Why is anvil rebound important?

[rdennett]

I have seen various videos from Trent Tye and others who make a rather convincing case that anvil rebound in meaningless.  A hardened face will certainly last longer if you miss a lot, but i wonder if the importance placed on rebound is some lore handed down but no one knows why it's actually important.  Daniel Moss's video in reaction to Mr. Tye's didn't really make a compelling case.  ISTM that all things being equal, an anvil made of mild steel will work just as well as one with a hardened face.  The anvil will likely deform over time, although this may take years, if not decades and there are anvils with hardened faces which are swaybacked.  Am I wrong?  If so, can you please explain why?  

[Frosty]

That's easy enough to determine for yourself, If rebound is meaningless or does what many of us say. Place a piece of say 3/8" steel plate on a wood block and do some forging. 

Or if you have access to a decent anvil do a comparison say bring a piece of 1/2" bar sq or rnd. doesn't matter place one coupon (test piece) on the tail of the anvil and give it 3 stout smacks. Then take another coupon of the same heat, place it over the sweet spot (centered over the anvil's waist) and give it 3 stout smacks with the same hammer. Once they've cooled measure them and compare how much they moved and compare.

Another excellent rebound test is a length of RR rail. First forge on it laying on it's flange rail up, then forge on it standing on end. Compare the work done as before. 3 smacks with the same hammer on the same size and temp. coupons.

It's been my personal experience that as fine an anvil as my 200lb Trenton anvil is, my 125lb Soderfors moves metal farther and with less effort by a significant degree. The Trenton is forged with a decently thick steel face where the Soderfors is cast and closed die forged Swedish steel, surface hardened to close to a 60 RC, on the face.

Miss a hard blow on the Trenton and you can ding it. Miss a moderate blow on the Soderfors and it will mark the hammer, I made my first veining chisel by flattening the edge of a sharp Craftsman cold chisel by smacking it against the face of my Soderfors with a 3lb. hammer. Chisel flattened to just shy of 1/8" wide and zero mark on the anvil.

I've forged on mild steel, I used to scrounge up enough to do some smithing in camp fires when I had a field job. The other guys would be knocking off a couple 6 packs and I'd beat "rescued" steel scrap into something else. If the steel you're forging is hot enough you can do useful work in almost any reasonably hard surface but a cast iron engine block sucks. A nice shiny "ultra-mafic" boulder on the other hand makes a superior anvil.

Of course that's just my opinion.

Frosty The Lucky.

[George N. M.]

This has been discussed to death over the years but the consensus seems to be that it takes less energy to forge on an anvil with good rebound.  Without going into the physics of it, it seems that a high rebound anvil more efficiently transfers the energy ("work") of the hammer blow into deforming the hot steel. IIRC it has to do with energy being reflected back into the work from the anvil.  Think of the anvil as a spring.  Some of the energy of the hammer blow deforms the work piece but some passes through the work and slightly deforms the anvil.  The anvil springs back into shape and this energy rebounds back into the work increasing the deformation.  So, a "springier" anvil which has a higher rebound will give more deformation per blow.  The rebound energy is only a percentage of the total energy of the blow but it is enough to be noticed in use.

As Frosty says, any heavy flat surface can be an anvil, including rocks or any other large mass.  I have always thought that a boulder of an amphibolite group rock which has a very tough, fiberous crystal structure, which has be cut flat would make a dandy anvil.

"By hammer and hand all arts do stand."

[rdennett]

What (Frosty is)  describing seems to be showing that inertia or mass under the hammer is more important than surface hardness, the latter of which should correlate with the anvil's rebound.  I haven't tried this since I don't happen to have any ball bearings handy, but it seems to me that the bearing would bounce to the same height on the tail of the anvil as it would over the sweet spot.  Is that the case?  

I would think a true apples-to-apples comparison would be to test a block of hardened and tempered steel against a block of mild steel with the same weight and dimensions and orientation.  It's my understanding that the hardened block will score better on the ball bearing test, but is it the case that it would move metal more effectively than the mild steel one?  

