# Best Types of Metal for which job?



## AssassinXCV (Jun 26, 2011)

Browsing through this forum i've read people mentioning they used a certain type of steel (example but might not be a real grade:  6506 Steel) What does that mean? Is the higher the number, the harder the steel is? Should i not have too hard of a metal since it will be harder to machine?

If i wanted to make a model internal combustion engine what material should i choose?

I just recently got a metal lathe, and i hope to get some of the parts made before i get a mill (parts such as the crank shaft, pistons, piston retaining pins). so i hope to know which material to use, so that i can start to gather what i need.

Anyone with experience with different grades of steel, or other metals, please share your knowledge.

Thankyou,

Ian


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## Rayanth (Jun 26, 2011)

Ian,

a typical engine is made from many different types of metal, depending on the particular need. For example, Steel holds up to stress better, so it is typically used for connecting pins, or any area where a great deal of stress is built up quickly. It also resists wear, and maintains its tolerances for longer, so may be used in areas where that is important as well.

Aluminum (aluminIum if you're european or australian) is lighter, cheaper, and easier to machine. Being a softer metal it is able to be machined at almost any cutting speed (within the usual sensible limitations), and thus is much easier to work with. For Internal Combustion engines, most components are made from aluminum. 

The numbers (6065, 7075, etc) are the Alloy. 6065 is probably the most common alloy for aluminum. PURE aluminum is insanely soft and almost worthless as a working material. it can be scratched with the back of your fingernail, it's that soft (however 99.9% pure aluminum does have its uses, see later). So it is mixed with other metals to strengthen it for various applications. 6065 might be considered an 'all purpose' while 7075 is used more in the aviation industry as it resists corrosion a little better. With aluminium you will also have a 'T' number, such as T3 or T6, which indicates its heat-treated hardness and is an industry standard scale. 

I am not familiar myself with the numbering system for steel, as i don't use it at work, but I am sure others here can help you with that.

The choice of materials is ultimately going to boil down to the application and type of engine. a Steamer is more likely to use brass, while an air-powered could be made entirely of brass or aluminum or almost anything, really. An internal combustion is most likely going to be a mixture of things but most are primarily aluminum, with steel for the pins, crankshaft, and counterweights. 

- Ryan

As an aside, I mentioned that 99.9% pure aluminum, despite its worthlessness for machining, does have uses Commercial airplanes use a regular aluminum alloy for the skin, that is then coated in a layer of 99.9% pure aluminum that's only a couple of thousandths of an inch thick at the most. Aluminum, if used properly, when it corrodes creates its own corrosion inhibitive layer. In other words, as the pure aluminum layer starts to corrode, the oxidation actually performs an additional protective layer for the regular skin underneath, that PREVENTS it from corroding even further.

The more you know ;D


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## AssassinXCV (Jun 26, 2011)

Wow, thanks.

Would you enlighten me about the numbering for Aluminum then? what's the difference between 6065 and 7075?

Thanks,

Ian


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## gmac (Jun 26, 2011)

Ian;
For the typical model engine, here's a Readers Digest answer;

cylinder heads, blocks, housings  6061 aluminum (7075 aluminum for more strength but more money)
connecting rods, pistons       6061 aluminum (2024 aluminum if you want to spend more money)
cams, shafts, crankshafts      C1144 Stressproof Steel (reasonable strength, reasonable machinability and cost)
valves                   303 Stainless Steel 
cylinder barrels (air cooled)     6061 aluminum or 12L14 steel (easy machining on small lathes) or cast iron
bearings, bushings           brass or 660 bronze

There are many alternatives - but these keep your stock to a minimum as well as cost. Most of these engines are not overly stressed nor are they run for long periods so it's hard to justify using higher performance metals. Suppliers like Onlinemetals.com have pricing that allows you to compare costs for the different alternatives. And be warned that many times your shipping costs will exceed the material costs! Also be aware that just because a material is listed doesn't mean they have it in stock, or will sell it in small quantities. Better to work with the common materials to start.
The suppliers also have charts describing the characteristics/specifications of the materials. Try the machine shops in your area for scraps since you are not after large quantities.

