Weight driven clockwork roasting spit

This is a photo of a weight driven clockwork spit (somehow or other it got up loaded on its side, sorry,) that I have a mind to make. The speed regulating “fly?”is driven by a helical wheel engaging an appropriate spiral pinion.

This has come out on its side😠 as well.
The pitch of the spiral is about 5/16”, it’s major diameter is about 5/8” and the minor diameter5/16”.
My guess that the spit is 18th century and might be French, these are only guesses.
All of the other pinions are lantern pinions and I can get my head round those but how is a spiral, if that is the right word, made.

Does anybody out there have any ideas an if necessary correct my terminology as my Google searching has been fruitless. I have found many pictures of clockwork spits but no information about manufacturing a spiral pinion.

Edited By SillyOldDuffer on 18/11/2022 17:48:24

It doesn’t answer the question of ‘how to make’ … but I think you will have better luck searching for worm and worm-wheel … because ‘loose’ as it may be, that’s what you have.

MichaelG.

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Edit: __ it hasn’t evolved very far from Leonardo’s design

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Ref. __ https://link.springer.com/content/pdf/10.1007/978-1-4020-5599-7_2.pdf

Edited By Michael Gilligan on 18/11/2022 17:25:58

I should think the one you pictured was sawn /chiselled /filed. Finer examples, as in music boxes, were spiral milled.

( It might be worth asking on a blacksmith  forum )

dave8

Edited By david bennett 8 on 18/11/2022 20:27:34

Curiously OD of the worm has a double taper - but in the wrong direction if you were hoping to maximise worm/wheel contact. So maybe they were trying to minimise the w/w contact so that pitch mismatch wouldn't stop the job ?

Michael Gillian, thank you for the worm thought, why didn’t I think of that🤔✅.

Chris LH, the unusual feature of this device is that the worm is driven whereas in most applications the worm is the driver.

A very interesting machine, Andy … do please keep us advised of your progress !

MichaelG.

You might enjoy browsing this lot, Andy

**LINK**

https://www.pinterest.co.uk/pin/spit-jack-to-rotate-the-spit-on-which-meat-cooks--319896379756119734/

MichaelG.

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Ref. __ https://www.abebooks.co.uk/9782701302188/objets-vie-domestique-Ustensiles-fer-2701302188/plp

… Ouch !!

Edited By Michael Gilligan on 18/11/2022 23:20:00

Probably easier to make on a treadle lathe with a very slow speed. Wrap a piece of string around it to mark the spiral, mark with paint that will go into the gaps in the turns of string. Follow the path with a file hand forming a rough groove. As you get some definition for the groove the file will follow it under power. Just a version of hand chasing a thread.

Am I daft,? in order to get this to run you need to spin the "fly" by hand, and when it stops spinning the spit will stop rotating.

No Dick you aren't daft, this is bugging me as well! It doesn't appear to work like a clock escapement but the rotation of the 3 armed fly would control the overall speed. But if you have to rotate this manually - what's the point? It would be easier to have a peasant with a crank handle attached to the ox or whatever?

I haven’t actually operated it yet but my understanding is that it runs powered by a weight on a rope wrapped round the wooden drum. The fly is there to keep the speed down presumably by air resistance. There is a neat arrangement that rings the bell when when the. Rope is nearly all run off the drum thus warning the cook to rewind the rope.

And don't forget the nay sayers that state a worm cannot be driven by a wheel.

Regards Ian.

Like Dick and Mike I fail to see how it can work, unless the fly is turned , UNLESS the helix angle can impart some power to the fly ? Looks more to me like a striking train ? Noel.

I've seen one of these working but sorry I can't remember where. 

Edited By roy entwistle on 19/11/2022 11:26:58

Probably in a BIG kitchen. Stately homes springs (?) to mind.

Regards Ian.

This one’s actually in my shed! I can see I’ll have to cobble up some method of getting it working😉

Noel S,

Fly mechanism driven by a fast worm is common in music box clokwork where it's self starting. Less crude construction and finish though.

But the nay-sayers don’t understand, and therefore generalise too much.

MichaelG.

lots of early automotive back axles had worm/wheel. They backdrive fine as long as the ratio isn't too high. I'm aware of several narrow gauge locos that use 5:1 worms as final drive, no problem

And rear wheel drive Peugeot cars up until they went FWD, don't know how many start worms though.