CPM MagnaCut Warping

Cypress Creek Knives

Cypress Creek Knives

CCK
Knifemaker / Craftsman / Service Provider
Joined
Dec 15, 2010
Messages
644
Good Morning everyone, I have heat treated about 60 blades in CPM Magnacut and about 20% of those blades have warped. My HT recipe is as Larrin suggests in his article. I do a 20 minute soak at 2050*F followed by a plate quench and a LN treatment. I then temper at 350*F for 2 two hour cycles.
I have found that my blades are going into the liquid nitrogen straight, but when I pull them out for tempering, some of them have a bow to them. Usually it is just a bow, but I have had the occasional twist develop as well. I am using .100" to .156" steel, with no bevels ground pre heat treat.
To try and correct this warp, I shim and clamp these blades during tempering, but it only helps so much. Does anyone have any ideas or suggestions on how to prevent or correct this issue?
I have found this steel to be less prone to warp than Nitro-V but quite a bit more prone to warp than S35VN.

I have tried straightening some of these blades post heat treat and have had a little success, but I have also snapped a couple of blades trying to get the warp out. In the end, I can take these blades to my surface grinder to clean them up, but I would like to avoid that as much as I can.

Any words of advice are welcomed and appreciated.

--Jared
 
I would suggest reaching out to Larrin himself. Asides for him being the most familiar with the steel. Yours and others experiences would be beneficial data and help him see the pros and cons and to make future improvements.
 
If the blades are similar in size and shape and your dewar opening is large enough you can try clamping them together before they go into the dewar.
example here - blades clamped. swipe to the last pic
you can use a carbide hammer (tagane) to straighten the blades (peening with the carbide tip). I do it all the time with a carbide chisel on long thin kitchen knives.
you can also stress relieve the material when you first get it from the supplier before you do anything else
 
HSC /// said:
If the blades are similar in size and shape and your dewar opening is large enough you can try clamping them together before they go into the dewar.
example here - blades clamped. swipe to the last pic
you can use a carbide hammer (tagane) to straighten the blades (peening with the carbide tip). I do it all the time with a carbide chisel on long thin kitchen knives.
you can also stress relieve the material when you first get it from the supplier before you do anything else
Click to expand...

That is what I would like to do, but unfortunately my dewar has a narrow neck.

I will look into that hammer, what are you using as a backing plate? Steel, granite,.. etc
 
80% of my blades wrapped until I made a slight change:

I now have the plates mounted vertically in a vise. When they were horizontal and you set the blade on the bottom plate, one side of the blade starts to cool before the other. So you have to be super fast getting the top plate on in time. But, when vertical the packet initially sets in at an angle. As you close the vise, the sides of the blades contact pretty much simultaneously.

vise.jpeg

That helped a lot. Now it's down to < 10% warping. But I recently had a MagnaCut blade warp on me. I was going to just toss it out. But I thought I'd try the hammer thing that H HSC /// mentioned. So I made this:

hammer.jpeg

It's just an old masonry bit I press fit into mild steel and tacked on to a hammer.

I works! I've heard about straightening hammers, but couldn't imagine it working. So for me it was darned near magic. I mean it was only a couple minutes and a blade I was going to toss out is now perfectly fine. I should have believed all the guys who use them long ago.

I set the blade on an anvil with the convex side up (the two ends of the banana pointed into the sky) and pounded 20 or so marks in the center of the curve.
 
Sando said:
80% of my blades wrapped until I made a slight change:

I now have the plates mounted vertically in a vise. When they were horizontal and you set the blade on the bottom plate, one side of the blade starts to cool before the other. So you have to be super fast getting the top plate on in time. But, when vertical the packet initially sets in at an angle. As you close the vise, the sides of the blades contact pretty much simultaneously.

View attachment 1725462

That helped a lot. Now it's down to < 10% warping. But I recently had a MagnaCut blade warp on me. I was going to just toss it out. But I thought I'd try the hammer thing that H HSC /// mentioned. So I made this:

View attachment 1725470

It's just an old masonry bit I press fit into mild steel and tacked on to a hammer.

I works! I've heard about straightening hammers, but couldn't imagine it working. So for me it was darned near magic. I mean it was only a couple minutes and a blade I was going to toss out is now perfectly fine. I should have believed all the guys who use them long ago.

I set the blade on an anvil with the convex side up (the two ends of the banana pointed into the sky) and pounded 20 or so marks in the center of the curve.
Click to expand...


I may have to try to mount my quench plates vertically. The only issue there is I'm heat treating 6 blades at a time and I dont have enough hands or shop space for 6 vertical mounts. Maybe I should consider forced air cooling by removing the blades from the foil and hanging in front of moving air.

That hammer trick sounds like black magic! i'm going to have to give it a shot. I no longer have an anvil in the shop but I have some railroad tie plates laying around.. maybe one of those will work.
 
Cypress Creek Knives Cypress Creek Knives I 'think' it's the little marks the hammer/chisel point leaves that does the trick. Maybe it increases the surface area on one side stretching it out? .... It's more likely black magic.

If it is the marks it would explain why you can't just use a ball peen hammer. It has to be something harder than the blade to make a mark. I'm sure you could just set the blade on a concrete floor and it would work.
 
