Machining A Flywheel

25 rpm? Are you kidding? I machine OE car flywheels of about 10/11 inches diameter at 200 rpm with carbide tooling and that isn't really pushing the envelope so to speak. It just means better tool wear than running at twice that and I'm running out of carbide tips so tool wear is important to me. At 25 rpm I'd never get anything done.

You don`t want to do B and C.If you pull the casting down onto the bolts it will distort and when you release it after machining it will not be true. You need to shim under it so that when you clamp it it will not be getting distorted. Once you have it clamped machine as much as you can in one setting including the bore. If I had to do something like that in a small machine,I would lay the faceplate on the surface table and use a height gauge while shimming to ensure it stays level within the machining allowances you have and when clamping set a dial indicator on the top of the casting adjacent to the clamp to check it was not getting distorted while I clamped it.Centralise by measuring with a rule. The 25 rpm seems very slow but I don`t use small machines so won`t comment. Mark.

1. Make taper mandrel
2. Bore casting

3 Mount between centres

1. Turn one face
2. Reverse and face again.

No distortion to speak of

You could, however, do it like they did it in full size- after all, that is what you are emulating. Oh, and Stephenson used the foreman's bowler hat to stuff the pistons.Boring stuff?

Ooops

Norm

.......my uncle cut up a leather belt to replace crankshaft shell bearings in the Western Desert......now that's lateral thinking for you. (He never did say whether the engine actually ran though, or for how long...!) --

Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"

The patent examiner needs firing in that case - there is of course prior art (Harrison used Lignum Vitae as a bearing material - for example, to construct the first ever roller bearings).

Regards, Tony

We are getting off the subject but there are major differences between roller bearings and plain ones( I think) The steam ships had brass(?) and the wear rate was appalling high. The replacements were as stated! Somehow lignum was used long before Chronometers were used in Ancient Rome( according to Shakespeare). The joke is that it was the Holy Wood in the good old days and could have formed the Ark of the Covenant. Back to Harrison-but perhaps another one!

Cheers

Norm

snip

To attempt to keep this thread on topic I would like to comment on this query. Absolutely no experience of Engine flywheels of this type but I will fly a drone and let someone else shoot it down ;-)

As I understand it there are two aspects in the balance of a rotating lump, Static and Dynamic. Static is relatively easy. Locate the flywheel on frictionless bearings. (available at your local skyhook stockist) give it a spin and mark the lowest point when it stops rotating. Prove a couple of times. Add plasticine to the high point until the stop point is arbitrary. Remove plasticine, weigh and calculate equivalent volume of CI to give that weight. Machine that volume away from the marked area by milling or drilling. Alternatively add some metal to the high point replacing the plasticine. Depends what is best visually. If frictionless bearings are not available then a mandrel through the bore and the unit set up on a grinding wheel balance or something similar. Any balancing should obviously be done when fully machined and with any bolts, keys in place. *** see later note.

Dynamic Dynamic balance will be a function of the "width" of the flywheel. The wider it is the greater chance of out of balance dynamically. I have some thoughts on doing this at home but not explored enough to put on paper!

*** Depending on the quality of your casting it may be sensible to roughly static balance before machining. This would then give you the "optimum" centre of balance for setting up the flywheel for machining. This centre point may be slightly different to the theoretical centre of the casting diameter. Again judgement would be made as to the final visual effect after machining

The above are my rambles whilst considering a problem that I have never actually confronted. Thank you for the brain excersize!

Balancing a flywheel is straightforward. This is the method I use for race engine ones I lighten and balance. Buy a couple of ordinary 1/2" roller bearings from your local stockist. Make sure they are the basic type without integral seals. You want as little friction as possible.

Make a mandrel a couple of inches longer than the flywheel thickness that is a tightish fit in the flywheel hole and with 1/2" registers on each end for the bearings. The mandrel must be very concentric i.e turned in a single operation between centres or at worst in a very good collet chuck. The tiniest eccentricity and you'll be trying to balance the error in the mandrel rather than the flywheel.

