Flywheel material

[Speedy Builder5Participant @speedybuilder5]

Farm Boy project.  Looking for material to make the cast iron flywheels.  They are 6″ dia by 0.80″ wide with straight radial spokes.

I have several exercise weights which could be be machined to suit, but would the material be a non starter.

Alternatively, I can buy relatively cheaply, 1″ thick aluminium alloy plate and thick walled tube to make a composite wheel.

I believe max revs are about 800rpm.

What are the views on the subject?

Bob

[JasonBModerator @jasonb]

Weights can be a bit variable and I’ve yet to find one anywhere near as nice as GR17 iron bar. Probably OK if you go with fairly chunky spokes, don’t mind plugging the oversize hole in the middle and don’t want to polish up the rim too much.

Have you considered a couple of discs of CI round bar which is what I mostly carve flywheels out of. M-machine would cut a couple of say 0.9″ thick slices.

If you go aluminium spokes and thick wall steel tube rim then make the rim a bit thicker than shown so you regain the weight lost from the spokes

[alecsParticipant @alecs]

Or just make it out of mild steel?

Weights can have widely variable quality of material and can have some very hard material if they were chilled quickly during manufacture. You could try heating them up to a dull red and letting them cool slowly to anneal them before machining. Weather is a bit warm for the traditional burying in the fireplace and leaving overnight in the embers.

[JasonBModerator @jasonb]

I’ve not had weights that are chilled, it is just the quality of the iron is a lot less being coarse and more granular. They are not the nicest stuff to machine unlike GR17 bar which is a joy to machine and a lot easier to cut than even a free cutting steel.

This is why I said go for a thicker spoke as the weights are not as robust as good iron, here is a bit I broke earlier you can see the very coarse grain and all the little voids on the machined surfaces.

 

[John HaineParticipant @johnhaine32865]

I see that Model Engineer’s Laser can work in 20mm mild steel.  Getting a laser cut blank with the spokes and bore already roughed out could save you a lot of time and effort.  Might still be worth thoroughly annealing before further machining – in my limited experience laser cutting can leave a hard region by the cut.

[Howard LewisParticipant @howardlewis46836]

The object of a flywheel is that it will have a latge momentof inertia to carry the engine round on non power strokes

The limit of how heavy it can be is set  the main bearings (I’ve seen a crankshaft broken by fitt ing a flywheel so heavy that it exceeded the maximum overhung load, and failed the crankshaft on fatigue.

To maximise moment of inertia it would be advisable to concentrate as much weight in the rim, being aware of the strength of the spokes, and the centrifugal forces to which they are subjected when the engine runs at above its nornal speed. (A flywheel, even small, failed by overspeed is dangerous!)

So a very dense, but strong, material is indicated. (lead is too weak, and Tungsten tends to be hard to come by), so cast iron tends to be a cost competetive compromise.

Howard

[DalboyParticipant @dalboy]

It is a shame that the man on e bay that use to sell the correct sized flywheels no longer shows them. I must have been lucky when I got mine for my Farm Boy.

I would go for a good cast iron blank and make your own.

A picture of mine for reference

During machining

And final fitting

[Speedy Builder5Participant @speedybuilder5]

Thanks for the advice. Might have to start looking for a small foundry or French GR17 unobtainium !

At least making a pattern is easier with a 3D printer these days.

Bob

[JasonBModerator @jasonb]

If you can find a cheap foundry it may be worth it but a couple I had cast here in the UK recently were not cheap.

Might find something from one of the European suppliers

https://www.ts-modelldampfmaschinen.de/schwungraeder/?page=2

https://www.ateliermb.ch/shops/gussteile/ch/contents/de/d10.html

[John HaineParticipant @johnhaine32865]

Just to repeat my suggestion of getting a laser cut “blank”.  I’ve dealt with MEL a couple of times for custom stuff, albeit in thinner steel, but great to deal with.  You need to send them a dxf of the outline (including the spokes and bore) to get a quote.

[Roger BParticipant @rogerb61624]

RCM offer a 124mm flying wheel although I think that is a little smaller than you require:

 

https://www.rcm-machines.com/en/model-engineering/flying-wheels

 

[Roderick JenkinsParticipant @roderickjenkins93242]

If you want to go down the route of purchasing castings then the Wyvern engine available from Hemingway uses 6″ flywheels. I have recently purchased a replacement head casting for the Wyvern so a query to Hemingway (Reeves) should establish whether they are willing to supply just a pair of flywheels.

Rod

[JasonBModerator @jasonb]

I did look at the slightly larger Centaur before posting some sources, at just under £100 each I decided not to mention it as with postage and paperwork to France things could get quite pricy.

Forrest Classics list a 6 1/2″ (PM Research) flywheel for a more reasonable £27 but being 5 spoke it may cause problems with governor weights.

[Speedy Builder5Participant @speedybuilder5]

Thanks for those suggestions, and some really good leads to French/ European suppliers.

Bob

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