Straightening CPM-M4?

H

huntingsgr8

Joined
May 25, 2015
Messages
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Can it be done? I recently ground and hardened a 240mm gyuto in the stuff and it took on a small, but irritating warp, maybe .040" to the right looking down the spine. I tried shimmed tempers at 400F, and 500F, but don't really know how to handle this stuff, it's my first time using it.
 
I've never tried it on M4, but a carbide tipped hammer has worked really well for me on AEB-L, which I had no success straightening with shimmed tempers. I made the hammer shown below using an old ball peen hammer and a piece of 1/4" carbide from McMaster.

XplUDvp.jpg
 
I have had excellent results using shims during tempers to straighten blades. 400°F is a good temperature to use. Lower than 400°F, it can be done, but isn't as effective and takes a few goes. Just remember, you can't clamp it straight and expect it to come out straight. You need to have a bend in the opposite direction by the same amount (sometimes a tad more).

With that said, after watching a video by Gary Creely using one of those carbide tipped ball peen hammers that Hubert posted above, I am seriously considering making one. You just place the blade down on a hard surface with the bow up (like the letter "U", not "∩") and tap in the middle of the bend. In less than a minute you can straighten a short blade with a slight bend in it. But if the blade is already ground, I don't know about that carbide tip putting dents all over the place.
 
Stuart Davenport Knives said:
I have had excellent results using shims during tempers to straighten blades. 400°F is a good temperature to use. Lower than 400°F, it can be done, but isn't as effective and takes a few goes. Just remember, you can't clamp it straight and expect it to come out straight. You need to have a bend in the opposite direction by the same amount (sometimes a tad more).

With that said, after watching a video by Gary Creely using one of those carbide tipped ball peen hammers that Hubert posted above, I am seriously considering making one. You just place the blade down on a hard surface with the bow up (like the letter "U", not "∩") and tap in the middle of the bend. In less than a minute you can straighten a short blade with a slight bend in it. But if the blade is already ground, I don't know about that carbide tip putting dents all over the place.
Click to expand...
Make one! They're great! I use a hammer to straighten warped AEB-L blanks out of HT. I do all the grinding post GT on AEB-L so it's not a big deal. I've done quite a bit of shimmed tempering on carbon steel knives, but this M4 is another beast. Bent in excess of 45 degrees in the direction I want it to move, it doesn't budge. I event wet to 475f on the last one. I've got it tapered from .083 at the neck to .050 at halfway to .045 1" from the tip, so hammering is probably off the table. I can keep trying with the shimmed tempers, but I'm none too optimistic.
 
I tried to straighten it on the last two tempering cycles from 1000F by trying to warp it the other way, by laying the warp up and putting the blade on one of my aluminum quench plates. It may have helped some, but hard to say. I also preferentially ground one side hoping to compel it to shift the way AEB-L does if you get too aggressive grinding on one side, but not much luck there either.
 
Stuart Davenport Knives said:
I have had excellent results using shims during tempers to straighten blades. 400°F is a good temperature to use. Lower than 400°F, it can be done, but isn't as effective and takes a few goes. Just remember, you can't clamp it straight and expect it to come out straight. You need to have a bend in the opposite direction by the same amount (sometimes a tad more).

With that said, after watching a video by Gary Creely using one of those carbide tipped ball peen hammers that Hubert posted above, I am seriously considering making one. You just place the blade down on a hard surface with the bow up (like the letter "U", not "∩") and tap in the middle of the bend. In less than a minute you can straighten a short blade with a slight bend in it. But if the blade is already ground, I don't know about that carbide tip putting dents all over the place.
Click to expand...
I use the hammer technique on ground blades without an issue, light taps is the key here. So far I never had a divot stay after the final grinding.
 
Hubert S. said:
I've never tried it on M4, but a carbide tipped hammer has worked really well for me on AEB-L, which I had no success straightening with shimmed tempers. I made the hammer shown below using an old ball peen hammer and a piece of 1/4" carbide from McMaster.

XplUDvp.jpg
Click to expand...
and how did you shape the tip conical?
 
I put my carbide bit in the drill press and just held a coarse diamond file against it, to get the right shape
 
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