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tap and die for screw caps., threaded lid

updated mon 31 may 99


Bob Wicks on sun 30 may 99

Hi Veena:
I read your post on die taps. I have been making screw top containers by
using the method that Michael Cardew lists in his book THE PIONEER POTTER.
Its a method that uses a small tool that you hold by hand and grooves the
inside of a cylinder that you turn. Then you cut from top to bottom in one
place and realign the ends so the threads are moved up one thread and seal
the join. This makes the top and bottom of the cylinder uneven so you just
trim them off and then attach it to a pot you made. You will note the when
you off set the piece that the grooves make a thread on the inside. Then you
allow it to dry leather hard and cover the inside with cooking oil to act as
a separator. Then take an even slab of clay and place it in the inside the
threaded neck and press it well in to the grooves. If you make this stick up
above the threaded neck, you can bend it over the edge and place any shape
you want on it for a top by pressing it in place. Then turn it on the wheel
after it is leather hard. Be sure the make a lid that can be twisted off
easily as some round handles work with difficulty.

The principle of this entire operation is that when you make the threaded
section and allow it to go leatherhard, it will have shrunk about 5-6% before
bisque and probably will not shrink much more. Then when you press the soft
clay in to the grooves that will shrink about 5-6% while the other piece has
already done most of the shrinking by now. This will allow for a nice fit
for a screw top lid. This may sound like a complicated process, but its not
and I think you will agree after you have done a few of these.

I wish you well with your project.

Bob Wicks Prof. Emeritus
Harrisburg Area Community College