A minor complication is the need to cope with two sizes of
entrance block that are in common use.
The blind borings are best made using a drilling jig and a
pillar drill that incorporates a depth stop. (This will cope with
both 18 mm and 19 mm thicknesses.) The 4 mm drill bit
should be ground to cut like a "slot drill" so as to give a flat
bottom to the boring. If such facilities do not exist a
4 mm "lip and spur" drill can be re ground to produce
a recess that is shaped like the cross section shown in drawing below.
It is hoped that there is enough information here, and on
the associated pages, to enable home manufacture of at least the
wooden components. There is no copyright attached to this design and
any person or company may manufacture it for personal or business
use, providing that due mention is made of the origin of the design.
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