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.

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