Fixing bends in a knife

[Mitch]

Hi all,

What technique/tools do you guys use if you have to remove a bend in a knife? I was working on one yesterday that had a noticeable bend which was making it incredibly difficult to get even bevels. I've been looking at buying a bending stick if they're actually useful, it'd be great to be able to offer this as part of the service.

The knife in question was a Furi Pro Chef's Knife 23cm, his very first knife so he's rightfully sentimental about it.

Also, is there much chance of snapping a knife when correcting a bend? This was the reason I didn't go too far into trying to fix it this time around.

[BeSharp]

I've tried it. Be very careful!

First, it depends on the steel. Some knives are made of steel with emphasis on toughness (i.e., Henckels. Wusthof). They take to bending back fairly well. But forget trying to straighten out a bent Shun! (Actually, I've never seen one; they just break off).

Second, I tried putting the end in a vise - too easy to apply too much pressure. Now I just tap on it with a hammer on the anvil part of my bench vise. Much safer.

[Ken S]

Good post, Chip. Useful information.

The steel does matter. I have cracked the hardened steel of a bent router collet and successfully straightened the bent tang of a roughing gouge. (Reavlizing the probable replies, the bent roughing was one of two I purchased used. I really only wanted the larger gouge. The price was right. I later replaced the bent and rebent tang for safety.)

Ken

[Mitch]

Good replies, thanks guys. I watched a video from CarterCutlery where he showed tapping on the blade as per Ken's suggestion, this is the most appealing over the options I've seen. I've seen a couple of different approaches brute forcing it, and I'm not too eager to try them. I'd be comfortable bending a Victorinox since I'm quite familiar with the steel, but anything else and I'll have to pass.

Do you have a particular hammer you'd suggest Ken? What do you use so that you don't leave hammer marks?

[Ken S]

Mitch,
It has been several years since I straightened the roughing gouge tang. As I recall, I placed it in a woodworker's vise with large flat jaws and gradually leaned against, using body pressure. The key word is gradual.
For knives, I might make a pair of wooden vise jaws, with one jaw being slightly convex.. Again, I would apply the pressure gradually.
I like your idea of sticking with Victorinox knives for this.
Ken

[John_B]

I don't think you will see bent knives that are hardened to 60 HRC or above. These knives are more prone to chipping and will break before they will permantly deform.

I have fixed a few bent tips by gently using vise pressure to do the work.

[Peter Eaton]

If there is a bend in a knife or bow then it likely got there when it was heat treated.

If could have been stacked with other knives and so heat differentials when quenched or it might not have been normalised before the heat treat and so stresses in the steel or a bad quench...many reasons in fact .

Now if it has been hardened as per specs then basically it will now be a spring with memory, so the bow will in stay in the spine. If you try to straighten then it is highly likely to snap and when they do it can send steel flying.

Yes I have straightened knives but they have been mass produced factory knives which are poor steel (lots about form top knife making companies!) and they will have been heat treated to a really low spec so they will sharpen easier....

[capt rich]

 No guarantee on bent knives. Some people insist to try, give them my hardwood bender and say, go for it.

[Naf]

Mitch,


Personally (not as experienced as some here)...


If I can't fix bent knife simply with vise jaws (similar to KenS approach), I tend leave it, as I not able fix it to any degree I will like better than original bend, if I break it by trying anything beyond that. I agree steel type / thickness make huge difference, but metallurgy(if right word)  way outside myrealm of expertise so would defer to pros regarding that. Good luck!

[Naf]

Sorry, missed hammer part, that seem not be answered.  I only use 40 oz (think) rubber mallet, and only on thin knives, if I gonna try hammer, for same reasons. But I rather have slight bend than Mar up finish. And I not "display" knives. Just finish picky.

[RichColvin]

I recently bought a Hardinge cross slide for my rose engine lathe, and one axis' lead screw was bent.  A friend referred me to this guy on YouTube.

https://youtu.be/hGO-835yWAU

May be applicable; not sure.

Rich

[Naf]

May be, Rich.

Also, I update my hammer answer with 7oz engineer hammer with thin piece of leather over/ under knife... thin knife.