Now just set the assembly on two big parallels so it can rotate freely. I use a couple of old cylinder heads but you could make a wooden support or anything else that comes to hand.

Finding the high spot takes a little finesse. Friction in the bearings means the flywheel won't always settle in exactly the same position - usually it will stop just before the true point. So find the approximate high spot, turn it clockwise a bit and let it fall back again, mark that spot, turn it anticlockwise a bit and let it fall back, mark that spot - the real high point should be between those two. Easier done than described.

You can use plasticene opposite the high point to balance things out and get a feel for how much metal needs to be removed. After you've done a few you get to know by the rotation speed how big the error is though. Then you just drill a a balance hole, test it again and keep at it until it's true. Again, practice gets you to that end point much faster after you've done a couple and know how much weight a given sized drill removes.

Accuracy is very good. My setup will easily register a pea sized bit of plasticene stuck on the rim at say a 5" radius. Less than a gram anyway at that radius. As good as factory balancing of production car engine flywheels if not better in my experience.

The scale speed of a stationary steam engine does not require a balanced flywheel. If a steam engine is going to reach dizzy speeds, it should have a governor with a couple of balls flinging around. ( and don't tempt further comment!)

Norman

This one definitely has large pair of balls -

I now just about have enough bits to bring this engine to life, it's my great grandad's who disembled it for cleaning just before he died in 1912. Grandmother threw a box of flywheels out in the 50's hence needing help from Pollymodels. It will be a year I guess before this all comes together, my day job prevents any great rate of progress, but does fund the workshop toys - cake, but can't eat it as often as I'd like!

Need to re-read the thread again got the bit about 200rpm that should be more fun than 25rpm but the turning operation needs a bit more thinking about.

Thanks guys

How was that then?

Just hang on minute there Steve. You can go that fast if you want to, and if your lathe has the power, but you do not need to - you are not trying to do quantity production and you are not getting paid. For cast iron a rough guide is that the surface speed should be something like 50 ft/min with HSS tools, and say 3 times as much with carbide. What you are usually trying to achieve as an amateur is a decent surface finish. Beyond that, it is what you, the lathe, the tool and the job are happy with. Dave Baker is a speed freak, anyway.

As for mounting the job, remember that the bits that you want running true are the surfaces that are NOT going to be machined. I would probably support it with packers under the outer ends of 3 or 4 spokes, arrange clamping dogs over the packers to minimise distortion (as you have already been advised), and 'clock' it to the inside of the rim.

Moi??? I take it that was tongue in cheek. As I've said both in this thread and previously I always sacrifice speed for tool life because I'm not doing volume production and I'm too tight to buy new inserts. I'm on the last few good edges of the handful of non ferrous DNMG inserts a mate donated to me

10 or so years ago because he didn't use that size anymore and I'm not looking forward to having to replace them. Partly because I don't know what make they are and don't want to get anything that doesn't work so well. I can pretty much make them last indefinitely for surfacing flywheels and engine blocks by not being too rough with them but I have to use them for turning pressed steel valve caps from time to time and those sometimes have a hard skin which really hurts the tips every now and then. Every time I hear one squeal I know I'm one more edge closer to running out of good ones and it grieves me enormously. I'll probably actually see what my Cronos diamond grinding wheel can do for them when I'm down to the last one before splashing the cash though. I'm sure I can resurrect most of them with a bit of gentle tweaking.

Anyway, last week I machined a Saab flywheel for a customer and took 2kg off it. O/D was a bit larger than the OP's flywheel. Probably 11 inches at the rim although the bulk of the material was removed from across the clutch face at a diameter between 10" and 6" so basically very similar to the OP's average cutting size. I've just nipped out to the lathe to check the settings and I machined that at 162 rpm and 1mm cuts. I tried 256 rpm and it cut fine at that but the swarf was flying into my face and it was also getting bloody hot so I went back to 162 which reduced the swarf temperature and trajectory sufficiently for it to only end up on my chest and in my pockets. I also felt 256 was pushing the tool edge a bit too much and didn't want to risk hurting it.

