Blade straightening question

P

panzerjunky

Joined
Aug 13, 2022
Messages
134
Just got all of my15 blades of diff shapes back from the heat treater ..all went well with the exception if 1 blade has a small warp (to be honest I expected much more) my question is this fixable?
The warp is behind the plunge line not affecting the blade (the part I want heat-treated) I was thinking I could keep the blade wet Rag etc. then block up the tip of the blade and the butt end Warp facing up. And heat a small band or area behind the plunge line (middle of the warp) with my torch and bring it back to straight with a c -clamp and my straight edge.
Do you think this might work or do You's fellas throw them away at this point????
Thanks Jerry
 
Heat treated 4 today, 3 warped. after first temper I used the three nail method between two angle irons in a vise with gentle heat to the spine (ground back to shiny and kept it to a less than straw colour). Two came out right away. Third it took several tries but got it eventually. I'm pretty new to this, but part of me thinks that if you can bend a knife to 90 degrees without it snapping, you should be able to apply light bending to straighten.

Not sure if this creates a little more stress in the steel or not. Maybe more experienced here can weigh in more on this method.
 
DevinT said:
Most makers use a carbide tipped straightening hammer.

Lightly hammer the cupped side of the area that has the bend in it. The surface will stretch and and push it straight.

Hoss
Click to expand...
I totally Thought you were messing with me. Like muffler belts etc. . But the process makes sense as I use it on other things like stretching springs for Gun smithing Will give it a try.
Thank You
 
Lehbauer said:
Heat treated 4 today, 3 warped. after first temper I used the three nail method between two angle irons in a vise with gentle heat to the spine (ground back to shiny and kept it to a less than straw colour). Two came out right away. Third it took several tries but got it eventually. I'm pretty new to this, but part of me thinks that if you can bend a knife to 90 degrees without it snapping, you should be able to apply light bending to straighten.

Not sure if this creates a little more stress in the steel or not. Maybe more experienced here can weigh in more on this method.
Click to expand...
First sir could you elaborate on the 3 nails method Please. And I agree how much can I bend it I mean the steel is hard the report came back at 1095 Min 59 max 60 HRC . Nothing to test against and I was not sharp enough to include a couple coupons for testing later. Grain ect. (Will do on next batch) Question 2 I keep seeing folks' reference " metal stress or relive stress. Where does this manifest itself in the final product???
Thanks For all your help, Jerry
P.S. are you heat treating yourself I sent mine to a professional HT company literally down the street. They ended up using a salt bath as to not warp the steel or at least have the better chance of not warping as I think I brought them to close to final grind so I as per the HT guy exposed the metal to excessive stress.
 
panzerjunky said:
First sir could you elaborate on the 3 nails method Please. And I agree how much can I bend it I mean the steel is hard the report came back at 1095 Min 59 max 60 HRC . Nothing to test against and I was not sharp enough to include a couple coupons for testing later. Grain ect. (Will do on next batch) Question 2 I keep seeing folks' reference " metal stress or relive stress. Where does this manifest itself in the final product???
Thanks For all your help, Jerry
P.S. are you heat treating yourself I sent mine to a professional HT company literally down the street. They ended up using a salt bath as to not warp the steel or at least have the better chance of not warping as I think I brought them to close to final grind so I as per the HT guy exposed the metal to excessive stress.
Click to expand...
Good Morning Jerry,
This is probably the easiest way to explain it.

Essentially I have two pieces of 2x2 angle, and using 3 heavy spikes I can force the blade into a reverse curve at the warp. Let it cool and see how far it springs back. Eventually if I do enough I might try to make the Walter Sorrells jig as its a bit of a pain in the ass for holding the spikes where you need them, plus blade and getting tension on the vise, but for now the angle iron works for me

I'm heat treating myself. Using 80CRV2, and forge treating. Out of the quench I'm pinching between the angles to finish cooling so it helps to keep it straight, and any warping is pretty minor. The worst one yesterday had a bow that created about a 1/16 gap on flat surface. For stress, I think if you are forging to shape, you should always anneal the steel to remove the stress of shaping the metal. The quench from what I understand creates a bunch of internal stress by changing the actual structure of the steel. I don't want to get into the actual metallurgy as I really don't understand it fully yet, and there are people here who know way more than I do about how it actually happens. I know tempering helps to relieve that, and bring it back from really brittle, to have more durability. The warp is how the blade wants to sit. By bending back, you are to a degree stressing the steel to a degree. I'm not sure how far is too much, and I'm sure it depends on the type of steel, overall hardness, thickness and shape of the blade etc. Good luck, lets see those Knives.
Ryan
 
I like the "stack-o-washers" method.

