Suitable high speed spur gears

[WindyParticipant @windy30762]

I have just got back to making my flash steam turbine.

The rotor is finished and now on with the reduction gear cases.

I could make the gears out of en24t or en8 but am concerned that not being hardened and ground that their life would be very short considering the high rpm.

The rotor pinion hopefully would be doing 80,000rpm?

The gears are 2 lots of 32dp 20t and 55t.

I thought of buying them but the prices for hardened gears was dear at the companies I looked at.

Does any one know of any gear supplier that have reasonable prices?

A friend mentioned that one of the gas turbine lads used the gears out of a small angle grinder for a reduction drive but doubt if there would be anything suitable for my project.

Lubrication might be a problem and if there was no weight limit would have a pumped oil jet.

I use a solid lube on a highly stressed part of my piston engined flash steamer with some sucess.

Is there something like that I could use on the gears or is oil the way to go.

Any suggestions welcome.

 

Windy

 

[WindyParticipant @windy30762]

[adyParticipant @ady]

Motor bike gears? Car gearbox gears? A worm drive reduction?

 

Some of the high end racing glowplug engines are doing 30,000 rpm and the model car versions must have a  gear system for transmission to the wheels.

 

80,000rpm…now that’s living on the edge

 

How do you engage/disengage the drive train? not exactly dog clutch territory is it.

Edited By ady on 30/08/2011 07:04:24

[JasonBModerator @jasonb]

I've used HPC for gears, don't know what you class as expensive but worth a look. Just enter DP and 32 in the box and it gives prices.

 

GMB Assoc are another I have used they are distributors for Boston Gears

 

J

Edited By Katy Purvis on 01/06/2015 11:50:49

[John Stevenson 1Participant @johnstevenson1]

Have a look at a cordless drill reduction gearbox, these run at high revs and are usually hardened and well made.

 

Plenty of dead ones about to choose from.

 

John S.

[DMBParticipant @dmb]

Try Muffett of Tunbridge Wells. They used to advertise regularly in Model Engineer years ago. Last time I checked, they had a website.

[WindyParticipant @windy30762]

Thanks for the suggestions.

The drive does not need to be disconnected it is straight to a prop.

I have looked at the model car sights but could not see anything suitable.

The motorbike gears are a possibility.

I had used Muffet gears on my piston engine pumps drive but they wore out frequently so I made my own out of en24t, which have lasted well.

Cordless drill gearboxes are a good idea and have looked at them.

A while ago a collection of second hand cordless drills where bought at a car boot for a few quid.

On stripping a quality one down it had three epicycle gear assemblies one with plastic gears.

What type of plastic would it be?

HPC will probably be the way to go if I don’t make my own.

 

Thanks again.

 

Windy

Edited By Windy on 30/08/2011 13:27:58

[Ramon WilsonParticipant @ramonwilson3]

Hi Windy,

 

I don’t know if it would be viable but if you have a wire erosion engineers nearby it may be worth checking them out. By using wire cutting the material can be prehardened and a number of them can be done at the same time (in layers) The finish can be very fine indeed certainly far better than cutting them on home kit and with great accuracy.

 

The programming required is very basic so if the blanks are prepared and hardened beforehand by yourself the cost can be kept to a minimum. Had this done for a set for a Kinner radial – all in gauge plate.

 

Hope this helps a little too

 

Regards – Ramon

[WindyParticipant @windy30762]

Thanks Ramon,

 

I have got the price from HPC for std unhardened 32dp gears (en24).

They do them in en36 as well and am waiting for their Email reply for a price to harden them as well.

If the price quoted in their cataloque for case or induction hardening is correct it would be an extra £66 to£96 per batch plus vat.

That makes it too dear for me.

Back to my new toy (Warco mill)

 

Regards,

 

Windy

Edited By Windy on 30/08/2011 17:48:59

[Richard ParsonsParticipant @richardparsons61721]

Windy I have head the dreaded “mmm grrrGRR WheEEE POOF” in too many times. Fortunately I took advice from the late Prof Chaddok and did my testing in an old ammo box which was surrounded my hard engineering bricks and sand bags. The reduction gears which ranged from bronze to hardened gauge plate often went home with their ‘teeth in a bag’. When testing use a very long ‘pokey stick’. A turbine disintegrating at between 80,000 to 2,000,000 rpm is not fun.

