The Micrometer

A bi-monthly review of the engineering of time

Issue 7   September - October 2017

Worn screw threads - or are they?

 

Some years ago I recall reading in an esteemed horological journal a piece of work undertaken by no less a body than a public-sector forensic department which suggested the threads on a 16th century clock were worn from repeated assembly and disassembly.  Now it maybe that I do not understand the word 'worn' as used by forensic scientists and horologists, but it seemed to me to be far more likely that the majority of the damage was due to plastic deformation and not wear.  Wear is a form of abrasion, and even assuming the clock was taken apart once every five years for four hundred years, this would only amount to 80 removals and 80 insertions that even if rusty could not really cause significant loss of material by abrasion.  On the other hand, plastic deformation can cause massive changes in geometric shape on just one enthusiastic insertion, especially when the threads are not at all well-formed due to the limitations in the tooling then available.  Tighten them 80 times in materials of questionable homogeneity and I suspect they would have discovered the real cause of the damage.

     The photo shows a modern high-strength screw that has suffered plastic deformation over its first few threads, the inset showing the V-form thread now deformed to a buttress shape.  To an engineer this is not wear.

 

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Regular readers will have noticed that I tend to include 'cameo' slots in The Micrometer on an engineering subject not related to horology.  Generally falling into a slightly expanded variation of The Micrometer's sub-heading 'The engineering of time (past)', I hope it is found of some enjoyment to those with a wider interest in engineering.

 

Guy Gibbons

 

Copyright (c) 2017  G E Gibbons     If you do not see the updated pages you expect, try again after by-passing or clearing your browser cache.  Guidance may be found at https://en.wikipedia.org/wiki/Wikipedia:Bypass_your_cache

The Micrometer

A bi-monthly review of the engineering of time

Issue 7   September - October 2017

The Micrometer

A bi-monthly review of the engineering of time

Issue 7   September - October 2017

Copyright (c) 2017  G E Gibbons        If you do not see the updated pages you expect, try again after by-passing or clearing your browser cache.  Guidance is at https://en.wikipedia.org/wiki/Wikipedia:Bypass_your_cache