Horses for Courses

[WolfieParticipant @wolfie]

OK I have just been studying the plans for my Stuart engine as I intend to buy some metal at the ME show. (Attending on Sat, look out for a badge with the Wolf on)

 

But how set in stone are such things? Why are some things brass and others mild steel. And why are the odd few bits cast iron?  And what the hell is ‘finished’ ??

 

My plans designate one particular part as ‘finished’ in the materials column. And whats the difference between silver steel and stainless steel??

 

And how do I tell what already in my stash is mild steel and what is stainless steel and what is silver steel??

[WolfieParticipant @wolfie]

Or Metals for purposes

[Jeff DaymanParticipant @jeffdayman43397]

You need to do some reading. Suggest getting Tubal Cain’s Model Eng Handbook as a start, maybe at the show, along with your metal.

 

Finished means the stock is to finished size and needs no further machining.

 

Material combinations have evolved over the centuries as engineering people figured out what ran on what without burning up or seizing. Word to the wise until you get some experience – go with the combinations recommended on plans, and don’t substitute, especially do not use aluminum on steam engines just because it is easy to machine.

 

If your stock rusts when left outside it is very likely not stainless steel.

 

Tubal Cain will tell you the rest. Do buy the book.

 

JD

[John OlsenParticipant @johnolsen79199]

Some brief thoughts:

 

Silver steel is a carbon steel alloy which can be hardened. It is normally supplied ground to size, and is good for making small cutters. (Can be hardened and tempered for this purpose.) It is stronger than mild steel in the as supplied form and is accurately ground to size, so is handy if you want to make some pins, like gudgeon pins for instance.

 

Stainless steel…comes in many variants, and is more corrosion resistant than  mild steel or silver steel. Useful for piston and valve rods. Not good running against itself.

 

Brass…again comes in quite a few variants, the sort of brass rod you will use for the engine is easy to turn for making things like glands (holding the packing or O ring that we talked about before.) It makes a reasonable bearing combination with steel or stainless steel. For an engine like yours you could use a brass piston with either an O ring or soft packing, and you will probably use brass for the main bearings.

 

Steel. strong, easy to turn although not as easy as brass, you will mostly use it for screws and fasteners.

 

Cast iron. used in the full size originals because it can be cast to complex shapes, and is one of the few materials that wears well against itself. Good for cylinders , pistons, and items like the bed plate of a stationary engine. Not good for highly stressed parts as it is brittle. (If you see a crankshaft that looks like a casting, it will be malleable iron or SG iron, specially treated variants that are less brittle)

 

Bronze/gunmetal.  Alloys of mainly tin and copper, mostly useful for bearings in our current context. More expensive than brass. (also used for boiler bushes where fittings screw in.)

 

Stuart often use brass stampings for connecting rods and eccentric rods. These are OK in a model context, but in full size would normally be steel with bronze liners for the bearing surfaces. Depends how much trouble you want to go to to get an authentic look.

 

regards

John

[WolfieParticipant @wolfie]

Thanks for that.

 

So what about the one designated ‘finished’ ??

[Les Jones 1Participant @lesjones1]

Jeff Dayman has answered that question in his reply.

Les.

[JasonBModerator @jasonb]

Can you tell us what the exact part and material is, this will narrow down what they mean by Finished, and which engine I assume its one of teh 10 range?

 

Easy way to tell most stainless steel from Mild or silver is with a magnet, most stainless is non magnetic.

 

There are exceptions where aluminium can be used on stem engines. For example the piston on my Fowler is HE30 alloy as this gives a smoother running engine (the originals often had hollow CI pistons to keep weight down).  This is a very common use on many model traction engines.I also see no problem in using alloy for bed plates and the like.

 

Jason

 

PS I’ve just got back with a couple of big parcels from College eng but there may be a few materials left for you tomorrow.

 

PPS Don’t miss the road steam models tucked away above the entrance, its easy to pass them by.

Edited By JasonB on 10/12/2010 14:34:58

[Jeff DaymanParticipant @jeffdayman43397]

Jason – re your statement:

 

” most stainless is non magnetic.”

 

This statement is not completely true. Austenitic stainlesses like the common 300 series are not magnetic but martensitic ones like 400 and 500 series are magnetic in varying degrees. For this reason magnet test alone is not totally reliable to ID stainless.

 

I recommend Tubal Cain’s book because in addition to a wealth of info on materials and machining it has a section with diagrams for spark testing materials. Along with a magnet and a file, reading this book section will allow the OP (original poster) to ID most common materials and establish their hardness, roughly.

 

Reason I mentioned no aluminum in steam models to the OP (who is obviously just starting) is that beginners tend to go hog wild with it and make bearings, cylinders etc out of it with awful wear and corroded parts as a result. Judicious use by senior ME’s like yourself with experience and judgement of required clearances can have good results as you have found.

