Why does size matter?

[Steven511]

This question has been bugging me all day, and I've yet to find any post on here that can adequately explain the answer to me of why heavier anvils are better - and before you type out that they are better because they give more rebound, I know. What I want to know is why heavier things give more rebound. I've mostly just heard they are better because they have more inertia and therefore don't waste the blow's energy by bouncing around, but that just doesn't make sense to me, because as far as I know the energy is still going into the anvil, it's just not moving it as much. However, I know that heavier anvils do work better, hence my conundrum. Have I got something wrong? Can anyone tell me what I'm missing?

[Lou L]

A larger anvil provides more potential energy.  Imagine crashing a car into a 6” diameter tree versus a 12” diameter tree.  The car will absorb significantly more energy hitting the larger tree before that tree gives.  When it come to anvils the difference is even less significant because a smith isn’t imparting enough force to benefit from the increased potential from the larger anvil.  This changes when you use sledge hammers and strikers.  In real use, the issue comes down to the anvil’s ability to handle the increased forces applied to it. Smaller anvils can be damaged by heavy striking.  If you are working alone this really doesn’t affect you unless you are Hercules. 

I still want an anvil at least 100 pounds heavier than my 150# Isaac Hill and I’m not sure why....

[Daswulf]

Sorry, I don't have the answers. But I can say there is little to nothing I cant forge on my 127# trenton with a solid steel top that I have tried. I'm sure larger stuff than a 3# hammer might be small for others but I'm content. Not an answer but a shout out to the smaller stuff. 

[Steven511]

Lou, I understand what you mean, but I also want to know just why and how larger anvils work steel better. I get that bigger anvils can take more of a beating, but I don't understand how they help with beating the hot metal on top of them.

PS; nice analogy, I do appreciate a good theoretical tragedy here and there.

[JHCC]

The force of a hammer blow striking hot steel can do one of two basic things: it can deform the workpiece or it can move the anvil. If the anvil is sufficiently massive or mounted with sufficient rigidity to resist being moved, that force will follow the line of least resistance and deform the workpiece. 

(This assumes that the anvil has sufficient strength and hardness to resist breakage and deformation itself.)

[Lou L]

They help because of potential energy.  They resist (and are able to return) more force than a smaller anvil can.  But in reality, because most humans can’t even challenge a 150 pound anvil with the force of their hammer! there is very little benefit to a huge anvil.  The benefits of a huge anvil in terms of moving metal are ridiculously small.  The psychological benefits are different.  Perhaps if you feel like your anvil is doing more work you will do more work? Who knows?

I guess it can be simplified to this:  If someone tells you larger anvils help you move more metal they are saying so because they spent a lot of money on a large anvil.  As Das already said, there isn’t much you can’t do with a 127# anvil.

There are other benefits to a large anvil,in terms of the size of the strik8ng area, the ability to support hardy tools, using strikers...etc...

[Smoggy]

Hammer supplies the force, the anvil resists it, the more force the hammer can deliver the more the anvil can resist, if it's big enough. Only then will the metal deform under the force of the blow.

The anvil and hammer only need to be suficient to do the work required, but bigger hammers and anvis can do more work when needed.

[Steven511]

JHCC, thank you so much! I comepletely forgot about the path of least resistance law! No more shall I bow to this "weight bounces energy back" nonsense, thanks to the wonder of basic-physics-that-I-really-should-have-remembered-because-I-learned-it-2-years-ago!

[BIGGUNDOCTOR]

Hey Steven, bigger anvils allow bigger hammers to be used on them. You don't want to go using a 16# sledge on a 70# anvil, but a 160# on up anvil - OK. I have heard a 10:1 ratio for anvil weight to heaviest hammer.  2" bar stock on a 100# anvil? Not really a good choice.  You want sufficient mass to back up the blow of the hammer. You fit the anvil to the work being done, just like with any other job you use the proper sized tools.  I believe that it was Francis Whitaker who did all of his work on a 175# anvil.

Have you checked in on the Nevada Blacksmith thread? What part of Henderson are you in? Henderson, or Hendertucky?

[Steven511]

I'm in Henderson, Biggundoctor. I have seen the Nevada thread and know that you need a bigger anvil to back up the hammer blow to work easier and faster. What I want to know is the physics behind why a bigger anvil moves metal better. Luckily, I think JHCC caught the drift of my rather poorly-worded question, and seems to have cleared it up. However, I'm asking in relation to physics, so if I find other pieces of evidence that contradict his theory, your theory, my theory, and at least 3 basic laws of science, I wouldn't be surprise

[JHCC]

1 hour ago, BIGGUNDOCTOR said:

2" bar stock on a 100# anvil? Not really a good choice.  You want sufficient mass to back up the blow of the hammer.

