Free Play of Wooden Screws

Wooden screws should be loose.

One advantage of this thread making method is that the fit of the screw to the threaded hole is adjustable. A loose fit will prevent the problem of presses that become stuck or difficult to use with seasonal humidity changes. Using large threads makes it possible for the screws to be quite loose. The tapped hole above is drilled at exactly 90 degrees; the screw can wiggle a little in any direction.

This allows the screws of a press to be adjusted independently (to a degree) and makes it easier to open and close the press without binding.

This is a typical fit between screw and tapped hole. One might wonder if this loose fit compromises the strength. In my experience it does not.

As an experiment I tried to break a screw. I was curious to know what would fail first and had expected that the screw threads would begin to shear off. As it turned out I was unable to break either the internal or external threads and the handle began to split. I tried again after putting hose clamps on the handle. The friction increased so much that the screw could not be tightened further, even with the use of plastic washers that were added to reduce the friction. I may try again with another screw that is prepared to receive a larger lever since I am still curious to see how the threads would fail. It is clear that under normal circumstances wooden screws are very strong.

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