Rgds

Dick

[WindyParticipant @windy30762]

Hi Richard,

Have seen a video of what happens when at high-speed material disintegrates and moves the test cell.

I will have to take serious precautions when testing.

Will make some form of brake so it’s not free running.

If the transmission fails get out of the way.

There are some blankets that the Drag racing fraternity use on the bell housings etc. in case of flywheel or clutch explosions.

I suppose it’s similar to bulletproof vests.

Maybe use something like them for safety.

Anybody got anything like that?

Windy

Edited By Windy on 02/09/2011 18:26:07

[WindyParticipant @windy30762]

Regarding suitable material for my gears and hardening.

I would have liked spiral cut gears but they are beyond my capabilities to make at the moment.

So it will be spur gears.

I have en8, en24t, en36, gauge plate and 2767 air hardening steel that I have used for my cams successfully but am prepared to buy a suitable material if need be.

I would like help in choosing a suitable steel for the gears that is very tough and could be hardened in a home workshop.

If the hardening is not possible at home a suitable firm near York to do the hardening.

HPC do case hardened en36 gears but for what I would have to pay a lot of homemade gears could be made.

I am concerned that case hardening at home would distort them.

Would a nitriding steel be suitable?

Any suggestions welcome.

 

Windy

Edited By Windy on 03/09/2011 09:40:39

[John Stevenson 1Participant @johnstevenson1]

Windy,

Going back to drills I didn’t realise that some were plastic gears, all the ones I have seen are hardened steel.

 

The air drills sold at machine mart and such are hardened steel, you can often see these on car boot sales very cheap.

 

Just had a look on Ebay and there have been loads sold for under £10

see,

 

Air Drill

 

Usual no connection

[Ian PParticipant @ianp]

Windy

 

I’ve followed this post and would like to be able to offer a solution but its not a subject something I know much about (High speed gears).

 

As JS suggested air tools might be a good source as I presume they use turbines small enough to be hand held so they must run as high speed.

 

What sort of overall reduction ratio are you looking for?

 

Ian P

[WindyParticipant @windy30762]

Hi JS and Ian,

 

Will have a look at some air tools have used them a lot in the body trade (cars not human)

Ideal reduction 7.56.

I allso have to do some metal spinning in stainless for the rotor covers.

Have done a little on my silencer ends in 0.012″ stainless, had a few failures but eventually won.

Any hints on spinning stainless, speed etc.

Thanks for the replies.

 

Windy

[adyParticipant @ady]

I would say they would have to be helical, like car gears.

 

Spur gears make a lot of noise because they simply aren’t suitable for high speeds.

[adyParticipant @ady]

steam turbine reduction gear

[adyParticipant @ady]

It also looks like you will need those fishbone type gears, to eliminate sideways forces.

 

The main gear above appears to use this principle with two opposites locked together.

 

chevron gear

 

 

[adyParticipant @ady]

The Superiority of Spur Gears

 

…just to confuse things…

 

They do quote spur gears as being used in WW2 Merlins and claim they were picked because they were more reliable.

 

I’m sceptical.

Pilots were expendable after x-number-of-missions and cost was a big factor in WW2.

 

Merchant ships went at 12 knots to save fuel and got massacred by u-boats,( the Government picked up the insurance tab for any hard $$ losses by a shipping company) and petrol engines got shoehorned into Shermans(known forever after as “tommy cookers”) because the yanks didn’t have any decent diesels but they could crank out petrol engines by the zillion.

 

So a jaded eye is required by the reader IMO.

[adyParticipant @ady]

Towards the end of the war Liberators replaced B-17s for heavy bombing because they were cheaper.

 

…they were also a lot easier to shoot down.

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

I will recommend the gear from drill reduction gear. I has builded the steam turbine with 10.2:1 reduction gear in enclosed case with servo oil (Direction assistend steering oil for car) without problem. I used the gear (who is hard enough for use in high revolution) from EGR valve who came from Peugeot Boxer with Puma engine (Ford diesel engine). Ask the Peugeot workshop if they has a damaged EGR valve they can give you or find in the place for car wrecking shop.

