The method that I use to make threaded screws requires a precisely made blank.
First the blanks are made square; in this case 1-3/4″ x 1-3/4″. Then the corners are sawn off to make them octagonal.
After being sawn to length the blanks are rough turned on the wood lathe. The far end of the handle end is turned to 1-3/4″ (to fit to the master screw; more later) and the narrower diameter (which is to be threaded) is turned about 1/16″ oversize for its entire length (1-5/16″ in this case). A small groove is turned at 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 bit of the router trims the blank to create a precise diameter on the part that will be threaded. In this case the finished diameter is just under 1-1/4″.
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 with the router lathe.
You can see the spiral pattern that the router leaves. The larger diameters near the handles will help them better fit holes bored through the press jaws. These are smaller blanks than the ones in the previous photos. These have 1″ shanks and 1-1/2″ handles.
The purpose of the starting groove is shown here. These were made a bit shallow to show how the thread starts.
The screw blank mounts to the end of the master screw with radiator hose and clamps.