Centering a cast flywheel

[davidyat]

Unless I make a flywheel out of bar stock, cast flywheels for me always seem off when I finish. By that I mean, finding the exact center where to make the shaft hole, the center webbing always seems to be "off" a little and I see ups and downs in the webbing when slowly turning. The outside that I machine is OK, but I'd like to learn how to stop the wobbling in the webbing. Cast flywheel always seem to have mold marks on the outside that make it difficult to chuck up perfectly in the lathe to machine the center hole for the shaft. Please teach me.
Grasshopper

 

[IanN]

Hi David,

My method (not necessarily the best in all cases - every situation has its own issues - some wheels will have eccentrics and cranks cast in)

1) Use a file to "fettle" the casting to remove all the flash

2) If both sides of the central boss (hub) need to be machined, chuck up the wheel and skim one side of the boss (usually only one side needs machining and the other cleaned by file and emery cloth so this step is unnecessary)

3) If possible, mount wheel in the four-jaw using inside jaws so the outer rim is clear, front, back and periphery (see first pic below) If this is not possible, mount on a faceplate (see second pic). Either way, you will probably need to use packing to prevent distortion and to make the wheel run flat and true. Set the outer rim of the flywheel to run true to the centre of rotation

3) Face the front and back (pic three) of the rim. If you really have to, skim the periphery, but it is usual to leave this unmachined and just cleaned up with a file

4) Face the boss and centre drill, then drill and ream (or bore) the hole for the shaft

It is usual to leave the outer peripheral surface of the boss unmachined

NOTE: The pictures are not mine - they are shamelessly copied from a couple of books by Tubal Cain

Hope this helps,

Ian

 

[deverett]

A small addition to Ian's reply.
When you set up the flywheel in the chuck, get the inside of the rim running as true as possible. You can always take a slight cleanup cut on the side of the hub to minimise any eccentricity when you are tready to bore the shaft hole. (Only the outside needs this treatment).
If you get the hub running true without paying attention to the inside of the rim, more than likely you will see it bobbing as it runs on the engine, and that looks a lot worse than any bit of bob on the hub.

Dave
The Emerald Isle

 

[davidyat]

Thank you, thank you, thank you. The first picture was worth a lot to me. I always want to learn something new and you both taught me a lot today.
Grasshopper

 

[Shopgeezer]

Keith Appelton has a video on machining cast flywheels.

 

[Steamchick]

Just a note from my own experience. Any mass imbalance of the flywheel can be used to counterbalance the piston/rods/cross-head and crank masses. This also helps the engine run smoothly which gives an impression of a better engineered model. I personally hate to see a beautiful model run "jerkily", as the low inertia of models (compared to full-size) significantly affects the appearance of a running model.

 

[TonyM]

We all have different ways. I prefer to set up on a face plate get the happy medium for all machined surfaces then machine the bore, one face and the O/D without moving the part. I also like to trim the inner side of the fly wheel just enough to clean up any runout. I don't think it's 'normal' to leave the O/D (perifory) unmachined as Ian or Tubal Cain suggest. I have never used a flywheel without machining the O/D. Generally castings are not that good.

 

[larryg]

On a spoked wheel I want the ID of the rim the be concentric with the OD of the rim. That means that I set up the wheel in the 4-jaw so the ID is running concentric with the center of rotation. Usually the OD of the rim is machined so it comes out concentric with the id of the rim. Usually the ID of the rim is not machined because that is where the spokes are. Lots to think about when getting the final product to run straight and look correct.

lg
no neat sig line

 

[Steamchick]

On a spoked wheel I want the ID of the rim the be concentric with the OD of the rim. That means that I set up the wheel in the 4-jaw so the ID is running concentric with the center of rotation. Usually the OD of the rim is machined so it comes out concentric with the id of the rim. Usually the ID of the rim is not machined because that is where the spokes are. Lots to think about when getting the final product to run straight and look correct.

lg
no neat sig line

Agree. I adopt the same strategy. But I do clean-up the spokes and ID carefully by hand with a file - as taught in a machine shop when I was a teenager. However, you must make sure the hub will still be close to the middle, before any machining. A small cut on the inside dia of the rim - just to make a concentric circle - without touching spokes - is usually sufficient to give a good appearance when running. Providing the outside is machined. But if the casting is good, and we'll centred before machining the bore for the shaft, some Victorian's didn't machine the rim/ OD at all. Maybe because the flywheel was larger than any available lathe? Or possibly to save cost? Theses engines were not for display, but functioning parts of industry, who's purpose was just making money. Just like today's industry. Try Close Burlinson on Beamiss website. I suspect the flywheel on mine haulage engines were not machined in a lathe..? Anyone remember?

 

[Steamchick]

Read Beamish... Spell check got me again!