Fasteners: Black Oxide or Zinc Plated?
 

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?

Re: Fasteners: Black Oxide or Zinc Plated?
 

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.

Re: Fasteners: Black Oxide or Zinc Plated?
 

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

Re: Fasteners: Black Oxide or Zinc Plated?
 

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.

Re: Fasteners: Black Oxide or Zinc Plated?
 

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

Re: Fasteners: Black Oxide or Zinc Plated?
 

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.

Re: Fasteners: Black Oxide or Zinc Plated?
 

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.

Re: Fasteners: Black Oxide or Zinc Plated?
 

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)

Re: Fasteners: Black Oxide or Zinc Plated?
 

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.

Re: Fasteners: Black Oxide or Zinc Plated?
 

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

Re: Fasteners: Black Oxide or Zinc Plated?
 

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

Re: Fasteners: Black Oxide or Zinc Plated?
 

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.

Re: Fasteners: Black Oxide or Zinc Plated?
 

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.

Re: Fasteners: Black Oxide or Zinc Plated?
 

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?

Re: Fasteners: Black Oxide or Zinc Plated?
 

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. :D

Re: Fasteners: Black Oxide or Zinc Plated?
 

Depends on your goal: corrosion resistance or price? Black oxide is generally less costly, bright zinc is more corrosion resistant. Consider where you live: Desert or rainforest?

Re: Fasteners: Black Oxide or Zinc Plated?
 

Are black oxide from a local hardware store typically similar in strength to alloy steel black oxide from McMaster? I've always assumed they were, but I have heard otherwise, so I always wondered.

Re: Fasteners: Black Oxide or Zinc Plated?
 

I know that in Florida things will rust just about immediately if they aren't kept in a climate controlled building.

Re: Fasteners: Black Oxide or Zinc Plated?
 

Our team standard is metric fasteners in black oxide, imperial in zinc. Helps with the inevitable sorting.

I'll be happy when everyone has moved over to metric. I'll be dead though :eek:

Re: Fasteners: Black Oxide or Zinc Plated?
 

Or get covered with mildew or mold if non-metallic.

Re: Fasteners: Black Oxide or Zinc Plated?
 

Mcmaster has a wider selection and probably a wider quality range. But the equivalent grade would be the same. I mostly use grade 5 which is in the middle.

Commercial bolt threads are almost universally better than shop made. The commercial threads are rolled rather than cut & leaves compressive strain in the threads.

Re: Fasteners: Black Oxide or Zinc Plated?
 

Sorry, not super familiar with the manufacture of bolts, but could you explain what you mean by "compressive strain?"

On another note, in 2012, 2220 used grade 5 stainless 1/2-20 (if I remember correctly) bolts as axles on our robot. We made it the entire season without bending an axle significantly. Not saying it was a good idea, but it worked in our case.

Re: Fasteners: Black Oxide or Zinc Plated?
 

http://en.wikipedia.org/wiki/Shot_peening this has some decent non-jargon explanation of the principle.

Essentially introducing residual compressive stress on the surface through plastic deformation leads to prevention of crack propogation, increasing fatigue life.

With a rolled thread you are also increasing strength through cold working (strain hardening) the material, which improves both fatigue and tensile strength, but makes the material more brittle. This is also why form tapped holes are stronger than threaded holes produced with a cut tap.

Re: Fasteners: Black Oxide or Zinc Plated?
 

To use the words I think in, my best guess as to what that means is you whack a thing so that each little bit of the surface wants to push itself apart/press against its own neighbor, which prevents cracks because cracks get pushed back together by this pushing.

Sorry if that was too silly, thinking in simple words helps me.

Re: Fasteners: Black Oxide or Zinc Plated?
 

Thank you very much for the explanations. That helped my understanding a lot.

Re: Fasteners: Black Oxide or Zinc Plated?
 

Not a bad way of thinking of it. Shot peening parts does something similar & is also specified when fatigue cracking might be an issue. (not for threads so i am drifting off topic) Rolling the thread also gives is a better surface finish than a cutting tool that leaves little micro cracks the form stress risers.

Re: Fasteners: Black Oxide or Zinc Plated?
 

I just like black. It looks better on aluminum so you can always tell when something has fallen out.

Re: Fasteners: Black Oxide or Zinc Plated?
 

Not usually during season, but I know 79 had some issues with cylinders rusting after a few years. The 07 bot in particular has a lot of rust on the cylinders.

Re: Fasteners: Black Oxide or Zinc Plated?
 

The only rust I've seen of any consequences are on robots improperly stored. So unless you're planning to store them in an outdoor location or unsealed space, you should be ok with whatever.

Re: Fasteners: Black Oxide or Zinc Plated?
 

Our workshop has humidity problems when the AC is off in the summer. All of our black oxide screws have surface rust on them.

Re: Fasteners: Black Oxide or Zinc Plated?
 

If you have a local Fastenal, it's often a better option price-wise than the hardware store, if you're buying boxes of 100, which we always do. #10 and 1/4" are the ones we buy in varying lengths. #6 and #8 we cut to size.

And -- WRT the question -- black oxide.

Re: Fasteners: Black Oxide or Zinc Plated?
 

For 3309 who is based out of Anaheim, CA; it gets very humid at night when the fog rolls in. we always have steel parts rust. We have to paint steel right away to avoid rusting by the time events start. we have had black oxide rust out on screws we frequently had to take apart. But black looks nice, so we just replace a lot of screws. The 2012 and 2013 robots have rusting issues, 2013 can't run its climber anymore.

I am always surprised how much water we have to drain out of our robot's pneumatic system after practice. Even when we are machining parts inside we can see condensation form after we leave them on a table.

Re: Fasteners: Black Oxide or Zinc Plated?
 

More often than not, Black Oxide Fasteners win out over Zinc Plated for most FRC applications in my book. With that being said, outside of FRC, Zinc Plating, specifically Zinc Chromate, is my preferred choice.

That being said, if aesthetics are of concern, you really need to figure out if you robot is going to see ANY moisture during it's operating (when it needs to be pretty) life. If so, Black Oxide can be a bit annoying, since it'll show rust fairly quick, and Orange isn't exactly hard to see on Black...

There's also "Black Zinc", which is almost the best of both worlds, the aesthetics of black hardware, with the corrosion resistance of Zinc (usually better than "Clear Zinc/Regular Zinc) and depending on the exact process, as good or better than Zinc Chromate. ("Black Zinc" is often Zinc Chromate with additional Dye to darken the finish).... But it's not easy to find COTS hardware (reasonably priced) that's finished with Black Zinc, so unless you're willing to send a bunch of hardware to the plater, might be better off to forget about it.

Re: Fasteners: Black Oxide or Zinc Plated?
 

We are almost all Black Oxide because we primarily use, Thread-Locking Alloy Steel Socket Head Cap Screws from McMaster. They are a little more expensive than standard screws but we don't generally have to worry about them falling out. We do have a selection of standard Black Oxide bolts for prototyping.