Making a Jovilabe (Jupiter Orrery)

[Stub Mandrel]

A week or so ago I started a thread trying to better understand the movements of Jupiter's moons.

As a result I came up with a series of gear pairs for an reasonably accurate (it should run for at least a year without significant errors) Jovilabe, or an orrery of the moons of Jupiter.

The basic plan is to have a more-or-less open topped box containing the complex gear mechanism, above this will be a 'Jupiter' orbited by its four Galilean moons. Jupiter will be at the same scale as the orbits but the size of the moons will be exaggerated ten times (so they are about pea-sized).

Underneath this, the sun will revolve around Jupiter once every 11 years(!) while an 'earth' orbits the sun. This will allow an oscillating pointer of cunning shape to indicate, on the far side of the base, the right ascension and zodiacal house (Boo! Hiss!) where Jupiter is residing.

This combines the two classic functions of a Jovilabe - where the moons are and where Jupiter is in the sky.

There is the potential to retro-fit a moon orbiting Earth as well.

It will all be driven by a stepper motor in the base.

So far I have made almost all the gears and tested out the basic arrangement - it's a challenge to avoid things clashing. I had to cut some gears over and under size so they could share the same spacings, which means some slightly odd teeth. As every gear pair is a pinion (small gear) driving a larger gear it is much less demanding of perfectly free movement and ideal tooth shapes than a clock. I also used involute gears which are more tolerant of dodgy spacing. there will be plenty of backlash, but as it will only drive in one direction, this doesn't really matter!

Some early progress, just trying out gear spacings, I have already made several changes. The real frames will be made of brass. The worst part will be polishing all the gears...

More pictures will follow as it evolves:

 

[Beulah]

Thread bookmarked. Love these projects.

[baggywrinkle]

Love it. The only time I ever had to cut gear wheels was as part of my apprenticeship in the RN....and ours were a foot across so dead easy to set up a dividing head on the milling machine.

[happy-kat]

This is a project to follow. A wonderful idea.

How big will the overall footprint be?

[Stub Mandrel]

The base box will be about a foot across, the Jupiter wheel will have 344 teeth and be 240mm across and be the biggest challenge as it will also be the engraved or etched top for the base box. I am not sure what scale to use I fancy a round figure like 1mm=100,000km, which would have Callisto on a wire 188mm long so overhanging the edge by about 30mm. The downside is that it would pass over the top of the Earth/Sun wheel. I will have to see how it looks, the challenge is making the working mechanism.

I cut the gears using a 'rack form hob', fairly crude approach that works well with a single pass for small gears and seems to tolerate using over/under-size gear blanks. Some of the teeth are not 'elegant' but they all run together well enough, only one has needed a little fettling so far.

[Stub Mandrel]

Last night I was able to do a trial assembly of most of the gears. A few more pics:

 

 

[catman161]

Fascinating. Very skilled work. Look forward to seeing the finished article in action. 

[Stub Mandrel]

'Earth disc'. Have to decide if I run with this antiqued look (photo-etched actually) or try and get things engraved. Its about 6mm across the outer diameter.

This will rotate once a year on a pin through the sun's nose (which may have a small orb on it) while it tracks around a 'whole sky' disk every eleven years or so(!) marked up with degrees, RA and the zodiacal houses.

Earth will sit on a pin through 31st December.

The Earth pin will control the motion of the Jupiter pointer.

 

[happy-kat]

Which finish would be more hard wearing? (for length of time letting it exhist/run)

[Stub Mandrel]

There won't be any wear on it, but the etch is about 0.2mm deep.

[happy-kat]

I'm thinking of being dusted/kept clean if it is not in a box

[Stub Mandrel]

10 hours ago, happy-kat said:

I'm thinking of being dusted/kept clean if it is not in a box

Don't say things like that...

[Stub Mandrel]

I've depressed myself by designing extras that mean another 14 gears... adds sidereal & terrestrial time and moon phase.

Heaven knows if it will work or just lock solid...

I've made a moon disc and designed the top of the machine. This will be etched not engraved, partly because I bought the wrong sort of brass...

[Stub Mandrel]

... I've also polished most of the gears made so far. In he end my finger started bleeding because of gear teeth digging in to it!

I have found special Windsor & Newton varnish to spray on them to combat tarnishing.

[happy-kat]

Looking lovely.

Would a dremmel with a polishing head (if you had one) help save your fingers.

[Stub Mandrel]

I have a world-beating dremel collection, but although they polish OK, I need to create a flat surface. The sanding drums would make a rippled surface so I'm using wet and dry on a granite slab.

[Gina]

You're a real perfectionist   Wonderful project - I'm most impressed

[Stub Mandrel]

Test polish of the Sidereal dial after etching but before cutting out (to the innermost of the two outer circles). This will rotate inside the right-hand circle on the dial, the index line on the main dial will indicate sidereal time. Similar dials for solar time and one with ten 'jovi-hours' for 'jovian' time that can be used to predict the red spot etc.

[Stub Mandrel]

Moon Phase Dial, the discs are opposite each other - it's a distorted perspective. Yes I know it's amirror image, I decided to flip the moons and forgot not to flip the Pleiades...

[Stub Mandrel]

Progress has been slow, I have 'proven' the gear train but am steeling myself to make the top plate which is a dial, takes all the spindles and is a 344 tooth gear!

[mapstar]

Really nice project Neil. Good to see an actual machining thread in the DIY section.

I See the mill has been busy mine has too its looking a lot less pristine now .

Interesting gear hobbing with all the different ratio's required. 

[Tsandi]

Can we have one that demonstrates the "do se do" the planets dance while changing places? Maybe the arms have sleeves that extend and retract?

I love that you're doing this!

[Stub Mandrel]

To my shame, this project is in the 'queue' - the challenge is making the huge 10" diameter gear with all that etching.

It will be several day's work which I would like to do in one go with no distractions (probably just an excuse that...)