Straighten During The Temper

I just used this technique the other day on my mini I am making and at only ~.035" thick I was very worried about overbending to straighen. Well I clamped it between to pieces of steel and it came out as straight as an arrow! Good trick to keep "on file" for those occasions when Murphy shows up.


-Xander
 
Ed Fowler said:
I learned my lesson many years ago: ..../snip/... Evidently my grinding methods obviously left stress in the blade that eventually caused the blade failure. This event remains prominent in my mind.
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ev·i·dent·ly /ˈevidəntlē/ Adverb
1. Plainly or obviously; in a way that is clearly seen or understood.

How is this conclusion so evident? This was a significant event for you. Can you share what type of testing revealed the origin of the stress fracture. This blade was ground from a file but not HT'd by you? I'm confused. If you did the HT, I have even more questions about you conclusions. Ed, you have my respect as a smith who is willing to help others make the best knives they can but as someone who is a prominent maker, folks tend to just "take your word for it." I was guilty of not questioning the "pros" too... until I started getting burned... "Why do you perform that operation?".... "... er... because makerX said so.". Whether it works or not, people tend to lose respect for your opinion when you can't back it up. That's why I think it is important for you to either shed some light here or point us in the direction of some evidence to support your claim. The whole, "These are my findings but come to your own conclusions" disclaimer is okay for the average advice giver but for a bladesmith with a regular magazine column, who mentors through classes, you have a greater responsibility to be transparent in your findings.

NickWheeler said:
I just wanted to say that I have used this technique and it has saved my bacon on a few blades. I like Rick 17% more after reading this thread. ;) :)
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Woo-hoo, that puts me into the double digits, now!!!!!
 
I was very new to knife making. I did not harden or temper the blade, just ground it on a 6" carborundum wheel and them a 1 x 42 inch belt grinder keeping it cool to avoid having to hardening the blade because at the time I did not know how to harden a blade. If the blade had had a fault in it I believe I would have seen it. The file was an old one that had been used for years. Looking at the fracture it just broke clean. If I had known what I know now I would have looked more closely. When the blade broke it was a loud pop.

Back in my high school days I decided to make a swamped six sided black powder rifle barrel from a medium heavy barrel. I did this with hand files, first took down one side of the barrel to my calculated depth, then another, filing each side caused the barrel to warp. It took me for ever to get it back to where I could see down the barrel using a highly altered arbor press.
This is the basis for my belief that how we grind a blade can create stress.

A gunsmith taught me how to do it correctly years later by only taking shallow cuts on opposing sides one opposite cut at a time. The next barrel I made shot much better and I did not have to straighten it.

I thank you for asking me why, I have not visited this thread for a while and that is why I have not responded sooner. I wish more would ask why of every knife maker, our art - science would progress more rapidly.
 
Ed, I believe that in the case of your gun barrel, the filing revealled the stresses that were induced thermally. With the little knowledge I have accumulated, I don't think that the removal of stock can induce any stress in steel. Load and thermal manipulation are the only things I can think of.

If you were new to knifemaking and had no knowlege of HT, how can you hold onto ANY theory you had at that time, without going back to reevaluate the physical piece?

Rick
 
Call it a lesson I believe I learned. As I was hand filing I don't believe thermal attributes were too significant. I could be wrong but a gunsmith told me he learned the same thing the hard way. When watching Dick IIams milling precision pieces he always took small bites from one side then the other when working on critical parts. I do the same thing when grinding my knife blades, alternating from side to side with each couple of passes.

Also remember the file was hardened and stayed hard when I was working with it, this may have been a factor. It hang on my kitchen wall for years before it broke temperature fluctuations were maybe 30 degrees f.

Every knife, every steel and method has its own variables, it is up to us to explore. As always you are free to chose as you please to work and this is a good thing.
 
