|James Veitch||05/03/2010 03:24:34|
|16 forum posts|
Please, a little clarity,
What are each of the following.
What does each of them look like (so I can tell them apart)
What is each type good for, or commonly used for.
What are the machining characteristics of each.
What is the rank, cost-wise, of each.
1. Cast iron
2. Carbon steel
3. High carbon steel
4. Bright steel
5. Silver steel
6. Stainless steel
7. Drill rod
8. High speed steel
9. Gun metal
Feel free to add any others that are commonly seen in the model engineer's workshop.
Thanks, Jim V.
18924 forum posts
I'll take the easy question on what they look like, someone else can tackle another of your questions.
1. Cast iron - this is generally a dark grey with a matt finish when cut. In the form continuous cast bar it will show small ridge lines along its length.
2-8 these will all look virtually the same. Drill rod is the American term for silver steel so these are the same. The only way to tell them apart is to do a spark test, a bit of searching on the web should give you some info. Stainless will in most cases be non-magnetic.
9 Gun Metal (and the leaded bronzes) this has an orange/yellow colour to it and is quite soft. The cast bar can have a slight spiral pattern around the outside of the rod.
|Tony Martyr||05/03/2010 09:35:22|
198 forum posts
A course on metallurgy is a tall order for a forum but there are some valid general points to be made - the main point being that you have to know what material you are working with and that it is appropriate to you requirements; ex-scrap of unknown content is asking for trouble
Cast iron may be seen in two different forms by the model engineer: as castings such as cylinder blocks and as centrifugally cast bar which can be used for high quality components such as pistons. Cast iron machines with a carbon dusty swarf but can be very variable in quality and contain chilled surfaces which are extremely hard and vesicles (air bubbles) - cheap cast iron is an oxymoron for a model engineer.
All steels are an iron/carbon alloy with 'high carbon steels' containing around 2% Carbon by weight. All straight carbon steels look the same but most steels contain other alloys to give particular properties and most practiced model engineers will probably be able to tell a bar of stainless steel which contains chromium and has a sort of yellowish tinge from a mild steel (>0.3% Carbon).
The BS standards (I am out of date) contain hundreds of steel alloys but most merchants divide them into 'mild steels' typically grade En8 and 'special steels.'
You should beware of stainless steels because they contain elements that means the material work hardens and can be very difficult to machine, in the case of manganese steels almost impossible which is why it is used as tool steel or HSS. I think most suppliers to the model engineers supply stainless in grade called 316 which is quite benign.
Silver steel is 1% carbon steel that contains other alloys and is always (?) supplied in ground rods which is how I identify it - its great advantage is that it can be hardened and tempered and turned into cutting tools (as Jason says 'in the US it is drill-rod')
Gun metal is a bit of a catch-all term but it is a type of bronze with a zinc content. You can tell the difference between brass (copper/zinc) and bronze (copper/tin) because the former is much more yellow. Bronze can be difficult to machine and particularly to drill but there are free-cutting bronzes which contain some lead. The main advantage of gun-metal in my working career was that it is resistant to hot sea water.
Most model engineers buy small quantities of metals from known suppliers and don't get caught out by using 'mystery metals' found on the scrap heap. When it comes to welding of these range of steels or non-ferrous metals a whole new book load of problems occurs as anyone who has tried welding monel metal (a nickel/copper/iron) will knowTony M
|Tony Martyr||05/03/2010 10:57:22|
198 forum posts
What I failed to mention was that the machining characteristics of different steels are the best means of rough identification rather than visual inspection. Using the same tool and surface speed on a lathe gives very different results with different steels that outwardly look the same. Some people can make similar crude identification from the sparks coming off grinding wheels.
It needs experience!
|Ramon Wilson||05/03/2010 11:27:56|
778 forum posts
James, your query indicates that of a beginner and as Tony says a tall order.
I can't improve on Tony's excellent overall description but I feel you may need a little more practical help.
As said all of these materials come in many forms and grades within their respective 'subtitles' but for the model engineer the knowledge of a few basics will help.
Cast iron is a relatively easy material to machine using conventional HSS tooling and or carbides. It is not normal to use coolant or cutting fluid when machining (Tapping excepted) Castings all have a skin which can be, though not always, much tougher than the material beneath. The hard spots mentioned can be a problem but reducing speed right down and or using carbide normally solves the problem. Continuous cast bar is 'lovely' stuff to machine, very homogenous and consistent quality. Once you have seen and machined a piece of cast iron you will have no difficulty in recognising it from then on !
Steels likely to be encountered at least to begin with are Mild steel either 'Bright' or 'Black'.
Bright is cold drawn and has on flat bar - at first look - a nice smooth flat surface. This can be misleading when you need something actually 'flat'. It's big draw back from a machining point however is that because of it's method of production it has high stresses 'locked' within itself and when a cut is taken these can release to a greater or lesser degree to produce some remarkable distortion. This can catch the unwary - it is best if possible to relieve the stresses by machining small amounts of each side gradually. This problem is not normally experience by turning round bar.
