Results 1 to 2 of 2

Thread: turn away for just a minute...

  1. #1

    turn away for just a minute...

    I typically cut a lot of 1/8" acrylic between November and March. Because I've had a couple of small fires when cutting acrylic, I've (almost...) always stood over the laser machine while it's cutting (usually filling out paperwork, unpacking substrates, packing finished product, etc., but with direct line of sight to the laser head).

    So yesterday I had a little space left on a drop of green acrylic that I'd used to cut shamrock shapes and decided to just finish off the drop cutting some extra shamrocks for she-who-must-be-obeyed. As usual, I turned on the air assist compressor to charge up while I sent the file to the laser, and then started the job. NOT as usual, I forgot to turn the valve that actually sent the compressed air to the laser so there was no air assist. After watching for a few seconds to ensure all was well, I uncharacteristically sat down at the computer to prepare the next job for the laser.

    Maybe 90 seconds later, I stood back up and immediately looked into the laser bed. Something looked odd and I looked closer to see that there was what appeared to be smoke smudges streaking across the protective paper cover sheet, plus a weird shimmering oval. As I peered closer, that shimmer suddenly turned into a yellow-ish flame, the cover sheet under it turned brown, shrivelled and disappeared, and a slumping green puddle appeared as if by magic. Yep, without the air assist blowing onto the cut, the intricate design that was being cut had caught fire. Acrylic burns fairly clear so all I initially saw was the heat shimmer of the flame spreading throughout the cut. When the paper flashed, the flame became visible for a moment, and then there was some black smoke. I yanked the lid open with one hand, reaching for the spray bottle of water with the other, while leaning forward and blowing as hard as I could. That actually put out the flame so that was that.

    The solid shamrock at top center was the first to cut, clockwise from the left. I watched it cut the small circle and left lobe before turning away, and it appears that the paper started to scorch a bit and smoke immediately thereafter, on the bottom lobe and stem... I missed that by only a second or two and likely would have realized I hadn't opened the air valve if I'd seen that... The beam was moving fast enough that the paper scorched but didn't actually become a sustained fire. Ditto when it jumped down and left to cut the outline shamrock. BUT when it got to the intricately detailed one in the middle, the fine details kept the beam in the same small areas long enough to build up heat until the acrylic caught fire in a sustained way, spreading around the cuts until it flashed the paper covering and I blew it out.

    Had to clean the black soot from the lens, and the belt that moves the head back and forth across the gantry shows a bit of melting along the back and bottom edge to the right of the head, but otherwise all's well. Ever hear anybody say that you should never turn away from your laser when it's operating on flammable substrates???
    Attached Images Attached Images

  2. #2
    Join Date
    Dec 2010
    Location
    NW Arkansas
    Posts
    1,951
    Blog Entries
    1
    Thank goodness you weren't far off. Could have been nasty. Yes, I stand really close when I'm cutting acrylic, I'm only 3 feet away at my desk, and anywhere in the office is less than 10 feet. Oh, camera would have helped right? NOT
    Woodworking, Old Tools and Shooting
    Ray Fine RF-1390 Laser Ray Fine 20watt Fiber Laser
    SFX 50 Watt Fiber Laser
    PM2000, Delta BS, Delta sander, Powermatic 50 jointer,
    Powermatic 100-12 planer, Rockwell 15-126 radial drill press
    Rockwell 46-450 lathe, and 2 Walker Turner RA1100 radial saws
    Jet JWS18, bandsaw Carbide Create CNC, RIA 22TCM 1911s and others

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •