James Cogbill]

Hazing Example_V1_082114.jpg
Hello,
I've been noticing lot's of CRAZING / HAZING when laser cutting Acrylic, specifically BLACK. By turning down the power and taking multiple passes, I've been able to remedy this condition. Obviously this isn't ideal, because of the increase in time. I've attached a photo for reference. Any tips to remedy this using single passes? If I figure it out, I'll be more than happy to share my solution with everybody. Thanks very much!

[Rich Harman]

Is that the bottom side? Looks like you may have a flame going on underneath while cutting.

I get the best results cutting thick acrylic when it is raised up off the table using a bed of nails, with a strong air assist. I also leave the paper on. I always cut in one pass.

[James Cogbill]

It's the top side. I use a honey comb table, with the acrylic raised up on stilts, with air assist; leaving the paper on. It seems to occur with 1/4" and thicker.

[Ross Moshinsky]

My guess is you don't have enough power to cut in one pass.

[Rich Harman]

I would check your alignment then verify focus. I always focus on the surface whether it is 1/16" or 1/2" thick. Is it cast acrylic? What's the power of your laser?

[James Cogbill]

Thanks for the feedback. It's a 60W machine.

[james moriarty]

dont know if this will make a difference but i find cast acrylic cuts better than extruded it cost abit more (and the black looks more black)

[Jerome Stanek]

I just ran a job using both cast and extruded Acrylic and the Cast cut so much better.

[Frank Corker]

That looks a little like acrylic sweat marks, where the vapour from the cut acrylic sticks to the shiny surface. Transfer tape might help prevent it. It might also be from having alcohol on it after it has been subjected to heat, a buffing wheel can help to eliminate small defects, scratches and a bit of blooming.

[Jerome Stanek]

I just recut a job that looked like that and used transfer tape. Ran the laser at 100mm 40% power 2 passes and the hit it 10 mm 85% power to cut .25 extruded acrylic with VHB tape on the bottom the tape was the thick stuff that doesn't cut very good but they came out nice and clean not like the first set.

[James Cogbill]

Interesting...so I would apply some transfer tape, or double sided tape; run the job and then remove the tape. I'll give it a go and report back. Thanks for all the feedback, everybody!

[Kevin Gregerson]

Check your optics. They may be dirty or the coating may have been cleaned off. What size lens are you using?

[Richard Rumancik]

..so I would apply some transfer tape, or double sided tape; run the job and then remove the tape . . .

I don't think you want to use double sided tape or VHB tape (very high bond). Jerome was using VHB for another reason (presumably to bond the part to another surface) . . . it is not intended to be removed. You want to use only transfer tape - it comes in various levels of tack. Basically it is a wide masking tape but more suited to the task. You need the tape to adhere well to your substrate so as to seal against acrylic vapor and smoke, but not so tacky that it is hard work to remove it. Sometimes a bit of heat will help release the transfer tape.

[Jerome Stanek]

I was using the transfer tape on top and the VHB on the bottom so when the letters were cut out you could mount them to a wall the letters were only 2.5 inches tall