Cheers
Garry


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## gmac (Jun 26, 2011)

Some basic data;

http://www.onlinemetals.com/aluminumguide.cfm

http://www.onlinemetals.com/productguide.cfm

Garry


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## Tin Falcon (Jun 26, 2011)

The technical answer courtesy uncle sam  USAF 1-1A-9 use of aerospace metals http://www.robins.af.mil/shared/media/document/AFD-091006-039.pdf

Mcmaster carr also has pretty good general data about the materials they sell
go to there web site type steel (or aluminum or brass etc) in the search bar and you will get a couple good pages of info. 
http://www.mcmaster.com/#steel/=cww3sr

for the most part with models the quick list
6061 aluminum. 
260 360 brass easy to machine
12L14 steel ,O-1 or W-1 drill rod for shafts
bronze for bushings 
durabar cast iron easy to machine self lubricating good for cylinders and sleeves. 

you want material that is easy to machine. strength and weldability may be important factors for lager IC engines that have been built here. 
Fly wheels can be just about anything I have made them from aluminum brass plastic and cast iron. 
fly wheel material considerations cost and weight. heavy and cheap and easy to machine. 
Download and look at plans this is another good way to learn what material for what application. 
same plans will say any material this mean the material choice is not critical this is the case for may small models. 
Tin


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## Mainer (Jun 26, 2011)

@Tin, isn't 360 brass the easily-machinable one, not 260? 

A bit more: The steel numbering,at least some of it, sort of works like this: XXYY, where X is the alloy and YY is the amount of carbon. So 1018 is a plain carbon steel with 0.18% carbon, which is too low for the steel to be hardenable. 1045 has 0.45% carbon, and that's enough carbon so the steel hardenable by heating and quenching.

L designated leaded -- a small percentage of lead is added to improve machineability. A common one is 12L14, or the brand name "Leadloy" steel. Although the stuff machines like a dream, I don't particularly care for it because it has a great tendency to rust.

Then there's the 4000 series -- 4140, 4340, etc., and dozens if not hundreds more.

My favorite steel is probably 1144. It machines to a nice finish, and it's strong.

Aluminum numbering works the same way, I think, although aluminum numbers often get a Tx suffix, like T4 or T6, which designates how it was tempered. 

Somebody has already mentioned the materials characteristics descriptions in McMaster-Carr. They provide a good quick summary. Or, go to an engineering library and find shelves of books on metallurgy....


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## Tin Falcon (Jun 26, 2011)

whoops you are right Mainer i will correct that
Ultra-Machinable Brass (Alloy 360)

The standard by which copper, brass, and bronze machinability is measured, Alloy 360 is also known as free-machining brass. Its lead content prevents successful welding but does provide lubrication to enable high-speed machining such as drilling, milling, and tapping.

260 is formable. 
Tin


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## jonesie (Jun 26, 2011)

ian, do what i do. at work i have to work with plans other then from the U.S. and have to make replacement parts for machines, and they will sometimes list material that is different then U.S. numbering so i will do a google search and look up the steel or other material,and it will give you all the info. you need and more.it will give you hardening info, what to use it for , what it is made of and other subsitutes. give it a try jonesie


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## AssassinXCV (Jun 26, 2011)

Thanks alot everyone, I'm going to go with what Garry mentioned to keep it simple. My next project i can choose which metals i want after getting some exp with this project.

Cheers,

Ian


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## Lakc (Jun 26, 2011)

AssassinXCV  said:
			
		

> Wow, thanks.
> 
> Would you enlighten me about the numbering for Aluminum then? what's the difference between 6065 and 7075?



