Master Screws

This page was originally posted on my blog.

This method of cutting wooden threads depends on master screws. These are used to establish the pitch of the thread being cut as wooden blanks are guided through a die. Above are my three 1″ diameter master screws and two of the brass nuts that are needed 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 (3TPI). Above that is a 4 TPI master screw and at the top a 5 TPI one.

The nuts and screws are easily switched out of the wooden threading frame. The brass nut can be unscrewed from its flange 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”.

At the opposite end of the master screw an identical shaft coupling is used to make 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 coupling to the 1-1/2″ outside diameter of the screw blank. For other screws this adapter isn’t needed since the outside diameter of the coupling matches that of the screw blank handle (1-3/4″). In all cases a short length of radiator hose and hose clamps are used to securely fasten the wooden blank to the master screw.

%d bloggers like this: