Weight driven clockwork roasting spit

[ANDY CAWLEYParticipant @andycawley24921]

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

[ANDY CAWLEYParticipant @andycawley24921]

[Michael GilliganParticipant @michaelgilligan61133]

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

[david bennett 8Participant @davidbennett8]

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

[ChrisLHParticipant @chrislh]

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 ?

[ANDY CAWLEYParticipant @andycawley24921]

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.

[Michael GilliganParticipant @michaelgilligan61133]

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

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

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

[BazyleParticipant @bazyle]

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.

[Dick HParticipant @dickh]

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.

[Mike HurleyParticipant @mikehurley60381]

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?

[ANDY CAWLEYParticipant @andycawley24921]

Posted by Dick H on 18/11/2022 23:49:32:

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.

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.

[CirclipParticipant @circlip]

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

Regards Ian.

[noel shelleyParticipant @noelshelley55608]

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.

[roy entwistleParticipant @royentwistle24699]

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

[CirclipParticipant @circlip]

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

Regards Ian.

[ANDY CAWLEYParticipant @andycawley24921]

Posted by Circlip on 19/11/2022 12:03:04:

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😉

[ChrisLHParticipant @chrislh]

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.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Circlip on 19/11/2022 11:10:38:

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

Regards Ian.

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

MichaelG.

[duncan webster 1Participant @duncanwebster1]

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

[ChrisLHParticipant @chrislh]

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

[Dick HParticipant @dickh]

Live and learn. It seems to have something to do with the pitch or angle of the threads on the worm. (SeeCog drives worm) (https://www.youtube.com/watch?v=ykeiByIel64&t=299s). I´m sure there are better illustrations out there.

[Mike HurleyParticipant @mikehurley60381]

https://youtu.be/vwF6z2tJHVA shows a similar setup in operation

[Mike HurleyParticipant @mikehurley60381]

Sorry, mean to insert a link there. This short video clearly shows that a gear will move a worm as it does initially, albeit with a bit of manual help to get things going. Antique spit roaster

In days gone by, I wonder how many kitchen skivvies have had a thump around the head from that flying arm whizzing round at a rate of knots? No health & safety back then…

Regards Mike

[david bennett 8Participant @davidbennett8]

There are down-loadable copies of Joseph Moxon's "Mechanics Excercises" contemporary book with detailed instructions for making these machines.

dave8

[Author]

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