Acrylic Fires

[Dan Wilhelm]

My day job is looking at burned things to figure out what caused the fire. I have now looked at two laser engravers (a 60W Trotec Speedy 300 and a 40W Epilog Mini) that have been involved in fires. In both cases, the user was cutting acrylic and it caught fire. Neither of the lasers were significantly damaged, but it makes me wonder how many SMCer's have experienced smaller fires while cutting wood or acrylic.

I just have a 60W GWeike LG500, but I have had a few flare-ups on wood when I forgot to turn on the air-assist. But I wouldn't think of leaving the cutter unattended during use. Then again, the laser is an amusement and occasional side job for me, so I don't run high volumes through it.

[Mitchell Tutty]

I've had a few flare ups, nothing to big, usually from driver error though, like running out of focus or over powering it. I've always been very vigilant of the laser, particularly when cutiting, so luckily I've been right there during any sort of flare up. I find it very important you have a little spray bottle full of water handy at all times for those little flare ups before they get out of hand.

[Robert Walters]

I can't recall who it was (someone here on SMC), but this is one picture of their laser that caught on fire when they just answered the door for UPS or went to the restroom I believe.

Also...
I believe there was a technical complication with their insurance, so the laser fire was NOT covered under their policy.
Be sure to check and confirm with your insurance company if you have the proper coverage, including current replacement value if applicable.


http://www.laserworks.jp/images/f03.jpg

[Henri Sallinen]

I've had a few flareups when cutting acrylics. I never leave the machine unattended when cutting this kinds of materials. If I see the acrylic catch fire, I just press stop and wait for the flame to go out. In all cases the flames were under the acrylics, not on top.

The reason for these flames is just too much power and have happened when experimenting with new sheet thicknesses or faulty settings for the current thickness.

[Joe Pelonio]

The only flares I have had with acrylic were minor, and limited to when a cut was withing 1/4" of the edge of the material. More often than not when cutting I apply transfer tape and mist it with water to avoid any flaring.

[Scott Shepherd]

We cut a lot of acrylic compared to most people I know with lasers. Last week we cut 5 sheets (4'x8') of 1/2" thick clear acrylic. I've been cutting it for years now and I've seen many flare ups and issues. I've studied the cutting for hours and hours, just staring at the cuts while it's running, trying to determine the rhyme or reason for issues (and to eliminate those issues).

Acrylic is a very trick thing to work with, in my opinion. It's unpredictable at best. One piece cuts great, no issues, the next piece, from the same sheet, with the same settings, flares up. One piece cuts great, the next piece blisters the back.

Cast acrylic is very strange at that thickness and has some properties that make it undesirable in many cases. You can cut cast quicker. It cuts a fair amount faster, but at the same time, the cast doesn't act as a true wave guide on the thick material and the exit cut seems to wander all over the place. Put a piece of extruded in, cut a 1/4" hole in 1/2" thick material and the hole is about the same on the top and bottom, put cast in and the hole is round at the top and shaped like and egg at the bottom from the beam getting deflected deep in the cut.

I'm really, really, really careful at all times when we have thicker acrylic in. I've never seen an issue with thinner acrylics, like 1/8", but we still watch it like a hawk and no potty breaks while acrylic is running.

I hope we can keep our focus on running it and never get too comfortable. It's just a very volatile material, in my opinion.

[Clark Pace]

Hi,

I have had a few myself. Mainly on 1/2 thick acrylic. My office wonders why I stay close the laser when it's operating. Some times it can look like you are not doing anything. But believe me don't step away please! I pause my machine if I have to leave the room. Sounds a little crazy right! Well consider this.

Another laser company close to my area who has been in business for many years left their laser for just a few to go into the house. Next thing entire shop and I believe part of the house is on fire. This just happened a few weeks ago.

Don't take the chance.

[Mike Null]

This topic has surfaced a number of times but it serves a good purpose.

Don't be lulled into thinking your machine can't catch fire! Stay with your machine at all times.

[Rodne Gold]

Major cause of Flare ups is too little air assist

[Scott Shepherd]

Major cause of Flare ups is too little air assist

I've not found that to be true on our end. I've varied the pressure widely over the years and it's not changed any of the behavior I have seen.

