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Why did my Flywheel Wobble?

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Steve Withnell18/05/2011 21:17:46
843 forum posts
222 photos
I've resolved the wobble now, but still don't understand what I did wrong in the initial machining.
The process I followed was this -
1. Set Flywheel casting (7 inch diameter) on the faceplate to run true (as possib le) against the flywheel areas that will remain unmachined.
2. Skimmed the front edges of the flywheel and the top surface, bored the hub as a series of ops without changing the setup.
3. Turned the flywheel over and set to truth using a DTI on the machined surfaces (1/10 clock).
4. Machined remaining front surface
5. Flywheel wobbles on the crankshaft.
I could understand if the final machined surface didn't run true, but the whole flywheel had a clear wobble. This process should be fool proof (or Muddle Engineer proof!) shouldn't it?
As above, I've sorted the thing, but don't understand why the wheel wasn't right first time.
blowlamp18/05/2011 21:34:48
1599 forum posts
105 photos
More than likely a problem with the boring tool, such as a lack of rigidity, wrong clearance angles (which cause the tool to rub), or off centre height, giving 'bell-mouthing', etc.
Could also be hard spots in the casting. Something like that anyway.
ady18/05/2011 21:46:02
612 forum posts
50 photos
Probbly a rubbing tool.
Ramon Wilson18/05/2011 22:58:23
1283 forum posts
367 photos
I would hazard a good guess that when you initially bolted this to the face plate it (the casting) was not quite flat and the bolting distorted it slightly. Your subsequent machining brought the rim true to the bore but once released any stress induced by bolting released - turning it over then may have compounded the problem. Turning a short stub mandrel and holding it on that may be sufficient to take very light cuts to be able to true it up. If it really wobbles theres only one way - Make sure one side is perfectly flat first then set it up again as true as possible and, clamping as lightly as the machining forces will allow, bore out the centre to take a pre turned sleeve (preferably cast iron) Loctite this in still on the face plate then bore and face this off to finished size - reverse as before.
Hope that's not teaching granny to suck eggs but been there and know how you feel - nothing worse than a wobbling flywheel to maximise irritation as it's plainly there for all to see
Regards - Ramon
Ian S C19/05/2011 02:56:21
7468 forum posts
230 photos
I usually carve my flywheels out of hot rolled mild steel plate, but for a casting I would start as you didand face off one side, but then I would turn it over and face the other side, and bore the hub, and withthe jaws on the inside of the rim which makes it so that you can do the outside at the same setting.
At least if the flywheel wobbles you know that things are going round! Ian S C
mgj19/05/2011 06:03:32
1017 forum posts
14 photos
i'd agree - it was most likely bent in the initial clamping.
One point that is important is only to use 3 clamps.Because then it will, like any 3 legged object, find its own "level" and it is very difficult to bend it. (Unless one overtightens on the spokes)

Edited By mgj on 19/05/2011 06:05:19

Gordon W19/05/2011 09:22:29
2011 forum posts
Just to be on the safe side, rough machine all over, then leave for a day or two before machining to size. This lets any casting stress out ( or rolling).
Steve Withnell19/05/2011 17:13:35
843 forum posts
222 photos
Loads of good insights - thanks guys
Steve Withnell19/05/2011 17:17:16
843 forum posts
222 photos
As a PS: here is the finished thing, wobble removed!
Thanks again
Ian S C20/05/2011 11:27:35
7468 forum posts
230 photos
If you clamp the wheel by the spokesit must have adequate packing between the spokes and the faceplate, so that the spokes don't get bent. Another way is to set up in the chuck nice and square, and bore the hub. Take out of the chuck and mount the wheel on a mandrel, and turn the rest of it between centers. Ian S C
Brian John14/05/2014 06:31:31
1484 forum posts
582 photos

Yes, I would have thought that boring the hub would be the first step in machining a flywheel. Are there disadvantages in doing this first ?

NOTE : I did a search for '' maching a flywheel'' but turned up no results.

Martin Kyte14/05/2014 08:32:04
2728 forum posts
48 photos

Is the Flywheel keyed to the crankshaft? This can often cant the thing over. I think I would bore the hub when machining the second face with the first now machined face against the faceplate as routine.

regards Martin

Brian Wood14/05/2014 09:14:39
2549 forum posts
39 photos

Hello Steve,

The one thing you haven't told us is how you corrected the situation having wetted all our appetites!

Please tell us, it might also help others.

Regards Brian

Andrew Johnston14/05/2014 11:17:23
6577 forum posts
701 photos

This is how I machined my flywheels; the front face of the rim and boss, the outer diameter, and crowning, and the bore all machined at one setting:


Then turned over and the rim and boss faced to final thickness.


Nigel McBurney 114/05/2014 14:59:01
999 forum posts
3 photos

I have often thought most flywheels have six spokes,and a awful lot of other castings/forgings were six sided yet most faceplates have two master slots set at 90 degrees making it easier for four spoke or square workpieces,though after a century or so Colchester did make six slot face plates by which time nobody was making flywheels. all the above are good comments though I will add some more, beware of workpieces that are stiffer than the faceplate overclamping will distort the faceplate. Holding work on stub mandrels can cause chatter problems as the bore on most flywheels is small relative to diameter. My method is mount three alloy blocks on the faceplate spaced two thirds up each spoke, then use three clamps on the spokes directly over the blocks,on heavier flywheels a further three blocks are mounted equispaced onto the face plate near the rim , three bolts screwed into the blocks are screwed outwards ,like chuck jaws , to just touch the inside of the rim.This helps to keep the flywheel in position and takes any radial strain off the spoke clamps . rough machine bore .o/dia and face ,sometime if the flywheel is spaced away from the faceplate the other face can also be machined .then relax the spoke clamps ,this allows any stress in the casting to be relieved but it remains in position ,held by the three bolts. Then leave as long as possible,tighten the clamps Finish by machining the rims and the bore last, on small wheels the hole should be bored a fewthou undersize and finish by reaming.

Use HSS tools for finish boring ,I have machined a quantity of flywheels from 6ins to 2 ft for steam and ic engines plus refaced rusty stationary engine f/wheels .

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