Warping during hand sanding

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Slikna99

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Apr 3, 2021
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I have a pair of 154cm knives I recently hand sanded and both went from completely straight to warped after hand sanding. I have them sitting on a 2 x 4 while sanding, clamped in my aluminum plate quench setup with another small piece of wood on top between the blade and plate to prevent scratches. Is it possible it built up enough heat during hand sand to warp it? Just seems crazy both blades did the same thing.

I went from 120-400 grit and noticed the warp in the middle of the blade. It’s been heat treated and tempered 3 times already prior to grinding bevel.
 
Doubtful that heat did it. Is it possible that your pressure varied and you ended up sanding out a shallow valley in the blade, making it look like a warp?
 
I've never experienced this, is it possible that the pressure from your hands caused the warping instead of the friction? Maybe you over tempered them and they lost their spring and you simply bent the blade and it didnt return to true?
You would notice the heat generated from hand sanding, it would have to generate enough heat to reach tempering temps to even mess with the temper. We are talking generating over 400F worth of heat for example. It's possible that the blade took some time to finish tempering and slowly took a warp, depending on how soon after tempering you started to sand it. My guess is that you didn't ruin the HT by hand sanding. Maybe 3 tempers was too many or one of them was at too high heat.
 
Slikna99 said:
I have a pair of 154cm knives I recently hand sanded and both went from completely straight to warped after hand sanding. I have them sitting on a 2 x 4 while sanding, clamped in my aluminum plate quench setup with another small piece of wood on top between the blade and plate to prevent scratches. Is it possible it built up enough heat during hand sand to warp it? Just seems crazy both blades did the same thing.

I went from 120-400 grit and noticed the warp in the middle of the blade. It’s been heat treated and tempered 3 times already prior to grinding bevel.
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I believe that you grind bevels uneven......
 
This is a completely flat ground chef knife so there is no “bevel” visible really. I am doing a satin type finish so I’m basically just sanding the length of the blade. I did focus on some areas more then others, but the blade was clamped completely flat on a 2 x 4. Maybe the wood is warped...

Looking down the length of the blade I can see it definitely took a warp, and I made certain to check after grinding that it was still straight. My only guess is that maybe grinding caused a delayed warp after I started hand sanding.
 
Sorry this happened so late in the game after hand sanding. I don't think you could generate enough heat to cause this. I've had blades warp while grinding, I guess due to residual stress relief. I could see something similar happening when hand sanding, especially if you took of a bit of material off with the 120 grit.

You can probably fix this pretty easily with a carbide tipped straightening hammer. After that, you might be best off going back to the grinder to get the divots from peening out and then hand sand again.
 
Yi
Hubert S. said:
Sorry this happened so late in the game after hand sanding. I don't think you could generate enough heat to cause this. I've had blades warp while grinding, I guess due to residual stress relief. I could see something similar happening when hand sanding, especially if you took of a bit of material off with the 120 grit.

You can probably fix this pretty easily with a carbide tipped straightening hammer. After that, you might be best off going back to the grinder to get the divots from peening out and then hand sand again.
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yikes... was hoping there is a solution that doesn’t trash the finish. I was considering clamping the middle overnight with washers on either end after a bit of heat from torch. Don’t know if I’ll have any luck that way though
 
Be careful peening a thin blade, the peens can quickly turn into dents that can be seen on the opposite side, and be very deep on the peened side. I did it on my last blade in a very similar situation as yours. I ended up shortening mine since the bend was near the tip, but the one dent I put in it is still visible.

I would try bending first. Very easy to build a hand jig from wood, a method utilized by Murray Carter. Just go slow by feel.
 
Justin W said:
Be careful peening a thin blade, the peens can quickly turn into dents that can be seen on the opposite side, and be very deep on the peened side. I did it on my last blade in a very similar situation as yours. I ended up shortening mine since the bend was near the tip, but the one dent I put in it is still visible.

I would try bending first. Very easy to build a hand jig from wood, a method utilized by Murray Carter. Just go slow by feel.
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That's good to know. How thick was the blade you peened? I just did one that was about 1/16" at the spine and luckily had no issue.
 
It was 0.063 inch stock, so about 1/16 inch, but with a distal taper and very thin at the edge where I hit it and left the dent. I went back a grit to 220 or so to sand it out, but it was getting pretty thin, so I stopped. I didn't want to reprofile the cutting edge yet. It may be a gift or a keeper at this point, definitely not for sale with a dent.
 
Justin W said:
Be careful peening a thin blade, the peens can quickly turn into dents that can be seen on the opposite side, and be very deep on the peened side. I did it on my last blade in a very similar situation as yours. I ended up shortening mine since the bend was near the tip, but the one dent I put in it is still visible.

I would try bending first. Very easy to build a hand jig from wood, a method utilized by Murray Carter. Just go slow by feel.
Click to expand...

I will try bending it next if my current attempt goes south. Thanks for the suggestions guys!
 
Good Luck, if worst comes to worst, you can always anneal it straighten it and re do the heat treatment. Better than starting again on a new knife.
 
A couple of questions. What type of steel are the knives? Differentially heat treated (guessing not)? My guess would simply be the interplay between the "flat" wood surface and the tapered knife blade. With any sort of taper you will never truly have the blade flush with the flat surface you are clamping too. While applying pressure when sanding it can bend the blade to conform to the surface its clamped too without heat. Just time and pressure (hand sanding baby!)is all is needed for a warp to blade A trick I used when I had this happen to me is a thin sheet of rubber or cardboard that would provide a flush surface under the blade to minimize any "bending" while applying pressure for the sanding process. This allows me to clamp my tang flush and provide a stable base for the blade while sanding. But I'm also an idiot so whi knows lol!
 
Thanks! It is 154cm stainless and not differential hardened. I ended up getting it straight with some light heat from a propane torch and some round bar I attached to my vise so when I applied pressure it could bend the knife slightly. Then I clamped it flat In my plate quench setup for a few hours and it Worked well. Thanks all
 
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