Yes, it was just for show how balls were prevent from falling during their course!

Not so evident (for me) on the previous images!

Hi Zooen,
not sure if this method helps to create the spiral path you need but it does hit all the circle positions you show in the 2D.
Basically I created the Hour glass inner shape and projected the 2D connection lines onto it (front lines then back lines) joined up the results to create spiral.
Duplicated it and rotated 180 thus getting the 2 start spirals needed.
Cheers
Barry
Added Final image.

Hi Barry,
Thank you for looking into the subject. It is an interesting alternative to start the creation of the main part of the hourglass. The hourglass, I reproduced it entirely (or almost) out of laziness perhaps, I took the Archimedes screw from Albert Karlen. In a classic way I used the sweeping inspired by a tutorial that I had done at the beginning of my learning of MoI3D, the realization of a telephone cable.

In the end, I will still do the Archimedes screw too. Theoretically when the balls have finished their course at the bottom of the hourglass, the Archimedes screw brings them back to their starting point at the top. But can it work? The inside of the hourglass should certainly always be filled with marbles. The balls are 8mm in diameter and the notches in the 8.4mm spirals.

- Zooen

Hi Zooen,
I think the elevator screw works as shown.
The balls enter from left & right and are guide vertically maintaining the 15.5mm Centres.
This way maintaining the 2 groove circuits.
Hope this helps.
Cheers
Barry

How they move ?
By gravity when the hourGlass is reversed or rotate the axe or ...?

Hi Pilou,
the screw rotates the hour glass is stationary.
Barry
Here is an example.
https://youtube.com/watch?v=Y712yhoaXZc&feature=share

So there is an electric engine ?

Hi Barry,

But yes of course! I was so focused on modeling that I didn't bother to seriously study how it worked.
Oh dear! at my age...!?!/###/!?!
Well, the screw is not an Archimedean screw. It is, as you say, an "elevator screw". The Archimedean screw is tilted (dixit Wikipedia)

Barry> the screw turns the hourglass is motionless.
In Albert Karlen's original hourglass, the screw is integral with the support (notches on the upper and lower parts of the screw). So would there still be a design problem?

But in fact, it may be a prayer wheel for an unknown deity!

- Zooen

Hi Zooen,
have looked at the 3D of Albert Karlen's Hourglass_12 and there's an option for section analysis so you can see the elevator screw.
It looks like the elevator screw is stationary and mounted to outer frame and the hour glass pivots around it.
So don't think it's motor driven just rotated by hand thus elevating the balls.
Hope this helps.
Barry
Ps are going to make one ?

Hi Zooen,

You might also like to look into the more modern application of this concept, called a ball screw and used in precision locating, for example machine tools.
https://en.wikipedia.org/wiki/Ball_screw

--Larry

Hi Barry,

In my opinion, the screw is integral with the support and it is the hourglass that we turn by hand. Maybe my en / fr and fr / en translations are playing tricks on me!

Here is the answer of Mr. Albert Karlen (on the site the area of the wood).
to Pilou's question: How does the Archimedean screw turn? by hand or by a motor, or simply by turning, or ...?

The screw does not turn, it is the hourglass which turns around the screw which it is integral with the support, in the state it is done manually but one can imagine adding a motor ...

- Zooen

Barry,

I tried to reply to your private message, but my PM won't send (it is stuck in "outbox"). Not sure what the issue is, but thought I'd try posting here instead.

I have attached NOD file based on your's.

Is this what you needed?

James
https://www.instagram.com/nodeology/

Hi James,
thank you works great.
I have added the option of duplicating and rotating the sweep to give a 2 start spiral.
Also an offset option of the revolved curve thus to retain the balls.
Finally boolean difference to complete it all in the Nodeditor.
Anyway again many thanks.
Barry
Happy new year.
Edit added second shape.

Cool! :)