Also, I always thought the issue with cast iron was that it was too brittle for forging and a miss could cause it to break, potentially injuring the smith.

[FlatLiner]

I agree with your first two paragraphs, you make some valid points. I have a diy post anvil made from two forklift tines welded back to back. It is relatively unhardened when compared to my swedish made sisco anvil. The post anvil definitely has more mass directly under the hammer and an errant hammer blow will mar the surface of it but it seems to move hot steel just as well as the sisco. I have a block anvil made from annealed s7 steel that seems to move steel as well as well as the sisco. My sisco has really bad edges and if I need "better" edges my annealed block of s7 or my fork lift tine anvils are my go to. 

As for cast iron, it is too brittle and too soft to make a decent anvil, unless like the fisher anvils it has a fully welded on hardened face plate.

[JHCC]

The simplest way I can put it is this:

1. All of the force of a hammer blow either deforms the workpiece or is absorbed by the anvil.
2. A low-rebound anvil absorbs more force.
3. A high-rebound anvil absorbs less force. 
4. The less force is absorbed by the anvil, the more force goes into deforming the workpiece.

It's often stated that a high-rebound anvil makes smithing easier because it helps lift the hammer on the upstroke. This is easily disproved, through the simple experiment of dropping a ball bearing on hot steel and observing the lack of rebound.

However, a high-rebound anvil does making smithing easier, but for a different reason. Because more force is available to deform the workpiece when forging on a high-rebound anvil, the smith is able to accomplish the same amount of metal movement with fewer hammer blows. 

[FlatLiner]

I could be wrong,

but I would think that physics shows a hardened ball bearing being dropped on a piece of red hot steel and not bouncing back up regardless of whether that red hot piece of steel is on top of a hardened anvil or on top of a piece of forklift tine, or on top of a sledge hammer head would show that as long  as the red hot steel is softer than the anvil it does not matter. If the hammer blow is going through the hot steel and the unhardened anvil is absorbing any of the blow or rebounding it, than the heated steel isn't hot enough. Of course a hardened anvil will out last a softer anvil over time. That is not up for debate. Since no one has ever really done a true scientific test taking all the parameters into account it is all up to conjecture, hearsay, and what we have been taught, etc. All the while being subjected to our own preconceived notions based on others conjecture, hearsay and what they were taught in a never ending loop of conjecture and hearsay.

I believe that if a true scientific test were done the differences between a mild steel anvil the exact same weight and dimensions of a hardened steel anvil, placed on the exact same size and weighted base, on the exact same surface, using the exact same sized hammer, weight and strike,  from the same angle and height onto two identically dimensioned pieces of the same metalurically identical steel, heated up to the exact same temperature. Would result in a difference so negligible that the average human wouldn't be able to perceive the difference.

At best it might just be a placebo based on misconceived beliefs that were based on old wives tales about the what, when, where, why, how's and merits of a hardened faceplate on a wrought iron anvil vs otherwise that has been passed down for countless generations of blacksmiths with no regard or ability to check the veracity of what they were taught.

The hardened faceplate might have originally been placed on wrought iron anvils to lengthen the life of said anvil once steel was invented since steel is inherently harder than wrought iron and with the hardened steel faceplate came a side benefit of better rebound from a cold hammer or hardened steel ball that over time caused the belief that the anvil with a hardened steel faceplate moves hot steel better, when that wasn't the original intent thereof.

But then again, I might be wrong and this has just been a mental exercise all done in fugility. My brain is about to explode.

[Mike BR]

It seems to me that there are at least three ways an anvil can absorb energy.  One is through the surface deflecting (and not rebounding strongly or quickly enough to put the energy back into the work).  A second is through the anvil structure flexing (think the 3/8" plate example). And the third is through the entire anvil moving downward under the blow and flexing the stand underneath.  The first can be minimized with a hard anvil face, the second through using a compact mass as the anvil, and third through using a heavy anvil.

No material is perfectly rigid, so if an anvil face deflects and absorbs energy under a ball bearing, it will deflect and absorb energy with a piece of hot steel under the hammer.  And any energy absorbed by the anvil doesn't go into shaping your work. 

