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Never done this before

If you overheated the steel in the gouge during sharpening, it may have become brittle and it was waiting for the opportunity to to break apart when it hit something very hard, like a rock, nail, knot, etc.
 
Well, you can't overhead the modern metals to the point where they lose their tempering. I am guessing that it was just a bad spot in that particular gouge. That does happen, though it is very rare. Looks like one of Doug Thompson's gouges. For unknown reasons, walnut seems to be hard on all cutting tools, more so than most other woods...

robo hippy
 
It is too late now but the thing to do would have been go back to the gouge manufacturer before regrinding and also take a magnet to your shaving pile to find the metal chip then see if they could diagnose the problem.
 
Thompson gouge, I inspected the log pretty carefully before starting back in on it again and found nothing out of the ordinary. There was bark on and it wasn't super clean, so a stone is a possibility. Relatively new gouge for me, didn't require serious re-shaping to get to the 40/40 grind, so I doubt I overheated it. A lot more grinding to get past this chip. No further incidents in finishing the piece.

Same log as the chuck problem I've posted in another thread. Evil spirit in the log perhaps, though four nice bowl blanks eventually emerged.

Here's what the log looked like immediately after discovering this.

tempImagexNd2Xv.jpg
 
I am guessing that you were turning thru the middle of that log. That means cutting lots of air and when it struck even a very small pebble that was it. That bang, bang,bang can take a toll if there is the slightest flaw
 
Had the same thing at the end of my gouge Saturday. In my case the cause was obvious. No obvious staining though so I wasn't watching for it
 

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Sintering is not an absolute perfect process. This can happen in powder metal technology as there is nothing perfect. It is a very rare event and chances are that the rest of the tool will be fine. If it would happen again get a hold of Doug Thompson, I know of no one who knows more about the process and he has the best guarantee available.
 
To be clear I'm not complaining about the tool. Unless it happens frequently I'd regard it as just a fluke resulting from how I was (ab)using the tool. I'd just never seen that particular kind of chip come out of a turning tool before and thought it was interesting. Did it to a bench chisel one time by dropping it on a hard floor. That one wasn't the tool's fault either!
 
I had the same thing happen while roughing walnut. I was in initial stages of a chainsawed blank, interrupted cuts, bark and inclusions. It was an M42 5/8 bowl gouge.

I use a 3 bevel grind on gouges (cutting,relief, heel). I made the relief too shallow, making the steel too thin. Steepened up the relief, but it could happen again especially with an interrupted cut hitting something hard.
 
It is my lowly opinion that it was something to do with the infamous "walnut's revenge retribution." I think this is the result of just one more malady out of China (like emerald ash beetle, etc.) where the tree tries to stiffen its defense against a foreign assault...and we end up with chipped tools. I sure hope that the walnut wins...
 
I hit my chuck one day with my Thompson V bowl gouge. I dulled the edge but took a nice cut out of the chuck jaws.
 
I think a couple of my chucks have gouges in the jaws from my McNaughton coring system. Haven't done that in a while though....

robo hippy
 
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