Straightening blades

I have hammered like the videos and it worked. The way Matt is describing with the bead blaster it’s doing the same thing. It’s peening the side you’re hammering on. Spreading the metal.
So if you hammer on the inside of the banana, it will work.
Hammering on the outside may bend it back straight, if you’re lucky and don’t break it.
 
Josh Rider said:
I have hammered like the videos and it worked. The way Matt is describing with the bead blaster it’s doing the same thing. It’s peening the side you’re hammering on. Spreading the metal.
So if you hammer on the inside of the banana, it will work.
Hammering on the outside may bend it back straight, if you’re lucky and don’t break it.
Click to expand...

Peening on the inside was definitely not straightening the blade for me. Maybe there is some potential for it to work both ways, so a person just has to try it once for themselves and find out which way works. Regardless, it did get my blades nice and straight when the clamping thing wouldn't work.

Also, bead blasting might actually work a little differently simply because it is not just one concentrated hit on the tip of a hammer head, it is more of a broad stroke all at once of media which might smoosh or spread the steel a little differently.
 
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I saw those videos or some like them quite some time ago. I tried tapping on the inside of the bow and it did nothing to straighten the blade. Next time I have a warp, I will try tapping on the outside and see if that works. R.C. Reichert, thanks for the information.
 
in my experience to straighten by clamping during temper, i need to find out how deep the bow is. i lay the blade on a countertop with the bow facing up, and using coins or washers, find one that fits the bow or just slightly thicker. then when i clamp my blade to angle iron, i use double of whatever washer/coin it took to fit the gap. if one dime fit the gap, use two dimes for the counter bend. also cool the entire fixture in lukewarm water before unclamping. for me this works about 19 out of 20 times. i do have one that would not straighten from 2 years ago, i plan to try the hammer on it.
 
john april said:
in my experience to straighten by clamping during temper, i need to find out how deep the bow is. i lay the blade on a countertop with the bow facing up, and using coins or washers, find one that fits the bow or just slightly thicker. then when i clamp my blade to angle iron, i use double of whatever washer/coin it took to fit the gap. if one dime fit the gap, use two dimes for the counter bend. also cool the entire fixture in lukewarm water before unclamping. for me this works about 19 out of 20 times. i do have one that would not straighten from 2 years ago, i plan to try the hammer on it.
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I would try it if it is 1/8" thick or so. I'm not confident how it would work if the steel was much thicker than that.
 
I see a lot of different trains of thought on this topic. This is how I straighten blades in my shop. I see people saying hammer on the outside and others say hammer on the inside. Both of these can work but thy are working in 2 different ways. If you are hammering on the outside of the bow then your not surface peening. Your just hammering the blade straight. Your stretching the steel on the inside of the bow. Basically the same thing your doing with 3 pins and a vise. Your hammer blows are concentrating the energy into the small arced section under the hammer strike and forcing it straight. The other way is to use a pointy hammer face of hardened steel. Think ball point pin size. Carbide works best but high speed steel works as well. You gently tap the inside of the bow. I really like this method as it allows you pinpoint precision in how you move the blade. The little peen marks are only a few thousands deep. These little “dents” are expanding the area around them which makes that surface larger which pushes the blade back the other direction. You can do a lot with surface peening like remove cupping and bacon. The other day I had a blade that was ground out of really really thin stock come out of the the oil so bowed you could of wrapped it around a paint can. I got it between the plates before the hardness set. It came out of the plates with about a 1/2-3/4” bow and the edge had some bacon. About 30-40 min with the peen hammer and I got it wrangled back to straight and no bacon. It still had a little funky ness but nothing that could not be ground out. I was quite proud of the make over I gave that blade.
 
JTknives said:
I see a lot of different trains of thought on this topic. This is how I straighten blades in my shop. I see people saying hammer on the outside and others say hammer on the inside. Both of these can work but thy are working in 2 different ways. If you are hammering on the outside of the bow then your not surface peening. Your just hammering the blade straight. Your stretching the steel on the inside of the bow. Basically the same thing your doing with 3 pins and a vise. Your hammer blows are concentrating the energy into the small arced section under the hammer strike and forcing it straight. The other way is to use a pointy hammer face of hardened steel. Think ball point pin size. Carbide works best but high speed steel works as well. You gently tap the inside of the bow. I really like this method as it allows you pinpoint precision in how you move the blade. The little peen marks are only a few thousands deep. These little “dents” are expanding the area around them which makes that surface larger which pushes the blade back the other direction. You can do a lot with surface peening like remove cupping and bacon. The other day I had a blade that was ground out of really really thin stock come out of the the oil so bowed you could of wrapped it around a paint can. I got it between the plates before the hardness set. It came out of the plates with about a 1/2-3/4” bow and the edge had some bacon. About 30-40 min with the peen hammer and I got it wrangled back to straight and no bacon. It still had a little funky ness but nothing that could not be ground out. I was quite proud of the make over I gave that blade.
Click to expand...

I tried hammering the blade on the concave side too and it did not straighten the blade for me. I think you are probably right though, maybe I was doing it wrong. All I know is that what I did worked and my blades are now straight.
 