To put it another way (along the same lines as my previous comment), it takes a much harder blow to deform a 2” bar. You therefore need a proportionally heavier anvil to resist that harder blow without deforming or moving, so that the bar remains the line of least resistance. 

[ThomasPowers]

Well to get physicsacal  you have to look at the entire system Hammer, Anvil, Anvil Stand, Earth

So lots cover some aspects with a gedanken experiment---though one you could prove yourself empirically---face hardness: think of having two large blocks of steel, one hardened and one annealed and dead soft.  If you hit both the same way with a hard faced  hammer the rebound on the hard one will be greater than the soft one as some of the energy will go into denting the soft one.  As we want all the energy to go into deforming the workpiece this is a bad thing. (I once had to use a cast iron ASO that would dent under a piece of 5160 round stock being worked---ugh!)

Now take the large piece of hardened steel and set it next to a block of hardened steel that is only a couple of pounds in weight and hit them sideways with the hammer.  If the large one is large enough it's inertia and the friction will overcome the impulse and it will stay still.  If the small one is struck stoutly it may fly.  If the work piece was between each one when hit, The energy of the strike will substantially go into deforming it on the first, heavy, block and will be split between deforming the workpiece and moving the block with the lighter one.

However we now have to take the system into account: if your heavy anvil is floating then some of the force will be dissipated in moving the anvil and so a smaller anvil mounted rigidly might work better. (This is one reason I do not like crisscross stacks of lumber for anvil stands---they are not nearly as rigid as vertically oriented lumber stands!)

I notice very well the difference between doing the same number of items using my 91# anvil vs my 165# anvil and both have similar rebound numbers in the ball bearing test.

The chance of damaging a small anvil with a heavy sledge has already been covered.

 

[Marc1]

On 7/7/2018 at 1:13 PM, Steven511 said:

This question has been bugging me all day, and I've yet to find any post on here that can adequately explain the answer to me of why heavier anvils are better - and before you type out that they are better because they give more rebound, I know. What I want to know is why heavier things give more rebound. I've mostly just heard they are better because they have more inertia and therefore don't waste the blow's energy by bouncing around, but that just doesn't make sense to me, because as far as I know the energy is still going into the anvil, it's just not moving it as much. However, I know that heavier anvils do work better, hence my conundrum. Have I got something wrong? Can anyone tell me what I'm missing?

Steven, I think you must clarify what you mean by 'better'.

I have two PW, one is 280 lb and the other is 480 lb. Which one is better? Neither. They are different, made for different jobs.

They are both just as good as each other. If someone says the bigger anvil is better, that means his smaller anvil is not suited for what he is doing on it and not that the additional weight on an identical quality anvil somehow makes it better. I also have a 20 lb Kohlswa. Are the bigger one better? Depends for what.  

Is there such thing as a better anvil? Sure, a Refflinghaus is better than a Peter Wright regardless of weight. A Peter Wright is better than a Chinese ASO regardless of weight. 

When is a larger anvil better suited than a smaller one and therefore 'better' to use than the small one? When you are forging a heavier object you want a larger anvil ... however ... when you are forging a smaller object, say you want to forge the details on the fingers of a hand, you will be hard pressed using a 300 pounder and you will be better off using the smallest anvil with a small diameter horn ... or using hardy hole tools. 

You could argue that having a large anvil is "better" because you can make smaller size tools in your hardy hole but you can not make a larger anvil if you have a small one.

That would be a valid argument.

However if you are forging a small hook with a one pound hammer on a 80 pound anvil or the same job on a 500 pound anvil, besides feeling a lot better for the satisfaction of the large anvil, there is no difference in your work providing both anvils are anchored appropriately. 

On that note, a tour of blacksmithing videos will reveal the little attention even seasoned smith give to the anchoring of their anvil and I cringe at the site of wobbling and wandering anvils.

In those cases, the better anvil is the one that is firmly bolted down on a solid metal tripod or large wooden stump.  

At this stage it is fair to say that "better" is overrated and very subjective.

 

[MC Hammer]

So far I think every one is spot on and I totally agree.  I'd like to only add one more thing, I think you always see guys looking for bigger anvils because they do not limit the work potential.  When I was looking for an anvil, I wanted something 150# or bigger.  My logic wasn't that bigger is bettter, but was that this size can be moved easy enough, can do small work, and I can use a 12 pound sledge hammer if needed.  It does what perhaps 90 lb anvil couldn't in that aspect.  I wanted a good all around shop size anvil and to me 150# plus was the way to go.

Something Thomas touched on too is what you have the anvil secured to.  If secured completely tight, it now becomes part of the mass.  It doesn't improve rebound, but it does figure into things.