But I would guess that the energy lost that way is quite small compared to the second and third paths above.  A ball bearing theoretically contacts a flat face at a single point, creating (initially) infinite pressure even though the total force is small.  Hot steel spreads the force over a much larger area, so the pressure at any point (and therefore the deflection) is lower, at least relatively.  And common sense says that the even a mild steel face won't actually deflect that far under a hammer blow against hot steel.  So it seems very likely that a lot more energy is lost to the anvil structure and the stand underneath flexing than to deformation of the surface.  

I do expect that the edges of a soft steel anvil would roll pretty quickly, even though it might hold up fairly well if you only worked over the sweet spot.  (You could always make a hardened block to use when you need an edge.)

[Frosty]

No Rdennett, that is not what I was talking about, "Rebound" and inertia are two different things, related and to a degree interacting but different.

Flatliner: I'm not going to contest your take on rebound, your version of "true scientific tests" are too tailored to what you want them to show. If your version of true science were even in the ball park, nobody would go to the trouble of heat treating hammers, dies or impact tooling in general for the thousand or so years humans have been doing so.

Your Opinion about the work done on horn, heel or heart being equivalent is demonstrably wrong. If you had much if any anvil time you would know that and not say such things. 

Rebound is the common term for the compression waves generated by impacts, returning after reaching the far reaches of the steel, be it anvil or piece of angle iron on a rack. A compression wave travels through the material at the speed of sound and will bounce back when reaching the end or a reflector. The speed of sound in "1%C steel = 5940 m/sec." From the engineeringtoolbox.  https://www.engineeringtoolbox.com/sound-speed-solids-d_713.html

How this effects hot steel on an anvil is this. Upon impact the hammer begins deforming the plastic steel, the compression wave generated conducts to the foot of the anvil and bounces back and returns the movement to the hot steel while the hammer is still moving towards the anvil and increases the amount of deformation. 

Rebound  means in this context, "Move back" just like Return means to "come back." Return would actually be a better descriptive term as the anvil is returning some of the force you imparted into it. however Rebound has been used for I don't know how long, hundreds of years certainly.

One of the things newcomers to any craft have to come to terms with is the Jargon (Trade language). In trying to understand the jargon you like everybody are trying to fit the jargon to familiar words. To avoid being constantly corrected, hopefully cheerfully, you need to fit your understanding to the established jargon. Learn the new vocabulary and usage.

Trying to argue your definitions changes nothing of the trade, it only annoys the folks you're hoping to learn from.

Make sense?

Frosty The Lucky.

[Irondragon Forge ClayWorks]

No scientific study just experience. I can move metal faster on my Hay Budden 106 pound anvil, which has 80% rebound with a steel ball bearing, than I can on my 110 pound Vulcan anvil which, has 50% rebound with the same steel ball bearing.

I still love the Vulcan my first London Pattern anvil and use it all the time, but if I'm moving a lot of thicker stock, I turn around and use the Hay Budden, using the same hammer. Both anvils are mounted to tree stumps.

I can't control the wind, all I can do is adjust my sail’s.
Semper Paratus

 

If I have a lot of thicker stock to move, I walk the 4 steps to the 30 pound Star power hammer.

[swedefiddle]

Good Morning Mr. Dennett,

Frosty has the best explanation I have heard described. The effort of the Hammer is, weight of the hammer X speed of the Hammer/squared. It is more important to hammer quickly, than to use a heavier Hammer. The effort of an Anvil is the return of the effort of the Hammer, the hammer effort is on the top, the Anvil effort is on the bottom (albeit over a greater contact point).

All heavy work on the Anvil, should be over top of the Waist where it has the most support and return. On either Horn, there is no support underneath. There will be a lot less return.