I think you missed the point, Ed. (which may have been my fault for not explaining). You made your swamped barrel from an existing medium heavy barrel. You had no idea of the heat treat it received prior to you working on it (same case with your file knife). Let's say the outer surface was slightly harder than the core. By removing material from one side you are releasing stress induced from the hardening process. Let me make an analogy... We have a fully erected circus tent.. evenly tensioned on all sides with guy lines and wooden stakes. Let's start popping stakes on one side.... the tent leans. Did you induce stress or release it? Now, we can go around to the tensioned side and loosen the guy lines a bit... the tent returns to a stable shape. You removed no other lines from the structure but rather equalized the distrubution of tension. If we needed to remove some of the lines, wouldn't it had made sense to first loosen all the tension?

That's what I see wrong with your file and barrel stories. It had very little to do with the act of removing the stock and more to do with not being properly set up ahead of time. Don't blame the filing and grinding when it was a lack of metallurgical planning that caused the problem.

That is the advantage of doing my own heat treat. I am not a slave to the pre-induced stresses from mill processing or mystery heat treats. I can grind how I want where I want, move the steel where I need it and afterwards, wave my magic wand over it(thermal cycling) to make everything alright again.



Rick
 
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Not to jump into the middle of this conversation (especially due to the fact I am not qualified to do so), I used this technique today and it worked perfectly! I have a few observations based on my experience HT-ing the different materials I have used.

Today's straightening was done on an 11" piece of Wrought Iron / 1095 SanMai. I was told that the wrought Iron can act as an insulator and cause bending and warping. I left the Edge thick for this reason but it still twisted, I am blaming the Wrought Iron!

I have been working with 1095 almost exclusively in the last few months and have noticed much more bend during the HT than in the past using other materials (1080, 5160, O1). I believe it has been caused by the Clay Coating, I try to keep the clay in even amounts on both sides. I have also noticed that in most cases it is happening at the plunge cut / choil where i have the most clay applied. My question is: would having more clay on one side of a blade cause the steel to cool unevenly and warp the blade? if so how much extra clay would it take to cause this?
 
It worked for me, 1095 dagger blade with a wrought iron core, warped at least 20 degrees in the quench (and I had normalized the crap out of it). 3 tempering cycles later, ramping the temp up each cycle, and she was straight.

Thank you very, very much. This should be a sticky.
 
On this subject, I have started adding a step to my quench for blades. Once the blade passes the pearlite nose ( about 5-10 seconds), I pull it from the oil and immediately set it in the aluminum plate quench vise. I lock it down for at least ten minutes. This has seemed to greatly lesson the warping during quench in hyper-eutectiod and damascus steels.
 
First, thanks to everyone for a very informative thread. Second, I have a couple questions.

Ed, don't you get a recurve in an otherwise straight blade by going through the pre hardening steps you describe?

Stacy, what are the tradeoffs of the extra quick cooling you get with the plates?

Thanks again,

John
 
So Stacy, you are using the latent heat and your quench vise to "set" the blade straight before going into temper cycles? That sees like a great idea. Is it the faster quench mediums common to hyper-eutectoid steels that causes more warping than with simpler steels? Or is it the prevalance of using clay coats of some sort rather than the steel/quench combination?


-Xander
 
John: Before we started the post forging 35 second quenches in room temperature oil, before normalizing cycles, we used to get recurve blades, the tip of an 8 inch blade would drop as much as a quarter of in inch. After we learned the benefits of the post forging quenches we no longer experience the drop in the tip and have never experience any blade warp. I believe the drop at the tip is very positively related to the warp in blades.

I suggest you give it a try and let us know what you find.

Again the only steel we use are 52100, and JD 5160 and as an unplanned experiment some 1084.
 
Ed, if you were select hardening the edge with a torch and still getting the tip to drop down a quarter inch.... I really don't know what to say. It seems odd to me. Tip drop is a common occurance on single edged blades ground thin at the edge with a little meat on the spine but the entire blade has to be full hardened for this to occur. (BTW, A great fix for that is quenching spine down... thanks, Kevin).

Do you get any warpage in the post forging quenches?

Are you select hardening in those steps, too?

