Does anvil mass have to all be steel?

[JamesBBrauer]

As the title suggest, can I fill some rectangular tubing with wet concrete, and weld a block of tool steel on top for an anvil on a pneumatic hammer I'm working on? From what I've read a 1:10 hammer to anvil weight ratio is a good rough guide. But I don't exactly get why this is the case. Is there some sort of shock pulse that rebounds the hammer, and cement would dampen it? Or is the idea just for the work piece to absorb all the energy from the impact? Or something else? thanks

[ThomasPowers]

You need the mass to provide inertial mass under impact so it has to stay rigidly attached. Concrete in a steel box tends to lose it's attachment under repeated pounding.

Can you weld up large chunks of steel oriented vertically?

[HWooldridge]

You might get there filling the tube with lead.

[Nakedanvil - Grant Sarver]

From a post I made a dozen years ago on the "Blacksmith's Virtual Junkyard". As true today as it was then:

You're forcing me to get into an explanation I've been avoiding. No problem, just have trouble explaining things sometimes. Well, here goes anyway. A lot of the following is pretty basic physics, but you probably never took the time to think through what is really going on in hammering.

The first thing we need to look at is why a hammer bounces off the anvil. We have all had the experience of striking the anvil, either intentionally or unintentionally. What happens? The hammer bounces back like a super ball, right? Why? Steel is a very elastic material. It can be deformed within certain limits (known as the materials elastic limit) and it will return to it's original shape. This is easier to imagine if you picture a coil spring (like a valve spring) mounted on a handle so it looks something like a hand hammer. Now, when you hit the anvil you can visualize how the end that contacts the anvil will stop and the other end will continue a little ways thus compressing the spring. Once all the energy has been absorbed by the spring, it quickly returns to it's original length pushing it away from the anvil.

Now, by stretching your mind a little, you will be able to understand that the EXACT same thing is happening to your hand hammer when it strikes the anvil! The face of your hammer stops when it contacts the anvil and the rest of the hammerhead continues downward for a moment, compressing the hammerhead. Of course it returns to it's original shape real fast, pushing it back up. Very little energy is lost in this process. A little heat where the two meet and a little internal heating of the hammerhead is the only loss.

If you can believe all of that we can move on to the anvil. In the above explanation I only considered what went on in the hammer. There's more. When the hammer strikes the anvil, it also compresses. The two compress inversely by their mass. If the place where you hit the anvil compresses, what happens to the rest of the anvil? It resists moving in proportion to its mass. When the top of the anvil springs back to its original shape down equally. If the anvil were made of a material with a low elastic limit it would permanently deform. Lead has a low elastic limit, but is malleable; thus it would deform and return little energy. Concrete has a low elastic limit, but is not malleable and will crumble.

What happens when we put a hot piece of steel in between? All three are compressed according to their mass and malleability and all three expand according to their elasticity. The hot steel has high malleability and low elasticity. As the piece cools down you can feel it losing malleability and gaining elasticity. Every time you hit a piece of hot iron it receives two blows. The first when you hit the piece and the second when the hammer and anvil return to shape. This all happens so fast as to seem like one blow.

What does all this have to do with your question? Be patient! I'm getting to that. Relating all this to a power hammer we can now understand a little more about what's going on. When a power hammer hits the anvil all of the same things happen. The ram of a power hammer must be elastic just like the hand hammer to get the best effect. If you have ever used a lead filled hand hammer you can understand why a lead filled power hammer ram is a bad idea. Concrete filled power hammer anvils are another BAD idea. Somebody ought to make a concrete filled hand hammer anvil to show these people just how bad the idea is.

Is concrete UNDER the anvil worthwhile? A qualified, yes! If the anvil has sufficient mass and a larger enough contact surface to prevent damage to the concrete. The top part of the anvil can compress while the bottom and the concrete resist. As concrete has a low elasticity it is necessary to have a large surface of contact. Putting elastic materials like rubber or wood in the interface help to make a better joint but rebound too slowly to help with the forging. Concrete blocks are most effective in isolating the shock from the surroundings.

Hope I didn't bore you guys too much, I skipped over some, might add to it later.

Edited August 14, 2009 by nakedanvil

[John Larson]

Concrete provides weight and sound deadening, but it powders when impacted. Which is why people use rubber or plywood between a power hammer base plate and a concrete floor.

I'd fill that box tube with lengths of cheap rod (rebar?), weld it top and bottom and grind smooth and square, and then cap with steel plate that can be drilled and tapped, for example, for attaching dies.

I'd say the anvil mass-to-hammer-head ratio needs to be more than 10:1. Think about a hand hammer weight and a regular anvil weight. A 10 pound hammer on a 100 pound anvil is not very attractive to most blacksmiths. In my 13 years as a power hammer builder I have steadily increased the ratio, beginning around 8:1. My standard machines use more than 16:1 and they work pretty darn well. I've built a couple of 20:1 machines that were not discernably different in performance. Bolt or weld together the hammer frame and base plate and anvil and you can pretty much count that weight into the anvil mass just like you can count a big steel mount for a regular anvil when they're securely bolted together. In all cases however, the real sweet spot for rebound comes from the mass of steel going straight down from the bottom die just like on a regular anvil.

BTW, enjoy the build process. Designing/building machines gives an immense boost to your self esteem (aka bragging rights).

[JamesBBrauer]

Thanks for all the expert advice. I'm getting that a cement filled tube would be the equivalent a hard faced deadblow mallet. Or that there would be a second order effect of the compressed/breaking/shaking cement in the relationship between the two masses and the modulus of elacticity that would wreck the energy transfer.

There is a long piece of 3 or 4" round (old carpet picker for a forklift) at one of the local scrap places that I might be able to get for a good price. Hopefully it is still up there and I they will let me cut it down to 3" lengths on-site.

And John, I do get proud of things I build myself. I get complements on a tandem axle trailer I made, and like saying I built it myself. Plus, thinking about how to make things is a productive way to occupy my thoughts. Instead of thinking about the last person that ticked me off, I am assembling things in my head. I read your site, and you make some awesome machines.

- James B

[mandomaniac]

Wow....
This info certainly changes my thinking.
I had been planning on simply filling a heavy walled square tube with sand (or maybe wheel weights) for an anvil base. After trying to research PH construction on the net, it seemed this was a fairly common approach to increase either anvil or hammer mass. The tube would be capped by a 3" thick piece of steel and a 1/2" plate to bolt interchangeable dies to. Even then, I don't think I would be anywhere near a 10:1 mass ratio since I was going to have a hammer in the 35-40# range. A 400# anvil base is a chunk!
Physics is physics, however. Thanks for pointing this info out.
Hmmmmmm..... maybe back to the drawing board! :o

[Francis Trez Cole]

At my metal store they have some 6" soild rounds scrap diffrent length. Thought I would sleve them in a steel pipe and weld it solid.

[Nakedanvil - Grant Sarver]

Francis: the losses from layering are probably negligible in practice. IF they have nice flat, square ends it should work fine. Weld the first slug in the bottom then turn it right end up, stack the slugs in it and heat the pipe before welding. The pipe will then shrink a bit and compress all the slugs. I'd do it. Bet it works great.

[Francis Trez Cole]

nakedanvil: they are all real square saving up.