Loco wheels cast iron grade ?

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Hi Bill,

I was reading up on cast iron a while back and remember someone saying that SG iron was stronger and better for wheels than 250 but that is only what I read I dont have any knowledge of it myself.

The plain disc wheels on my electrics are in EN8 steel but I bought them in so I guess that is not based on which is best but more a cost and convenience in production thing.

Sorry, not very helpful but hopefully someone more knowledgeable will be along shortly.

Ron

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Bill,

17D Miniatures is where I purchased my wheels, they have a website. The only thing is most of what they produce and stock is 5" and 7 1/4". They do offer a machining service though and wheels is one of the products they list but how it works price wise when its not a stock item I dont know. It would certainly be worth giving them a ring as I have found them really helpful.

Tel: 01629 825070 Mon - Friday 9.30 - 5.00. Also the website has an enquiry form you can send them.

Ron

Edited By Ron Laden on 09/09/2019 18:51:40

Cast iron is strong in compression but relatively weak in tension. And it is not ductile, so wouldn't stand up to the hammering from the track and out of balance forces. In contract SG iron is processed so that it is good in tension and compression. As examples both the front axles and crankshafts on my traction engines are SG iron castings. It's a PITA to machine as it chatters more than an Islington lovie. Cue a response from Jason saying it's no problem. However, for disc wheels steel will be even better, probably cheaper and less messy to machine.

Full size spoked wheels consisted of a cast iron centre with a shrunk on steel tire. The steel tire had good wear and shock load capabilities and being shrunk on put the cast iron centre in compression.

Andrew

My only experience of machining ductile iron (SG) is in modifying lathe chucks, and I found it so much better to machine than mucky, dusty regular CI.

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It is certainly not as easy to machien as a free cutting steel or grey cast iron but I do think some of teh chatter problems also come from the crankshaft shape.

This one I roughed out the two main lengths before doing the pin.

Here you can see the chatter on them but teh pin which has been finished is better

Once the throws at the ends can be removed a lot of the chatter can be reduced buy effectively shortening the length buy sticking half of it up the spindle which allows a decent finish.

This one turned out OK too.

The Americans seem to use it more for some of the smaller castings on their engine kits rather than the gun metal that gets used over here and I have not noticed chatter on them so this goes some way to pointing to the length and shape of the crankshafts being part of the problem

There is a good number of keyways on that last one Jason, is that off a traction engine.

Yes, the 2" Fowler. It's about 9" long. Keyways from left to right

Flywheel

Slow Pinion

Fast Pinion

Valve eccentrics

Pump Excentric

Unused

Very nice Jason, some quality engineering there I fancy.

Your welcome Bill, but as I mentioned they dont list 3.5 inch gauge as stock so you will have to see what they say.

Ron

Wot, no splines?

Both my crankshaft and front axle are long 'n' thin. So definitely a candidate for chatter. But when it happened it proved difficult to get rid of. Eventually cured it by forcing a block wood against the work piece to add damping. It also explains why the diameter of the eccentric side of my crankshaft is different on the two crankshafts.

Andrew

There are hundreds if not thousands of model locos out there with ordinary grey cast iron wheels.

I doubt many of those cast wheels are from such good iron as a bit of 250 bar, do you know what grades the suppliers use? I suspect it is harder.

Andrew, you don't get splines on a 4 shaft engines crankshaft, at least not this one as they are on the 2nd shaft.

Yes needs a good sharp HSS or **GT insert anf small DOC to get rid of the chatter as a normal insert tends to deflect the long shafts more unless you are able to resort to a cylindrical grinder.

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Not my specialist subject at all, Andrew ... So please explain gently:

What, then, does the word ductile mean in relation to the thousands [probably millions] of iron grids and covers in our roadways etc. ?

I can only assume that 'ductile' is a relative term rather than a binary one.

MichaelG.

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Edit: ... a brief self-help exercise found this:

https://willmanind.com/what-ductile-iron/

Edited By Michael Gilligan on 10/09/2019 07:30:17

"cast iron" as used by Andrew in his reply can be taken as referring to grey cast iron

The ductile irons are like Andrew goes on to mentioned such as  SG iron where the iron structure is different so they are less brittle and more ductile

Have a look at 500/7 iron for your manholes as opposed to the usual 250 bar that most on here refer to when talking of cast iron bar. Our crankshaft castings are more likely from 700 grade which is even more ductile. Numbers tend to denote tensile strength.

Edited By JasonB on 10/09/2019 08:34:18

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 So ... "cast iron" is another Model Engineering jargon term [?]

I think I'm happy with Willman's explanation.

MichaelG.

Edited By Michael Gilligan on 10/09/2019 08:54:31

That would have been the preferred option, but my cylindrical grinder is only 12" between centres.

Andrew