The Micrometer

The engineering of time

Issue 21   June 2025

 Decorative heat bluing of steels

Trials on a PID-controlled* bluing box

Bluing box

After a brief introduction to methods of heat bluing steels, the author comments on the dependency of the achieved colour on both temperature and ‘soaking’ time at this temperature before describing the design, manufacture and uses for an electrically-heated bluing box under digital temperature control.

Components ranging from 15 mm long clock hands and small screws through larger instrument hands right up to machine toool ball handles have been successfully heat blued in the PID-controlled bluing box.   Fully illustrated with photographs and schematic drawings, there is no single solution to all decorative bluing issues, and the bluing box is not entirely without limitations in its performance.   The paper concludes that it is a valuable, mess-free addition to the workshop, and those needing primarily to colour steel components may wish to consider its merits.

* PID: A Proportional-Integral-Derivative digital controller capable of maintaining the bluing box hotplate temperature to within ±1°C of the Set Value (SV).

Decorative heat bluing of steels (6 MB)

Readers are invited to share their own experiences with decorative heat bluing of steel and, in particular, their experiences with a PID-controlled bluing box.

 A clock mainspring trilogy

A short three-part series

Two mainsprings

How clock mainsprings work is generally not well understood, and in the professional world mainspring design and manufacture is undertaken by very few companies world-wide.   Curious to better understand why barrel-wound mainsprings as fitted to clocks deliver the torque they do, the preliminary thoughts on his understanding resulting from his many trials and subsequent analysis are presented in this trilogy of papers.

The first part discusses the shape of the torque vs turns curve of a typical barrel-wound clock mainspring, introducing the effect of barrel wall hooking on the shape of the curve.   Part 2 discusses mainspring fracture and suggests that the traditional 'peg and hole' clock barrel hooking is little better than a failure waiting to happen.   The third and final part discusses methods of estimating the torque required by a clock based on a limited statistical analysis of past successful designs, also introducing the suggestion that the science of springback as applied by engineers to folding sheet metal might also offer some insight into mainspring performance.

Mainspring trilogy Part 1 (2.2MB)         Mainspring trilogy Part 2 (881KB)         Mainspring trilogy Part 3 (967KB)        

Readers are invited to share their own thoughts on the author's work.

 Clock lines

An exploration of driving lines for weight-driven and fusee clocks

Clock lines

Clock lines have received little engineering assessment in the horological press, with much opinion being based on received wisdom and what has been found to work.   This three-part paper (in pdf format at the links below) explores representative clock lines from an engineering perspective: Part 1: Stranded steel and brass/bronze lines, Part 2: Natural gut and synthetic lines, and Part 3: Comments on the significance of creep together with a few concluding remarks.

Part 1 investigates the different types of construction of stranded steel and brass/bronze lines.   Part 2, which is perhaps the most significant, reports on the author's creep trials on natural gut and nylon-6 synthetic lines conducted over a 6-month period and their extrapolation to a 20-year in-service life.   Part 3 discusses the possible implications of creep on non-metallic weight-driven and fusee lines before drawing together a few overall remarks.

To complement the three part paper, an Appendix has now been added describing the manufacture and testing of crimps for eye splices.

Clock lines Part 1 (689KB)         Clock lines Part 2 (1.6MB)         Clock lines Part 3 (212KB)         Clock lines Appendix (666KB)

Readers are invited to comment on the papers and make any recommendations leading to a greater validation of the author's concluding remarks.





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