Herringbone Gear

Strangely, I couldn’t see an appropriate ‘Topic’ for this … so it’s just another “Tea Room” job:

My brother has just sent me this photo from

Flax Mill, Burton Bradstock, Dorset

A rather nice old Herringbone Gear, sitting outside and slowly rusting.

Seems a shame … it was presumably a tricky piece of casting !

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MichaelG.

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Edit: __ Just found this, to watch later:

https://player.bfi.org.uk/free/film/watch-come-with-me-to-bridport-1951-online

Edited By Michael Gilligan on 08/07/2023 08:51:55

I once had a book published in the 1930s about "modern engineering practices" and that had a photo of a chap in the Citroen factory standing next to a very similar herringbone gear. It was inferred that the Citroen double chevron logo was derived from their specialisation in producing these gears.

John

Citroen (and I think David Brown) made a big thing of this kind of gear, but I havn't seen one on the flank before. They are typically on the circumference to cancel axial thrust forces.

Both styles illustrated here:

**LINK**

https://en.wikipedia.org/wiki/Herringbone_gear

MichaelG.

Richard Roberts built those mills in the first decade of the 1800's, remarkably early for the (non-mining-parts-of-the) westcountry..

..don't know how old that particular gear is, don't suppose there was a foundry name on it?

Some lathes had herringbone gears in the gear head, a very expensive way to get smooth running. Common in ships to do away with end forces while getting the smoothest drives.

Presumably the pinion got the advantage of no end thrust. Although seeming complicated there wasn't much extra work for the patternmaker and in this size any fettling would have been by chisel so not bothered about not having a run through the teeth for a file.

W E Sykes, my employer back in time (1910 - before my time... to avoid the wags), invented a machine to cut double helical gears. Previous methods required a gap as the helical gear shaper cutters couldn't meet at the same position.

As Bazyle points out, they avoid the axial load produced by meshed single helical gears. The avoidance of a central gap was said to make stronger gears. The rotation had to be such that oil, being virtually incompressible, would not be trapped in the 'vee' of the teeth.

The gears were usually used for large reduction gears, such as turbines.for electrical generation, possible ships. We made the machines, not the gears. The company had examples of a one tooth helical gear meshing with another with multiple teeth, to show the continuous contact at all positions of rotation.

Bill

Here is a patent showing the general movement of the cutting tools, plus the shape of the cutters. Single helical cutters had the front face ground at a right angle to the helix angle. The double helical cutters were ground so that the cutting edges met in a flat plane. By the time I saw them, there was a chamfer along the face of one edge, and a curved groove along the other.

Double helical gear cutter (1923 patent)

Bill

And finally, on the last page of this article, the bottom photo shows a somewhat distorted double helical cutter showing the form of the cutting edge on the gear profile.

Double helical cutter (p45)

Sykes uses the term 'herringbone' (as do others) in his patent for the machine, to indicate continuous teeth, but in the factory we referred to all such gears as double helical, perhaps because the Sykes 5E machine could be used for both single and double helical gears, as well as straight (cut) gears, up to 63 inch diameter.

Bill

Here's a photo of a herringbone epicyclic gear - all the gears, sun, planets, and annular are all herringbone, and it works fine.

Is that 3D printed, Gary? And what's the pressure angle, it looks quite large, although it may be the effect of the helix angle, also large (45 degrees?).

Bill

The Citroen logo was chosen to symbolise their competence in cutting herringbone or chevron gears.

I was told by a past acqaintance that David Brown's gear cutting machine (in Manchester? ) floated on a pool of mercury to isolate it from external tremors.

Best regards,

Swarf, Mostly!

Thanks for your three consecutive posts, Bill

MichaelG.

Thank you, Michael.

These gears are an interesting, if niche, product.

Bill

No longer being the owner of the book to which I referred in my earlier post, I found a couple of snippets through a search of one available to buy. It may, or may not, interest you to see that "the teeth were cut using end mills on specially constructed machines".

I wish I hadn't given the book away, now!

John

Would the gear in Gary's picture be energy wise or a high friction waster?

Bill: The gear was 3D printed. It's about 50mm in diameter and 12mm thick. It was printed all at once and is impossible to disassemble.

Thanks, Gary. Of course, being double helical, I hadn't thought of (dis)assembly. It's impressive that small clearances can be acheived.

It's interesting what 3D printing can achieve, hopefully metal processes will come along for the amateur/hobby market at some point.

Bill

High load helical and spur gears and those that act as timing gears, as in printing presses etc, tend to have the tooth flanks ground after hardening. That would be pretty difficult with that type of tooth!

The double helical toothed gears that were made by the company I worked for (Allen Gears) always had a groove between the teeth to allow the grinding wheel to run out at the end of its pass. The slight addition in length wasn't an issue and gave the oil a path to escape. Their main product was epicyclic gears, the fact that the thrust load was cancelled out by helical gears with opposing left and right hand teeth was ideal for that use.

A previous comment mentioned Sykes gear shaping machines, there were a few of those when I was at Allens, they were gradually phased out as faster and more accurate machines became available, they were mainly used to cut spur coupling teeth.