 

For beginners in general I stand by my “no aluminum in steam models” advice statement for minimum disappointment. Just my opinion, your mileage may vary.

 

Before we all write out the Encyclopedia Britannica for the OP on his many questions, I suggest again he do some reading and research for himself as a starting point. After all, I’m sure that is how many of us gained experience in ME at least partly.

 

JD

[JasonBModerator @jasonb]

My term “Most” refered to the 300 series which as you say are the most common and likely to be 99% of what is sold to the ME trade. And I would rather run a magnet over all my silver coloured metals than leave them all out in the rain only to find the majority covered in rust, but each to their own. I do also believe ther are certain cases where stainless steel will also rust so the rain test is not fool proof either.

 

J

Edited By JasonB on 10/12/2010 16:10:40

[TerrydParticipant @terryd72465]

Hi Wolfie,

 

as already said silver steel is ground all over and looks a bit like the ‘Brushed’ stainless steel finish you see on some mobile phones etc.  Stainless itself is usually a very good surface finish and looks quite polished.  Bright mild steel (BMS or BDMS) has a good surface finish but is a sort of grey colour when compared with the others.  Black mild steel (used for ‘wrought iron’ gates and fences etc as well as many other uses) is mild steel but still has the dark/mid bluey grey  scale on from the rolling mill.  The spark test mentioned is done by touching a piece of the steel you want to identify to a grinding wheel and noting the shape of the sparks made.  Some people find this easy to do but I never developed the knack of.   As for reading I would certainly follow John Olsen’s advice.  Also, ask the guys where you buy the metal to help you identify these and they will usually be pleased to help.

 

Hi Jason,

 

You’re right, I almost missed the models next to the bar and only noticed them on my way out.  I enjoyed the show but I think it was less busy than last year, at least that was my impression.

 

Regards

 

Terry

Edited By Terryd on 10/12/2010 17:08:55

[JasonBModerator @jasonb]

Just to complicate the issue it is also possible to buy “precision ground mild steel” this will also have the “brushed” look that terry describes.

 

Whatever you buy try to arrange some way of keeping the different metals apart, either by storing in separate compartments or arranging a colour coding system with a dab of paint or nail varnish on the end of the bar.

 

J

 

Terry I notice the newer 280s have a lever operated tailstock, something I must get round to doing on mine, you will hopefully get one with that feature.

 

 

[TerrydParticipant @terryd72465]

Hi Jason,

 

I’ve just remembered reading Sir Alec Rose’s book about sailing round the world alone in his yacht back in the 60’s.  He had stainless fittings on his aluminium mast and apparently had severe corrosion problems.  He had them changed for mild steel (I think,  my memory’s not what it was) in New Zealand and had no problems afterwards, It was something to do with the electrolytic reactions involved when in a marine environment.

 

Thinking about it it may have been Sir Francs Chichester in Gipsy Moth.  I really must get my memory checked with a 50000 mile service

 

Terry

Edited By Terryd on 10/12/2010 17:27:52

[,Participant @nousername29627]

You said ‘Stuart’ at the start of your post. I always thoight that they sold KITS and not just plans so  ‘finished’ on the parts list means that the part is supplied with the kit already  finished to size and doesnt need any further machining. – or am I missing something?

Phil

[Sub MandrelParticipant @submandrel]

In Tubal Cain’s ‘Model Engineer’s Handbook’ is a diagram showing the different sparks produced by various metals when ground. I have found this the most useful book of all for reference for all sorts of things.

 

 Neil

 

 

 

 

[Jeff DaymanParticipant @jeffdayman43397]

Neil, that’s exactly why I recommended that book (twice) above. It’s a good one all right.

 

JD

[DMBParticipant @dmb]

Hullo Terryd,

You are probably right – Stainless doesnt like seawater. I once read a corrosion article about Stainless screws and boltshaving  been used on a wooden yacht and it was found that where they were hidden from sight inside the wood and permanently wet, they developed patches of corrosion which would eat the bolt away rather quickly until it failed so I understand Bronze is back in favour.

John.

[Chris TriceParticipant @christrice43267]

You sometimes get a reaction between car alloy wheels and the steel/iron hubs they’re bolted to. A friend had an old TR7 that refused to give up one of its wheels even with no wheel nuts on without an almighty whack.

[TerrydParticipant @terryd72465]

Posted by John Coleman 1 on 10/12/2010 21:42:23:

Hullo Terryd,

You are probably right – Stainless doesnt like seawater. I once read a corrosion article about Stainless screws and boltshaving  been used on a wooden yacht and it was found that where they were hidden from sight inside the wood and permanently wet, they developed patches of corrosion which would eat the bolt away rather quickly until it failed so I understand Bronze is back in favour.

John.

 

 

Perhaps the old timers knew something after all

 

regards

 

Terry

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, the WPS no.30 Workshop Materials is another useful source of information also.