During the temper, clamp the blade to a bar, use a clamp and some washers to counter the bend a bit, then temper.

After you cool it down check for straighteness, then do it again if needed.

Haven't tried the hammer method, I'm gonna have to give that a go though.

Small, light taps right?
 
A.McPherson said:
I like the "stack-o-washers" method.

During the temper, clamp the blade to a bar, use a clamp and some washers to counter the bend a bit, then temper.

After you cool it down check for straighteness, then do it again if needed.

Haven't tried the hammer method, I'm gonna have to give that a go though.

Small, light taps right?
Click to expand...
that's how I do it, but I use pennies. I always do the first temper without any bending, though. Paranoid of creating any cracks with that brittle, as quenched steel
 
Lorien said:
that's how I do it, but I use pennies. I always do the first temper without any bending, though. Paranoid of creating any cracks with that brittle, as quenched steel
Click to expand...
THIS!!!!

I had a really long and tall 52100 Santoku that took a warp during quench. I forgot to run the first temper cycle. Went to clamp the blade up using the 3 point method, and SNAP!!!!
 
There are some good threads about warp to be found with a search.
Here is one by Rick Marchant showing the wooded anvils and Japanese straightening boards we both use:

Wooden Anvil & Mallet

Last night I was forging and noticed a bit of twist in my blade. Deciding to learn from experience and not duplicate my mistakes I made a quick and ugly wooden anvil/mallet from scraps I had on hand. The mallet is from a pecan limb I had lying around. I know it is not the prettiest tool...
www.bladeforums.com www.bladeforums.com

Here is one on warp in general:

Blade Warp

There has been a lot of threads and posts about blades warping. Some comments about warp; WARP HAPPENS It isn't a plot against you, or bad steel, bad grinding, bad HT, etc......WARP HAPPENS. Warp is an inherent problem with heating and working steel. You do your best to alleviate the problem...
www.bladeforums.com www.bladeforums.com

I have close up photos of my boards somewhere. I'll find them and post then later.
 
The carbide tip hammer peening method is so easy and exact.
I have fixed completely banana shaped (cryo can do that) blades with my carbide hammer. One disadvantage is that you have to grind the marks away if you peen in an area that won't have bevels. Most of my blades are 95% bevels so it's not a problem for me.
 
Stacy E. Apelt - Bladesmith said:
There are some good threads about warp to be found with a search.
Here is one by Rick Marchant showing the wooded anvils and Japanese straightening boards we both use:

Wooden Anvil & Mallet

Last night I was forging and noticed a bit of twist in my blade. Deciding to learn from experience and not duplicate my mistakes I made a quick and ugly wooden anvil/mallet from scraps I had on hand. The mallet is from a pecan limb I had lying around. I know it is not the prettiest tool...
www.bladeforums.com www.bladeforums.com

Here is one on warp in general:

Blade Warp

There has been a lot of threads and posts about blades warping. Some comments about warp; WARP HAPPENS It isn't a plot against you, or bad steel, bad grinding, bad HT, etc......WARP HAPPENS. Warp is an inherent problem with heating and working steel. You do your best to alleviate the problem...
www.bladeforums.com www.bladeforums.com

I have close up photos of my boards somewhere. I'll find them and post then later.
Click to expand...
I love the slotted 2x4 idea. Will be trying that out on the next set instead of messing around with three nails. Light heat, give it a bend, rinse repeat.
 
OK, here are photos of my Japanese straightening board and handle.
The straightening handle is made from oak and the board maple. The board is about 16" long, 2" thick, and 4" wide. Any wood should work.
There are three size slots in the board - 1/8", 1/4", 3/8". Each slot has curved cuts except the thinnest slot.
The handle can be used to remove warp as well as twist.
The straightening board clamps in the big vise, which is next to the forge and quench tanks. Right out of the quench you can straighten any warp or twist in seconds. After tempering, minor tune-ups are also simple.
It takes very little pressure to bend the blade, as seen in the photo where I am bending a wakizashi with one finger.

