Why is rebound important?

[rdennett]

A lot of articles on blacksmithing emphasize the importance of rebound when determining the quality of an anvil.  I believe the idea is that this somehow makes the metal move more easily by resisting the force of the hammer blow from the underside.  Please correct me if I am wrong about that.  Given that we are hitting hot metal which has next to no rebound, I am not quite sure I see the point.  It seems to me that mass under the hammer and securely fastening makes more difference.  That said, I am not a professional smith and have only a tiny fraction of the experience of some of those here.  Can you please enlighten me?

 

Thanks, 

Rob

[Frosty]

Pretty good question Rob, I like understanding what's going on even if I am taking it on faith. 

Rebound is a shortening of the term Elastic Rebound as it applies to an anvil. Any impact causes a compression (sound) wave that travels through the anvil at the speed of sound for the given alloy. Cast iron tends to be self damping because of the large carbide particles where uniform iron or steel presents a uniform material compression waves can conduct through. While your hammer is decelerating on the hot iron the compression wave travels at the speed of sound to the far side, rebounds and travels back. For an anvil say 12" from face to foot a couple microseconds . . . maybe. 

So while the hammer is still decelerating pressing the hot iron/steel against the anvil the compression wave generated by the hammer's blow returns and impacts the bottom of the work. The hammer blow is literally striking from top and bottom. 

It's not magic even if it does seem like some sort of hoodoo BS but it is a significant force multiplier. 

Frosty The Lucky.

[ThomasPowers]

Well I once owned a cast iron anvil---220#, 100 kilo, that would DENT, PERMANENTLY DENT  under 5160 when I was hammering on only the red hot metal.  All energy that went into deformation of the cast iron was loss to working steel.  I think it's to do with the difference between elastic and inelastic collisions if I recall my  physics textbook.

Gray cast iron has graphite lenses not carbides,  White cast iron has the excessive cementite.  Why one drills easily and the other wrecks drillbits.

[Irondragon Forge ClayWorks]

I like to think of it as the hammer hits the steel the anvil hits back. My 110 pound Vulcan has less rebound than the 106 pound Hay Budden and the metal will move quicker/better on the Hay Budden. I still like the Vulcan (my first London pattern) and use it a lot but if I'm working larger stock the Hay Budden is the go to anvil. The difference in rebound is not that great Vulcan 70% Hay Budden 85% but the way the metal moves is definitely different.

[Frosty]

Yeah, graphite not carbides I figured someone would correct me sooner than later. Thank you. 

Your Vulcan and for that matter a Fisher has less rebound because the steel faceplate and cast iron body have different resonant frequencies so the sound wave can't conduct smoothly it self damps. It's what makes the so quiet. Wrought bodies and steel faceplates have much closer resonant frequencies making them louder and more effective. Solid cast steel being homogeneous is typically louder and more effective moving steel. 

If I had the money and facilities I'd like to see if it's possible to shape the foot of the anvil into a lens that focuses the rebound energy at the initial point of impact. Don't get all excited I'm just skyballing an idea I've wondered about for a while. I have no idea if it's even remotely possible or worth the effort.

Frosty The Lucky.

[ThomasPowers]

Sounds like a senior project for a mechanical engineering student; Hmmm MechEs are in the next building over...

[Latticino]

As previously noted, if nothing else the rebound is a good indicator of both the hardness of the anvil face as well as the quality of the attachment between the top plate and the anvil body (in anvils that have this configuration).  Some folks aver that it doesn't make a bit of difference because the hot steel you are supposed to be hitting is always significantly softer than any anvil face.  This is a somewhat valid point, though there are two corollaries: 1. you aren't always hitting red hot steel.  Planishing blows are commonly made at a black heat and the difference in rebound is very perceptible there. 2. You still don't want your anvil face to deform easily from either missed hammer blows or have accelerated deformation or abrasion over time.

My feedback to those who don't think the rebound test is worthwhile is, then why not just use unhardened mild steel anvils?