My favorite colour is Blue. Just my $0.02 cad

Neil

[FlatLiner]

Rdennet, anvil rebound isn't as important as some people will tell you it is. There have been and still are many successful and talented blacksmiths and bladesmiths from around the world that use unhardened and non traditional anvils every day and they are turning out some amazing work. I am willing to bet that they do more pounding on hot steel in one day then some of the top posters on this website do in the same day. If someone has enough time to post on a message board, in multiple threads, in multiple categories, multiple times throughout the whole day and into the night, then it's pretty apparent that they do more keyboard pounding then they do pounding on hot steel. A simple search engine search for Brian Brazeal anvil will result in a mild steel plate anvil stood on edge with the edge ground into various fullers or a plate laid flat as a striking anvil, YouTube is an amazing source of information, the smiths on there are always willing to answer your questions if you reach out to them. There are smiths on this site that are running successful smithing operations and running successful YouTube channels, they don't usually post as much because they are busy smithing. There is a smith in southeast Asia that goes by the name of amazing kk daily that uses a simple unhardened post anvil. There is a successful bladesmith on a different website that has posted pictures of his setup that he prefers to use, and no it's not the 200 lb fisher anvil that sat untouched for five years, it's some blocks of unknown steel one laying length wise the other standing up on end. the important thing is to treat this sight like google or the library, you will find all kinds of information, some of it useful, some not, some good, some bad. And most important of all is to actually get out and do some pounding on hot steel on whatever you can get your hands on.

[George N. M.]

FlatLiner, I've been thinking about a reply since I read your post this morning.  I agree with you regarding anvils.  Anything can be used as an anvil if that is what you have available.  Even a block of wood can be used but it erodes pretty quickly and you breath a lot of wood smoke.

Some of what gets said in discussions of anvils is affected by the tendency towards tool envy.  That is, the inclination of some folk to think that if they just have the right tool, anvil, hammer, left handed widget polisher, etc. that it will magically increase their skill level.  So, conciously or unconciously people are always wanting the bigger, better, newer, more expensive tool and have a tendency to justify that desire by depreceating older, small, and less expensive tools.

Where I take exception to your post is your slam at some folk who post here.  One thing you do not seem to consider is that some of us have been doing this for decades and have picked up some experience and knowledge along the way.  The key is not how much forge work a person is doing right now but whether they may have in their head the information that may help someone with a problem, not matter when or how they accquired that information.  And, everything posted here is just one person's take on a particular issue.  There is no requirement that anyone give that opinion any credibility or weight.  That is the fundamental truth of the internet.  If someone gave out information that was actually dangerous or dead wrong other posters would be on it in a heartbeat.  Although it is something I try to avoid myself some people can be kind of curmudgeonly and irritable at times.  Again, that is the nature of the community.  And some folk are dealing with problems, physical and mental, which can affect their choice of words or phrasing.  Basically, give us a break and the benefit of the doubt that everyone's intentions are good.  Also, I do not want to start a flame war about this.  If you want to discuss it further I'd be glad to do so via PM.

"By hammer and hand all arts do stand."

[Nobody Special]

For anyone that considers rebound unimportant, I suggest you try forging on hard dirt as an anvil, a block of wood, a stone anvil, a cast iron wonder, or mild steel. I have on each. Rebound of course relates to mass and hardness. If the anvil is light, or lacks hardness, more force will be dissipated into the anvil or tend to affect it kinetically (i.e. it moves the anvil or passes through it into whatever is supporting it) rather than going into the work. Of course, mass isn't really the same as rebound, it's just that if you hit a 3-gram anvil with a 10 lb hammer it's the anvil that moves, no matter how good the rebound.

Sledgehammer heads have great rebound, but a big block of mild steel may be a better anvil, partially due to their size. Forging can be done on a number of surfaces and there are simply times and uses where softer anvils with less rebound may be better for your purpose, but in general use, this often isn't the case.

Rebound isn't the only consideration, but a hardened surface of the right material composition makes a great deal of difference in the work, not simply in preventing deformation of the tool. That difference is not only not negligible, it's rather extreme. I'm rather surprised you feel that no one has tested this scientifically, Flatliner; I've seen rather extensive papers on the matter from everyone from toolmakers to dissertations by physicists and engineers, some of which you may be surprised to find enjoyed forging. And although you note that cast iron is too brittle and soft to make a good anvil, you might find it weird that most of the time although yes, it is brittle, it's actually harder than mild steel and has greater compressive strength. Still a lousy anvil though.