A hell of a lot of money. 8)

Somebody had to say it 

7075 is wonderful stuff, stronger then many steels, machines great, and designed to drain your wallet.


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## Tin Falcon (Jun 26, 2011)

6061 common structural grade aluminum
2024 aircraft grade contains copper extra work to anodize.
7075 jig plate or marine grade. 
Tin


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## Rayanth (Jun 26, 2011)

Sorry I came back late, just posting to apologize for my misleading '6065' in my first response, rather than '6061' as others posted. It is indeed 6061, it was just late and my mind couldn't separate numbers quite that well 

I'll leave the rest of the discussion in the hands of the experts who have their heads on a little straighter than mine  :big:


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## AssassinXCV (Jun 26, 2011)

Just checked out OnlineMetals.com, the 6061 2"x2"x12" is $23 :O Just realized how expensive metal is.
; though looks to be cheaper than trying to get thick UHMW.


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## Rayanth (Jun 26, 2011)

This is why I was looking into alternative 'practice' materials, in a question I asked in the Q&A forum. I knew this wasn't going to be a cheap hobby, but I'd like to keep costs down where I can 

- Ryan


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## Dave G (Jun 26, 2011)

I pick up alot of al. at engines shows and flea markets at times. Some of it will be marked with the type it is and some will not. If it isn't marked I will look for blue paint which is 6061. Most suppliers will paint the ends of the bar for identification, this applies to steel as well and probably can be looked up on the net. I use 6061 for almost everything but highly stressed parts like connecting rods. For these I use 2024 al. 1144 stress proof is what I use for crankshafts and for cylinders I use 12L14. 4140 can be bought in a soft state or preheat treated to 28-32 Rockwell C scale. I use alot of the preheat treated 4140 for anything requiring good strength or for good wear properties. If you have a rigid machine and good cutting tools, 4140 at 32RC is not very difficult to machine and polishes well. For anything that will need to be harder than 32 RC, such as a governor trip I will use O-1 drill rod and flame harden myself. My valves are made from 303 SS and seem to hold up well. Stay away from 304 SS, This steel will make you pull your hair out. I once received a sizeable suggestion award where I worked for substituting 303 for 304SS on a job we were doing. The machining time was reduced 75% and the tooling costs were reduced as well. You shouldn't weld 303 though. For bushings I use 660 bronze. 1018 steel is called Cold Rolled at times and is a mild steel that is good for many parts but has a tendency to move around after machining because of the process used to make it. Hot Rolled steel won't move as much after machining. 
 Be careful when making parts from O-1 tool steel. I have made parts with this steel and hardened it in a furnace properly and a week later it will be warped beyond use. 

During my apprenticeship I was assigned to the tool heat treat dept for a few months. There we learned to identify steel types by the spark it created when touched to a grinding wheel. I have a small box of sample steels that are marked as to type, When I am unsure of the type of steel I may have I will spark test it and compare to my samples. 
 Don't be too hard on yourself when trying to learn this stuff as there is alot to learn and some of my best naps where during metalurgy class, Dave


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## shred (Jun 26, 2011)

Be careful with color codes-- there is no standard to them (or there are a lot of different standards, same mess either way); I have 6061 with blue ends and 7075 with blue ends...

For 90+% of what we do, the exact metal doesn't really matter. Where it does, often the engine designer will call it out. 

Off the top of my head, the primary concerns for the HMEM types are which metals wear well when rubbing on each other and also what is needed for highly stressed and/or thin section parts. Machine-ability, availability and cost is also a concern (see: 304 stainless, avoiding thereof)


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## AssassinXCV (Jun 27, 2011)

This is great! I'm sure i'll learn lots in my metalurgy class next semester.

Since i just got a lathe, but not a mill yet (maybe later next month?) I can start making some of the parts for the engine that require the lathe: 12 valves, crankshaft, 6 pistons, flywheel, 12 push rods if i decide to go with the OHV design over other OHC.

^^That should keep me busy for a while.