[Buzzkill]

My current anvil is around 120 lbs mounted on a steel tube tripod which is not fastened to the floor (or anything else) since I move everything outside to forge.  When I forge with hammers around 3 lbs or less nothing noteworthy happens.  However, when I use something like a 6 lb. hammer, the anvil and stand tend to walk around a little bit over time.  I do think there is an inertia component at play here.  For the sake of discussion, if you had a 1200 lb. anvil suspended by chains you would probably still be able to forge reasonably well on it with a 3 pound hammer.  A 100 lb anvil suspended in the same manner would probably move around a bit too much though.   However, if the 100 pounder was securely fastened to an immovable stand there might not be any noticeable difference in how the steel moved compared to the larger anvil when using small hand hammers.

[Marc1]

I understand what you are trying to say, but anvils are not made bigger to make up for poor anchoring. There is and always will be a disconnect between the anvil and it's stand. Good anchoring will minimise it and a good relation between hammer mass, work mass, and anvil mass is required to achieve optimal results. 

A more interesting debate would be ... can the stand be made part of the anvil mass? So if my anvil is 100 lb and my stand is 100 lb, will the anvil behave like a 200 lb anvil if I anchor it appropriately? 

What if I push two universal beams in the ground until I hit bedrock, weld a 3" plate on top and weld the anvil to it? Will the earth became part of the mass of the anvil?  

 

[Lou L]

I still don’t understand how what JHCC said is any different from what the rest of us have said.  There is a dearth of high school physics teachers right now in this county (they are so hard to find that incompetent ones are still treasured).  The ramifications of this problem are becoming apparent.

Steven, let me suggest an experiment (it can even be a thought experiment):

Get a hammer and a piece of clay.  Put the clay on top of a pillow that weighs two pounds and hit it with the hammer.  Then put a two pound cut off from a two by four on the ground, put the clay on it, and hit it with the hammer.  Then put ten pounds of solid wood on the ground, put the clay on it, and hit it with a hammer.  You will see a difference between the pillow and the two pounds of wood because of the density of the pillow.  You will see negligible difference between the two and ten pounds of wood.  (Assuming your sw8ngs are similar).  If you swing hard enough you may break the two pound piece of wood.  The same swing won’t break the ten pound piece of wood.  That is the major benefit of a big anvil.

[JHCC]

29 minutes ago, Marc1 said:

So if my anvil is 100 lb and my stand is 100 lb, will the anvil behave like a 200 lb anvil if I anchor it appropriately? 

Kinda. Rebound is a function of the continuous depth of steel beneath the hammer blow, so the discontinuity between anvil and stand means the mass of the stand doesn't add to the rebound. However, it does add to the overall mass and therefore to the total inertia. When I mounted my 148 lb Mousehole (The Undisputed King of Anvils) to a steel stand of just over 150 lbs, I ended up with a 300 lbs anvil system that really doesn't move around much at all.

[Marc1]

Sure, so what if you actually do a full weld between your steel stand and your anvil?

And what if the stand is 1000 lb of steel? In other words, can you add mass to your small anvil and make it into a big anvil?

After all some anvils were built by adding pieces together and welding them. 

And if not why not?

 

[JHCC]

Yes, a full penetration weld between an anvil and a sold stand would create a larger anvil. Just tacking down the corners wouldn’t do it, as that does not create a continuous mass. 

Why not? Well, the heat from such a weld could easily mess up your heat treatment. Without the means to reharden, the benefits of added mass would be outweighed by loss of rebound and surface durability. 

[Marc1]

Not really ... I'll try to explain in my own words.

The anvil mass has an inherent potential energy or inertia if you prefer. The kinetic energy of the hammer needs to get into the work to do the forging and the inertia of the anvil return as much as possible rather then fiddle away into the ground or shaking about. 

The anvil can do this according to mass, hardness and shape. The part of the anvil that works best is where the centre mass is. An anvil shaped like a prism or a cube will work as a unit. An anvil shaped like an hour glass will only use the potential energy stored in the upper section. The lower section will be almost useless. Just like stands will not add mass to the anvil in any measurable way or a second anvil welded to the upper one will not make the anvil twice it's size. Sure making the mass more stable will avoid losses from vibration or lateral movement, but that is as far as the stand can go.

The mass of an anvil needs to be continuous, no gaps, no waist,  no little legs, no welds to another shape or change in density for the anvil to work as ... well ... an anvil. 

One could make a bigger anvil by cutting an anvil above the waist where it is still the full size of the body. Machine it nice and flat, and place on a mass of metal of similar density and fully weld it to it. 

