Alan - I've never heard of a "flattening hammer". Where can
you get one of these items?
When you are refering to a “flattening hammer”, do you mean a FLATTER
used by blacksmiths?
A flatter looks similar to a hammer except the face is flat and about
2" X 2" square. The side opposite the working face is flat, round
and much smaller than the working face.
Set the object to be flattened on an anvil. Set the flatter on top of
the object with the square face down. Hang on to the flatter handle
keeping the square working face parallel with the top of the anvil.
Strike the back of the flatter head with a hammer of the appropriate
size. Repeat the last step as needed to get the desired affect.
With steel, this is done with the steel red hot. Softer metals may be
There are many blacksmithing tools and technics which also work, on a
smaller scale, in a jewelry fabrication shop.
I hope I have been helpful.