Is my router bit toast? - It was smoking hot.

[Randall J Cox]

I'm building a decent router table fence with adjustable fronts and dust collection. I just routed a 24" stopped dado in some 3/4" plywood. I will be mounting a 24" blue aluminum t track in the dado to hold my hold down fingers on my router table. When I was done routing, I let the router stop and lifted the piece of plywood and not only was the bit smoking (a lot) but there were globs of sawdust glowing very red. I put them out quickly to keep the rest of the sawdust from igniting. I/m glad I wasn't using any dust collection where the red embers would have been sucked down into a sawdust pile! Anyway, do you think my carbide bit is toast? I know you can lose the temper in steel when it turns blue. But what about carbide? It, the router bit, turned black. Randy

[Lee Schierer]

It sounds like possibly your bit was dull and there was no place for the chips to escape. How deep was your cut. A full 3/8 x 3/4 dado in one pass is pretty aggressive. Router bits generate a lot of chips and if they can't get out of the cut the will produce friction on the bit.

[Randall J Cox]

It sounds like possibly your bit was dull and there was no place for the chips to escape. How deep was your cut. A full 3/8 x 3/4 dado in one pass is pretty aggressive. Router bits generate a lot of chips and if they can't get out of the cut the will produce friction on the bit.

Yes it was the whole enchilada in one pass, not to bright huh... I have a 3 hp PC router and didn't force the cut very much, tried to let the bit do the work. But, the channel was indeed clogged with semi-burnt sawdust when done.

[Matt Day]

Live and learn.

Has the bit turned a dark rainbow color?

[Edwin Santos]

Even though you have a powerful router, I think it would be wise to take small bites in multiple passes. Also, the lack of dust collection may have contributed to your problem of packed chips and sawdust.
It's hard to say whether your router bit is salvageable or not. The heat build-up would not be good for it.

When faced with operations like this, I often make a first pass with a spiral upcut bit in a smaller radius. Then change bits without moving the fence, and make your final passes with the 3/4" bit. The first pass will act like a clearance channel for the subsequent passes. I admit I'm super conservative but if you have the patience, it's safer and easier on the tools.

[Derek Cohen]

I know you can lose the temper in steel when it turns blue. But what about carbide?

Randall, I would imagine that you are safe. I doubt that you have the capacity to even begin the approach the limits of Tungsten Carbide's tempering level.

Regards from Perth

Derek

[Charles Lent]

If it was me, I would toss the bit. The carbide may have survived, but the rest of the bit and shank have likely been affected. At high speed it will likely break, and the absolute last thing that I want flying around in my shop is a piece of a sharp router bit. To me, it just isn't worth the risk to use that bit any more.

Charley

[Randall J Cox]

It did not turn rainbow color. And even though I have never heard of carbide losing its temper (like Derek said) I think I will err on the side of caution and toss it and called it a learning lesson. I even knew better when I started that I should route some of the wood out before going to the full depth and width. Ever now and then I think I am smarter than I really am.... ha ha thanks for all comments.

[Lee Schierer]

What brand router bit was it?

[Carl Beckett]

Are the shanks and bodies of router bits tempered? I assumed not (but never thought about it!!)

Unless the shank is tempered and there is a concern that some structural damage occurred, I see no reason to toss it. My philosophy to router bit wear is 'if it still cuts good enough, its still good'.

So just use it and take lighter passes. In fact on popular sizes like 1/2" and 1/4" dia straight bits, I have more than one. I might abuse some duller ones and save the pristine sharp ones for finish/critical work.

[Randall J Cox]

What brand router bit was it?

It came in an MLCS anniversary kit of about 35 1/2" shank carbide bits that I bought about 35 years ago.

[George Yetka]

I believe if you had the dust collection on you would have cleared some of the dust, eliminating the friction. Plus the air moving over the bit would have cooled it. I think it would have been safe.

On the next one I would plunge full depth at both ends then run it in 2 passes

[David Utterback]

While agreeing with the comments above, it may be glue and/or non-wood contaminants that contributed to the problem.

[Matt Day]

Tossing it seems silly and a waste. I’d guess you weren’t even close to the temp needed change the properties of the metal.

Unless you just want to buy new router bits, which is a good enough reason for me!

[Richard Coers]

I assume that is a standard two flute bit. An uncut spiral would not have had the same issue. Pitch that cheap bit, no need to have it sharpened, nor attempt to dress it with a diamond stone.