Router Sets Wood Chips & Dust on Fire

[Harvey Pascoe]

Holey smoke! I've never seen anything like this before. Just installed a new and more powerful router in my router table and was testing it using a large bit taking only a moderate cut on a piece of scrap pine. As I'm running it through, I suddenly notice that the chips and dust lodged around the dust port are glowing red. I immediately shut everything down and grab a fire extinguisher and run to the dust collector where I expect a major conflagration or even dust explosion. Fortunately that didn't happen.

I've never seen this happen before and the odd thing was that the bit was not burning the workpiece, only the chips. Just wondering if anyone has had this experience and whether it is related only to soft woods like pine, which I never use? All feedback would be appreciated as this is no minor issue.

One other thing I did was, due to the fact that this is a much more powerful router, I reduced the speed from 23,000 to 16,000 RPM. Could that be a factor? I find it very odd that there is virtually no burning on the workpiece yet it set the chips on fire. This event just scares the hell out of me.

[Van Huskey]

Wow, glad all is well! Don't know what you call a "large bit" but if it is what I call a large bit (panel raiser etc) the spindle speed was probably too fast. Router and shaper tooling evacuate heat through the chips (as you learned) and too high a spindle speed or too high a feedrate transfers more than acceptable heat out through the chips. If you post either the exact bit or diameter of the bit someone can recommend a reasonable speed. I wouldn't use 16,000 unless the diameter was less than 2" but that is slightly conservative I believe.

[glenn bradley]

That's a new one on me. Larger bits should turn slower so maybe that it(?). There are generic speed charts online. this intrigues me. Any possibility of a pic of the dust port you refer to?

[Lee Schierer]

I find it difficult to believe that the cutter caused the wood to get hot enough to burn. It could however, be caused by a hidden nail that you cut through or possible by sawdust hitting the arc from the motor armature. I don't think it had anything to do with your router speed. I suggest closely inspecting the work piece for a hidden piece of steel or check the arcing of the brushes on the armature while running that same bit at the same speed setting. I would be very careful when using this router until I figured out what caused the fire to start.

What brand router is it?

[Jon McElwain]

Hmm, I was recently running a 3-1/4 router, inverted in a table using a 3.5" dia ogee panel bit with no heat buildup to speak of.

[Harvey Pascoe]

The bit was a 1-1/2" new cove bit cutting about 3/8" deep. The pine moved though easily and with no laboring of the router - like a knife through butter. No, there were no nails which NEVER find their way into my shop.

Router is a Porter-Cable 8902, brand new. The dust port is a typical one situated in the fence, but in this case not near the bit which was burried in the wood. The distance from the top of the router motor to the port in the fence where the fire started is about 4-5" plus the workpiece was over the top of the router and bit, so I can't see where the motor brushes could have caused it. Were the brushes arcing, it should have ignited the high dust content within the router table cabinet, which is enclosed, so I discount that possibility.

The dust and shavings coming off the bit were very hot. It could be that the pitch content of the pine combined with heat simply resulted in combustion. I noted that it was some very fine, stringy shavings almost like hair that got trapped in front of the dust port that first ignited. I mean this happened right in front of my face and I saw the whole thing.

[Harvey Pascoe]

UPDATE: I just replicated my set up of yesterday and examined it more closely. The piece of wood involved was not pine, but maple. The location where the fire started strongly suggests static electicity was involved, being within the dust port of the aluminum fence. My dust tubes have grounding wires but I suspected that the continuity to ground is no longer effective, so I put a meter on it. NO CONTINUITY !!! Case closed, it was static electricity what done it. In addition to repairing my grounding I am going to add a grounding wire to the router fence as well.

[Lee Schierer]

Static electricity generally doesn't have enough energy to ignite a fire on wood chips or shavings, there just isn't enough energy there. Dust has to be extremely fine like flour to ignite from static. I doubt your router bit makes powder that fine, particularly taking a 3/8" deep cut. Even if you did generate a very fine particle of wood dust, it would have to be adjacent to many others to generate enough heat from combustion to ignite a shaving. Dust concentrations would have to be so thick you can't see through them for an explosion to occur. I still suspect a piece of the wood you were removing went through the motor in the cooling air flow and was ignited by the arc of the brushes and then was sucked into the dust port where it lodged against accumulated shavings.