Not that anyone would want to do such a thing

[Latticino]

Lou,

You are using the term "potential energy" to describe forging on a large anvil in a way that I'm not really familiar with.  In my experience this is a fairly good simple description of what most physics and engineering texts refer to when using that term:

"To summarize, potential energy is the energy that is stored in an object due to its position relative to some zero position. An object possesses gravitational potential energy if it is positioned at a height above (or below, for negative potential energy) the zero height. An object possesses elastic potential energy if it is at a position on an elastic medium other than the equilibrium position."

In this case I believe that inertial effects are more relevant than potential energy.  Generally the more an object is moved from it's resting position the more potential energy it stores.  For the ideal large anvil, it moves very little from its resting position (particularly it's forging surface) when the overall forging system is working to greatest efficiency.  That is maximizing inertia of the anvil, not it's potential energy.

Marc1,

I think it is still inertial effects, even with the oddly shaped anvil designs you are positing.  Striking through the center of mass, or as close as possible, utilizes the optimal mass of the anvil/stand assembly, and transmits the force more directly down to the earth.  When you work out over the tip of the horn, for example, you put a torque on the assembly, and no matter how well affixed, you will dissipate some of the energy of your strike to the rotation of the assembly rather than deformation of the stock.

At least that's my theory...

[JHCC]

I think Lou meant "inertia" when he said "potential energy". Give the guy a break: he teaches English, not physics.

 

[Marc1]

The physics at play in hammer/anvil/hot steel system seem simple and many try to explain them with the Newton laws. There is more to it than a few forces.

To begin with when one hits an anvil with a hammer, and lets keep the hot steel aside for a moment for simplicity sake, what we are talking about is a collision.

When hammer and anvil collide, according to Newton, the same force is applied to the anvil and to the hammer.

However what we need to know is what happens next. The  effect of the force applied to the anvil is what entertains the thought of it's suitability, and here is were mass, hardness and shape play a role. 

When the hammer strikes the anvil, or rather when it strikes the work and the work transmits the blow to the anvil, the molecules of steel transmit the force to each other, and each molecule in turn returns the favour in the opposite way.  The force of the blow that was vertical to begin with, will fan out into the mass of the anvil and each molecule will transmit some of the force to its neighbouring molecule. Imagine a tin bucket full of bearings. You hit the bearings at the top of the bucket with a hammer. if the blow is fast enough and the bucket soft enough, the sides of the bucket and not only the bottom will bulge out and the bearings will mark the whole of the bucket. 

In the case of an anvil shaped like a cube, a good proportion of the force will go in the base, in the case of an anvil shaped like an hourglass, very little of the forces have a chance to transmit to the base. The cube and the top side of the hourglass behave like a single object and no amount of mass added to the lower section of the hourglass will contribute in returning forces upwards.

For whoever is interested in the physics of anvils and hammers, it is much more complex than just Newton laws, and the way to start is to study the laws pertaining collisins.

Here is a small article on the subject that when not covering all aspects gives a good indication of what happens. 

I love the conclusion at the bottom in relation to the much tooted "rebound" .

Rebound should matter but it does not ...

https://www.calsmith.org/Resources/Documents/technical_documents/techdocs_thephysicsofanvils.pdf

[MC Hammer]

14 hours ago, Marc1 said:

Rebound should matter but it does not ...

So why bother hardening the face of an anvil if rebound doesn't matter?  I understand the science explained in the article, but sometimes you have to stand back and look at those that have used hardened faced anvils for the past 300 years +/-  These guys fed their families by being blacksmiths so if something worked better, made them more efficient, allowed them to do more work, they adopted it.  The hardened face that produced better rebound added something to the equation that gave the smith an advantage or he would have quickly abandoned the new fancy hard faced anvil and went back to his wrought iron anvil square or whatever he was using that didn't have a hard face.  The testimony of history sometimes outweighs the lab coat conclusions IMHO. 

I think if you could time travel and took a 150# hard faced anvil of your liking back with you to the middle ages or before and dropped it off to a smith working back then on his mild steel block or whatever, he'd ditch it in a heartbeat for the hardened faced anvil.  Perhaps only because of its durability maybe, but perhaps he would discover it helped him be more efficient and work at the forge longer not really understanding the physics of everything, but knowing there was something advantageous about the time traveler's new gift.  I think if you sat him down and explained the article to him and the science he'd say "Yes, but the new anvil works so much better, how do you explain that?"  Perhaps I'm wrong, but having used an ASO when starting out and getting a hard faced anvil eventually I noticed a huge difference in how long I could work and how much more the hot steel moved.  Was the new anvil larger (more mass) yes and that plays into the equation, but there was also something about the rebound that helped.  I guess how does my observation fit in with what the article puts forward that rebound does not matter?