Jovilabe

Maybe **LINK**

or: **LINK**

Well-found, Bandersnatch

I had not seen those before.

MichaelG.

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.

Unlike "Omnia enim vestra sunt Ganymede, quam", which might be considered unsuitable for children.

This one claims to be to scale:

**LINK**

I think making the planets/ moons ill be one of the most enjoyable bits of the whole project.

Neil

Doesn't the rotary table need to move in turn with the spindle in order to hob gears? I know...Ivan law? possibly wrote a book about some of it and described making rack hobs on the lathe?

It sounds a bit trickier to actually get a machine to do that in the first place. Unless theres some new fangled encoders, the tradition machines needed to be geared to a set ratio.

Michael W

Like Michael I'm having trouble understanding the detail of how the blank and rack-form cutter are moved to cut gears.

I've got a 1950 book with a section on making gear wheels. It describes three 'formed-cutter' methods and three 'generating methods' for doing the job.

As an aside, the book highlights the advantages of involute gears, which there is both a method for making them with a fast, continuous process well suited for mass production, and also another method (generation) that can cut the highly accurate tooth forms necessary for precision work. The book says that it is much more difficult, if not impossible, to generate cycloidal teeth. I mention this because I've not come across such a clear explanation for the dominance of involute system before.

Anyway, the rack-form method looks to me like a variation of the "Sunderland gear-shaper" method in which a rack is driven sideways across the blank. At the top of the blank the cutter cuts to the full depth of the tooth, whilst at the sides it shapes part of the tooth form on the flanks.

The bit I don't understand, and I think it's related to Michael's question, is my book stating "Between each cutting stroke of the tool the relative positions of the blank and the tool are changed to correspond to a small amount of rolling of the one pitch surface on the other." (This is different from periodically indexing the blank though 1 pitch so as to cut teeth around the full circumference of the blank, which is clear enough.) The movement is also different from the action of a hob-cutter, where the hob and blank both rotate. Unlike a rack, the hob is in the form of a screw.

Hopefully a few photos with a short explanation might sort me out!

Thanks,

Dave

NO, because it's a rack form it just cuts a series of tooth spaces at a time, the blank rotates and each space gets between three and seven cuts, so each tooth has a series of facets. Anything at 20 or more teeth is perfectly servicable, certainly in small sizes.

Neil

Exactly like your rack, except its a circular cutter, no spiral.

You can see in your picture that each pass will make three cuts on the gear

Turn the gear by half a tooth and move the rack by half a tooth-spacing and you get another, different, three cuts. Make more and more cuts at slightly different settings and the shape rapidly approaches a true involute.

All these are cut with just one pass, made with a 'rack' tooth at centre height to get a full depth space. The gears work fine so frankly I couldn't be bothered to take another set of cuts and double the chance of a cock-up.

That makes sense. " Make more and more cuts at slightly different settings and the shape rapidly approaches a true involute."

Now I've 'got it', I've realised that it must be fairly obvious in practice to see what needs to be tweaked to improve the shape of the teeth, if anything.

What does the rack cutter look like? Something as simple as this perhaps?  If I'm understanding correctly your earlier "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."

Side View

Front View

If it's that easy I might give it a try!

Thanks,

Dave

Edited By SillyOldDuffer on 03/10/2016 15:51:32

Edited By SillyOldDuffer on 03/10/2016 15:58:14

Petty much, except only six flutes cut with the corner of an end mill to give a bit of front rake, and a rather fatter cutting section.

Neil

Many thanks Neil, specially for the fatter cutting section hint. You've saved me the 'fun' of discovering that a thin version of the rack will most likely bend.

Cheers,

Dave

Don't make it too fat, or you will get fed up of having to wind the work completely clear before rotating the blank

I went for 5/8" 1/2" would probably be OK although less allowance for resharpening.

I think I have cut all the gears now, except the great big 344-tooth gear and two 30-tooth idlers for Callisto, so its drive can get around the 53-tooth gears for Ganymede and Europa (I'm driving Callisto from Io not Ganymede, don't ask why, I don't know - it just worked out like that).

I've done a quick mock up of the 'lower stage' - discovered I can drive two gears from the same 12T pinion BUT their spindles will need to be on opposite sides of the central spindle so the driven gears don't clash. Lots more spindles to add, mostly for the 'jupiter orbit' drive (six gears five pairs at 5:1 and one at 17:57) but also the Calisto idler.

This isn't for gear spacing, although it helps 'prove' the gear pairs, just to confirm the order and spot any clashes.

Obviously some spacers will be needed, not least for the bevel gear that receives the main drive from the stepper.

Well, it;'s more fun than brain training and probably twice as effective

Next - the upper level

Looks good. Gosh you work quickly, I'm still faffing about with my rotary table. Thanks for the earlier tip about cutter fatness.

Dave

Some model helicopters use 10 T 0.7 mod pinions

A few more photos,

First for Dave, a view of the cutter and gear making setup:

The results of several evenings and weekends:

All indexed according to the spindle and their place in the stack!

Two pics of a trial assembly, a few gears flop as they are on the wrong size spindle, and some spindles are too long. No spindles for the train of 12/60 gears or the bevel drive and, of course, no 344 tooth gear yet*.

Of course, Mr Stoopid has bought a big bit of CZ108 instead of compo... methinks I may be looking at etching rather than engraving for the dial! Bucket of ferric sir?

Neil

Thanks for the picture Neil. Nice timing: the silver steel I needed arrived today so I can have a go. I'll try and emulate your cutter, which isn't quite as I visualised it. (My version would have had less clearance behind the teeth.)

Impressive progress with the project. Presumably you crank out gears with one hand, the other hand does the forum and you simultaneously edit MEW with your feet.

Dave

Since we have some latin-conversant contributors on this thread, can someone tell me what the latin would be for (Chas) made me, which I might stamp on some of the bits I make?