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## AssassinXCV (Jun 28, 2011)

If someone can quickly reply before i leave to pick up some metal, my pistons will be 3/4" Diameter made with 6061 AL. Should i by 7/8" Rod so that i can have a clean surface by taking a layer off? Even if no reply, i'll go with that just to be safe.


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## Rayanth (Jun 28, 2011)

AssassinXCV  said:
			
		

> If someone can quickly reply before i leave to pick up some metal, my pistons will be 3/4" Diameter made with 6061 AL. Should i by 7/8" Rod so that i can have a clean surface by taking a layer off? Even if no reply, i'll go with that just to be safe.



I believe it is recommended to go oversize, and trim to form, as you can't really guarantee the dimensions are true when you pick it up. Better safe than sorry.

- Ryan


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## AssassinXCV (Jun 28, 2011)

Just got back now. some how i spent 3hrs there :big: mainly just looking around. Came back with 8 stainless steel rods 3/8" x 4" (for the valves), and a 5 foot piece of 1" 6061 aluminum rod ($5). I'll have to see how well that cuts with my wood bandsaw with the metal cutting blade on it, so that it will actually fit on my mini lathe.

EDIT: Was able to get through half of it with a hacksaw and WD-40 in 5min, then bandsawed the rest in 2min. not bad.


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## Swede (Jul 30, 2011)

This is a good thread packed with excellent information. As I've gained experience over the years, like many others, I've found some favorite metals that can do most of the jobs we need.

One thing on metals cost - we generally work on a very small scale. If I'm welding up a flat bed trailer, I'm concerned about materials cost. But for a small engine, I'd rather have a superior metal, even if it costs a bit more. Especially if a part is more complicated, as a superior metal can contribute to fewer mistakes and less scrapping.

Maybe already mentioned - watch out for the stresses in steel when you have an asymmetric part to machine. Let's say you want to machine a "U" shape using a mild steel flat stock. That C1018 cold-drawn flat stock looks really nice and clean, but cut out the inner portion of the "U" and it'll warp like a pretzel. Use hot-roll instead. You can tell the difference in that hot-roll has a black, scaly surface, while cold drawn (cold roll) steel has a pleasing, clean surface. This is all very applicable to crankshafts especially, and hot roll 4140 or 4340 is the best choice.

The black mill scale can be removed from hot roll or heat treated steel with a pickling solution. Works like a charm. Salt & Vinegar, diluted muriatic (HCl) acid, sulfuric acid, all work. But watch out for hydrogen embrittlement.

For mild steel, why use 1018 when 12L14 is available? 12L14 is glorious stuff.

With aluminum, I now rarely buy 6061 when 7075 is available. Yes 7075 is expensive and scarce, but what a material. Machines like a dream, and I will readily replace a mild steel component with 7075-T6, as the aluminum is both harder AND stronger than C1018.

Tool steel... for me, it's all A-2, all the time. For years, I used O-1 which is good steel, but the heat treatment... what a pain! Coat with a borosilicate glass like keep-bryte, or watch 0.008" fall off the part as ugly scale. Instead, the A-2 parts go into a stainless foil envelope. The envelope is heat treated, removed from the furnace with tongs, and swished through the air or set on a drill press table. The parts come out grey, purple, blue, and squeaky-hard. And A-2 tempering temperatures are very high, typically 700 f or more to get the same hardness as O-1 would see at 350. This means A-2 parts can see service under higher temperatures.

Brass/bronze - if given a choice, give me bronze, purely for cosmetic reasons! What is more lovely than aged bronze, buffed occasionally with a soft cloth, rather than a nasty brass that corrodes more readily and can turn green?

That's all I can think of for now. Materials can be very complex, especially when dealing with hardening carbon steels. A good furnace is a huge boon to a home shop, and opens up all sorts of possibilities for advanced work.