Couple of interesting videos posted on this subject, that I haven't gotten the chance to watch in great detail yet.  The one by Daniel Moss seems a bit more rigorous (the first one):

Warning Language Alert

 

Warning Language Alert

 

[ThomasPowers]

That second one I find to be specious.  I've worked on a bunch of different anvils and have noticed that working on harder faced larger anvils uses less energy.  Empiricism trumps theory; as theory is hardly ever taking into account all the factors involved.  There are some lovely theories out there showing that heavier than air flight is impossible. They can make interesting reading on long flights...

[Frosty]

I Like video #1, I may not agree but it'd be more cherry picking details than actual content.

Calling the second video specious is generous of you Thomas.

I call anyone who deliberately misunderstands an issue to prove a point dishonest.

Rebound has nothing to do with bouncing your hammer back up so you don't have to lift it as far. That thought was put forth by beginners who had opinions without knowledge.  I'll spare you Dunning Kruger's article but that's the gist. 

The second video is steaming stinky dung, pretending to be a cupcake.  As a matter of personal policy. Lie to me once and  I don't trust ANYTHING you say. This guy is on my loser list. 

Yes, I differentiate between a yarn and a lie. A good yarn is for entertainment or instruction, see parable. A lie is for gain, either to cheat someone or to get out of trouble. 

Frosty The Lucky.

[Randy Griffin]

I saw the second video last year. Well, part of it. I turned it off.

I haven't watched any of his videos since.

[basher]

I have found rebound and anvil hardness to be irrelevant when it comes to results from forging hot material. I have many anvils of many construction and lots of diferent hardnesses .all forge well. I can feel no difference between them when working hot steel. I would happily forge hot steel on a large block of mild steel.

hardness will play a factor with regards to the anvil or hammer denting with missed hits and the longevity of the anvil if used in an industrial way.

and people like something they can measure.....

 

 

[ThomasPowers]

Basher; do you notice the difference between using a 100# anvil and say a 400# anvil?

[Benona blacksmith]

I have personally met and talked with Dan Moss I would trust his word over Trenton Tye. If Trenton Tye told me it was raining I would go outside to see for myself. 

[ThomasPowers]

On the other hand a person can win the Nobel price in Physics and still be able to make a fool of himself in Medicine.

[Randy Griffin]

13 hours ago, basher said:

I have found rebound and anvil hardness to be irrelevant when it comes to results from forging hot material.

So, does this mean those cast iron aso's we all steer clear of are actually worth their weight in gold? Or rather $4-$6 per lb. like some of the more cherished names?

[Frosty]

Owen: I can feel a distinct difference between my 206lb Trenton and my 125lb. Soderfors. More than one of us think hot steel moves more effectively on the lighter anvil. It's spent many club meetings on the floor with any number of anvils, some old some brand new and it's usually one of if not THE lightest. I'm not going to say it's the club favorite but it's top of the curve.

I know it's been I don't know how long, 30-40 years since I noticed the height or how level an anvil is within reason, I automatically compensate. I have to wonder if you've been doing this so long you no longer notice about a little difference in the effectiveness of an anvil?  Within reason of course.

Frosty The Lucky.

[Benona blacksmith]

3 hours ago, Randy Griffin said:

So, does this mean those cast iron aso's we all steer clear of are actually worth their weight in gold? Or rather $4-$6 per lb. like some of the more cherished names?

Absolutely not. Cast iron ASO's are dangerous as is an anvil that's too hard.  A piece can fracture off and hurt someone badly. I dont even like my 250 lb cast iron swage block for the same reason. My buddy got hit in the chest with a piece of my swage block. I much rather use my Holland anvils swage black that's a ¼ the weight.

[Latticino]

Unlike Frosty anvil height is one of the things I notice pretty quickly.  Perhaps I just haven't been doing this long enough, but I think it is more a factor of my height at just over 6' 2" and relatively poor eyesight.  Within a reasonable range of anvil weight and condition (say 85-250# with at least a 4" x 4" flat and blemish free surface near the center of mass and at least one edge with a section of 1/8" radius and one of around 1/4" radius) the two main things I notice about an anvil are the height and how well the anvil is affixed to it's stand and the stand  to the floor.  The local group shop I often work in has 12-16 anvils on hand at any time, but almost all of them are setup for the blacksmithing director who is around 5' 7".  After working on one of the lower anvils for an extended period I get aches in my lower back (possibly as much from bending over to focus on the steel with my poor eyesight as trying to reach it with the hammer and maintain the correct angle with the tongs).

