This hammer is a happy accident for how it came to be. I was working on my first batch of Magnacut steel and after the cryogenic treatment, I found most of my blades had picked up a banana shaped curve in it. I first tried shim tempering which has worked extremely well for me in the past. However this time, it only worked on a few blades.
I knew other makers talked about using a 3 point bending method. So I put my blade in my arbor press, and broke part of the tang right off. Well, that is not going to be a good way to go for this hardened steel. I tried using a hardened steel ball peen hammer, and shattered the front of a Nakiri. That wasn’t going to work either. I was thinking I would need to anneal the whole batch and try to heat treat them again.
In talking with Dr. Larrin Thomas, he pointed me to a post on Blade Forums. In the post one of the members HSC was using a carbide chisel to straighten his blades with good success. One of the other knifemakers I talked to was Dan Bidinger, he showed me a carbide ball he inserted into a hammer and said it was working well for him. After seeing and researching carbide chisels and straightening hammers many others have used/made, I felt this carbide ball inserted into a hammer was the best way to proceed for testing if I could make it work.
I ordered a couple Ø3/8″ carbide balls and picked up a ball peen hammer. I drilled out the back and soldered in the carbide ball. I was able to straighten the blades I broke during my earlier attempts and knew I wanted to bring these helpful tools to other makers.
The hammers now feature a brazed carbide ball in the back of the peen and the carbide is approximately 90 HRC which allows it to dimple the hardened blades and not shatter them.
What has worked the best for me has been to put the knife with the warp on the anvil in the shape of a U and just to one side of where it comes up, hit the top side with the hammer to bring the blade back down straight. I do 1 or 2 hits then check the knife of my surface plate and by eye to see where the next hits need to happen.
With some moderately hard hits based on the diameter of the dimple left in the steel the 4 oz hammer leaves a 0.0025″ deep divot and the 8 oz hammer leaves a 0.0051″ deep divot. Me being on the heavier hand nature, I feel I prefer the lighter hammer, but they both work extremely well from my testing.