Can a knife warp from grinding?

H

Harley Boatman

Joined
Jun 21, 2020
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I always lay the blade down and make a mark on the edge with a drill bit before I grind in my bevels to keep the edge straight. That being said, somehow the tip walked way off to one side. I didn't go past my center-line marks but it is not straight at all. I also grind freehand and with no gloves so it didn't get very hot. I'm just confused how this happened when none of my other knives have done this.

Here's some photos to help explain:

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The blade can warp during grinding if there is residual stress. I have had it happen with AEB-L. Most of the time, it straightens back out when grinding the other side to match.
 
Harley Boatman said:
Yeah this is AEB-L. What do you mean by residual stress?
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It is just stress that is built into the material. There is a wikipedia page about it. Imagine a material, say a thin strip of wood, that has a rubber band attached on either side. Say the two rubber bands compress the thin strip evenly so it remains straight. Now, when you cut one of them, the stress on that side is relieved and the strip will want to warp towards the side that still has the rubber band pulling on it. Residual stress can be purposely introduced into a blade to straighten it, e.g., by peening the material with a carbide tipped hammer.

I only grind AEB-L after heat treatment, so I don't really know the best way to deal with it in your situation. You have plenty of thickness left it looks like, so I would just heat treat it and then deal with whatever warpage is left after heat treatment.
 
Good to know. Thanks guys. I have another blank of the same shape that I'll do after HT. This one I'll just see what I can do post HT. Worst case the knife is screwed up but I've learned a new lesson👍
 
Harley Boatman said:
Good to know. Thanks guys. I have another blank of the same shape that I'll do after HT. This one I'll just see what I can do post HT. Worst case the knife is screwed up but I've learned a new lesson👍
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There are lots of threads here about AEB-L warping and how to fix it, including the thread AEB-L warpage woes I started a while ago. In my experience, straightening during temper cycles does not work with AEB-L. The only method that has worked consistently for me is using a carbide tipped straightening hammer. I built the one shown below, there are more details about it in the thread I linked above. Good luck with your blade, I think it's going to work out fine.

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H Harley Boatman
Do you by chance grind with a push stick, aka, piece of dowel with a finishing nail head for blade to ride on and push or other device?
 
Harley Boatman said:
Nope, I just rest the spine on my index and push with my thumb. I've learned that I prefer to burn my thumb before ruining a HT 😂
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I hear that, and it's how I grind, too. I just know it's easy to push too hard with a stick, and it is entirely possibly to bend a blade from pushing too hard grinding. Whether you can manage that on a short blade I dunno, of course. Something to be aware for, though.
 
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