Originally Posted by DELurker (Post 1312009)

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from matweb.com...
1018 steel versus 6061-T6 aluminum versus ASTM A526 galvanized steel

I could never bring myself to use aluminum for a shaft. It is too weak (comparably) to take that shock and torsion loads, as well as being more prone to unannounced catastrophic failure over steel (steel bends and then breaks ... aluminum has a much smaller deformation period before it snaps under the same loads). I'd rather use a steel shaft so that I could press-fit it into a bearing. The surface properties of aluminum just aren't good enough (at least for me) for rotating or direct-contact sliding.

Originally Posted by yash101 (Post 1311895)

I wouldn't say "significantly stronger" but yeah, it can be stronger per unit of weight.

Originally Posted by DELurker (Post 1312009)

I disagree, although I will point out that stainless steel (302, 303, 304, 316) is a specific and (typically) less durable subset of steels (without getting into hardenable stainless such as 440C). The 3x price differential on stainless makes it less than desirable for teams to work with in the raw, aside from the additional tooling needed to properly work it. However, I will support my original contention with the following links and tables...

Reference #1
Reference #2

from reference #2...
........................................Aluminium. ................Steel
Density, ρ kg m−3...............2,700......................7 ,800
Young modulus, E N mm−2....70,000....................210,000
Shear modulus, G N mm−2.....27,000....................81,000
Poisson ratio, ν.....................0.33........................ 0.3

from matweb.com...
1018 steel versus 6061-T6 aluminum versus ASTM A526 galvanized steel

I could never bring myself to use aluminum for a shaft. It is too weak (comparably) to take that shock and torsion loads, as well as being more prone to unannounced catastrophic failure over steel (steel bends and then breaks ... aluminum has a much smaller deformation period before it snaps under the same loads). I'd rather use a steel shaft so that I could press-fit it into a bearing. The surface properties of aluminum just aren't good enough (at least for me) for rotating or direct-contact sliding.

Originally Posted by artdutra04 (Post 1312074)

I've been using 2024 and 7075 for shafts on FRC robots since I was in college in 2010, and have never had one fail. Plus, I absolutely love machining 7075 aluminum on mills and lathes. With good carbide tools, you can machine it like a hot knife through butter, as it does not have any of the galling issues that plague softer aluminum alloys. It's my second favorite material to machine after Delrin.

Originally Posted by artdutra04 (Post 1312074)

Originally Posted by magnets (Post 1312108)

You're not looking at the right alloys. AndyMark steel parts are 4140 stainless with a yield strength of 60200 psi, but 7075 aluminum (vex pro parts) have a yield strength of 78,000 psi. Also, I don't really follow the shaft argument. Any 3 CIM gearbox that I've ever seen uses an aluminum shaft. Same with our climber.

Originally Posted by DonRotolo (Post 1312126)

We're all shafted now and then.:o

We've digressed significantly. I think the OP has a better idea of how to work with Galvanized Steel, and aluminum versus steel probably deserves a thread of its own. Or?

Originally Posted by jman4747 (Post 1312154)

Also on the steel vs 7075 shafting thing, personally reducing drive train inertia is a priority... really dislike drive train inertia.

Originally Posted by Ether (Post 1312218)

What do you mean by "drivetrain inertia" in this context? Are you concerned about the moment of inertia of the output shaft of your gearbox? And if so, why?

Originally Posted by jman4747 (Post 1312297)

I mean to say the total mass of all my moving parts and the friction between them to increase the efficiency of the drive train itself.