Head Aches

[John PurdyParticipant @johnpurdy78347]

Can you imagine the head aches involved trying to get your head around making a model of this in your workshop?  Bevel gear is bad enough without throwing  herringbone into the mix!

John

[John Doe 2Participant @johndoe2]

A job for 3D printing, if I ever saw one ! (for a model that is).

What is the purpose of this teeth arrangement ? Removing end thrust on the pinion gear ?

[Michael GilliganParticipant @michaelgilligan61133]

You might find this discussion interesting, John

https://www.model-engineer.co.uk/forums/topic/herringbone-gear/

… from July 2023

MichaelG.

[Martin King 2Participant @martinking2]

Just a thought; is this possibly where the Citroen logo came from? Or is it from some gears in their gearboxes?

Cheers, Martin

[Michael GilliganParticipant @michaelgilligan61133]

I can recommend referring to  the previous Thread [now Topic], Martin

… and not just because I started it.

MichaelG.

 

[Ady1Participant @ady1]

and all done with no computers

They were clever and highly skilled folk

[SamsarandaParticipant @samsaranda]

Martin it is definitely where the Citroen logo came from, prior to manufacturing vehicles they were gear manufacturers and specialised in the form that was their logo.   Dave W

[John Purdy]

On 3 January 2024 at 18:24 John Purdy Said:

Can you imagine the head aches involved trying to get your head around making a model of this in your workshop?

 

I suppose it depends a bit on the individual’s workshop. Those with a home foundry may take the same route as the original and make a small casting box to do a segment of the teeth and make several copies like cores which can then be placed into the main sand mould taken from a simply turned pattern. I have seen replacement full size traction engine gears done this way.

Those with CNC would no doubt take their chances with some small ball ended cutters

Those with conventional machines would get a lot of praise if they could pull it off.

[Nigel Graham 2Participant @nigelgraham2]

Prior to M. Citroen inventing the method for cutting herringbone teeth (opposed helical), gear manufacturers were partially there with stepped gears. These are simply spur gears laminated so the teeth on one overlap the gullets on its neighbour.

The double form is indeed to remove the end-thrust a single helical gear generates, and prior to Citroen’s development helical gears of opposing hands were sometimes laminated to give the same effect.

At the other end of the sophistication scale are, or were, “Knuckle” or “Hollows-&-Rounds” gears; with simple hemicylindrical teeth and gullets, relatively easy so cheap to make. With no proper rolling action, they give a lot of friction and an oscillating velocity ratio, and were suitable only for slow-moving, rough duty like simple winches. They were obsolescent by the early years of last Century, as gear-cutting advanced and customers wanted better quality.

 

What were those photographed, on?

[John PurdyParticipant @johnpurdy78347]

For everybodies info the picture was sent to me by one of the members of my ME club (VIME) accompanied by the following description:

“This double-helical bevel gear was made by Citroen (note the similarity of the company logo!) and installed around 1927 in the Miřejovice small power plant on Vltava, to transfer the torque of the Francis turbine to the generator. The diameter of the bigger wheel is ca. 2 meters. It worked flawlessly until 2011, when it was moved to the park in the nearby town Kralupy as a technical monument.”

Kralupy is in Czechia next to the Vltavou river. If you go to Google Earth you can find the picture in a park on the south bank of the river just to the left of the smaller of the two bridges.

John

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