Reminder! Keep A Close Eye On The Laser!

[Ed Maloney]

I know this has been discussed plenty of times, but I got the scare of my life last night.

I was running a sample acrylic item on a scrap sheet of black acrylic that had room on it to fit the piece. I was watching the laser closely since I wanted to check to see if some of the optimizations I made to the vectors was working.

Blower on, air assist on, and the masking on the bottom only. As I was watching it, there were some flare-ups which I usually see on clear acrylic so I wasn't immediately concerned. After a second or two this flare-up didn't go away and got bigger. The masking then caught on fire. I first hit the reset button and got the laser head out of harms way, then turned off the blower and the air assist. I kept the lid shut and after what seemed an eternity the flames went out.

No damage to the laser and I cleaned the lenses and ran the sample (nervously) on another sheet. It worked out fine, no flare-ups, but I called it a night!

[Dee Gallo]

Close call, but good save Ed! We all need these reminders, thanks!

[Ed Maloney]

Something strange is really going on.

Just now I was cutting a whole sheet everything looked fine, and it flamed up again and must have been on fire under the sheet since my honeycomb grid is now brittle and has gapping holes in it when I pressed lightly on it. Exhaust seems to be fine and the air assist as well. I've been using this type of cast acrylic for years. I just sent email to Epilog support. In the meantime any suggestions?

[Michael Simpson Virgina]

Make sure the blower is blowing. Start a vector cut with the lid up. If you put your finger under the nozzle you should feel and hear the air change pitch. Its also possible that the mask has had some sort of contamination at the factory or distributer.

[Frank Corker]

That is very good advice from Mike. The nozzle on mine was giving me some problem. I traced it back all the way to the compressor itself and the air intake protector (made of metal) had corroded over blocking air being sucked into the compressor. Cleaned it, pressure at the nozzle was amazing.

[James Terry]

I wish we could see some videos or photos of these things happening. Nothing is more motivating than the image of a destroyed laser or workroom.

[Ed Maloney]

Flame1_800x600.jpgFlame2_800x600.jpg

[Ed Maloney]

Well it happened again last night. New tube, no exhaust leaks, and plenty of venting holes in the material.

I believe what is happening is that when the cuts are detailed and close to each other and in a small area. Ya know sometimes when you are cutting acrylic and it may flame up a little in an area, but dies down when the beam moves on? Well - I am guessing that since the piece had lots of cuts in a small area, the laser didn't have an opportunity to get away from the problem area.

Opinions, comments?

[Chuck Stone]

I find it sometimes when there are too many nodes in close proximity. Now I've
decided that no matter what the file is, I'll go in and manually delete the ones
that look superficial to me. I know Trace adds tons of unnecessary nodes, and
even duplicate lines. If I set the power to *just barely* get through the material,
it does me no good if the laser goes over the same lines again..

[Mike Mackenzie]

Ed,

One thing to keep in mind is the cutting grid. When you cut acrylic it turns to a liquid and builds up in the honeycomb. It could be that this is what is igniting. Try giving the honeycomb a good cleaning.

[Scott Shepherd]

A couple of years ago I cut a lot of thick acrylic. I tried to determine what caused the flare ups. I never could. It was a totally random event. I repeatedly cut the same thing and one time it would cut great, one time it would flare up.

Last week I just finished cutting a bunch of 1/4" acrylic. I cut 45 pieces with no issues. I cut 45 more pieces and it flared up on a large number of them. One piece would blister badly on the backside, the piece beside it, same shape, would cut smooth and no blistering. One time it would be the part of the right side of the table, one time it would be the part next it it. It all came from the same sheet and was within .003" of each other in thickness. I came to the conclusion back then, and once again last week, that there is no logic involved.

[David Fairfield]

Seems its usually acrylic that starts the fires. But I've had a few small ignitions with paper, and chads that heaped up under the grid. Never with acrylic. You can never let your guard down, Mr. Murphy is always waiting...

Dave

[Richard Rumancik]

A couple of comments . . . when you cut acrylic it goes from solid to gaseous state - I suppose the gas could condense on a cold surface as Mike is implying. The gas is flammable, and ideally the exhaust system mixes it with enough air fast enough that it quickly dissipates. But the actual airflow around the material, through the honeycomb, etc is very unpredictable. There is a lot of turbulence and there are also probably some dead spots where there isn't much flow. So in the right circumstances, the gas could build up and create a flare for a few seconds.

Now to get a material to burn, you need to get the temperature up past its ignition point. But in the middle of a sheet, with a straight cut, this probably won't happen as the material will absorb the heat and dissipate it quickly (unless it is very thin film.) But if you are cutting at the edge of a sheet, or cutting alongside a prior cut (leaving a web of say .025" acrylic between parts) the temperature of the thin strip can approach the ignition point. Now add a bit of a flare to the thin web of acrylic and you have a fire. Parts with lots of contours and detail cause the beam to dwell in one area for a long time, so that area will hold the heat and the temperature will rise.

[greg lindsey]

I keep one of these by each machine. Bought from HD for about $7. Peace of mind for a few dollars.

[Neil Pabia]

If you can find it, there was an old fire extinguisher that used Halon gas to put out the fire, it worked great and left no residue. I know they stopped making them a while back and replaced the gas with something similar.