4. Screw and nut assembly
We have seen in Chapter III that screws and nuts may be made from horn. The following paragraphs describe three particular techniques of threaded assembly, which can be very useful to horners.
Threading a screw is an easy task. The same screw will therefore be used in the three cases examined. The original feature of the method lies in the technique used for nut threading.
Figure VII.8 shows a screw-tipped rod which could, for example, be a lamp support screwing into a tap-threaded base. Figure VII.9 shows the two parts before they are screwed together. It will be seen that the base (the nut) is tapped through. This is usual when the nut component is not very thick. In this case, nut threading presents no problems.
When the nut component is thicker, it need not be threaded through, but only to a depth sufficient to accommodate the screw. As it is difficult to thread to a precise depth, it is preferable to thread the nut component to a depth slightly greater than the length of the screw. Before threading the nut component is, in any case, drilled through (figure VII.10).
Figure VII.11 illustrates the depth of screw cutting recommended for this type of assembly (in mm).
In figure VII.12, the hole is neither drilled nor threaded completely through. This is known as recessed threading. It is used especially when the surface of the nut component opposite the surface which receives the screw must be, for aesthetic reasons, free of drilled or threaded holes. This technique is also used when the nut component is too thick to be completely drilled through.
Figure VII.13, which shows the parts before they are mounted, indicates the recommended depths of drilling and threading according to the screw diameter.
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