Bali-Flipper32 said:
I may have to try to mount my quench plates vertically. The only issue there is I'm heat treating 6 blades at a time and I dont have enough hands or shop space for 6 vertical mounts. Maybe I should consider forced air cooling by removing the blades from the foil and hanging in front of moving air.

That hammer trick sounds like black magic! i'm going to have to give it a shot. I no longer have an anvil in the shop but I have some railroad tie plates laying around.. maybe one of those will work.
Click to expand...
I just use the 3"x3" little anvil on the back of my (uncommonly stout) bench vise. I hit the blade with so little force that it doesn't take much mass behind it.
 
These are mine. I use a 20 kg anvil, the surface is nice to check straightness on.
YThjMJW.jpeg
 
Sando said:
Cypress Creek Knives Cypress Creek Knives I 'think' it's the little marks the hammer/chisel point leaves that does the trick. Maybe it increases the surface area on one side stretching it out? .... It's more likely black magic.

If it is the marks it would explain why you can't just use a ball peen hammer. It has to be something harder than the blade to make a mark. I'm sure you could just set the blade on a concrete floor and it would work.
Click to expand...

HSC /// said:
Anvil for backing

If you do a search for a carbide chisel with my name you’ll see more information about it
Click to expand...

I did some reading on these straightening hammers on the forum and I am going to give it a shot. Right now all I have is a ball peen and a carbide masonry bit. I'm gonna give that a try.
 
JTknives JTknives straightens like this, and every blade he has ever sent back to me has been straight.
 
Bali-Flipper32 said:
I did some reading on these straightening hammers on the forum and I am going to give it a shot. Right now all I have is a ball peen and a carbide masonry bit. I'm gonna give that a try.
Click to expand...
You might want to ease the point on the masonry bit a bit. I cracked a blade peening with a masonry bit before I made a proper peening hammer from a piece of carbide. You can get some diamond discs for a rotary tool from Harbor Freight for cheap, and they do a good job shaping the carbide. Just put the carbide in the drill press and then use the rotary tool with the diamond disc to shape the point.
 
Hubert S. said:
You might want to ease the point on the masonry bit a bit. I cracked a blade peening with a masonry bit before I made a proper peening hammer from a piece of carbide. You can get some diamond discs for a rotary tool from Harbor Freight for cheap, and they do a good job shaping the carbide. Just put the carbide in the drill press and then use the rotary tool with the diamond disc to shape the point.
Click to expand...
I will have to get a piece of carbide. Where would I source that?
 
I made a straightening hammer just like Sando posted a photo of with a ball peen hammer. Dulled the point with a Dremel tool and it works AWESOME. I heat treated the hammer head, annealed, it so I could drill it with a regular drill. Cut masonry drill with Dremel tool and JB welded it in place. I couldn't believe how well it worked. The small divots are easily ground out post HT.
 
Bali-Flipper32 said:
I will have to get a piece of carbide. Where would I source that?
Click to expand...
I got a 1/4"x2" piece from McMaster-Carr, see link below. I scored it with a diamond wheel, wrapped it in a rag before clamping it in a vise and then hit it with a hammer to get two 1" pieces. If you have a broken carbide end mill or drill bit, I think it would work just as well.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
www.mcmaster.com www.mcmaster.com
 
Sando said:
80% of my blades wrapped until I made a slight change:

I now have the plates mounted vertically in a vise. When they were horizontal and you set the blade on the bottom plate, one side of the blade starts to cool before the other. So you have to be super fast getting the top plate on in time. But, when vertical the packet initially sets in at an angle. As you close the vise, the sides of the blades contact pretty much simultaneously.

View attachment 1725462

That helped a lot. Now it's down to < 10% warping. But I recently had a MagnaCut blade warp on me. I was going to just toss it out. But I thought I'd try the hammer thing that H HSC /// mentioned. So I made this:

View attachment 1725470

It's just an old masonry bit I press fit into mild steel and tacked on to a hammer.

I works! I've heard about straightening hammers, but couldn't imagine it working. So for me it was darned near magic. I mean it was only a couple minutes and a blade I was going to toss out is now perfectly fine. I should have believed all the guys who use them long ago.

I set the blade on an anvil with the convex side up (the two ends of the banana pointed into the sky) and pounded 20 or so marks in the center of the curve.
Click to expand...
I had huge issues with AEBL warping. I had my plates mounted like this. I drilled and taped holes in each corner. Once clamped I take my impact driver and screw the plates together. I then dunk the whole assembly in ice water before removing the blade and transferring to the liquid nitrogen. My last batch was perfectly straight.
 
Sando said:
S Scaniaman You're look much nicer than mine! I didn't have the patience (or foresight) to anneal and drill like L LCoop did.

Why do you have two different shaped points?

H Hubert S. Thanks for the tip! I'll make that change.
Click to expand...

:) I didn't anneal. I drilled the hole with the solid carbide drill bit that I then flipped over and made the hammer's "tip" with.
The other one is made from a stone carving chisel I was using before I had a hammer. Maybe there is an idea to peen over a longer section sometimes, I don't know.
 
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