An anvil can best be thought of as a mass "at rest" and floating in space... with a rapidly moving ram (tup) heading toward a collision with it. A workpiece is inserted into the space between the two objects, and is "crushed" between them at the moment of collision.

All other factors being equal, when the rapidly moving ram (and workpiece) collide with the "stationary" anvil, the amount of force generated at the face of the die(s) is partly a function of the mass of the anvil. The greater the mass of the anvil, the more slowly it will react (accelerate) "away" from the ram and workpiece upon being struck, and thus the greater the force that will possibly be developed between it and the moving ram (tup) in the act of accelerating the anvil from rest.

Slower acceleration of a larger anvil mass results in an anvil that moves a smaller distance in response to each "collision" (blow). The workpiece is "trapped" between the two objects, so when the anvil moves a smaller distance "away" from the ram upon being struck, more of the useful energy of the ram is imparted to the workpiece... instead of simply "pushing away" an anvil that is not massive enough.

The best analogy that comes to mind would be the act of kicking a small stone, versus kicking a large boulder. Since the mass of the foot (and a boot) is relatively large by comparison to the stone, the foot decelerates very little at all during the collision. The kinetic energy of the foot is imparted to the small stone with relatively little force being generated between the two, as the stone accelerates very quickly away, and travels a fairly large distance in doing so.

When the same foot (and boot) collide with a large boulder, the much greater mass of the boulder does not accelerate from rest very quickly, and travels a very small distance (or seemingly not at all)... so a much larger force is generated in the end of the foot (and the boot) at the moment of impact, as the foot (and boot) are decelerated very quickly.

If we then tape a marshmallow "workpiece" (or something similar) to front of the foot (and boot) "ram", we see that it is barely dented when we kick a small stone "anvil", and squashed completely flat when kicking the large boulder "anvil"... as more of the kinetic energy of the foot (and boot) "ram" is imparted to the marshmallow "workpiece" instead of simply pushing the small stone "anvil" away. Therefore, we can readily see that bigger really is better, at least as far as anvil mass and forging efficiency are concerned.

In an actual hammer installation, and in response to each blow being struck, the anvil moves (accelerates) downward against a cushion, a foundation of some kind, the earth itself, etc. or whatever happens to be beneath it at the moment of impact. As anvil mass increases relative to the size of the ram, the anvil itself reacts less quickly to each blow of the ram; therefore relatively less force is in turn exerted upon the cushion, the foundation, the earth etc. Thus, a heavier anvil also means less noise, and less vibration and damage to surrounding objects. "Bigger is better" in this aspect as well.

Since most traditional foundation materials such as wood, concrete, and even the earth below the hammer are relatively resilient, and as the "necessary movement" of the anvil is relatively small; the cushion between the hammer and the foundation is usually sufficient in controlling the movement of the anvil to acceptable levels. The nature of the foundation itself usually has little noticable effect on the "efficiency" of the anvil or the effectiveness of the forging operation, and primarily serves to keep the hammer installation from sinking during use.

In some older, "traditional" hammer designs (particularly mechanical hammers), rather elaborate timber cushions were often specifed between the anvil and the foundation; often as a result of making the anvils as small as possible to keep the initial cost of the hammer down, and a smaller anvil requires greater freedom of movement. The resiliency of the timber allows the "necessary movement" of the anvil to take place with each blow. However, timber is relatively "springy"; so mounting bolts were usually necessary to keep the hammer from going "airborn" after each blow, particularly if the anvil is too small to begin with. If the bolts are made too rigid, the upward return "spring" of the entire anvil/hammer assembly may repeatedly break the bolts. In the case of larger hammers, wood cushions were specified simply because no better cushion material existed at that time.

Alternately, If a relatively small traditional hammer/anvil assembly is bolted to a relatively large foundation that is too firm, the lack of necessary anvil movement may generate unacceptably high forces during forging. This can cause dies to break or the dovetails in the sow block to give way, particularly when forging cold, thin, or hard materials.

The Phoenix forging hammers are all designed with sufficient anvil mass and adequate base area so that they will be appropriately efficient, cost effective, and stable in operation. Modern polymer cushions can be provided, and are highly recommended. These are custom-engineered and produced by VibroDynamics for each installation. Depending on the size of the hammer and the nature of your installation, no additional foundation may be required.

Also in this regard, the Phoenix forging hammers are intentionally designed so that the vertical axis of the forging forces, the center of mass of the frame, and the center of mass of the anvil are all in line with the center of the base within a percent or two, and the center of rotation is very low; meaning that there is no significant overturning moment. As long as the supporting surface beneath the hammer is level, and the cushion between the hammer base and the supporting surface is appropriate, all Phoenix hammers with an anvil/ram ratio of 15:1 or greater do not need to be bolted down. If the dimensions of the anvil are such that they do not need to be installed in a foundation pit to acheive the desired working height, a simple "corral" that encloses the edge of the base and the and the anvil cushion is usually sufficient to keep the hammer in place and safely in operation.

In summary: The mass and velocity of the ram at the time of impact determine how much potential energy will be available for each blow. The mass of the anvil determines how much of that energy will be available for forging the work. The remainder is lost creating useless movement (downward acceleration) of the anvil, and potentially damaging vibration to the property around the forging operation. The heavier the anvil, the less energy that is wasted.

So, the "efficiency" of the anvil is based upon the total potential energy of each blow (100%), and expressed as the useful percentage of that energy that is available for deforming the workpiece. Beyond a 35:1 anvil/ram ratio, the efficiency is already 90% or better, and increasing the anvil weight much further than this results in rapidly diminishing return in forging effectiveness for the investment in material. Anvil/ram weight ratios of 15:1 - 25:1 generally produce the most effective forging for the total cost associated with building and powering a given forging hammer. In hammers of 10,000lb or greater ram weight, 35:1 or larger anvils may be advisable to keep damage to surrounding property to a minimum.