Fasteners: Black Oxide or Zinc Plated?

[DonRotolo]

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?

[jeremylee]

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.

[Cory]

Originally Posted by Travis Schuh

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.

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

[JCharlton]

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

[Ether]

Originally Posted by Cory

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

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

[FrankJ]

Originally Posted by jeremylee

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.

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.

[cadandcookies]

Originally Posted by FrankJ

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

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.

[Cory]

Originally Posted by cadandcookies

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.

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.

[VioletElizabeth]

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.

[cadandcookies]

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

[FrankJ]

Originally Posted by VioletElizabeth

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.

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.

[Al Skierkiewicz]

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

[Andrew Schreiber]

Originally Posted by Travis Schuh

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.

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.

[pyroslev]

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.

[mman1506]

Originally Posted by Travis Schuh

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.

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