Ember, and almost fire in my shop

I was cutting the 4th sheet of a furniture project from 0.75 inch thick oak plywood (appleply) in the basement. Before with the same router bit I cut 2 sheets same size 1 inch thick oak appleply.

was this item:

I was in the room, with my back towards the shapeoko, sanding (dust mask, noise protection…), and did not mention anything, my wife smelled it in the first floor.

All the other parts went well, and all the sudden that happened:

Google Photos

(how can I include photos?)

In another topic a loose router bit was blamed to cause some heat by friction. I am pretty sure that was not the case here. It was a 0.25 inch bit.

Can it be that this one was already dull? It still felt sharp when I checked it with my fingers.

Is it possible that a dull router bit causes such a disastrous outcome? After almost 4 sheets? (the size was 2x4feet each)

(I have a fire extinguisher in the shop, and sincerely hope will never need it…) I removed the ember and chips in a can, closed it and brought it out. I am happy that the dust removing system does not work properly yet, otherwise with the ember in the dust bag… unimaginable.

Please help. TY!

Can I recognize when a router bit gets dull? And how?

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With proper dust collection, or at least chip clearing from the slot, this would be less likely.

That said, any chance your plywood has metallic contaminants. I had a sheet that I thought I saw throw sparks when I cut it on the table saw. After I knew I saw sparks on the CNC, I looked closely and found that there was a band of ferrous fragments. Looked almost like glitter and was really delicate. I continued with the cut and watched closely. Nothing more than those first few sparks, but I was paranoid checking my plywood after that.

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AFAIK the appleply is the finest you can get, of course it is possible to have some metal chips in it, will check it. May be, since it happened at two places separately. Today I was too shocked to do anything at the machine yet.

And yes: the thing with the dust removal:

I had a Xcarve before, that had a Z-axis independent dust shoe, the shapeoko attaches it to the router, so with thicker materials the brush curtain of the shoe is compressed a lot. Now as you see I have a otherwise excellent Z-axis independent system attached from pwncnc, excellent thing. BUT! the router itself blows air downwards, so the chips are blown out of the dust shoe, neither of my vacuums only nearly had enough power to get the dust / chips out of the way. For that purpose I intend to attach another router, a Kress (AMB) 800 FME, what does not blow air to the cutting site. Hope / expect then the dust removal will work again properly.


definitively it was a dull cutting bit.
this is the one after I took it out:
not a cheap one: was a Freud
These are the cutting edges:


Another one in my collection also had a colored tip:
the edges:
also not cheap, a Bosch:

both solid carbide.


check the cutting edges always, at least when the tips start to turn blueish.

brand new Carbide3d #201:(can post two links only in one post, so image to compare in the next one)

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comparison, brand new #201 from Carbide3d:
Google Photos
What I did not read yet anywhere, is, that a dull tool is a fire threat. Was surprising. I always learn the hard way. Hope for another reader that experience can be a heads up.


Another issue with heat buildup come from slot cutting, where both side of the bit are constantly engaged with material, even if not cutting, it is still rubbing.

I would 110% look at how you are doing your tool paths to eliminate slotting if at all possible.


That Bosch is a downcut bit, it will take a lot of heat and stress if you’re not on top of chip clearing. Also good to decrease the DOC to prevent chips from jamming up in contour paths. I’ve been using the same C3D #201-Z bit I bought with my machine 3 years ago. :slight_smile:

I’ve done a lot of cutting with it, all wood. I think it’s getting close to end of life, can hear a little more stress on the cuts. But it’s barely warm to the touch when I pull it out for tool changes. Anytime your tooling is taking that much heat to the point of discoloring them, that’s a problem. Likely a dull tool or an issue with speeds/feeds/depth of cut stressing the tool.

And I go with pretty much everything is a fire hazard. Sparks from your brushes, excess heat in the router motor, airborne sawdust, old extension cords over amped, any dull tooling, the list goes on. Just a few weeks ago I was getting embers off a dull band saw blade. Cast Away anyone?

… and another thing! :smiley: :smiley: :smiley:

Dull bits and slow cuts make great fire starter powder. If you’re making powdered wood, then you need to change something.

The Bosch was not used in this project, just to show how dull a cutting edge is when the bit turns blue. Now I use the #201 from Carbide3d.

You mention the brushes: is there any way to check their end of life? With a former router a workpiece and a router bit was destroyed because the router stoppe due to the used up brushes.

On the Dewalt you can peek through the vent holes on top with a flashlight and see how far forward the wire attached to the back of the brush is. But even that is kind of a pain - the easiest is to pop off the 4 screws holding the top cover on and that gives you full access. I think the Makita and C3D routers have brush port covers you can unscrew on the sides. I had about 150 hours of run time on my Dewalt and the brushes were wore to nothing, but YMMV.

If you have a Dewalt, here’s the full rebuild procedure. I found I had bad bearings too:

Well, the easiest and “cheapist” way is to set a schedule to change the brushes every year or two or whatever. They don’t cost as much as a good piece of walnut with 12 hours built into it!

That way you don’t need to worry about “end of life.”

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TY! I have a Dewalt 611 in my other CNC machine (XCarve) what I do not use any more, kind of replacement / spare part. Changing the brushes is not too difficult with this one. loosen 2 screws if i remember right.

absolutely right. Will do so, just marked the day of first use on my router, change the brushes within 1 year. Thankfully the shapeoko comes with a pair of replacement ones.

Nothing wrong with changing brushes bit the brushes are up top. The pic has the router base and material burned. Either bad luck or maybe the material slipped causing the router motion to stall and heat up the material. Just spitballing.

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