October 12, 2022
I try to avoid technical matters here in the blog on the grounds that we have an entire magazine to cover the “hard stuff.” Besides, very few topics can be adequately handled in just a few hundred words. My last posting mentioned herringbone gears though and it occurred to me that many of our younger readers may be completely unfamiliar with this once dominant gearing system. So if you think fabric patterns or deck planking when you hear the word “herringbone” — this week’s blogs are for you. Only certified gear people recognize the herringbone in the French car brand Citroen’s logo. It is there because Mr. Citroen was an early adopter of the technology. At a time when loads and speeds were increasing more rapidly than rolling element bearing technology could accommodate the concept of using matched right hand and left hand helical gears for thrust and overturning moment cancellation became popular. Strictly speaking, herringbones are a sub-set of “double helical” gearing but gear people quickly saw that there were important design and functional differences. We can credit a British engineer, Percy C. Day, with bringing herringbone to the United States via his 1912 paper in the Journal of the American Society of Mechanical Engineers [Volume 34, Issues 1-6]. Shortly afterwards, The Falk Corporation convinced him to move to Milwaukee and bring the herringbone system with him. His legacy lives on there, even long after the herringbone gear is obsolete — in their basic gearing system having a transverse DP system at a 30 degree helix angle. Other major American gear makers used the system with machinery produced by the Farrell Works using Sykes patents out of the United Kingdom. The Sunderland machines were imported from Britain but there were very slight differences which prevented mixing elements made in one system with those made in the other. Another change over the years that caused engineering argument was the addition of a chip relief groove between the helices. To some die hard herringbone fans, this reduced the “gear with backbone” to just a double helical with a very small gap. Exactly what we were hoping for, argued the groove advocates. “Now the teeth have a uniform stiffness across the face width instead of being stiffer in the middle.” The argument would go on for years. Next time: Unique problems with making herringbone gears.