Master Screws

This method of cutting wooden threads depends on master screws. These are used to guide the blanks through the die and establish the pitch of the thread being cut. Above are my three 1″ diameter master screws and two of the brass nuts that are essential for their use. The bottom screw is a ‘double start’ screw; meaning it has two threads intertwining (a double helix). Even though it looks like the finest of the three it is actually the coarsest at 3 threads per inch (3 TPI). Above that is a 4 TPI master screw and at the top a 5 TPI one.

The nuts and screws are easily switched out on the threading frame. The brass nut can be unscrewed and replaced to substitute a master screw of a different pitch. The black steel part on the right is a shaft coupling; in this case it connects the master screw with a bit brace which is used to drive the screw by hand. You can see this on the video, “Threading a Wooden Screw” (Earlier post)

At the opposite end of the master screw an identical shaft coupling is used to enable a connection with the wooden screw blanks. Here is the set up for my smallest (5 TPI) screw blanks which have 1-1/2″ diameter handles. The white plastic part is an adapter which makes the transition from the 1″ inside diameter of the shaft coupling to the 1-1/2″ outside diameter of the screw blank. For my standard (4 and 3 TPI) screws the adapter isn’t needed since the outside of the coupling is the same diameter as the screw handle (1-3/4″)

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