 

Do not use gearoil or motoroil, the thick oil will rob the effect of the turbine and give loss of revolution. My steam turbine is ballbeared while the reduction gear is plain beared in sintered bronze running on piano wire as shaft and the gear wheel running in the servo oil. Revolution out of reduced gear is about 3500 who is acceptable for model steam boat

Edited By Jens Eirik Skogstad on 04/09/2011 08:02:50

Edited By Jens Eirik Skogstad on 04/09/2011 08:04:44

[Ian S CParticipant @iansc]

ady, not all Shermans were petrol, The New Zealand army used M4A2/ Sherman 3 with GM 6046 engines, these were two diesil truck engines geared together side by side. The main cause of fire was the amunition storage, The ammo was later stored in wet compartments. This seems a lot tidier than 5 petrol enginesmounted radially, or in fact a radial aircraft engine(this was the origional engine, and the reason why the tank was so high,nice target). Sorry OT. Ian S C

[BogstandardParticipant @bogstandard]

Just to get this project back on track.

 

I am sure you could easily revert over to mod gears and if so, a cheap source is here.

 

Gears

 

They could be very easily be case hardened by yourself.

 

 

John

[Richard ParsonsParticipant @richardparsons61721]

I was trawling through my previous posts and looked at this one. There is another cause of problems. These are the bearings.

The dreaded “mmm grrrGRR WheEEE POOF” which happens when the gears fail is one problem. A break such as you suggest may be of little use. When the load comes off, a turbine wheel it will spin up very quickly (very very quickly). Think of the energy the disk contains and the heat dissipated by the break and the forces involved

There is another dreaded noise which is the “mmmm gRUK (and sometimes the ‘Clunk’”. The ‘gRUK’ or the less damaging ‘sKREEeeek’ is when bearing welds up. A light wheel running at say 80,000 rpm has a huge energy. Think of the forces required to stop that little number within say ½ to 4 rotations. I have had bearings where the lubrication has literally been vaporised and heated to read heat, the bearings (mainly of ‘delta metal’ melt. I have had ball bearings becoming welded together. The best failure of the lot happened when an alloy casing caught fire. This one caused huge consternation amongst the people who gave me the casing – it was an old aircraft instrument. Ok it was originally powered by air an cold air at that. I was using flash steam ay about 250°C. The original wheel ran at about 60,000 rpm, I was running at 170,000 according to my oscilloscope.

When testing, I always started with an air puff test then worked up slowly with longer and longer runs. Eventually I would start running on flash steam. My testing was for different reasons to yours. I was investigating power losses. Yours are to produce a small high powered engine for racing. A race lasts for how long? Four to five minutes? With four five races in an afternoon? Your turbines would be serviced after each meeting with perhaps not more than nine meetings a year. Mine were often pushed beyond their limit.

Using bits from air tools might be O.K. but remember air tools are used in short bursts of a few seconds. I do not think I have heard ‘Windy Billy’ (even a Die Grinder) running for more than a minute or two at a time. So your turbines will have run for much longer and to be much more rugged and efficient.

Small turbines can be fun and one can become addicted to them.
Rgds

Dick

 

Drat the ‘smileis’

Edited By Richard Parsons on 08/09/2011 11:11:13

[WindyParticipant @windy30762]

The bearings I am using are hybrid ceramic angular contact.

Might go to full ceramic if there are problems?

If you look at the thread flash steam the video shows the piston engine run from start to finish done in 1miniute 25seconds.

Hopefully the turbines 5 timed laps will be in the 11 to 10 second bracket?

When testing the various sized De Laval nozzles with the flash boiler they were red hot at the inlet to them.
Depending on the nozzle size the pressure was from 450lbs to 1000lbs.

It burst the generator on one occasion when the nozzle was reduced to a certain size.

It will be a long haul to finally finish the turbine.

I am using a tried and tested pumps and generator system so that side should be no problem.

Gearing seems to be the Achilles heel at present.

It was pointed out to me that home case hardening could have problems with small DP gears and cause them to be too brittle if it is too deep?

The good thing about model engineering is that it keeps the brain active even if you don’t reach a successful conclusion.

 

Windy

Edited By Windy on 08/09/2011 13:47:46

Edited By Windy on 08/09/2011 13:52:57

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