How to anodize Shimano cranks
Custom anodizing parts is usually pretty straight forward…until you find yourself wanting to anodize your Shimano crankset with the non removable steel spindle. I want to show you how we got great results on this crank arm we anodized for a customers latest build.
From Metal Finishings LTD, “Anodizing is an electrolytic process which coats a metal substrate with a protective oxide layer. The anodized coating on aluminium increases corrosion resistance and wear resistance, is electrically insulative, provides a good key for paint or adhesive and is often used as a decorative finish. The oxide layer that forms on iron or carbon steel is commonly known as rust, which readily flakes off and actually promotes the corrosion of the underlying material. So an anodizing process for steel would not be terribly useful.”
With most bike parts, you can simply dissasemble the parts leaving only the aluminum to take to the anodizer but with Shimano cranks, the steel spindle is permenantly bonded to the aluminum crank arm so you have to find a way to completely keep it out of the anodizing solution. That solution is roughly 10% to 15% sulfuric acid so your masking needs to be able to withstand that chemical attack for 30 minutes to an hour.
3d printers once again are coming to the rescue here where we need quick, afforable and adaptable solutions. There is a huge range of filaments you can use with most 3d printers and they all have their advantages. Thankfully in our case, polypropylene is available as an affordable 3d printer filament that can resist sulfuric acid and is easy to print which makes it a great solution for creative anodizing masking solutions.
To protect the Shimano crank spindle from the anodizing solution, I 3d modeled a sleeve that threads into the end of the spindle that I was able to 3d print and then seal the end with a silicone based caulk.
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