After 38 years, I finally learned how to make wood threaded nuts and bolts on my last project, the hand-cranked scissors lift model.
The secret turned out to be using maple and soaking it for 7 days in mineral oil before threading.
I had a piece of 3/4" maple dowel left over from this last project, so I decided to make 3 bolts and nuts.
For the maple nuts, they were not soaked 7 days first, they were just kiln dried maple from Menards. I did spray WD-40 on the tap as I threaded the 5/8" pilot hole. I washed the mineral oil from the bolt end, rubbed with wet rag, then Titebond II glued the bolt head to the shaft. Hopefully this gives a good bond to the glue joint between the bolt head and shaft.
I made all the cuts on the nuts but one on the miter saw. The last piece is dangerous to cut on the miter saw, so I sawed it either on the band saw or scroll saw.
I learned the Mineral Oil for 7 days secret from a youtube video showing how to make 2.5 inch diameter threads in maple. In that video, for the huge nuts, he gave the standard proportions for the head of the bolt and nut to make them look realistic.
The tap works much better if there is an entry radius. I put the board with the 5/8" pilot hole for 3/4" threads over my 1/8" round-over bit on the router table and rounded both ends of the pilot hole.
I got a little tear-out at the tap entry and exit sides of the nut. If one wanted to avoid tearout, for these 3/4" threaded nuts, one could start with 3/4" thick stock, and make several 5/8" pilot holes along say a 12 inch long piece of wood. After the tapping done with the tearout, just run the board thru the planer until you achieve the desired 5/8" thickness, which would remove the tear-out.
Real steel nuts have a round-over on the top and bottom of the nut. I decided to try the wood lathe to create them.
For the bolt head, I glue the head to the bolt, then just chuck on the shaft in the lathe.
For the nuts, there is not enough length to chuck on 1 end, turn the roll-over, then flip it around and do the other side. I came up with a simple fixture to do it in the lathe.
It only took me 28 years, but I finally figured out how to make wood threads !!!!!!!
As I design more hand cranked models in the future, I may incorporate more threaded shafts, bolts, into them.