Step 1: Buy a Hammer

I bought a plane setting hammer for one euro.
It is in pretty good shape and will only need minor improvements.

Step 2: Start the Process

Saw off the head. So you can use a drift to punch out the remaining part of the handle in the head.

Step 3: Sanding the Head

After you have taken out the handle, you start sanding the hammer head to take off any rust or gunk that is on there.

Step 4: Sanding the Handle

When you are done sanding the head you start sanding the handle to bear wood (remove dirt or lacker)

Step 5: Sawing the Wedgeslot

When you are done sanding you start sawing a slot for the wedge. Dont go too deep. But dont make it too shalow. Or the wedge wont go deep enough.

Step 6: Fitting the Head

Now you start putting on the head. You want it to sit tinht but not too tight. USE A WOODEN MALLET not a steel hammer. or you will damnage the handle and head.
After the head is on you put glue on the wedge and hammer it in using a wooden mallet. Otherwise the wedge will crack.

Step 7: Making the Handle Finish

Using terpentine and boiled linseed oil in a 1 to 1 ratio you make a small amout of th mixture (doesnt need to be alot)
You apply it wearing gloves and with a piece of paper towel. You can allso put some of the mixture on the head to prevent it from rusting.