Aluminum Cornhole Boards

We have a great patio for playing cornhole. Here’s the view from our patio on a clear day:

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We started out by buying a “Franklin Sports Fold-N-Go Bean Bag” set:

Franklin Sports Fold-N-Go Bean Bag

The problem is that we left them outside 24/7.  Since they are made of very low-quality wood, they quickly began to rot.  I attempted to prevent further deterioration by sanding and painting them with a waterproof paint that matched our patio furniture, but eventually mother nature broke them down and now they look like this:

2014-02-09 16.10.042014-02-09 16.10.18

Very sad.

So I decided to design a new set of cornhole boards that would be impervious to the elements. At the same time, I wanted to design them to be completely sustainable by applying cradle-to-cradle design principles. My thought is if someone like me (who is not a professional engineer) can design and build a product that is completely sustainable, then real engineers who work at real companies have no excuse to not build products to such a high design standard.

Before I got started, I laid out my key design criteria:

  1. Completely weatherproof – can be left outside in the elements for years without any deterioration
  2. All materials must be sustainable “technical nutrients” that are infinitely recyclable with no degradation (no “downcycling” or C2C Banned Chemicals)
  3. No manufacturing waste – all manufacturing byproducts must be completely recycled.
  4. Simple to manufacture – I should be able to manufacture the boards in just a few hours using simple machine shop tools.
  5. Aesthetically pleasing – hopefully they will still be nice to look at if form follows function.

Sustainable Materials

To be truly “cradle-to-cradle” the board must be made out of a material that produces very little damage during its initial production, has a nearly infinite usable life, and can be infinitely recycled after its useful life.

Materials like plastic and uncertified hardwoods fail the first criteria – they produce too much environmental impact during their initial production. On the other hand, using recycled plastic or recycled hardwood would eliminate this concern.

Materials like iron or steel fail the second criteria – they will corrode over time and thus don’t have an infinite usable life.

Finally some plastics and softer woods that must be lacquered or painted to prevent rot fail the third criteria – they are not able to be 100% recycled.

There are a number of material options for building a sustainable cornhole board.

  • Aluminum – aluminum is infinitely recyclable without any degradation. It never needs to be “downcycled.” Aluminum is also extremely resistant to corrosion, as aluminum oxide produces a thin protective layer, leading to a dull finish but production against further corrosion.
  • Stainless steel – stainless steel is infinitely recyclable and extremely resistant to corrosion.
  • Certified wood – wood is renewable and can be grown sustainably.
  • Bioplastics – Instead of being made from oil, bioplastics are made from plant starch. Parts can be 3D printed from bioplastics, eliminating manufacturing waste.

Out of these options I chose to use aluminum, as it is easy to work with, can be left outside for millennia without corroding and is 100% recyclable at the end of life.

Galvanic Corrosion

Any time you put dissimilar metals in contact with each other, you create the potential for galvanic corrosion. Essentially, galvanic corrosion happens because different metals have different electrode potentials. When you put dissimilar metals with different electrode potentials together inside of an electrolyte, electrons flow from the more cathodic metal to the more anodic metal, causing corrosion in the anodic metal. This is exactly what is happening inside of a AA battery. In a standard alkaline battery, the positive terminal is made out of manganese dioxide, a highly cathodic metal, while the negative terminal is made out of zinc, a highly anodic metal. The two metals are immersed in potassium hydroxide, a highly basic alkaline electrolyte. Electrons flow from the manganese to the zinc, corroding the zinc and producing an electrical current.

Obviously we don’t want our cornhole boards to corrode, because then they wouldn’t last forever and thus wouldn’t be a “sustainable” product. So we should do everything we can to prevent galvanic corrosion.

In order for galvanic corrosion to happen, you need four things:

  1. An anode (a metal with a high anodic index, like aluminum)
  2. A cathode (a metal with a lower relative anodic index, like steel)
  3. An electrical path between the two metals (two metals in direct contact each other)
  4. An electrolyte surrounding these two metals (which can be rain, fog, dew or simply the air itself)

If you prevent any one of these four things from occurring, you will prevent galvanic corrosion.

You could prevent the fourth criteria from occurring by sealing the whole thing inside a “clean room” and never letting it go outside – but obviously we want to keep our cornhole boards outside through all types or fog and rain.

You could prevent the third criteria from occurring by electrically isolating the dissimilar metals. For example, if you want to put a steel bolt through an aluminum hole, you could electrically insulate the bolt with a plastic bolt sleeve. Or you could slather a corrosion-inhibiting agent like Loctite Zinc Anti-Seize on the bolt shank. But then you would be violating the other design principle of making the entire product completely cradle-to-cradle sustainable.

So we are left with choosing materials that have the same anodic index, so that we don’t have an anode and a cathode in the first place. This means if we make the board out of aluminum, we will also have to use the same grade of aluminum for the bolts.

Examples of Cradle-to-Cradle Products

My favorite example of a cradle-to-cradle product (which hasn’t been C2C certified) is the Klean Kanteen Reflect water bottle. The bottle is made of just three materials: Stainless Steel, Bamboo (for the cap) and Silicone Rubber (for the seal). Stainless steel is infinitely recyclable and doesn’t leech estrogenic hormones into your body like almost all plastic water bottles. Bamboo is one of the fastest-growing woods, so it is extremely easy to grow it sustainably. Silicone rubber is also completely recyclable.