'Black' mild steel on the other hand is 'hot rolled', has varying surface 'qualities' and is not always square on its edges or very round but exhibits little, if any, movement after machining.
Both these materials are ideal for home machining and uses include linkages, con -rods structural parts etc. Preferably use coolant but can be machined dry but cutters will wear quickly
Leaded 'freecutting' mild steels EN1a etc are excellent to machine, a little softer than the above but much easier to produce a really good surface finish, lathe or mill. preferably coolant again.
The lower carbon steels likely to be encountered for instance EN3b EN8 are slightly tougher and used for similar parts likely to be subject to a little more stress.
Higher carbon steels as said can be heat treated to a hard enough state to use as a cutting tool or a surface much more resistant to wear than in it;s soft state. The two most likely to be encountered are Silver Steel - available in vast range of diameters -metric and imperial - and is easilly recognised by it's ground bright silver finish. Gauge plate again in a vast range comes flat normally pre ground all round but some times has cut edges on the wider flats. Despite iits appearance it is not always truly square
Both are tougher to machine than mild steels. Use coolant or cutting fluid
Stainless I have less experience with but some are magnetic, not true stainless but considered 'rustless steel' Some stainless is notorious for work-hardening. It is most important to keep the tool sharp and cutting.
High Speed Steel is what you will use as a cutting tool. It is not normally available to the home user in its soft state and in most instances though not all comes ground either in square, rectangular or round form. It's only 'machinable' by grinding and has the property of retaining its edge under higher heat build up than carbon tool steels.
'Brasses or Bronzes' of which 'gunmetal' is one covers an enomous range. Normally used for bearings or fittings (because of it's propensity to resist corrosion) it is also used for castings of lighter stress components as well as major items such as cylinders. Machining again is relatively easy but requires absolutely sharp tools. A tool previously used on steel - if only once -will tend to 'push' the material as opposed to a clean cut.
Drillng of bronzes can be difficult because of work hardening. Again sharp tooling and small cuts - drilling in steps - will prevent workhardening.
As Tony says the subject is considerable, this scratches the surface and I'm ceratin their will be more o come for you - However I hope this goes a small way to expand that already posted.
The one factor to be borne in mind is that all these different materials have differing cutting speeds - that is the rate they rotate for their diameter on the lathe or the rate of the cutter on the mill - a subject in itself and catered for elsewhere on here as I recall
Kind Regards - Ramon
So far no one has commented on the costs involved. How long is a piece of string I guess. Tony sums it up well in that you need to know what you have. Buying it should guarantee that but not from a 'car boot' sale for instance. Then you do need that experience to be able to make a judgement.
The best of luck in your endeavours James
Edited By Ramon Wilson on 05/03/2010 11:34:05
Edited By Ramon Wilson on 05/03/2010 11:40:53
|3309 forum posts|
As an addition to Ramon's reference to Bright Drawn MS.
Rather than become bogged down in light cuts both sides, normalise the material by heating to red and hold for a short time before allowing to cool slowly, yes you will have a dull blackish surface which will clean readily, but you are now free to cut as you will as most internal rolling stresses will have been relieved. As long as any round products are evenly machined fine, however if you turn any form of cranked or offset shape [eccentric] then you will have to normalise beforehand also.
|Jeff Dayman||05/03/2010 12:00:52|
|1896 forum posts|
I would suggest you spend some time with at least Wikipedia to get the basics of metallurgy.
At this stage of your knowledge the book Machinery's Handbook would be a very wise investment. It has a mountain of info on metals and every other aspect of mechanical work. The sections on drills taps threading etc. are invaluable. This book is pricey but worth every penny. I have used mine almost every day of a 30 year working and modeling life.
|Ramon Wilson||05/03/2010 12:12:06|
778 forum posts
Yes, totally agree with KWIL James, I just didn't want to add too much 'extra' at once. Taking cuts does work reasonably well but it can be a pain as it doesn't always aleviate the stress equally. If theres nothing else though it's the best method of dealing with the problem.
Stress relieving however if you are in a position to carry it out is much the better option on BMS. As an addition to KWILs good advice if you can get hold of some fine fire ash bury the (red) hot metal into it it will cool a lot slower than in air
|147 forum posts|
Perhaps I've missed the point but in 50 years of engineering I have never taken EN8 to be 'mild steel' This would be used for things like axles, cranks and piston rods. This material will take great punishment. Grades like EN57, EN58, 316, 319 are all 'stainless steels' of varying compositions, some magnetic some not. EN19 for keys etc. The list goes on.
