MEM Corliss build Flywheel

[JasonP]

My build of the Mem Corliss is very slowly progressing. While I had some time over the holidays I thought I would start thinking about the flywheel. I have a problem. The OD of the flywheel is 7.25" and I've only got a Mini-lathe with a 7" swing. Being a Mini-lathe, that's not even usable swing as I can't get tooling onto the outer rim at anything like that diameter.

So I'm trying to think about alternatives. The planes show a fabricated flywheel, which I guess is a possibility, except the outer rim and inner rim are a press fit together. Where can I source those parts ready made? I can drill the spoke holes, just can't turn the inner rim to a press fit diameter.

Anyone in the US made one of these on a Mini-lathe? Any suggestions?

Thanks,

Jason

[wagnmkr]

What mini lathe are you using, and can you get / make a set of risers for it?

[crueby]

To make it fit the lathe you have, reducing the diameter of the flywheel to 7 or just under is always an option.

[steamer]

Got a picture?

Here's a common way around maximum swing.     Using a boring bar that's been reversed and reach around the OD...  ( I know this is NOT a 7" lathe, but it illustrates the method)

That way you can reach without having to run the saddle under the part.    Rigidity will suffer, but it's a way forward.    Did I mention we need pictures?

Dave

[RReid]

I've used the basic technique mentioned by Steamer several times to turn flywheels on my Taig lathe which were just barely clearing the bed. You needn't worry about reducing the diameter of the flywheel a bit to fit on your lathe either, the difference between 7" and 7.25" is trivial.

[Jasonb]

If you do use a standard right hand boring bar don't forget to run the lathe backwards when using it 

If it's an insert boring bar then stick an insert intended for aluminium in it which will cut better at those diameters as they are sharper than the standard ferrous inserts.

<a href="https://www.youtube.com/watch?v=3YZ0mKAzMgE" target="_blank">http://www.youtube.com/watch?v=3YZ0mKAzMgE</a>

[pgp001]

Here's what I did.

Note the use of lead weights to dampen out any vibration.

[JasonP]

Look at all you chaps with your big lathes!

When I said it's a 7" swing, I meant 7" swing over the bed, so 3 1/2" radius. I cannot physically fit a 7" round piece of stock. I can (and have) used the boring bar method on large diameter parts and yes, rigidity sucks.

The biggest I can turn would be 6.9", but in reality it's 6.5" as that's the size of stock I can get, which is getting a little small for the scale of the engine (I may be over thinking that).

Option A is to machine the flywheel out of a single piece with a max OD of 6.5"
Option B is to fabricate a 7.25" flywheel, but I don't have a source for the stock and machining the inner rim to a press fit could be out of my capabilities. The inner rim is 6.875" and getting it to press fit dimension 

[Jasonb]

We are also all showing proportionally larger flywheels. These were to illustrate the method of turning not to show off teh size of our machines, the method applies to any lathe being pushed to it's limits. We were showing you that you can get tooling onto the rim which you said you can't

Someone in the US would be best pointing you to materials but over here we can get 168mm OD thick wall tube which would be about right for a minilathe version if you want to machine the "Tee" from solid.

[vtsteam]

What material is the flywheel going to be made from?

[vtsteam]

If cast iron, grab a tape measure, and pay a visit to your local friendly auto mechanic, explain your situation, and ask if you can have a discarded brake disk rotor, assuming it's the right size. The hubs are generally in the range of 6" - 7-1/2", though the rims are larger. Cut off the rim with a hand grinder cutoff disk.

I think wagnmkr's suggestion of making a temporary 1/2" riser block for your headstock is a good one if you can't find a rotor hub under 7" and above 6.5".

[TerryWerm]

Maybe this idea is wacko, but what would be wrong with making a flywheel of a workable diameter (6.5") but redesigning it a bit to give it a heavier rim? Might even have to make it a bit wider as well as thicker so that it looks proper, but I would think that it would work.

[pgp001]

If you have a milling machine with enough capacity, that can be pressed into service to machine the outside of a flywheel using a rotary table.
You will not get the same finish as on a lathe, but when needs must..........

Phil

[MJM460]

Hi Terry, not a wacko idea at all.  You are on the right track by suggesting a heavier rim on a smaller OD, as it’s the moment of inertia of the fly wheel, not it’s mass that is important.  Mass located at a larger radius from the axis of rotation has a greater effect than mass close to the axis.  The calculations are relatively simple and I can help with the formulae if required.

Hi Jason, the other thing to remember is that for a double acting engine like the Corliss, the flywheel only has to get it past the dead centres without stopping.  Once this is achieved, further increase in flywheel inertia simply reduces the speed variation.  Of course this is more important when slow rotation is required, most model engine flywheels are much larger than the minimum required.

If you do not feel up to the solutions already suggested to get around your lathe size limitations, make the flywheel from the largest practical diameter, based on your tooling and available materials.  Your engine will run fine with that, providing all the other more critical issues are correct.

I suspect that most flywheels on models are sized on “looks about right” basis, which of course becomes a self fulfilling expectation of what looks right.  And of course, for a scale prototype the proportions of the original are more important.

MJM460

[Jasonb]

As the OP mentions going down to 6.5" will affect the look of the engine. These engines typically had a fairly thin but wide flywheel rim section and at 1.5" wide already would start to look wrong if made much wider or too thick. If you look at the MEM logo at the top of the page that is the sort of thing that looks right.

If the 6.5" option were used then the best place to increase the weight without spoiling the look would be to have a thicker leg to the "T" where the spokes join. You can buy 6.5" OD DOM Tube with suitable wall thickness

Looking at Speedy metals I can't see much in the way of thin walled tube that could be slipped over a 6.5" centre section but if anyone in the US knows of a source of short lengths of 7" OD x 1/4" wall DOM type tube then that could be bonded to a ring of 6.5OD material to form a "T" section