KleanKanteenReflect

 

Design

I designed the board in Solidworks. Here’s what the final result looks like:

Cornhole4

Cornhole5

Bill of Materials for Bolted-Together Boards:

  • Side Beams: (4) Unpolished 6061 Aluminum Bar without Certification –  1/2″ Thick, 3″ Width, 36″ Length – $37.00 Each on McMaster Carr, $31.15 Each on Amazon (w/ free shipping!) = $124.60
  • Cross Beams: (4)  Unpolished 6061 Aluminum Bar without Certification –  1/2″ Thick, 3″ Width, 72″ Length  –$64.91 Each on McMaster Carr, $49.69 Each on Amazon (w/ free shipping!)  = $198.76
  • Top Beams: (4) Unpolished 6061 Aluminum Bar without Certification – 1/2″ Thick, 3″ Width, 24″ Length – no cost – taken from each cross beam (72″-43″=29″ remaining)
  • Legs: (1)  Unpolished 6061 Aluminum Bar without Certification –  1/2″ Thick, 2″ Width, 72″ Length  – $39.82 on McMaster Carr, $40.70 on Amazon (w/ free shipping!)  = $40.70
  • Sheets: (2) Unpolished 6061 Aluminum Sheet – 0.050″ Thick, 48″ Width × 48″ Length – $155.53 on McMaster Carr = $311.06
  • Bolts: (48) Aluminum Hex Head Cap Screw – 1/4″-20 Thread, 1-1/4″ Length, Fully Threaded – $10.21 per pack of 25 = $20.42
  • Nuts: (48) Aluminum Hex Nut – 1/4″-20 Thread Size, 7/16″ Width, 7/32″ Height – $6.41 per pack of 100 on McMaster Carr = $6.41
  • Locking Washers: (48) Aluminum Split Lock Washer – 1/4″ Screw Size, .49″ OD, .06″ min Thick – $8.22 per pack of 100 on McMaster Carr = $8.22
  • Total Material Cost: $710.17

Bill of Materials for Welded Boards (no bolts):

  • Side Beams: (4) Unpolished 6061 Aluminum Bar without Certification –  1/2″ Thick, 3″ Width, 36″ Length – $37.00 Each on McMaster Carr, $31.15 Each on Amazon (w/ free shipping!) = $124.60
  • Cross Beams: (4)  Unpolished 6061 Aluminum Bar without Certification –  1/2″ Thick, 3″ Width, 72″ Length  –$64.91 Each on McMaster Carr, $49.69 Each on Amazon (w/ free shipping!)  = $198.76
  • Top Beams: (4) Unpolished 6061 Aluminum Bar without Certification – 1/2″ Thick, 3″ Width, 24″ Length – no cost – taken from each cross beam (72″-43″=29″ remaining)
  • Legs: (1)  Unpolished 6061 Aluminum Bar without Certification –  1/2″ Thick, 3″ Width, 36″ Length  – $40.70 on Amazon (w/ free shipping!)  = $40.70
  • Sheets” (2) Ultra-Corrosion-Resistant 1100 Aluminum Sheet – 0.050″ Thick, 24″ Wide x 36″ Long – $28.37 Each on McMaster Carr = $56.74
  • Total Material Cost: $420.80

Bill of Materials for 1/4″ Welded Boards:

  • Side Beams: (4) Unpolished 6061 Aluminum Bar without Certification –  1/4″ Thick, 3″ Width, 36″ Length –$27.27 Each on Amazon (w/ free shipping!) = $109.08
  • Cross Beams: (4)  Unpolished 6061 Aluminum Bar without Certification –  1/4″ Thick, 3″ Width, 72″ Length  – $30.55 Each on Amazon (w/ free shipping!)  = $122.20
  • Top Beams: (4) Unpolished 6061 Aluminum Bar without Certification – 1/4″ Thick, 3″ Width, 24″ Length – no cost – taken from each cross beam (72″-43″=29″ remaining)
  • Legs: (1)  Unpolished 6061 Aluminum Bar without Certification –  1/4″ Thick, 2″ Width, 72″ Length  – $20.28 on Amazon (w/ free shipping!)  = $20.28
  • Sheets” (2) Ultra-Corrosion-Resistant 1100 Aluminum Sheet – 0.050″ Thick, 24″ Wide x 36″ Long – $28.37 Each on McMaster Carr = $56.74
  • Total Material Cost: $308.30

Manufacturing

I bought the aluminum from McMaster Carr.

I got the bars and sheets water-jetted at Precision H2O in Hayward, California.

Then I got them welded up at Ras-Co Manufacturing in Hayward, California.

 

Finishing

To finish them off I went down to the Oakland Tool Lending Library and borrowed a buffer.

I polished them up using some buffing pads and some Brasso metal polish.

 

Finished Product

Aluminum Cornhole Boards

Aluminum Cornhole Boards

 

Aluminum Cornhole Boards

Aluminum Cornhole Boards

 

Metal Cornhole Boards

Metal Cornhole Boards

Will Martin is an energy analyst and expert on peak oil and alternative currencies. He is an MBA graduate of Cornell University, where he was a Roy H. Park Leadership Fellow and concentrated on studying sustainability in business through the school’s Center for Sustainable Global Enterprise. Prior to his MBA, Will worked in the energy industry, living in Singapore, Houston and Dubai. Will is a recipient of the 2012 “Pioneer Award” from the Association for the Study of Peak Oil and Gas (ASPO-USA). He currently works as a carbon trading commercial adviser in the San Francisco Bay Area. Will is a bitcoin enthusiast and in 2014 published the book “Anonymous Cryptocurrencies,” which became a #1 best seller in 3 Amazon categories and was the first book to be sold on a decentralized marketplace.

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