I agree with the previous posts in that you should, wherever possible, label your material as to grade. How many poeple have been caught out, (me included), when welding two bits of 'mild steel ' together find out afterwards that the weld 'suddenly' falls apart. Suppliers like M-Machine actually specify the grade of material they are supplying. It would be nice if all raw material suppliers did this as routin. There is a standard colour coding.
Mr C, Would it be possible to have a short series written covering the range of materials we use describing basic composition and best area of use. I seem to remember this was done in M.E. many years ago. Since the introduction of the new codes, (220M07 etc) it must be very difficult for new entrants and indeed the old hands to know what is best to use.
|David Clark 1||05/03/2010 12:50:59|
3357 forum posts
I will put a basic article into Model Engineers;' Workshop.
On sale 19th March.
Hows that for service?
|Ramon Wilson||05/03/2010 13:00:53|
778 forum posts
Er I think perhaps you have missed the point - I don't actually say EN8 to be a 'mild steel' but a 'low carbon steel' which in my experience it is, certainly tougher than mild steel I agree and ideal for the parts you describe.
This subject, we all know, is immense and the idea taken up by DC is perfect timing.
|David Clark 1||05/03/2010 13:08:09|
3357 forum posts
EN8 is a through hardening carbon steel.
It is most often available as round bar.
It is not suitable for case hardening as it may crack.
It is tough but fairly easy to machine.
I asked Dave Fenner to do a basic article on workshop materials
a while back and the result was scheduled to go into issue 162.
Just coincidence that someone asked for an article and it was already in the magazine.
|458 forum posts|
Hi David, would it be asking too much if a cross-comparison to some international nomenclature could be made? I'm sorry the EN numbers are totally useless outside GB. I think the most detailed ones would be the W-numbers (eg . the 'ordinaryl' stainless steel is W-nr. 1.4301) or (more complicated, I admit) the nomenclature referencing the composition (same stainless = X 5 CrNi 18/9 or the free-cutting leaded steel is 9 S Mn Pb 28).
These designations I pulled from my supplier's catalogue.
Same problem with Aluminium. The T-numbers as common in USA - unknown here. When I buy aluminium profiles it is called AlMgSi0.5 There are some other qualities, but this is the most used stuff
I am sure digging in the Internet can solve most of these mysteries, but something written would be useful I think
|1198 forum posts|
So true Hansrudolf, given the power of T'internet, it just shows how lazy some can be. There are so many conversion tables out there for anything you could wish for, but for the sake of pushing one or two buttons. At least YOU are trying. Lay some time aside to have a look down this list :-
I have another one on another which gives a comparison between the old and new designations, It may even give Werkstoff No's , will have a search.
Forgot this one :- http://www.roymech.co.uk/Useful_Tables/Matter/Strength_st.htm
Edited By Circlip on 05/03/2010 19:20:14
Edited By Circlip on 05/03/2010 19:23:55
18924 forum posts
And here is one that will give you 58different standards from 36 countries, think David would have to fill several volumes to cover it all
|147 forum posts|
Thank you David. That is service indeed.
|147 forum posts|
Ramon. it just shows how we each perceive a particular grade of material. Where do we draw the line between lo, med or high carbon? I am looking forward to the article.
|chris stephens||05/03/2010 23:08:31|
|1045 forum posts|
I think you will find that EN8, described as a "40" carbon steel, is classed as a "medium carbon steel" . Low carbons are EN1A, EN3B and EN32B. Or do you mean you have found it to be "low" compared to say EN31 or BD2.
|James Veitch||06/03/2010 02:53:52|
|16 forum posts|
Thank you everyone for your contributions to this thread, and thanks David, I'm looking forward to the article in MEW.
The comments given above show that, even between experienced machinists, there is controversy, if not confusion. As a novice I am totally confused. Admittedly I pick up odd bits of steel where I can find them (due to cost) and try machining them. Some work and some eat up my tools and send shudders through my equipment. I guess what I would wish for in a MEW article would be some sage advice to KISS, keep it simple, if that's possible. I know there are a thousand spices but I'm just doing basic cooking. I'm reminded of the old "80/20 rule," that is 80 percent of the work is done by 20 percent of the workers. Is this true with engineering metals too? Like 80 percent of the time when making "X" a novice should use "Y" type steel so find some and stick to it till you gain some experience. Talking of experience I appreciate the advice given above on how to tell one type metal from another. That gives me something to look out for. In geology there is a well known set of field test used to identify what kind of rock you have in your hand. You start by trying to scratch glass, then scratch the rock with a pen knife, and so forth. Is there even a rough procedure used for metal. Example, step one: colour, step two: heft (is it heavier or lighter), three: is it magnetic, four: does it scratch deeply, etc.
Oh, well, just babbling, told you I was confused.
Once again thanks for all the very fine comments.
|147 forum posts|
James, Don't worry about being confused, we have all been there. For the kind of parts that we make at home the spec of the material is not vital MOST of the time. Just remember its a hobby so enjoy yourself making the parts.
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