(The propane tank is not as close as the photo makes it look)


straightening jig 4.jpgstraightening jig (2).jpg
 
Last edited:
Lehbauer said:
Good Morning Jerry,
This is probably the easiest way to explain it.

Essentially I have two pieces of 2x2 angle, and using 3 heavy spikes I can force the blade into a reverse curve at the warp. Let it cool and see how far it springs back. Eventually if I do enough I might try to make the Walter Sorrells jig as its a bit of a pain in the ass for holding the spikes where you need them, plus blade and getting tension on the vise, but for now the angle iron works for me

I'm heat treating myself. Using 80CRV2, and forge treating. Out of the quench I'm pinching between the angles to finish cooling so it helps to keep it straight, and any warping is pretty minor. The worst one yesterday had a bow that created about a 1/16 gap on flat surface. For stress, I think if you are forging to shape, you should always anneal the steel to remove the stress of shaping the metal. The quench from what I understand creates a bunch of internal stress by changing the actual structure of the steel. I don't want to get into the actual metallurgy as I really don't understand it fully yet, and there are people here who know way more than I do about how it actually happens. I know tempering helps to relieve that, and bring it back from really brittle, to have more durability. The warp is how the blade wants to sit. By bending back, you are to a degree stressing the steel to a degree. I'm not sure how far is too much, and I'm sure it depends on the type of steel, overall hardness, thickness and shape of the blade etc. Good luck, lets see those Knives.
Ryan
Click to expand...
Thank you That make a lot of sense. I am building Walters straightening tool as we speak just waiting for the round Delrin to show up .
 
Has this happened to you with the blade straightening jig?

I've had a few blades that just won't stay straight. I use the carbide hammer process; the blade is perfectly straight. But, when I take 'em off the surface grinder the warp comes back.

The last weirdo blade that did this, the bow was about 0.005" deep. So I put it back on the grinder with a shim under the bow and ground off 0.005", flipped it over and did another 0.005". Now it stayed. A little thinner than what I wanted, but at least I didn't have to throw it out.
 
Sando said:
Has this happened to you with the blade straightening jig?

I've had a few blades that just won't stay straight. I use the carbide hammer process; the blade is perfectly straight. But, when I take 'em off the surface grinder the warp comes back.

The last weirdo blade that did this, the bow was about 0.005" deep. So I put it back on the grinder with a shim under the bow and ground off 0.005", flipped it over and did another 0.005". Now it stayed. A little thinner than what I wanted, but at least I didn't have to throw it out.
Click to expand...
This happens to me as well, often when grinding the bevels. I usually straighten the blade again with the carbide hammer before moving to 120 grit.
 
Had a blade that warped. Straightened it out by getting a magnet and placing it at the highest part of the warp. Then just push down until the two ends meet and flip to the other side to get the middle to meet with the ends. I typically leave a little more meat on the blade to prevent severe warps and then grind down them that do. They generally come out at a great thinness.
 
Hubert S. said:
This happens to me as well, often when grinding the bevels. I usually straighten the blade again with the carbide hammer before moving to 120 grit.
Click to expand...
Why didn't I think of that!

Yeah, I've had some warp while grinding. Depending on the purpose of the knife and the amount of warp, I either lived with it or though it away.

I'll try a second straightening next time. Thanks Hubert.
 
I use pennies and a bar and straighten in the temper the large majority of the time, for the last 14 years. I recently came across the carbide hammer idea and made one. So far I have to say it works very very well. Straightened out a half a dozen stainless blades and a couple of forged 80CRV2 swords as well with no malfunctions.
Here's a quick video that shows the hammer and an illustration of how many taps it takes... a zillion!
 
I really need to make myself one of those carbide tipped hammers.

Jason, one thing I noticed about yours, the carbide end mill looks flatter than others I have seen that have a more rounded tip to them! But it got the job done!
 
You must log in or register to reply here.
Back
Top