Carbide Peen Hammer Straightening Tip

Huntsman Knife Co. LLC.

Huntsman Knife Co. LLC.

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Hey guys,

I've been using a carbide tipped hammer to straighten my blades for the past 9 months. While I had success on some blades, there were many blades that simply would not respond to even hundreds of hammer taps.

As some of you know, I make lots of machetes and other long thin blades from Z Tuff and 3V with low tempers that are highly warpage prone.

I made a big breakthrough in my technique that I discovered by accident and wanted to share. This all happened when I was being lazy and decided to straighten a blade on my granite kitchen counter top and was able to actually feel the reverberations and pitch of the hammer taps clearly for the first time. There was so much reverberation on my countertop from the little taps that it actually shook the whole house and caused the cups on my counter to start humming in sympathetic resonance. It was pretty dang cool!

Using this discovery, I've been able to straighten even the most severely warped blades in my shop in minutes with only light tapping. (Is this what it feels like to be a real bladesmith? 🤣 )

Guys that forge alot and have been using hammers on an anvil for years probably already know this instinctively but for us stock removal luddites, I want to share so you can stop being frustrated with stubborn warps.

I'll film a video on this for you guys when I'm back in the shop (or kitchen) so you can see it in action and I can better explain it.

THEORY

While we are taught that carbide peening works by stretching the surface of the steel to correct warps, I'm not sure this is the whole story. I now think carbide peening has an additional effect similar to shot peening where its reliving stress in the steel and not just relying on stretching.

You can hit the blade a thousand times and leave a thousands marks and many times the blade wont budge at all. If stretching the surface was the only mechanism of action, the warpage should be corrected after a huge number of taps.

Instead, I've discovered that hitting the blade in the right place, with the correct energy distribution is the real key to fast and effective straightening and its all about FEEL and SOUND.

THE SETUP

1. Use a THICK granite block.
- In the past, I've done my peening on a thin piece of granite or a steel plate backing. using a big ole piece of granite helps you to better feel and hear what is going on with your hammer strikes.

2. FEEL and LISTEN
- Find where the bow in the steel is, use your fingers to secure the blade and start tapping just like you normally would.

- NOW, is the real key, feel and listen with your ears and try to get the hammer taps to resonate.

- Hammer taps that create a dull thudding sound and rebound the energy directly into the hammer are effective.

- Hammer taps that creating a sharp pinging sound and don't reverberate the energy back into the hammer are not working and won't straighten your blade. When the energy is being scattered instead of being sent directly through the blade, its not doing the work it needs to relieve the stress in the steel. Its just getting converted into sound and hurting your ears + leaving a mark on the blade you have to grind out later.

If you are getting sharp pinging sounds and not feeling any resonance in your hammer taps. This is not the right spot on the blade to be hammering, move on and try another area.

Here is a diagram below.

Basically, we want the energy of the hammer tap to go through the blade and bounce DIRECTLY back into the hammer. You can really feel when this is working as your hammer taps will feel really bouncy, almost like you are hitting a trampoline. The steel will feel soft.

7TURj8r.jpeg
 
Well, you sort of found an answer, but it is a bit different than what you said. The straightening is from stretching the concave side. As you discovered, the surface opposite te area being stretched HAS to be in contact with a hard and smooth surface. It can be an anvil face or a block of granite.

You are correct that the sound tells you you are doing it right. And that if the piece is in solid connection with the hard undersurface you will get more hammer rebound.

Where you went astray is it is not the rebound energy, but the energy delivered to the one surface and not the other. This moves the steel molecules sideways and stretches the surface to straighten the blade.

If there are multiple warps you have to work them in the order that allows the underside to be in contact with the hard surface.

Now, for the nerds - The principle that makes the surface stretch is in Newton's third law of thermodynamics. "For every action there is an equal and opposite reaction".
The action is the very hard carbide striking the blade surface. If the blade was not sitting on another hard surface, it would be moved away from the hammer (your second sketch).This would not straighten the blade much or any. In the situation of the first sketch, the force (action) cannot push the steel away from the hammer, so it causes plastic deformation by dislocation and pushes the steel sideways as the opposite reaction. (Young's modulus has something to do with that.)
 
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I have been using the little anvil section on my 5 inch bench vise but it do feel I need to swing harder than what I hear other people doing so I snagged a peice of railroad tie from a friend and now just need to get it surfaced.
 
Seedy Lot said:
I have been using the little anvil section on my 5 inch bench vise but it do feel I need to swing harder than what I hear other people doing so I snagged a peice of railroad tie from a friend and now just need to get it surfaced.
Click to expand...
Ive long fussed over how hard I should swing.

Now Im doing gentle taps and really just letting the hammer and the weight arm do the swinging. The hammer is probably traveling about 5 inches. The real key for me is to try to get a rhythm where the hammer is kind of bouncing off the work piece.
 
I kinda let the hammer bounce with a little force added to the swing, very little. I will see if I can get a video one of these days of it. It's not a real hammer swing or anything like that, but more like letting it bounce up, hit the web between my thumb and fore finger and add a little more oomph on the way down. You gotta have the steel backed by something hard to work; I use my granite surface plate to check for straightness and to fix the warps.
 
Jewelers/silversmiths use the same technique to make curves and raise bowls and even teapots. Millions of light blows to the surface will curve or dish the silver or other metal. We use forms that are curved and hardie tools with large balls on the shank. Once you get a rhythm going it is just thousands of "tap-tap-tap" and reannealing. The blows are just firm enough to deform the metal against the hard backing surface. Depending on the desired final surface, you may use hammers with deferent ball diameters or flat/curved faces.

I make a copper/silver/brass mokume block about the size of a hockey puck and raised a bowl from it this way. The first stage was drawing the puck out on the anvil into a sheet about 6" round and then peening it and shaping on the forms until it was an 8" bowl. I had to torch anneal the metal every 10 minutes to keep it soft enough and avoid cracks, as non-ferrous metals will work harden in hammering. It took a long time to finish that bowl.
 
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