I read an article in Hot Iron News Winter 2000. Nahum Hersom made hammer handles from old pallets. I have access to some of those. I have had trouble with hand cramp pain, he mentioned using an octagonal faceted handle. I think he is right, the flatter sides put less psi on my hand than an oval or rounded handle, and the octagonal facets feel good, and keep the blood flowing, and allow easy indexing and alignment. I combined this with the Hofi technique of a conical shape or tapered handle so that a loose grip will keep the hammer secure due to the fatter wedge at the end of the handle.
I tried all this out on an old 32oz Ball Peen. I used white oak from a section of pallet, and shaped it using a sand paper wheel on an angle grinder. I purposely left it a little irregular, the uneveness feels really good, like walking on a loose brick floor, no fatigue.
I used linseed oil to install the handle and grinded my own steel wedge and ground barbs on the face of it, then rammed it home and cut it off and ground it nearly flush. I coated it in linseed oil.
It is shown on my Wife's dining room table. She doesn't know I took photos in there.
I am going to make some more this was my first.