 

Terry I think you are right the show seemed a little less busy this year, it was practically like a goast town by half past four. One or two les regular traders me thinks also.

 

Regards Nick.

[John OlsenParticipant @johnolsen79199]

Yes, stainless is tricky stuff and for best result you should really consult an expert. It is prone to Chloride cracking, and since seawater is full of chloride ions, the stainless steel needs to be carefully chosen for best results in marine applications. In particular, stainless will give trouble if it is buried in timber and hence not exposed to air. It is also generally a pain to machine.

 

Another fun aspect of stainless when it is in wire form for rigging is that it will give no warning before it does go. Those of you who have ridden motorbikes will probably be familiar with the idea of inspecting the cables once in a while, and discarding if you see broken strands. Ordinary (high tensile I presume) bowden cables will give you a warning like this before failure. Stainless steel cables, as used for rigging on sailing dinghies do not give any warning before failure. I used to look at mine every time it was rigged, which is essentially every time it went sailing, and nver once found any signs of distress….but after about three seasons of use a cable would go, right next to the swaged connection of course.

 

All this is by way of suggesting that you don’t use stainless unless its properties are really needed for the job.

 

regards

john

[TerrydParticipant @terryd72465]

Hi John,

 

I must admit that when I used to sail Dinghys (is that a real word, it doesn’t look right) I always had galvanised steel stays and never had a problem.

 

I just realised, that’s something Nora Batty might say – ‘galvanised steel stays’ 

 

Terry

 

PS I think I agree with Andrew who said in a posting that we need some more expressive Smileys, – most of those presented on the forum never get used!

[Frank DolmanParticipant @frankdolman72357]

     I think ‘dinghies’  Terry

[TerrydParticipant @terryd72465]

thanks Frank,

 

I pride my self on my spelling and usually have no problems but just had a dyslexia moment then, 

 

Terry

[WolfieParticipant @wolfie]

Hi all, good replies.

 

I bought the Model Engineers handbook earlier on advice from here. Good read. While it explains about materials, what it doesn’t do is tell what each would generally be used for. 

 

As for the steam engine, I only have a plan, not a kit. I’m building it from scratch. So I don’t have the ‘finished’ piece. 

[TerrydParticipant @terryd72465]

Hi Wolfie,

 

The problem is that there are different alloys within each type of material and this composition decides the particular properties of the material depending on what it is to be used for. 

 

First it is necessary to understand what each property is. For example ‘Malleability’ means that a material can be hammered into shape  The particular type of mild steel used for car bodies has to be malleable in order that it is shaped easily into complex shapes but retains it’s strength (the presses used to shape panels are after all just great big hammers).  Copper is also malleable but it has other properties which make it unsuitable for this purpose. Some mild steels are used for machined components, malleability is not so important here but the ability to machine well and leave a good finish is, so elements are added to give it good machining properties, and so on and so on.

 

Another property is ‘ductility’ this means a material can be drawn out into a wire, obviously copper is very ductile hence it can be used to make wire, it also has good conductivity so is used for electrical cable.  Some mild steels have good ductility and can be drawn into wire form and used to make cables, some higher carbon steels have these properties but are stronger and make high tensile cables.  Lead is malleable but not ductile,  Some brasses are hard and lack ductility and are great for engraving, some have good bearing properties (but not as good as bronze) some machine well.  Brass also resists corrosion and is attractive to look at and takes a good polish.

 

Tools need to be hard but usually tough (glass is hard, Curly Wurly is tough), Mild steel cannot be made hard but if we add carbon to the alloy (and other elements to produce say silver steel or HSS) it can be hardened by heat then cooling quickly and then toughened by tempering that hardness.  How much you temper it depends on the application.

 

What I’m really saying Wolfie is that the material has to fit the job it is to do.  It is the application that chooses the material not the other way round. and there are so many materials one can only give general guidance.   If you are making a beam, it will be in tension, cast iron is poor in tension and good in compression, but mild steel is good in tension so that is the material (brass would be too expensive and lack strength to resist bending).  If on the other hand you are making a support column than cast iron could be used.  If you are making a plain bearing journal than Bronze is probably best, but mild steel is unsuitable.

 

This is not knowledge you can pick up easily in a short time except for a cursory overview.  you need to look at the plans, see what is recommended and try to understand what properties are needed in that application  You need to study plans and articles in Model Engineer and other magazines and books, see what others have written and read more widely.  Local libraries usually have good engineering sections and can get books on loan about model engineering and techniques.  The Workshop Practice series has good references and is cheap on Amazon.  Build models by all means if you are impatient to get on but follow the plans even if you don’t understand why at first.   For in depth knowledge there is no real alternative but study and  asking others, both are necessary but be specific when asking.

 

You might start here.

 

Best regards and good luck

 

Terry

Edited By Terryd on 11/12/2010 12:46:21

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