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Just how burnt is my gouge?

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Forum topic by Danpaddles posted 548 days ago 639 views 0 times favorited 4 replies Add to Favorites Watch
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Danpaddles

530 posts in 814 days


548 days ago

I have been carefully sharpening an old carbon steel gouge. I wanted a shallow angle on it, so every time I walked past it, I would pick it up and run against my belt grinder (about 240 grit, a 2 inch wide belt). I used this approach so as not to overheat it, thereby drawing out any heat treatment.

As I got down close to a very nice shallow angle today, almost done, when the front 1/8 inch of the gouge turned blueish. Whoops! I supposed the relatively small amount of metal, as the angle became less, didn’t have enough heat sink capacity.

I let it cool, and started back to grind off a little more of the metal. The blue went away quickly, but has the edge lost its temper, even if it is not (still) discolored? If so, how should I go about re-tempering it?

thanks for your thoughts.

-- Dan V. in Indy


4 replies so far

View David Kirtley's profile

David Kirtley

1274 posts in 1500 days


#1 posted 548 days ago

The edge would be softer as indicated by the color. The softening probably doesn’t go too far. You could either grind back a bit more or if you want, you can re-harden and re-temper.

Generally, you harden it by heating it bright red and quenching it (probably in oil if you don’t know the exact type of steel.) Test it by trying to cut it with a file. If the file skips off of it, you are there. Temper it by heating gently to get the proper straw color. You can do it with a torch or depending on the handle material, you can put it in the oven for a while at about 400F and let it cool in the oven. If you want to be more accurate, the initial heating should be to the curie point where it is no longer able to attract a magnet.

I suggest practicing on something cheap if the gouge is a good one. It’s not hard but does take a little practice.

-- Woodworking shouldn't cost a fortune: http://lowbudgetwoodworker.blogspot.com/

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Grandpa

2984 posts in 1178 days


#2 posted 548 days ago

I wouldn’t mess with trying to re-temper the gouge. I would use it and when the blue edge gets dull sharpen it again and go on. I doubt you will notice a great deal of difference. I have seen more damage done with do it yourself methods than good. To put it bluntly there are a lot of ways to ruin things and I have applied most of them at some time in my life. Just use it and forget the blue is there.

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Danpaddles

530 posts in 814 days


#3 posted 548 days ago

Ya, Grandpa, I was kinda thinking maybe I’d just use it the way it is, and see how bad it is. I will run a file over it, anyway. If it goes limp, I’m not out much.

I’m pretty sure it was a good tool, top of the line 30 years ago. And I will not have to spend a lot of time with this gouge, I usually use a flatter one.

Thanks, guys.

-- Dan V. in Indy

View rum's profile

rum

145 posts in 1088 days


#4 posted 548 days ago

I don’t think you’re off much. Blue is still pretty hard, scroll to the bottom of this link.

http://www.technologystudent.com/equip1/heat1.htm

and the rockwell chart at the bottom of this page (blue is about 600F):
http://www.m4040.com/Knifemaking/Steel2.htm

Worst case I’d say you’re still well into the R54+ range and likely you only drew the temper on the very edge so you’re well within the “doesn’t matter” range.

I wouldn’t re-temper it. you’re way more likely to make things worse than better.

I’d also switch to using an oil/water stone once you’ve hit the profile
Something like :
http://www.toolsforworkingwood.com/store/dept/THO/item/NO-FS76
then you won’t have to worry about burning, you’ll remove less metal and it’ll be sharper to :D

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