These are the calculations. As you can see three spindles are needed for the moons, whilst the jupiter year train will be an over-under sequence and the earth/jupiter gears will be 'sun and planet' with the sun as the planet and jupiter as the sun, if that makes sense! With involute gears hobbed onto under/oversize blanks (by two teeth) I think I can get the gears to mesh OK.

I'm talking to myself here…

The earth/sun gears work as well

Not quite the Antikythera mechanism, but very do-able, I reckon.

I've wondered that too. I think the weakness at the moment are my 50:10 gear pairs, I think 10-tooth gears will be challenging for hobbing involute gears so i may go up to something like 80:16.

The biggest challenge will be the big circular gear (which will can actually be the main base with some piercings instead of just a huge hole. Not least, cutting the teeth on something that big doh! – of course t a rotary table on the shaper will solve that. .Also, what to engrave on it; obviously degrees around the edge, but what to put in the void? Perhaps scales?

I think the sensible way to progress is to make the upper gears mechanism – the top picture, between simple steel frames. Assuming it works, it then becomes worth considering the extra effort to add the bottom train.

Of course the fun bit will be making & painting all the little planets and moons.

By the way proposed scales:

Jupiter globe & moon orbits 1mm = 10,000km (jupiter ~14mm diameter, largest (callisto) orbit radius 188mm, smallest (Io) orbit radius 42mm. Earth at this scale will be 1.2mm.

Scale for moons 1mm:1,000km which will make them ~3-5mm in diameter. A better scale for earth as it will be 1/2" across (12.7mm). In the unlikely event I add earth's moon it will be ~3.5mm across.

This keeps the overall size reasonable ~380mm biggest orbit over a 300mm base while the moons are large enough to see and a 1:10 exaggeration of their sizes is easy to understand. The base could have an oblate ring to show the size of jupiter at the same scale as the moons.

Telescoping tubing obtained & 14 and 28 tooth wheels done.

The big wheel will be a flat plate on top of the 'box' with all the gears inside, it should be easy to cut the teeth if I fit my rotary table to the shaper where the angle plate would normally fit. Just a long slow job!

I will have to get all the axle/pivot locations marked on the gear, most of them will fall on four arms at 90 degrees, but two of them can lie on a curve between the two arms.

I can also leave a ring at the right diameter to show the size of Jupiter at the same scale as the moons (142mm diameter).

Possibly I can engrave or etch various things onto the plate. One thought is etching little drawings of things like the Voyager probes, which might take a bit of ingenuity.

I might add a Latin motto:

"Omnia enim vestra sunt Europa, quam"

Might be a good choice

Neil

Hydrogen, helium and methane

Me to spin it slowly and spray on very fine lines.

I'm churning through the gears like nobody's business. The combination of a a rack-form hob and power feed makes it very easy to do these small ones.

14T looks surprisingly good, the 12T one is a bit bit crude but works fine. I'm having to make some amendments to make sure i don't end up with bits of metal moving through each other though… my second version worked, but i would have had to levitate it on magnets…

Yep, I'll post a photo in a bit. Made out of silver steel using a simple cutter ground to the right angle on the end and then reduced to give the right shape, then cut a series of grooves.

Making a gears is just – set a tooth near centre of cutter to rotary table centre height (no great accuracy required, do by eye against tailstock).

Turn a blank or blanks, move to mandrel in chuck on rotary table. Set cutter to just 'kiss' blank, then move to side and apply 1.50mm in-feed (to allow 0.01mm for the kiss..)

I have a spreadsheet that gives me how many times I need to pass zero and then a reading 0.0 – 5.9 to set the dial for each tooth.

I have given up with multiple passes at different settings, at 0.7 mod anything down to 20 teeth looks fine with a single pass, smaller gears look a bit 'peg like' as do ones cut on blanks about 1 tooth too small, but they all seems to run together. No doubt there will be backlash but I'm banking on the fact that the pipe-in-pipe arrangement will generate enough friction to stop things waving about.