Back when I made them I would find the straightest smoothest Hickory I could find, no knots, maybe at least 6” in dia but not much more. Cut it way longer than necessary, split it in qtrs. Then using a froe split them down to about quarter to half dollar size. Take those pieces and put them up against a rafter, hammer four or five nails in next to it, then bend the nail over it to hold it in place, all the while trying to keep it as straight as possible. After a year or so, take a piece of wood, longer than the Hickory, with a V groove cut in it , lay the Hickory in the groove. clamp one end down and shape down with a spoke shave turning it as you go. Final shaping can be done with a scraper, one like Acer makes would be a great time save and sand paper.
I wouldn’t use a saw to cut it with because you are cutting across grain, splitting will help keep the grain in line.
MY2CW, Tim C.
PS: I learned the hard way, sprinkle a little 7dust on them to keep the bugs out.TC