# What level of warp is acceptable from commercial heat treatment?



## merlijny2k (Dec 22, 2018)

Hey, I sent in 2 blades for heat treatment. Both came back bent some 3mm out of alignment. I am a bit disappointed since it is clearly more than I can fix on the grinder (4 and 2mm steel thickness), and i will have to risk breaking them trying to get them straight. Blades are 20cm and 14 cm total metal length. 

Is this an acceptable condition to receive your blades or should the shop have made more effort to straighten them in tempering? My first blade from them came back straight so it is my first time dealing with warped blades out of heat treatment.

Thank you for your advice.


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## The Edge (Dec 22, 2018)

I've never sent anything off to be heat treated by someone else, so I can't really answer your question. Part of me wonders how thin your knife was when sending it off? Any time I've had problems with warping, it's because I ground the knife way too thin prior to heat treatment. Steel goes through incredible stresses during hardening, so it's bound to happen sometimes ( I have a friend who works with mass flow oil pumps, where they are hardening 7' long shafts, and they usually foot the bill when something goes wrong). For knives, I've found if I just do the initial grinding, leaving everything fairly thick, the heat treat process goes smoothly. Needless to say, it sucks, losing time, material, and money, but the question is always going to be, "why is it warping in the first place?" Sorry for your loss, but can't say more than I already have, and maybe someone else has more experience in dealing with such things. I'm still interested in more details though.


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## RDalman (Dec 22, 2018)

Was potential straightening promised or part of the deal? If not, maybe you learned something. Talk to the service provider.


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## Matus (Dec 22, 2018)

I understand that you are taking abound HT of blanks that were not ground yet. In general I would not consider that amount of bend normal. As Robin suggested - talk to a rep of the company - maybe they will suggest some changes or it may turn out that they are not set up to do the kind of HT you need. But most likely you will end up going somewhere else next time.


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## pennman (Dec 22, 2018)

What steel is it? Occasionally XHP, CPM 154CM, and damasteel warp on me. Fairly easily to straighten in an oven at 350 degrees with some pennies and a couple clamps.


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## merlijny2k (Dec 23, 2018)

They were ground before HT. The larger one asymmetrical as well. On the large one it is the tip that is most out of whack, so i suppose it is fair to say the geometry is the major culprit. On the smaller one however the blade is straight but the handle is bent, which I find odd.

They promise to temper it twice in a casing if it isn't straight and then send it off with whatever problem is left for you to deal with yourself. In case of the bent handle I am somewhat doubtfull that has actually happened. The bill is 19 euro's per knife. I have no idea if that is on the high or low end of the price spectrum. Being in the Netherlands I unfortunately don't know of many alternatives to get your HT done.


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## RDalman (Dec 23, 2018)

A big part of knifemaking (atleast somewhat efficiently) is in optimizing pre HT geo to reduce the hardgrinding. Also, in the straightening alot can be done, during quench even. So when sending out, not having full control of the process like this, it gets tough indeed. And I think you're typically better off doing more of the grind post HT. It sounds a bit expensive for sure, but if it's done small scale one blade handled at a time, sure... If it's hung in a vacuum furnace with 50 other blades, it would be a profitable price for them


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## merlijny2k (Dec 23, 2018)

Thanks for all the advice! I paid the bill. Now to see if I can get them straight without breaking them.... I think i'm going to try that peculiar hammering method I saw somewhere on the forum first.


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## pennman (Dec 24, 2018)

merlijny2k said:


> Thanks for all the advice! I paid the bill. Now to see if I can get them straight without breaking them.... I think i'm going to try that peculiar hammering method I saw somewhere on the forum first.


What steel is it?


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## merlijny2k (Dec 24, 2018)

O2 and 440C


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## merlijny2k (Dec 24, 2018)

I did the chisel hammer thing from the thread about bending and it worked like a charm!! As straight as if nothong ever went wrong.


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