Mild steel: 12L14
Med. carbon steel: 4140
Aluminum: 7075, 2024, 6061 in order (keep welding and/or anodizing in mind, that may force a choice)
Tool steel: A-2 (O-1 or W steels are fine if no heat treatment is needed.
Stainless: 303, she's for me... ;D


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## JDRay (Aug 2, 2011)

I'm slowly refining my first engine design (simple swashplate design), and am about to go purchase materials to start making it. Initially it will run on air, but I'd like to be able to run it on steam eventually. I've read on this forum that brass will leach out its zinc and eventually deteriorate to the point of unusability, or worse, critical failure. I thought about steel, but am not sure I want to deal with a somewhat-difficult material for my first machining job. Then, of course, there's aluminum. From reading this thread, it seems like 7075 aluminum would be tough enough to stand up to the stresses the push rods will encounter, particularly if I harden them. But then they'll be harder than the swash plate, which will be made out of the same material as the cylinder block (same piece of bar stock), which would mean that the cylinder block is the same hardness as the pistons/push rods. Is this bad? How about making the whole thing out of 7075 and only hardening some parts (pistons and swashplate)?

For reference, here's the latest iteration of my engine design. Mind you, I'm new at this, and am probably overlooking a few critical factors. Any feedback is welcome.  

Thanks.

JD


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## Groomengineering (Aug 2, 2011)

Hi JD. 

From my somewhat limited knowledge zinc depletion seems to only be a problem in thin wall boiler type applications, a chunk the size of your cylinder should outlast us all. If it were me I would use cast iron for the cyl, steel for the swash and valve, and either steel or brass for the pistons. I would also add a guide plate on top of the cyl for the piston rods. Not saying this is the best/only way..... Just my $.02. ;D

Nice looking design btw.

Cheers

Jeff


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## JDRay (Aug 3, 2011)

Thanks for the tips. Actually, after reading some yesterday, I think I'm going to make it out of 416 stainless.

I modified the cylinder so it has guide holes on the push rod end, added some springs to keep the push rods against the swash plate when they're not under load to reduce clatter, and put in an input tube and exhaust manifold. Oh, and I modified the valve plate some so there's less surface to create friction against the rotating cylinder plate. The center rise around the axle is actually 1/64" taller than the rest, meaning that the valve plate will never actually contact the cylinder block. If 1/64" is too much gap and I get leakage, I can always mill that down a bit and tighten things up. I think the design is essentially done. As far as I can tell, it should scale well. With three pistons pushing at all times, it should develop a reasonable amount of power for its displacement (half inch piston with inch and an eighth stroke, six pistons overall).

I'm having a lot of fun with this, and I haven't even cut metal yet.

Do you think I'd be better off with brass pistons rather than stainless? I was thinking to make the pistons out of the same bar stock I use for the axle.

Thanks.

JD


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## NetworkMetals (Dec 5, 2011)

7075 Machines a lot better than 6061 in terms of hitting tolerances and surface finish. Especially on smaller lathes and older bridgeports.


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## Mosey (Feb 28, 2012)

Swede  said:
			
		

> This is a good thread packed with excellent information. As I've gained experience over the years, like many others, I've found some favorite metals that can do most of the jobs we need.
> 
> One thing on metals cost - we generally work on a very small scale. If I'm welding up a flat bed trailer, I'm concerned about materials cost. But for a small engine, I'd rather have a superior metal, even if it costs a bit more. Especially if a part is more complicated, as a superior metal can contribute to fewer mistakes and less scrapping.
> 
> ...


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## Ken I (Feb 28, 2012)

Keeping costs down....Hmmm we all want to do that.

Materials scrounged form scrap yards and scrap bar ends etc from production shops (particularly if you can ID the grade) go a long way to keeping costs down.

But.... and this is a very big but - mystery metals are all good and well for small and uncomplicated parts but if you are going to be investing a lot of labour into something like a crank or block it is best to spring for a correctly speced piece of stock.

2c

Ken


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