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Look at the state of these two 1/4in bits (see upload). These are best-quality bits made long ago by Trend in the UK, and both were professionally sharpened in the past year. But today as always, I find they blacken up like no other bits I use (including Chinese). I think I must be doing something wrong with them. What is it? I use them almost exclusively to cut natural wood - mainly these days, adjustment slots in jigs. I run them at or close to the router's maximum speed. I plunge my cuts by sensible degrees. And yet ... There's the 'coffee grinder' effect of chips trapped in a narrow slot. Nasty smell of burning. Is that it, and is it actually unavoidable? Or is there some lick that I have been missing these past 30 years? Any advice gratefully received.

Cheers
Mark
 

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incorrectly sharpened...
any other bits doing that???
 
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Mark, the bits are getting too hot. I agree with Stick that this is most likely caused by not being sharpened properly. Once the bit has changed color like that you have lost the temper of the HSS.

I use a couple of Trend products that I think you could make good use of: their diamond card sharpener and their Tool and Bit cleaner. Both products work very well and I will post a thread tonight showing how to touch up a bit.
 
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@Mike...
those look to be carbide bits..
pretty sure any ways...
 

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Is the wood you are using very pitchy? Resin buildup will slow the chips from clearing the cutting edge like they should and would generate heat.
 

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guardoff,

When ever I had a bit get too hot, it went to a yellowish/purplish/blue never black. The black I found on my bits was from the wood being heated to char then smearing on the outer surface of the bit. Also the bluing or charring occurred only at the point of contact; nearly the entire length of both bits is discolored in the pic.

Those aren't plunge bits; they don't have the plunge bit crossbar between the carbide tips that would clear out debris before it could burn. Wood binds up in the hollow between the carbide, heats and burns.

Plunging a non plunging bit requires the router to be moving as the bit is lowered into the cut.
Is it possible the bits or wood has come in contact with something?
Did the bits burn before the 1st resharpening?
Have you tried a 3rd bit, diff brand and duped the process to see if it burns?
 

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Yes Stick, I was trying to make a point. Some times you just can't short cut an explanation; my bad. Tool steel has lost its temper when it changes color like that. For a carbide tipped bit to overheat and change color like that it has been improperly ground when sharpened. There is not enough relief behind the carbide and the wood is hitting the steel of the bit or the cutting angle is ground wrong which has the same effect. My guess is that when the bit was sharpened it was ground on the outside surface to restore a sharp cutting edge. It is acting as a scraper instead of cutting. It is easy to verify this by checking the actual diameter across the cutting edges. If it is smaller than what it is supposed to be by a fair margin this is what happened. Every time a bit is properly sharpened it will lose a tiny amount of diameter which will not effect performance and this will be in thousandths of an inch. Incorrectly sharpened bits will be reduced by hundredths of an inch. If the shear angle of a carbide tipped bit is altered it will result in friction and heat.

I bought one cheap bit that had too thick of a paint coating on it which caused instant burning of the wood and tremendous heat on the bit. I took it back for a refund.

Trend's Tool and Bit cleaner does a great job of removing resins and rust; it also lubricates the bit. Any build up on a bit will result in heat being generated so this is an easy way to avoid that happening. Priced here at $12 a bottle it is cheap insurance. 20 minutes with Tool and Bit cleaner salvaged these bits I got in a package deal.
 

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Discussion Starter #8
Thanks to you all. Mike, I look forward to your post about touching up a bit. Stick, those are two-flute bits with TC cutters. Ghidrah, you say these are not plunge bits, and that does surprise me. Fact is, I am only raising the issue after all these years because this forum gives me the opportunity to do so. The biggest issue, I think, is the quality of the bits' recent professional sharpening (which was their first sharpening ever). So I will slap the work down on their counter when I am next in the shop and demand an explanation. They are nice people and will surely have something intelligent to say. Which I will report back to you, and you can all tell me how wrong they are.

To be continued
Mark
 

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gaurdoff,

As Mike and Stick pointed out likely bad bit sharpening.
Still I've never seen a bit, let alone 2 side-by-side with nearly identical scorching for most of the length of the bit including the shank.
It's bugging the crap out of me, at what point in the process did the smell of hot metal, burning wood, the sound of a strained router or the visible burned results in the cut area were you prompted to stop and question?
 

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Ron, this sort of overheating happens without notice. No way to tell until you stop the bit. The cut can even look normal.
 

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I have. :(
 

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here too but Dan did it...
 

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Dan must have burned mine too then. Shame on you Dan.
 

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A lot of mine seem to be burning - in pine. This thread is very helpful.
 

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A lot of mine seem to be burning - in pine. This thread is very helpful.
tell Dan to put router down and stand back..
problem solved...
 

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Too late; it's (the bit) toasted.
I just know you are hanging your head in shame...
but that grin kinda negates the sincerity...
 
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