Anyway 162 was very comfy and the insert was unmarked after shifting 2kg of material so perhaps not quite the 200 rpm I'd originally estimated from memory. So OK let's compromise on something a bit slower, especially when getting through the hard surface skin but anything less than 100 rpm would be utter tedium. 25 rpm is just plain silly and I doubt if you'd get much of a finish at that speed either.

As for SFM I don't know where you've got your data from but my carbide insert catalogue suggests anywhere from 200 to 500 for grey cast iron depending on the hardness and malleability. That would equate to 85 to 212 rpm for the O/D of the OP's flywheel and of course more for the bits closer to the centre. Obviously the higher end of that is sacrificing tool life but somewhere in the middle seems to accord exactly with the speeds I use myself.

Finally the bulk of the metal these tips of mine shift is in flycutting blocks and heads of which I do many more than flywheels or other jobs. I run the cutter on an adjustable bar from about 8" to 10" cutting diameter for most jobs so in fact pretty analagous to flywheel machining. The speeds I settled on after much experimentation is 180 rpm for cast iron and 550 rpm for aluminium so again exactly what I end up using on the lathe although I hadn't previously given it much thought. At 180 rpm I can flycut iron blocks all day without marking a tip and that's on interrupted cuts of course which are harder on tools than continuous ones. For that reason I don't use such deep cuts though. 0.5mm is plenty on iron at that speed.

Woa! woa!. Steve now tells us that this artefact was constructed in at the beginning of the last century. Consequently, even adding anything which belongs to more than 100 years younger to it is alien to its survival.

Here we are, products of another age offering suggestions to emasculate the true worth of great grandad's contribution to mechanical engineering. To suggest further is to be compared to putting a moustache on the Mona Lisa!

I look forward to its appearance on the Antiques Road Show at a later date.

We have quality, we have history and a sense of purpose. Thank you Steve for bringing light and hope to our jaded miserable little lives.

S- nore man

Thanks Charles -" and 'clock' it to the inside of the rim" that's the key learning for me.

Steve

I think he must have had a twisted sense of humour, some of the cylinder bolts are 17/64ths cycle thread...

On yer bike then

Regards, Tony

It is almost 60 years since a bunch of 18 year olds who had no education and left school at 14, went into uniform. In 6 weeks, they had full charge of aircraft of which 4 still survive and 2 are still in 'full battle order'. Those who should have acted as mentors to these 6 week wonders were servicing aircraft which were landing one every minute. There were 4 'senior men', perhaps they were only boys but those aircraft left behind stood in readiness for whatever was going to come. The Spitfire squadrons stood in readiness to defend London. These boys in the their greasy overalls must have caused more grey hairs to the men who had survived hundreds of hours of combat. To have a Merlin engine cut out mended by a boy, was a dreadful way to die! Those Merlins never faltered. There men dying in a submarine- and an aircraft and a scratch crew took off to help. The little Devon had the engine covers hastilly put back and the vital service was missed. Old VP-981 failed that day but she flew with the Battle of Britain Memorial Flight. I had a beer with its first fitters only a few months ago. One of the 4 died in screams as his sabotaged plane plunged into the ground on take off. It was the Queens Birthday 1949. He was only a boy! His name is on the Roll of Homour. His pilot sacrificed his life to save schoolchildren under the stricken plane. He swerved to avoid a hospital and finally lost it all in a dead single engine avoiding a house. You see, I was the other 'senior' boy and I held the highest rank but with only 6 weeks training.

Fred Higginson died in those flames and with every long bone broken in that tender body. Four men went into the burning petrol to bring 3 torn bodies out. The years have taken another of the four and there are now only two of us left. Both of us are, incidentally, disabled from those days.

'When you go home, Tell them of us and say For your tomorrow, we gave our today'

...thank you, Norman....amem to all that. --

Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"