This section needs a lot of work yet....  There are numerous issues for many of the components.  

Cylinder Selection...

Cushions

Bore size

Cylinder length

Mounting 

Port Size

More....

The larger the bore, the more air (CFM) will be required.

The longer the cylinder, the more air (CFM) will be required.

Bore Size Considerations

If you have an un-limited air supply (CFM at your needed pressure), this is less important.  Most of us do not.  The goal is to use the smallest bore size you can that will support reasonable performance.  

There is a significant guideline to consider to establish a minimum bore size for any given ram weight (actually total falling weight).  The force that is generated to "lift" the ram assembly needs to be 3.5 to 5 times the total ram assembly weight.  This is necessary to ensure that the ram can be cycled at a rate that supports reasonable forging capabilities.  I stated a range because are differing opinions about what is the minimum.  I have not tested the range, but personally recommend using the upper end of it to ensure you don't build a hammer that will not perform well.

The point may seem moot because you could just crank up the pressure to get the force you want...  Well, that may not be a good idea because some cylinders are limited in the pressure they can support AND, even if the cylinder is rated for high pressure, there will be more wear at higher pressures.  My recommendation is to do your calculations using 80 PSI.  That will give you some wiggle room for pressure when you want higher performance than you probably normally need.

  Area x pressure equals force (Area is different on each side of the cylinder piston)

Cylinder Length Considerations

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