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RobertMunford

heat treating ulu's made from saw blades

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I will begin by explaining what happened in the past and then what happened with these 4 blades.  I have made 5 blades from saw blades in the past and had no problem keeping them straight during the heat treat.  This time I made 4 blades again from saw blades and had everyone of them warp.  

So the first part of my question is what made these blades warp.  I normalized them x3, and had my oil at about 140 degrees F.   I know there are probably a multitude of different things that I did wrong, so I plan on sorting through all the advise and find the two or three things I didn't do.  

Second part of the question is would it be possible to normalize and straighten then reheat treating or would it be a waste of time.

As always any and all comments are welcome.

Thanks to everyone on here that is willing to share their knowledge.

 

Robertmunford

aka Bob

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5 hours ago, RobertMunford said:

So the first part of my question is what made these blades warp.  I normalized them x3, and had my oil at about 140 degrees F.   I know there are probably a multitude of different things that I did wrong, so I plan on sorting through all the advise and find the two or three things I didn't do.  

How did you quench them?  Straight down into the oil and hold?  Swish the blade in the oil?  Are the blades bi-metallic?  Is your grind consistent?  

5 hours ago, RobertMunford said:

Second part of the question is would it be possible to normalize and straighten then reheat treating or would it be a waste of time.

This should be just fine, but they may still warp if you don't solve that issue.  

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8 minutes ago, Jerrod Miller said:

How did you quench them?  Straight down into the oil and hold?  Swish the blade in the oil?  Are the blades bi-metallic?  Is your grind consistent?  

This should be just fine, but they may still warp if you don't solve that issue.  

I went straight down and held still.  The bi-metallic I can not tell as I do not know.  If you consistent grind by is the bevel the same all the way around the edge, yes it is.

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When you are working with thin steel, you’re going to have to deal with some amount of warping. I can only think of a couple of times I had a long (>6”), thin knife come out of the oil exactly how it went in. I found that using a larger container for my oil helped immensely (an old ammo can as opposed to a capped pipe), as it allowed for more even cooling. Another thing to note with thin knives is that they will move under their own weight for a brief period while the martensite is forming and they are still ductile (you can also gently straighten them in this phase). If you leave them to cool in a way that allows them to sag, warps can appear from out of nowhere. My philosophy with warping has been to learn how to both prevent and fix it, since sometimes it is almost unavoidable. 

Do you have any pictures of the warps? That might also help diagnose the problem. Hope this helps!

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Aiden how do you straighten warped blades?

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Did you do a trad single sided grind, that will amplify the tendency to warp.  You could try grinding them after you HT them.  You might also try binding several of them into a stack and HT'ing the whole thing, the extra mass may help, or you could clamp them between two pieces of mild and then doing the HT.

g

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Posted (edited)
3 hours ago, Doug Adams said:

Aiden how do you straighten warped blades?

The most effective time to straighten is right when you pull the blade out of the oil, as the steel takes some time to fully harden (martensite formation), and is still ductile enough to bend gently in a vise or with thick gloves. After that, the best time is during a tempering cycle. I like to temper once at a low temperature (like 350 F) then clamp the blade to a piece of angle-iron with shims to bend it in the opposite direction as the warp. Then I temper again slightly higher (~25 degrees F), and often that is enough, especially for simple warps. If I can't get all of a warp out in one or two tempering cycles, I carefully heat spots along the spine until the oxides turn blue then counter bend it with a three point jig in a vise. The hotter you get the steel the easier it is to undo a warp, but the more hardness and strength you lose through tempering, which is key to keep in mind with these techniques.

Edited by Aiden CC

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Posted (edited)
On ‎3‎/‎7‎/‎2019 at 1:21 PM, Aiden CC said:

When you are working with thin steel, you’re going to have to deal with some amount of warping. I can only think of a couple of times I had a long (>6”), thin knife come out of the oil exactly how it went in. I found that using a larger container for my oil helped immensely (an old ammo can as opposed to a capped pipe), as it allowed for more even cooling. Another thing to note with thin knives is that they will move under their own weight for a brief period while the martensite is forming and they are still ductile (you can also gently straighten them in this phase). If you leave them to cool in a way that allows them to sag, warps can appear from out of nowhere. My philosophy with warping has been to learn how to both prevent and fix it, since sometimes it is almost unavoidable. 

