Fasteners: Black Oxide or Zinc Plated?

[craigboez]

Over the past few years we have standardized on our fastener sizes, but so far we have not chosen a standard finish. For most SHCS, BHCS, HHCS, etc, the options for carbon steel bolts are either unfinished/black oxide/phosphate, or some sort of plating like zinc.

I tend to like the plating because of the corrosion resistance and nicer look. They are more expensive, and sometimes available in fewer lengths. What does your team use?

[asid61]

I don't usually see corrosion resistance being a problem, but they're both super strong. Generally I have no preference and go with what's cheaper.

[AllenGregoryIV]

Pretty much always Black Oxide because they are cheaper but we have some zinc floating around as well.

[RoboChair]

Chromium plated hardware, be blingin' in gold! I love me some Mil spec hardware.
"Deadly deadly chromium."

But really, Stainless! It's great if you can get quantity discounts.

[asid61]

Originally Posted by RoboChair

Chromium plated hardware, be blingin' in gold! I love me some Mil spec hardware.
"Deadly deadly chromium."

But really, Stainless! It's great if you can get quantity discounts.

Why stainless, out of curiosity? Isn't it weaker than black oxide?

[Cory]

Originally Posted by asid61

Why stainless, out of curiosity? Isn't it weaker than black oxide?

Almost 3x weaker than alloy steel fasteners.

There's no reason to use stainless fasteners on a FRC robot unless they're the only thing you can buy.

We prefer the look of black oxide to zinc coated.

[BrendanB]

We typically purchase black oxide bolts since they are cheaper and the black hardware does look nicer on the robot. We purchase zinc plated nuts because our team colors are black and yellow so black and gold hardware looks nice.

[RoboChair]

Stainless is an all around good fastener, but if you want strength then it will not be your best choice I agree. It is still stronger than your average hardware store box of bolts. Also I messed up my previous post meant to say "Cadmium" plated(which is yellow/gold in color)

My humor aside this is my overall ranking of hardware from a strength and aesthetic outlook.

Cadmium Plated Mil Spec hardware(yellow gold color with an insane amount of sizes to choose from)
Black Oxide
Stainless Steel (relative tensile strength is 41% black oxide, 116% Grade 2 cheap steel bolt, 58% of Grade 5)
Zinc Plated(I don't really care for zinc besides it being dirt cheap)

[FrankJ]

The finish really doesn't relate to the strength. Mil-Spec gets you quality control that your average bolt doesn't get, but unless it is surplus, you are also paying for documentation you don't need. Cadmium is more expensive because of environmental issues. You really don't need it unless we finally get a water game.

[Cory]

Originally Posted by FrankJ

The finish really doesn't relate to the strength

In the context of this discussion it does, since it represents alloy steel (black oxide/zinc plated) vs stainless.

[DampRobot]

Black Oxide. Even if it isn't stronger, it still looks way cooler.

[FrankJ]

The OP was black oxide vs zinc plated. There are also other ways to get black including zinc chromate. That can be steel or alloy steel, stainless would be neither. (OK stainless is a steel alloy but you don't typically plate it) Personally I kinda like the black. I wouldn't use stainless unless I happen to have them on hand. In terms of typical FRC it is more of a preference than an engineered decision though.

[Travis Schuh]

Originally Posted by asid61

I don't usually see corrosion resistance being a problem, but they're both super strong. Generally I have no preference and go with what's cheaper.

I am curious to see if teams in humid places like Florida have any corrosion issues, particularly once a robot has been retired for a few years. Robots in California are hardly the most rigorous use case.

[Richard Wallace]

Originally Posted by Travis Schuh

Robots in California are hardly the most rigorous use case.

Kinda like classic cars in California. They last a lot longer than their counterparts in Michigan.

Back on topic: Black Oxide. Best cost, looks cool, what's not to like?

[JesseK]

When we first started using hex stock on our robots, one of the students joked that we should make all of our own bolts from the hex so we could then anodize them black or purple and achieve a nice weight savings. I'm thinking we should try it on a couple of non-critical connections just for giggles.