The method that I use to make wooden screws requires a precisely made blank.
First blanks are made square; in this case 1-3/4″ x 1-3/4″. Then the corners are sawn off.
After being sawn to length the octagonal blanks are turned round on the lathe. The far end of the handle is turned to 1-3/4″ to connect to the master screw and the narrower diameter (which is to be threaded) is turned roughly 1/16″ oversize for it’s entire length. A small groove is turned near the end. This is where the thread will start.
The “router lathe”. This device rotates the blank while slowly advancing the router from right to left. The spinning bit of the router trims the blank to create a precise diameter on the part that will be threaded. This will be the major diameter of the screw.
On the left is a blank roughed from the wood lathe. On the right is a blank that has been further reduced to a precise cylinder by the router lathe. These blanks will be used to make screws having 3 threads per inch. The diameter of the screw is about 1-1/4″.
You can see the spiral pattern that the router leaves. The larger diameters near the handles will provide for a better fit in the holes bored through the unthreaded jaw of the press. These blanks are smaller than those in the previous photos. The finished screws are about 1″ in diameter with 5 threads per inch.
The purpose of the starting groove is shown here. The grooves are slightly shallower than the final thread depth and show the beginning of the thread.
The screw blank mounts to the end of the master screw with a short length of radiator hose and clamps. This is one of my small screws with 1-1/2″ diameter handles.