[Rodne Gold]

Ok , blow on a candle from 10 ft away and try put it out....

[Clark Pace]

Yes the air assist may help reduce fires from the top, but i've found if you are doing thick acrylic it get hot enought on the bottom, that the acrylic combusts. the few flare-ups I have had oveer the years come from the bottom of the piece. So don't trust the air assist. Just my own 2 cents. It only takes 1 time

[Chris DeGerolamo]

Had a fire a few years back cutting slowly through acrylic. Lost the grid because molten acrylic stuck in the comb itself. Other than that, we got lucky it was caught in time...we do not have someone sit with the machine 100% of the operating time.

[Dave Sheldrake]

Major cause of Flare ups is too little air assist

Yup, every time.

cheers

Dave

[Clark Pace]

Glad to hear everthing was ok. I would say you don't have to sit in front of it, but at least be in the same room where the laser is pretty visable.
Had a fire a few years back cutting slowly through acrylic. Lost the grid because molten acrylic stuck in the comb itself. Other than that, we got lucky it was caught in time...we do not have someone sit with the machine 100% of the operating time.

[Jon Sollee]

Our air assist all the way up and our vacuum table at full power really keeps the fire going... I have burn the out of plywood and acrylic. Seems like the airflow keeps the fire burning even when you try to blow it out... Im no fireman, just learned from experience.

[Scott Shepherd]

Ok , blow on a candle from 10 ft away and try put it out....

Well, if you want to play word games, then try to light a match when the wind is blowing 10 mph vs. 50 mph. You won't light either one.

That means nothing. The majority of my experience tells me the fires start from the air not clearing UNDER the work, not the presence of high air volume on the top side of the piece. I have NEVER seen a fire start on the top side of acrylic. It's always on the bottom. If you can get good air flow- not air pressure, but air flow, under the work, you can help prevent them to some degree.

Synrad recommends like 1 psi. Synrad being really wrong on cutting acrylic is highly unlikely.

I've tried from 1 psi to 60 and I've not seen 1 ounce of difference in flare ups or cut quality.

Your mileage may vary. All our lasers have air going through the kerf, not air blowing across the top of the work, so maybe you're machines require something different.

[Kev Williams]

Honeycomb tables are great for smoke removal and providing a convenient cutting surface. But they do zilch for airflow beneath your work.

If your material is sitting on top of a honeycomb table, you may think you have plenty of airflow under the material, when in fact you have nearly none, even if you're using a 2000 cfm blower. All the air is moving around the edges of the material, but not around the bottom. The vacuum from the blower actually seals the material to the table, so anywhere under the material ends up being a total dead-air space. No air moving = easy for fires to start. And no way to 'blow it out' if if a fire DOES start (speaking of candles ;) )

You need to raise the material off the table to create a space for air to flow, that way the blower (vacuum) can draw air under it instead of just around it. And if you cover the open areas of the honeycomb around the work piece, more air will be forced under the material. Do this, and you'll find it's nearly impossible to create a fire even if you try, and you'll likely find you need much less air assist, if any.

HOW to raise the material is the $64 question, but there's many ways...


.

[Dan Hintz]

If your honeycomb table is actually a vacuum table, too (such as the case with the ULS design, and Trotec's if you purchased the vacuum table option), then you have airflow through the crack you just lasered. Not a lot, mind you, but with sufficient SP it should be ebough to kill off (most) flames. Still, you gotta watch it as nothing is foolproof.

[Jerome Stanek]

I raised my honeycomb up with some .5 stands. I can see the smoke going under it

[Scott Shepherd]

I raised my honeycomb up with some .5 stands. I can see the smoke going under it

I cut a glass full of 1/2" diameter circles (circles because they don't mess with airflow like a square will) and I just put a handful of them on the table, put my acrylic on it, and then cut away. When I cut new circles, I cut different diameters out of different sheets because the thickness varies a lot. That way I can grab all the ones the same size and know they are the same thickness.

[Bert Kemp]

I screwed round head screws all around the bottom edge of the honeycomb, it raised it about a 1/4" off the table and works just fine.