That being said, I've used a fair number of different anvils in my short time as a smith, having attended a variety of schools.  I remember being particularly impressed with an older Peddinghaus that I used at the NESM.  Because of it's extremely hard face, even in a school setting, the surface was pristine.  Probably completely subjective, but it also felt like my hammer blows were more effective.  Kept bashing my knuckles when forging near the horn, due to the lack of standard London pattern cutting shelf, but I'd probably get used to that in time if I hadn't picked up a dream 275# Fisher from a friend who found it too large for him.  This large anvil gives me a huge center mass working surface, a more effective horn, and is much quieter than my former 125#  Peter Wright.  I now have too many anvils for my small shop and will probably be letting one go in the near future...

[Randy Griffin]

4 hours ago, Benona blacksmith said:

Absolutely not. Cast iron ASO's are dangerous as is an anvil that's too hard.

Yeah, bad example to get my point across. Should have said maybe we're paying too much for London patterns when we can get good anvils for cents a pound at the scrap yard.

However, I believe good anvils with good rebound help most people. When you've been doing this as long as some, maybe rebound is not so important. If you can swing your hammer with enough force and accuracy, you could forge on a piece of wood.

I, on the other hand, need all the help I can get.

[Glenn]

One more opinion and examples of rebound.

 

[ThomasPowers]

Of course a lot of these are discussing the bounce of an anvil not if work actually is more efficient on a harder anvil.   Big problem in designing experiments: are you testing what you think you are testing? 

(Discussed in Quality Control  classes with lots of examples of stuff passing their factory tests with flying colours and failing in the field.)

[Buzzkill]

I look at it this way:  If it was just about a solid mass under the hammer, then why would anvil manufacturers have gone through all the hassle and expense of forge welding hard plates to the anvils once hardenable steel became an option?  Seriously, it was a HUGE endeavor to add that feature and properly harden the steel.  The cost per pound of hardenable steel compared to wrought iron, the amount of fuel required to bring the mass up to forge welding temperatures, and the need for something like a waterfall to harden the plate are not things that would have been ignored just to add a relatively minor feature to an anvil.    If there was only a negligible advantage to a hardened surface, anvils would have been wrought iron top to bottom and they could have saved a boatload of money in manufacturing to just grind the surface and get them out the door.  That would have made them far cheaper for smiths to purchase as well.

When tens of thousands of people who use a tool all day every day to make a living are willing to pay up for a specific feature it's a pretty safe bet that there is at least as much benefit as there is cost to that feature.

[ThomasPowers]

Like tail fins on late '50's cars?

You would wonder why so many cast iron ASOs are being sold nowadays----but the general public doesn't know any better and Gresham's Law applies to anvils too with everyone so focused on cost over utility.

[Buzzkill]

Big difference TP.  Tail fins in the 50's and cast iron ASO's today do NOT fit in the same category as an expensive upgrade that tens of thousands of working people use *to make their living*.   Tail fins didn't cost much extra nor did they significantly affect the performance of the vehicle.  Very few people used vehicles in a way where that feature would affect their ability to make a living.  Today I think you'd be hard pressed to find many smiths who make a living using an anvil who use cast iron ASO's daily to create their work for sale.

All things are not equal.

[JHCC]

1 hour ago, ThomasPowers said:

Of course a lot of these are discussing the bounce of an anvil not if work actually is more efficient on a harder anvil.   Big problem in designing experiments: are you testing what you think you are testing? 

Exactly. A much better test would be to drop a known weight from a known height on a series of anvils to test their respective rebounds, and then to repeat that same weight drop test on the same anvils with a workpiece of known plasticity and measure the latter's deformation. That would more accurately assess the degree to which rebound correlates with moving metal. If indeed there is such a correlation, then working an anvil with greater rebound means fewer blows to achieve the same amount of work product, which in turn means less fatigue for the smith.

7 minutes ago, ThomasPowers said:

Gresham's Law applies to anvils

I'm not sure I give this assertion any currency.