[How do I?] Fly Wheel Turning

[jtrain]

I have a small fly wheel casting for a model steam engine about 3 inch diameter. How and or where do you start to machine it on the lathe, eg; use a four jaw chuck and hold the center hub, or the outer rough surface, and get it roughly running true and bore a hole and use a mandrel, or what other ways of doing it that is more proper. Which surface should be done first?
John

 

[DMS]

Pics of the flywheel maybe?

Kind of depends on your lathe (size wise). If you can fit 3 inches in your 4 jaw, I would load up the flywheel, center it as best you can, then make your center hole. The best way to do that would be to drill/bore/ream. That will give you a straight, smooth well centered hole. If you are looking for a good fit on the shaft, I wouldn't just go with a drilled hole, as the size is going to vary from the size marked on the drill, and it will not be that smooth.

I would then mount on a mandrel between centers, and take light cuts to true up the outsize edge, then face front and back.

I have only done this once (in school), the flywheel was zinc (die cast). It was spoked, and we had a fixture mounted on the lathe that held the wheel with pins through the spokes. This was the order we did things as I recall. The flywheel was slightly smaller, about 2 inches. It was for a small wobler type air motor. We got rough cast parts, and finished them as part of the class.

 

[12bolts]

John,
Does the casting still have a centre stub on it? Dont cut it off! Grab hold of that to do most of the machining, then when the OD is done, you can bore the centre out.

Cheers Phil

 

[Tom Griffin]

John,

When machining a casting, machine the largest surface first and make sure everything cleans up before moving on to the smaller features. Also make sure the casting is centered. In other words, don't take a bunch of material off one side only to find out that there's nothing left to machine the features on the other side. On the other hand, don't just clean up one surface and assume the rest will clean up. You may need to take more off the face of the flywheel for instance, to get the face of the hub to clean up as well. Check all the surfaces to be certain there will be material left before cutting anything. Depending on the quality of your casting, there may be tons of stock everywhere, or it may be a challenge get everything to clean up. Just take your time and don't machine anything until you are sure. It's easy (and fun) to remove material, but pretty darned hard to put it back on! :banghead:

For your flywheel, try to grab it on the hub so you can access both sides and be sure that it's running true. An easy way to get it running true is to touch each side with a piece of springy wire as it turns, kind of like truing a bicycle wheel. Then machine as much as you can in that set-up (face, outer diameter, bore, etc.), flip it around in the chuck or re-mount it on a mandrel and machine the other side. Once you get some of it machined, then you can use an indicator to get it running dead on.

Tom

 

[Bill Gruby]

John;

In addition to Tom and 12bolts, please look at the center hub. Occassionally the will do you a favor and cast one side longer that the other. This is the side you want to chuck on. Continue as Tom said and work from large to small.

"Billy G"