Best Types of Metal for which job?

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AssassinXCV

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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.
 

Swede

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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

 

JDRay

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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

Swash Plate Motor.png
 

Groomengineering

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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
 

JDRay

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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

Swash Plate Motor.png
 

NetworkMetals

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

Mosey

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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.

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.

OK, I like cold rolled for it's nice, smooth surface appearance. I don't have to work to make it look nice. So, if I use hot-rolled, and pickle off that scaly surface, how do I make it smooth and nice looking? I don't have a surface grinder. I don't want to machine a flat bar just to make it nicely finished, so what do I do?
I am making brackets for DRO's on my mill, that do not require much machining or strength, just some threaded holes and a large cutout along 1 side. Or do I go with 7075 or even 6061? Then with Al. I have to paint it, which is OK.

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
 

Ken I

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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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