I wish Thomas Powers was still with us; not only could he have explained this better, but he would have had eight citations on the subject. You can still find some of the works though if you dig enough, although you may have to go beyond the Googlesphere. But feel free to try your own experimentation or do things your way; if the metal doesn't move better for you on heavier (or even the same size) anvils with better rebound, you can always tell me "E pur si don't muove".

[wirerabbit]

Here you go. Enjoy.

 

https://calsmith.org/resources/Documents/Technical_Documents_Page_Files/techdocs_thephysicsofanvils.pdf

[FlatLiner]

I have to apologize, I had some things going on in my life and I took out my frustrations on the people of Iforgeiron. I know it's no excuse but I let my hot headness and emotions get the better of me. I realized it and took a step back for awhile. So I am sorry Frosty, moderators, and others I may have offended.

[Frosty]

I'm glad to see you posting again. I went a bit off the rails too. What I thought was just responding to points sure looked like I was responding to your personally. It wasn't intended that way and I'm sincerely sorry that's how it came out. It was my bad and I've regretted it since. 

I'll take it as a personal favor if we can shake hands and come out talking hot iron and hammers. Please?

Frosty The Lucky.

[FlatLiner]

No problem Frosty. We are good.

[patrick]

This is an interesting discussion. From an engineering point of view, the ball bearing rebound test as done by blacksmiths is really a hardness test. it is a variation on the old Shore Scleroscope hardness test that was essentially the same thing but with a graduated column to contain the ball and allow for quantification of the rebound height. A more modern version of this kind of test is a Leeb hardness test which measures the return height of a spring loaded pin that is "shot" against the test item. There are ASTM standards for both of these tests, though I am not aware of the Sclerosocpe test being used much anymore. I first encountered the ball bearing test on anvils probably 20+ years ago when I read about it on another forum hosted by Jock Dempsey. Assuming blocks of equal mass and different hardness, the rebound of any of these test methods will be higher for the higher hardness block. When you use the ball bearing test at a blacksmithing event to "test" an anvil, you are really just getting a feel for the hardness of the anvil surface. This does not account for variations in geometry (heel vs center of mass for example), the fact that a blacksmiths hammer is much heavier than the ball bearing used in the test or that the hammer is accelerated by the smith and has a much greater velocity and momentum than the ball bearing. Plus, each smith will have a somewhat different swing, hammer grip, hammer weight, shape etc. In addition to these variables, there are variables associated with the workpiece itself (material, temperature, yield strength at that temperature, thickness/height, etc.) that will also influence the user experience. The ball bearing test was proposed as away to eliminate these sources of variation when comparing anvils to each other, but it does not really give you a good idea about the user experience.

If the question is narrowed from "does rebound of an anvil matter" to "does hardness of an anvil matter" then you can begin to factor in some of the experiential observations that have already been shared. Clearly, excellent work can be done on both hard and soft anvils. Anvil mass and distribution of that mass can matter, assuming the anvil is not anchored to some larger mass. Chambersburg Engineering published data on a study of the effect of anvil mass for closed die forging hammers and concluded that an anvil to ram weight of 20:1 gave the best performance, meaning that ratio transferred the most energy from the ram into the workpiece. larger anvil to ram ratios did not result in increased efficiency. This was for steam hammers with the steam used to accelerate the ram against the anvil. Of course, a hard anvil will last longer than an soft one, but assuming you only pound on hot steel, the anvil hardness is unlikely to make much difference to the deformation experienced by the workpiece. The one benefit I can see besides longevity to a hard anvil, and where rebound could matter, is if you are a blacksmith that likes to keep a hammering rhythm by tapping the anvil when you are not striking the workpiece. In that specific case, the anvil rebound (hardness plus geometry effects) will tend to throw the hammer back up, minimizing the effort required to lift the hammer for another blow.

All of the above assume hot working. If you are doing cold work, things may be different.

The article linked by wirerabbit is quite good, though pretty math intensive.