Do you have any pictures of the warps? That might also help diagnose the problem. Hope this helps!

ok here are some pics.  the problem I have is I do not really have a spine on these ulu's.  the pic with the circle on it is where the high spot on both blades is.  I laid them on some paper towels I don't know if that was enough to hurt them.  they are traditional grinds only on one side, which allows for them to be used for just about anything that you want to use them for.  One lady that I gave one to used it to skin her deer, cut it up, and then to cook with.  you DO NOT want to get on her bad side.  LOL  I am using a gallon can for my oil and had it some where around 130-140.

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Edited by RobertMunford

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15 hours ago, RobertMunford said:

ok here are some pics.  the problem I have is I do not really have a spine on these ulu's.  the pic with the circle on it is where the high spot on both blades is.  I laid them on some paper towels I don't know if that was enough to hurt them.  they are traditional grinds only on one side, which allows for them to be used for just about anything that you want to use them for.  One lady that I gave one to used it to skin her deer, cut it up, and then to cook with.  you DO NOT want to get on her bad side.  LOL  I am using a gallon can for my oil and had it some where around 130-140.

Like Geoff mentioned, an asymmetric grind can contribute to warping in heat treat, and in some cases, it can be better to save the grinding until after. If you set them down on a surface to cool, that could have contributed to the warping, with the side on the surface cooling at  different rate that the side in the air. Either clamping vertically in a vise or handing it by a wire through one of the holes could be a good way to let these cool. It looks like you could try to take some of the warp out in a tempering cycle if you could make jig to force a counter-bend and put it in the oven. As long as you don't overheat the edge, you could try more aggressively heating with a torch as well.

If you go the rout of re-quenching, you could try clamping between two flat plates after coming out of the quench. I've done this for some Sakha style knives, which are concave on one side and convex on the other and love to warp. I quench, straighten by hand with welding gloves/a vise, then sandwich them between two pieces of 2x4 and stand on the top. Gives decent results and sometimes I don't have to do any correction in tempering/grinding. That approach might work for these as well.

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Thank you Geoff and Aiden for the advice.  Soaking it up and when the rain stops or at least lightens up some will try to make them straight.  I put them on paper towels so they wouldn't cool completely before getting them into the oven.  The paper towels may have been damp from humidity and then stacking them on top of each other didn't help either.  So will hang them individually.  I will have to figure out how to do it quickly because the lady that will be going my laser etching wants 6 to 10 of them to put in her display case. 

Thanks again Aiden and Geoff for taking the time to answer my questions.  I value the advice that I get on here, this is the only forum that I have visited that people were friendly and willing to answer questions.   No one has wrinkled their nose or called anyone stupid or dumb, and that means a whole lot to me and I am sure many others as well.  

So THANK YOU one and all.

RobertMunford

AKA Bob

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On 3/9/2019 at 9:51 AM, Aiden CC said:

It looks like you could try to take some of the warp out in a tempering cycle if you could make jig to force a counter-bend and put it in the oven. As long as you don't overheat the edge, you could try more aggressively heating with a torch as well.

Bob, 

It looks to me like Aiden's suggestion of straightening in temper could very well do the trick for you (simple bow).  If possible, I would heat up the ulu, then put it in your counter-bend jig, then put the whole thing in the oven to soak at temp for a while.  Least likely to break that way.  

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9 hours ago, Jerrod Miller said:

Bob, 

It looks to me like Aiden's suggestion of straightening in temper could very well do the trick for you (simple bow).  If possible, I would heat up the ulu, then put it in your counter-bend jig, then put the whole thing in the oven to soak at temp for a while.  Least likely to break that way.  

Thanks Jerrod looks like I have a little break in the rain for the next couple of days so will try to straighten the little buggers.

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