The contact block or contact arrangement like the pivot
comes in many shapes and sizes, some are very complex with adjustments for
the rake or angle of the key arm, and spring loaded or with crush bar
tighteners of gap adjustment, in this key it will be simplicity itself just
a simple gap adjuster with lock nut and built in isolated resting post, with
room for enhancement later. the one factor common to all good keys is a
solid contact block with no movement when the contacts close, its
construction is very similar to the pivot, there should be two inches left
over from the construction so far, and this remaining material is cut into
two 1inch lengths, Two1/4 holes are drilled in the 3/4 side, to make sure
the holes line up it is a good idea to clamp the two pieces together before
drilling, same care being taken as in the pivot, then two more 5mm
holes are drilled, 8mm in from the other 3/4 side
The pictures below will clarify the construction, the whole assembly is
pushed together on the ceramic plates, at the same time using a steel or
similar bolt a brass nut is held on the inside of what will become the top
see below top right, then the whole assembly is heated up again very hot and
soldered together including the brass nut, the bottom hole will be
countersunk to take a small 4BA bolt with a nylon washer, with another nylon
washer on the top this will be the isolated resting post, the 4BA bolt is
cut so that when the key is assembled the arm will be horizontal a 2BA bolt
with locking nut is now screwed into the top and will be the gap adjuster,
the description of the construction of this part has been kept simplified as
it is fairly obvious how it is made from the pictures, I am hoping whoever
may be tempted to make this key will have grasped the rather basic concepts
without to much detail, however anything that seems unclear can be discussed
on the group website. |