Personally I think the reason why you are not experiencing warpage is positively related to the fact that only 25% of your steel ever hits Acm and even less turns to Martensite in the quench. Perhaps I'm mistaken but I believe the majority of the blade is a mix of course/fine pearlite and upper bainite. You could probably pound out any kinks with a heavy maul at that point.

bladsmth said:
/snip/... I pull it from the oil and immediately set it in the aluminum plate quench vise. I lock it down for at least ten minutes.../snip/...
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Stacy... Do you have a picture of that quench plate set up? That sounds like a good step to me.


Rick
 
I'll try and shoot a photo tomorrow. It is a pipe vise and two aluminum plates. Slide in the blade, and flip the clamp arm over. Give the handle a spin....that is it. The same vise, minus the plates, is my twisting vise.

The plate quench just assures even cooling from BELOW the pearlite nose. The oil or brine quench does the work of getting the steel below 900F. The plates will hold the blade straight as it cools, and keep everything that way until after the martensitic conversion.
On damascus, you are dealing with different metals in a laminate, and different cooling rates. This can cause warping in the best of conditions. The plates help this ,too.

After all the great input form this thread, I am making a clamp setup to hold blades during temper, and think the final result will be very little straightening needed.
 
Again, great thread. Finally met a blade that this method couldn't fix. It's a large chopper with a cleaver line nose that starts at 5/16" at the ricasso and tapers to a little under 1/4" at the "tip". The blade is almost 2" wide though and is flat ground until HT then blended into a full height convex. Vicious cutter.
There was a warp that I tried 3 times to cure with this method and it just wouldn't hold. Must be the thickness.
I wonder what the structure of the steel is in a warped blade. I wonder if there's irregular grain size in the problem areas.
 
SBranson said:
Again, great thread. Finally met a blade that this method couldn't fix... /snip/
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It doesn't always work... which begs the question "Why?". What makes it work on some and not on others?... hmmmmmm

SBranson said:
/snip/... I wonder what the structure of the steel is in a warped blade. I wonder if there's irregular grain size in the problem areas.
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Now that's an interesting question.

Rick
 
Rick: We never get any warpage on the post forging quenches. The entire blade is quenched in room temperature oil. We start with anywhere from 2" to 6 inch round bars and are very careful not to overheat or work the steel too cool. Forging is done evenly from side to side and all other hammer blows are to what will be the cutting edge.

I know it seems odd, Rex could not believe it either, until he saw it happen. It was this phenomenon that led us to using the 35 second post forging quenches on every blade. This happened with 52100 steel.

Selective heating and quenching only happens when we harden the blade, after three 2 hour annealing heats at 988f.

Our blades have usually have more martensite than 25 % (depending on the proposed future use of the blade), if I knew how to draw and post it on this outfit I would offer a greater explanation. To try to explain it verbally we end up with a martensite pyramid inside of the blade, this extends from below the quench line and extends above the quench line, the top of this pyramid is surrounded by unhardened steel. It is kind of like a laminated blade, but all from the same steel.

A metallurgical engineer took our seminar last winter and could not wait to take his blades to his instructors. He could explain it, but felt there was much more to it than we can explain, hopefully I will be hearing from him in the future.

The outside of the blade starts getting harder when we test for hardness from the spine down, when we reach the top of the pyramid it starts getting harder rapidly, evidently due to the influence of the martensite pyramid.

Rex can explain what happens in technical terms, I explain in terms of performance and what I can see.

I hope this answered your questions.

Again I hope you feel free to try what we do and see if it works for you, when you test your experimental blades to destruction you may be amazed.
 
If making a knife your way wasn't so darn labour intensive Ed, I'd crack one open for an look-see. :p:p
The one I carry on my belt daily though is about the best knife I've used. It's looking a little worse for wear but it just seems to hold up to anything. I've smashed it will a hammer using it as a froe, used the tip to dig things out of lumber half expecting to snap the tip off but it just keeps on keepin' on. :)
 
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