Suitable high speed spur gears

[Richard ParsonsParticipant @richardparsons61721]

Windy there is another form of turbine you might look at. I know it is normally regarded as a pressure/expansion engine but in reality they have been found to be a ‘mass flow’ engines as are turbine. The engine is the Wankle engine. A three lobed engine having three steam inlets and exhausts. An interesting idea to sit by the fire on a cold winter’s evening with some pots of beer to fuel you thoughts and a sketch pad to record them on.
Rgds

Dick

[WindyParticipant @windy30762]

Richard that would certainly tax the old grey matter.

The sad thing is I dont drink beer now as I have gone tea total.

Sob, sob brings tears to my eyes.

 

Windy

 

[adyParticipant @ady]

It might be worthwhile doing a bit of research on the propulsion system they used in the ss united states.

Much of the design was classified until the 1970s.

 

She was made in the 1950s and cranked out enough HP to rival a modern nuclear powered supercarrier built, like, yesterday.

She was capable of going ASTERN at 20 knots.

 

ss united states

[Richard ParsonsParticipant @richardparsons61721]

Windy The problem is that involutes gears actually slide across each other. At your speeds gears with the life of say 2 million rotations (which at normal speeds would last years) at your speeds (80,000 rpm) would last for about 25 minutes. That is if you can get such gears.

There may be other ways of building your reduction gear. The first was invented by an American clock maker Aaron Dodd Crane. It is the daisy wheel gearless clock drive. You will find an example here.

The other method is the ‘Harmonic Drive’ you will find a good example here at http://www.hds.co.jp/HDS_hp_english/english/principle/index.html . This one is less mind blowing than Aaron Dodd Crane’s design which I made for a clock I gave to my daughter.

If I had known of C.M. Musser’s idea about Harmonic drive when I was into turbines I would have tried it. I have not yet figured out how to make the ellipses without a CNC machine but I think it could be done. With a CNC lathe it would be a doddle. They claim that there is no wear on the teeth.

Jens Eirik Skogstad writes about using piano wire in sintered bronze bearings. I did the same they lasted about ½ hour then I tried sintered carbon (battery electrodes) but these were no better. But bearing in mind my reasons for my turbines were different from yours. I was always trying to push the envelope over the limit

[WindyParticipant @windy30762]

When trying to find an alternative to gears for the reduction drive for the turbine I came across the Harmonic Drive but it was too complicated for me.

I was hoping there was an alternative to gears for high speed drives but have not found anything suitable yet.

Ideas always welcome.

Windy.

Edited By Windy on 09/09/2011 19:34:58

Edited By Windy on 09/09/2011 19:36:01

[Richard ParsonsParticipant @richardparsons61721]

Windy The only complicated bit is getting the metal for the flexspline. Cutting the teeth on the inside of it can be done in the lathe with this . You can also use it to cut the external teeth on the elliptical gear and slotting the flexspline.

The teeth are just 60° prisms an the do not slide as involute gears do Yesterday when I wrote I had forgotten something. The elliptical bits could be made with an elliptical chuck used by Ornamental turners. There is a picture of it here You would only need the simple version of it. Remember you can make anything if you try (and can get the materials)
Regards

Dick

[Anonymous]

Posted by Richard Parsons on 10/09/2011 10:23:46:

The teeth are just 60° prisms an the do not slide as involute gears do

 

Oh dear, I thought that one of the advantages of the involute tooth form, in theory at least, was that the contact was a rolling, not sliding, one? Theoretically, for spur gears I thought that the rolling contact was a line, and for parallel helical gears it was a point.

 

I thought that one of the reasons that helical gears were used in high speed drives was that more than one tooth pair was in contact at a time, so they should run more smoothly than spur gears, where only one tooth pair is in contact at a time. If the spur gears were perfect this shouldn’t matter, but with the inevitable backlash it leads to small impacts every time the line of contact is passed from one tooth pair to the next.

 

Regards,

 

Andrew

[Richard ParsonsParticipant @richardparsons61721]

Andrew – The way in which the harmonic drive works is the ‘teeth are inserted and retracted almost radialy. You could make them involutes’ in shape but in the size that ‘Windy’ will need these would almost be prisms. I will agree that the involute does have a rolling contact but there is always some slide. Helical involute the teeth alo produce ‘side thrust’ hence the double helical or (I cannot spell it as it is French) the ‘Eshervis en Vee’

As the ‘blurb says “The mating portion of each tooth is subjected to very little slide motion. Therefore, motion loss due to friction is reduced substantially, enabling the Harmonic Drive® to maintain a high level of efficiency, and allowing driving motors to be made smaller.”

The real snag is (again from the blurb) “The flexspline is made of special steel with a higher resistance to fatigue.” The Devil is always in the detail! getting that stuff may well be very difficult. But it is well worth a try. And what you would learn on the way to making one which worhed would be worth a “guniea a box”. you might get help ftom the folk who make them. The worst an E-mail to them with a few pictures would produce is silence.

Regards

Dick

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