stuart flywheel - making it run true

[mulac321]

hi ive been working on my stuart 10v and i had a go at the flywheel. i think i rushed it a bit... when i mount the finished flywheel on the crank shaft and into the brass bearings the outside of the flywheel runs very true however looking into the flywheel i can see alot of "wobble". im quite disapointed and i think i will buy another flywheel of stuart engines to have another crack at it. any tips for making the flywheel look perfect when in rotation? even better can it be repaired? bearing in mind i have drilled the centre hole.

thanks
Calum

 

[metalmuncher]

Hi I'm just starting on machining a six inch flywheel for a hotair engine. The way I do it is line the inside of the rim up to run true, It doesn't matter so much about the hub being a little out as its not noticed so much. Hold a rod in the toolpost that way if you want to go between the spokes you can. Hope this helps, nothing worse than a wobble on your flywheel.

Regards Metalmuncher.

 

[Dave G]

Hi Calum, When I turn flywheels I like to chuck on the ID of the outer rim in three places with the 3 jaw chuck. Preferably close to the flywheel spokes with at least one spoke touching a jaw of the chuck and in the direction of rotation that if the flywheel were to slip in the jaws when turning it would be bolstered by the chuck jaw itself. I like to turn the OD first because of the interupted cut of the casting irregularities. If you finish the bore and the faces first and then the flywheel happens to slip or move during turning it will be difficult to re tram your flywheel and finish. After turning the OD and leaving a small amount of stock to clean up later I clean up the face next and finish this to size. Next comes the drilling and boring of the hole. I normally will center drill then drill the hole 1/32 - 1/16 undersize and then bore the hole to size with a boring bar.
Reaming the hole after drilling will not necessarily give you a true running hole, that is why I bore to size and if you're not comfortable with boring to size, leave a little to lap out later. Before removing from the chuck you must go back and finish the OD. I don't like to finish any one surface until most of the stock is removed from all surfaces. Now the OD, one face and the bore should be true with each other. Reverse the flywheel in the chuck leaving the face that hasn't been turned yet exposed. Clamp on the OD of the flywheel and take a light cut on the face to clean it up. Once cleaned up stop the lathe and measure the thickness of the flywheel. If you were lucky the flywheel will measure the same thickness all around. If you weren't lucky the flywheel will need to be moved in the chuck to get the back face to run true. The easiest way I have found to do this is to measure the flywheel thickness in multiple places and find the high spot and the low spot. At the thinnest portion make a mark on the face with a marking pen. Place an indicator on the face of the part and rotate the chuck by hand until the indicator point is at your mark. Tap on the flywheel face with a brass hammer to upset it the amount of variance in your measurements. This should now have the rear face running true with the lathe spindle and then recut the face and then remeasure. This should have all your surfaces running true now and allow you to finish the thickness to size. I hope this helps, Dave

 

[maverick]

It seems that Metalmuncher has the recipe for this setup. If the spokes and other cast surfaces are set to run as true as possible,
the machined surfaces (O.D. , sides and bore) can be cut and have as little apparent wobble as possible.
As far as repairing the casting, bore out the center and press in a plug and have another go at it. The thickness and O.D. may need a cleanup cut
to run true.

Best of luck,
Mike

 

[mulac321]

thanks for your advice guys, i will let you know how i get on on sunday.

thanks
Calum

 

[RollaJohn]

Calum: I don’t understand your problem. When starting to create a part, whether from bar stock or castings, the first thing to determine is what surface will be the reference datum. Then everything else should be laid out and machined in relation to that surface. It sounds like your reference surface is the outside rim of the flywheel and that you have bored the axle shaft hole concentric to that successfully since you say it is running true. Now don’t stop the machining operations on the part, but continue removing chips from those surfaces that are not concentric or parallel to this surface. Face the sides of the rim, spoke area and hub, and turning the inside diameter of the rim and the outside diameter of the hub without cutting the spoke area completely away are the steps you have not completed yet. When they are completed the flywheel will be spinning with all surfaces running true and to your satisfaction.

 

[portlandron]

I do mine along the lines of what Dave has outlined but with the final step being mount the flywheel on a mandrel in the lathe and take very light cuts to true it up if needed. By doing this it is running true to the shaft bore.

 

[metalmuncher]

Calum: I don’t understand your problem. When starting to create a part, whether from bar stock or castings, the first thing to determine is what surface will be the reference datum. Then everything else should be laid out and machined in relation to that surface. It sounds like your reference surface is the outside rim of the flywheel and that you have bored the axle shaft hole concentric to that successfully since you say it is running true. Now don’t stop the machining operations on the part, but continue removing chips from those surfaces that are not concentric or parallel to this surface. Face the sides of the rim, spoke area and hub, and turning the inside diameter of the rim and the outside diameter of the hub without cutting the spoke area completely away are the steps you have not completed yet. When they are completed the flywheel will be spinning with all surfaces running true and to your satisfaction.

Hi, I can't agree with machining a flywheel casting all over. the only surfaces that need machining if its set to run true are the rim and both sides of it and the face of the hub. theres no point in using a casting if you are going to machine it all over you might just as well use barstock. Leaving it as cast is true to prototype and looks much better. Thats how I do mine but we all have different ideas and thats as it should be or it would be a dull old world. Regards Metalmuncher.

 

[RollaJohn]

Metalmuncher, I agree with your comment. The idea behind my post was due to Calum's comment that "looking into the flywheel i can see alot of "wobble". im quite disapointed" , and what measures that can be taken to correct his perceived wobble.

 

[metalmuncher]

Metalmuncher, I agree with your comment. The idea behind my post was due to Calum's comment that "looking into the flywheel i can see alot of "wobble". im quite disapointed" , and what measures that can be taken to correct his perceived wobble.

Rollajohn, I made the same mistake when I machined my 10V many moons ago, tried to correct it by remachining it but it looked terrible. In the end I just bought another casting and made a better job of it. Nothing like learning from your mistakes and its something you never do again. Regards metalmuncher.