Unless you are getting zapped by static from your aluminum router fence there is no reason to ground it.

How does air get into your table to feed the dust collector when the bit opening is covered? Unless you allow air into the chamber you may be starving your DC.

[Pat Barry]

The chances of static electricity starting a fire in your woodchips and shavings is next to impossible. I would nominate that for the Mythbuster show on TV. The sparks from your router motor could easily start a fire, however as you said the 4 or 5 inch separation likely makes that a non-issue here. Sounds more like friction of the bit in the trapped shavings and chips - basically how you would start a fire by spinning a stick in some fine shavings to create enough heat.

[Greg Portland]

One other thing I did was, due to the fact that this is a much more powerful router, I reduced the speed from 23,000 to 16,000 RPM.

Set your router speed based on the bit diameter, not the power of your router. For example, if you had a 5HP shaper you'd still need to run that narrow bit at high RPM.

The piece of wood involved was not pine, but maple. The location where the fire started strongly suggests static electicity was involved

No, it was not static electricity. I agree with Pat, something in your setup caused increased friction. Maple is particularly prone to burning & the router creates a nice breeze to stoke any embers.

[Will Overton]

If the bit is buried in the wood with the fence a good distance away, how were the chips getting into the dust collection port in the first place?

[pat warner]

Have seen chip fires caused x routers.
Witnessed one wherex the operator way over abused the machine with a dead cutter.
The chip was a friction chip. Very fine recut stock. Depositied in the waste and lit off.
The other event: Accumulation of fines (particularly soft wood) under the motor cap, worked into the brushes.
Lots of friction here, shot hot chips into the waste. Both conditions from poor house keeping and abuse.
Have busted many cutters (steel & carbide), have gone through steel & lead (bullets), no fires.
Always something to be aware of tho.

[Chris Padilla]

UPDATE: I just replicated my set up of yesterday and examined it more closely. The piece of wood involved was not pine, but maple. The location where the fire started strongly suggests static electicity was involved, being within the dust port of the aluminum fence. My dust tubes have grounding wires but I suspected that the continuity to ground is no longer effective, so I put a meter on it. NO CONTINUITY !!! Case closed, it was static electricity what done it. In addition to repairing my grounding I am going to add a grounding wire to the router fence as well.

I'm with the others, it was likely NOT static electricity. It it VERY difficult to get static electricity to ignite sawdust and/or chips. Also, exactly how did the current flow through the chips to heat them up? There must be current flow to do this and I just don't see the path.

Further, "grounding" plastic is exceedingly difficult seeing how it is an insulator (very few free electrons to move). To fully cover all the spots on plastic that might harbor charged areas would require many wires...so many that you might as well use metal duct. Now that one you can effectively ground with a single point.

[Matt Day]

I think Harvey is just trying support the dust collection business by trying to justify those grounding fliers you get with every piece of dust collection equipment.

[Cody Colston]

Forget static electricity causing the fire. That's a red herring.

If you don't have dust collection in the cabinet but only in the fence, it's a good bet that the friction from the cove bit buried in the stock ignited the shavings. BTW, not only will the bit and stock run hot but the router will also run hot if there is no air moving past it. You need DC on an enclosed cabinet as well as through the fence.

You stated also that you ran to the DC expecting to see a "major conflagration or even a dust explosion." It sounds like you may be a bit infatuated with the idea of wood dust acting like a grain elevator...hint, they are nowhere near the same condition.

A spark in the dust collector drum would smolder like a cotton mattress, not flame into a major conflagration. AFAIK, there has never been a documented case of a dust collector explosion from wood dust igniting.

I can testify that if you dump the contents of a DC drum onto a live flame, it will respond similarly to throwing gasoline on a fire. DAMHIKT