Gearing Up With Acetal

Posted: February 18, 2016 in Acetal, Basic Plastic Tips
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There are a lot of flashy “do it yourself” projects that hobbyists get in to with plastic but one application that keeps coming up that you might not think of is the simple gear. The general reasoning to use a plastic gear as a replacement for a metal gear make intuitive sense: the plastic gear will often be mated to a metal component and the fact that you have a plastic on metal connection now should greatly increase the life of the mating components. The problem is hobbyists do not really know what to use: we’ve heard of HDPE, UHMW, nylon and even polyurethane be requested by the DIY community for a home made gear application. But how suitable are these plastics for the application?

Actually – not very. Most plastics cannot be machined to tolerances as tight as metal be but many plastics, especially the polyolefins such as HDPE and UHMW, are very soft and could have the gear teeth quickly lose their shape once that gear starts working. Nylon is better, but it cannot take much impact at all – especially in the cold – meaning it is considered to be fragile. The best material for the application is actually acetal. Acetal is a very hard plastic that machines very well and holds excellent tolerances. It is widely available in rod stock from plastics distributors across North America. The gear in the picture below is made of white, homopolymer acetal. Black copolymer acetal is also widely available and would work well too – its properties are slightly worse than homopolymer in some respects but it is also less expensive.





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