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  #1  
Old 01-03-2021, 01:57 PM
shereefb shereefb is offline
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Join Date: Dec 2020
Posts: 5
Default I started a serious fire and lost my machine

Last day of 2020, I came to work in the morning to gushing sprinklers that had drenched the shop.

I left a job running overnight on a stinger 3 x3, a serious fire started and was fortunately put out by the sprinklers.

This was 100% operator error on my part, and no fault of the machine. I'm sharing here to learn more from my mistake(s) and hopefully share the learning with others.

First some facts:

1. This was a 7 hour job, on 1.5 inch MDF, half inch downcut bit.
2. I only had the primary vacuum pump on, not the secondary
3. I was around the job for the first four hours, got tired, and decided to go home
4. It's clear that the fire started in the MDF itself. So it wasn't the machine or anything else around it.
5. There was a shop vac, half-filled with saw dust right next to the machine and it's completely melted
6. There was a lot of "caked and compacted" dust packed in the dust grooves

My assumptions:

1. The dust wasn't getting properly removed. Perhaps I needed an upcut bit with such thick MDF. So that added the fire potential.

2. Leaving a shopvac next to the machine filled with dust made things worse.

3. Perhaps I was using the wrong speeds, and the bit got too hot. I can't imagine that since there were no problems for the first four hours.

4. All the pieces (four of them) have been cut all the way through before the fire started. Perhaps the vacuum wasn't strong enough to hold them in place (I didn't have tabs designed) and the pieces moving around cause the fire and the friction (see this video for an example: https://www.youtube.com/watch?v=D2xo...=GaryGCampbell).

Lessons learned:

1. Watch how dust is getting removed. If it's accumulating, then manually shop vac, or change the bit

2. Don't leave flammable objects next to machine

3. Don't leave machine unattended! And pay special attention to the job when the profiles are fully cut out.

4. Use maximum Vaccum!

That's all I have, I'm still very new to all this, and this was a big punch in the gut. Any help/guidance/wisdom from you would be appreciated.

Hope this story saves someone out there from unnecessary damage.

More pictures here:
https://www.dropbox.com/sh/jok8f4zmd...0Z7TAkGXa?dl=0

Please take a look and let me know your thoughts. It's an expensive lesson and I'm hoping I can benefit from it and benefit others.

And Happy New Year everyone.
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  #2  
Old 01-03-2021, 03:08 PM
mfirlotte mfirlotte is offline
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Join Date: Dec 2013
Location: Quebec, Canada
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So sorry to hear. What a terrible accident and outcome. I hope this new year brings something better for you.
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  #3  
Old 01-03-2021, 05:13 PM
de5 de5 is offline
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Join Date: Jan 2011
Location: Honea Path, SC
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Again, so sorry this happened to you. I never cut MDF, but I do cut a lot of Sapele hardwood up to 8/4. I make only the 1st pass of a profile cut with the downcut bit. Then I continue to full depth with an upcut. This gives a perfect surface from the downcut and also makes the more expensive downcut bits go further.

Since the downcut bits don't clear the chips efficiently, a lot of heat is generated when you try to cut deep with them. In MDF especially you are just compacting dust upon dust. There is no reason to ever do this because only the surface of the wood benefits from the downward cut of the flutes.
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Last edited by de5; 01-03-2021 at 06:13 PM.
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  #4  
Old 01-03-2021, 06:02 PM
Logan Y Logan Y is offline
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Join Date: Mar 2019
Location: Kansas
Posts: 193
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I believe Gary stated in the Camster training that more fires are started from downcut bits than any other. If I use a downcut I typically only do the top pass like people have stated for a nice finish. I use upcuts and monitor chipboard to ensure I'm evacuating chips and the heat from the cut efficiently.

I don't know how long your bit was but always ensure you have enough cutting depth. I've tried to make a 2" deep cut before with only 1.5" of bit sticking out. It obviously didn't go well. My collet ended up burning the wood and if I hadn't been sitting at the computer and hit space then esc pretty fast it could have gotten ugly.

Running at full vacuum wouldn't have made a difference, if anything it would have exacerbated the issue. The problem with heat generation when using a vacuum table is the pull of the air through the spoilboard acts like a bellows and feeds the fire. It then sucks the fire through the piping as shown in your melted PVC.

Thanks for sharing your experience. It's something we can all learn from and hopefully it'll help someone from making the same mistakes.
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  #5  
Old 01-03-2021, 10:36 PM
Jim Becker Jim Becker is offline
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I also suspect that the downcut tooling was a good part of the reason that the fire may have started. It largely comes down to chip load and one of the things it's supposed to do which is slough off heat from the cutter. At first, things will appear ok because there's enough rotational force present that at least some of the chips will still escape because the cutting path is still shallow. But as it gets deeper, the downcut begins to pack material in there and less and less heat is released outward away from the tooling and the material. And MDF produces extremely fine chips/dust which can become almost like cement. Dust extraction isn't going to pull them out. Forced compressed air might to a certain extent, but deep in thick MDF, the going gets tough. So...the heat builds to the point where the tooling gets hot enough to not only start getting dull, but also to the point that it reaches the ignition point of the material, itself.

I was very worried about this when I was cutting some architectural reproduction work for a client out of 1.25" Extera MDF this past year...I used a compression bit, but really should have been using an upcut all the way. The packed in stuff was tight enough that tabs weren't even needed...and it was hard to get the parts out of the background!

It's a wonderful thing that the sprinklers killed the flames before the damage went beyond what it did for sure. The burt is bad as it is, but it could have been "wow"...
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  #6  
Old 01-04-2021, 12:08 AM
Charlie_L Charlie_L is offline
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Join Date: Mar 2012
Location: Wisconsin
Posts: 1,724
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Thanks for sharing these painful learnings. You are not alone. Others here have reported similar events.

Another consideration might have been the toolpath. A job that is seven hours may have things that could be done differently? Feeds, spindle speed, cut depth and other design items would maybe reduce cut time significantly?

Also, learn about restarting a job after stopping. It is easy and creates a way to take a break or finish another day.
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  #7  
Old 01-14-2021, 03:40 AM
Qumaner Qumaner is offline
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This is a frustrating thing. I hope I can learn from this lesson and stop such accidents from happening again.
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  #8  
Old 01-14-2021, 02:32 PM
tmouse tmouse is offline
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Join Date: Aug 2014
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That length of time on a bit cutting MDF is a lot. MDF dulls bits fast
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  #9  
Old 01-15-2021, 01:59 PM
keithrhyde keithrhyde is offline
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Join Date: Jun 2016
Location: Winchester, Virginia
Posts: 372
Default Fwiw

I think the take away here is to not leave your machine unattended for many reasons not just fire. I know with my vacuum it pulls the sawdust chip down into the cuts which even my 3hp Oneida DC cannot overcome. When I have finished cutting through I have to blow the chips out of the cut. The first time I thought I had not cut through the material since I could not see the spoilboard. As Jim stated stop and restart if necessary. I have lost count of how many times I have hit pause and escape. After four years I still hold my hand over the space bar until I am sure even if I have air cut and it looked good. It is a machine and you have to be very careful.
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