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JTknives said:
I see a lot of different trains of thought on this topic. This is how I straighten blades in my shop. I see people saying hammer on the outside and others say hammer on the inside. Both of these can work but thy are working in 2 different ways. If you are hammering on the outside of the bow then your not surface peening. Your just hammering the blade straight. Your stretching the steel on the inside of the bow. Basically the same thing your doing with 3 pins and a vise. Your hammer blows are concentrating the energy into the small arced section under the hammer strike and forcing it straight. The other way is to use a pointy hammer face of hardened steel. Think ball point pin size. Carbide works best but high speed steel works as well. You gently tap the inside of the bow. I really like this method as it allows you pinpoint precision in how you move the blade. The little peen marks are only a few thousands deep. These little “dents” are expanding the area around them which makes that surface larger which pushes the blade back the other direction. You can do a lot with surface peening like remove cupping and bacon. The other day I had a blade that was ground out of really really thin stock come out of the the oil so bowed you could of wrapped it around a paint can. I got it between the plates before the hardness set. It came out of the plates with about a 1/2-3/4” bow and the edge had some bacon. About 30-40 min with the peen hammer and I got it wrangled back to straight and no bacon. It still had a little funky ness but nothing that could not be ground out. I was quite proud of the make over I gave that blade.
Click to expand...

Thanks for the clarification on this method.

See here's the thing...
The following is a picture of a knife I made (it was just one that I scrapped long ago)... You will notice the bend, concave is on the right side. This blade was actually perfectly straight before I started hammering on it. Just as a test, I started hammering on the right side on the straight blade and it concaved to the same side I was hammering on. Shouldn't it go the other way if I was in fact spreading out the metal on the right side? It's not getting any straighter by continuing to hammer on the now concave (right) side. Makes no sense, lol.

 
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Well what are you using to hammer with. What could be happening is your hammer is softer then the blade and your anvil is hard. As you hammer it your anvil is actually peening the other side while you hammer is not doing anything to the surface. You hammer has to be hard enough that a file won’t scratch it. We are talking really high Rockwell hardness here. My small peening hammer is made from a ball peen hammer that I drilled out the peen side and pressed in a busted off tap that I ground into pointy dome.
 
Here’s the tip of my peening hammer.
I ground it to somewhat of a point.
But if what you’re doing works, definitely do whatever works for you.

92C6302D-70D6-4EB3-A811-71F0E2666760.jpeg
 
JTknives said:
The other day I had a blade that was ground out of really really thin stock come out of the the oil so bowed you could of wrapped it around a paint can. I got it between the plates before the hardness set. It came out of the plates with about a 1/2-3/4” bow and the edge had some bacon. About 30-40 min with the peen hammer and I got it wrangled back to straight and no bacon.
Click to expand...
Was that one of my blades? (The big one?). If so, that was actually a blade i profiled and ground the bevel on some 18 years ago - long before you guys taught me to grind bevel AFTER HT. sorry about that. I was wondering what all the little marks were . If what you describe is in fact this blade, you did an incredible job! It is almost dead straight, and just a tiny little “S” curve at the tip. I can post a photo if people want to see what the marks look like. (I am sure most will sand out)
 
JTknives said:
Well what are you using to hammer with. What could be happening is your hammer is softer then the blade and your anvil is hard. As you hammer it your anvil is actually peening the other side while you hammer is not doing anything to the surface. You hammer has to be hard enough that a file won’t scratch it. We are talking really high Rockwell hardness here. My small peening hammer is made from a ball peen hammer that I drilled out the peen side and pressed in a busted off tap that I ground into pointy dome.
Click to expand...


Hmm....I was using a ball peen hammer and it was creating little divots on the blade while the ball itself was not incurring any damage. It's a good point though and I will try rigging something up with a carbide tip.

You are doing this on a fully hardened, tempered blade? My previous blades were edge quenched, so maybe what I was doing before (tapping on the covex) works better for a blade with a soft spine vs a hard spine??
 
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Cushing H. said:
Was that one of my blades? (The big one?). If so, that was actually a blade i profiled and ground the bevel on some 18 years ago - long before you guys taught me to grind bevel AFTER HT. sorry about that. I was wondering what all the little marks were . If what you describe is in fact this blade, you did an incredible job! It is almost dead straight, and just a tiny little “S” curve at the tip. I can post a photo if people want to see what the marks look like. (I am sure most will sand out)
Click to expand...
Yeah that big cleaver shaped blade out of O1. I think it was what .060 -.070 thick? I have never see a blade come out of the quench that bowed. But I caught it in time between the plates. When I set it on the plate the tip and tang was probably 3” off the plate. I tried to get it as straight as I could for you.
 
R.C.Reichert said:
Hmm....I was using a ball peen hammer and it was creating little divots on the blade while the ball itself was not incurring any damage. It's a good point though and I will try rigging something up with a carbide tip.

You are doing this on a fully hardened, tempered blade? My previous blades were edge quenched, so maybe what I was doing before (tapping on the covex) works better for a blade with a soft spine vs a hard spine??
Click to expand...
Fully hardened and tempered blades.
 
JTknives said:
Fully hardened and tempered blades.
Click to expand...

Thanks. Come to think of it...tapping on the convexed spine should (tell me if you think I am wrong) be a perfectly fine method of straightening an edge quenched blade I would think because it has just enough "give" in the spine to not be super springy or brittle. Probably not the best idea on a fully hardened blade though.
 
JTknives said:
Yeah that big cleaver shaped blade out of O1. I think it was what .060 -.070 thick? I have never see a blade come out of the quench that bowed. But I caught it in time between the plates. When I set it on the plate the tip and tang was probably 3” off the plate. I tried to get it as straight as I could for you.
Click to expand...
well - you did an incredible job! Here are a couple pictures for the folks showing the marks resulting from your peening:
upload_2019-8-3_11-4-7.png

upload_2019-8-3_11-4-44.png
definitely just about the size of a ball point pen tip. for my purposes just fine! Thank you for the extra effort :). Interesting the other three blades did not warp (at least I do not see any peen marks on them). Probably a result of the larger blade, and bad grind job??
 
I even gas shielded those blades in the oven because thy where do thin I was worried about decade.
 
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