Frame building basics #2.0 - materials, utilization and ease of manufacture

Bicycle frames these days are mainly made from steel and aluminium. There are advantages and disadvantages for both, but either are used extensively.

- Aluminium

There are different alloys available for both aluminium and steel. For example an aluminium frame can be made from 6061 aluminium, but handlebars are made from 7021 and rims made from 6106 series alloy. Different alloys have different properties that work for very well for certain applications, but not overly well in others. Some areas need extraordinary stiffness, others need to be flexible to make sure the parts don't shatter under load.

Aluminium frames are considered stiff, light but having shorter „lives“, due to the fact that the material/alloy has a limited number of cycles of use(1 million for aluminium, 7-10 million for steel, 12 million+ for titanium etc).

 

- Steel

For steel, it's a bit more tricky – there are many different alloyed and non-alloyed materials available + proprietary materials.

For example, most frames might have a marking of „HI-TEN“ steel – this basically means it is made out of a material that has high tensile strength. It does not certify/quantify what is considered high.

Some of the more common steel based materials can be classified as low-carbon steel (none to very little alloying elements), low-/alloyed steel (cr-mo steel) and corrosion resistant steels ( stainless, 304 or 316 series). Low carbon steel is the weakest of the bunch but also the cheapest to use (and easiest to manufacture with), while stainless steel frames take a lot more work to make them - tougher material and while welding the frame needs to be purged (cleaned out, argon is flooded in to replace regular air mixture to avoid cracks, porosity and poor weld beads).

- Excotic materials

There are also more exotic materials available – titanium, carbon fibre and bamboo/fibreglass.

Titanium is the most expensive of the bunch, where custom frames start from 800 usd / 720 eur upward with wait times of months. The most commonly used alloy is TI6AL4V, where titanium is alloyed with aluminium and vanadium.

Carbon fibre has become a lot more prevalent is the bicycle world and even rather cheap bikes have full carbon frames. Carbon can be a finnicky material, but if you take good care of your bicycle, it will be just as strong as a steel frame.
Carbon fibre frames can be built at home, but you need some specialized equipment for best results - a low pressure capable vessel, availability of good epoxy (West system) and good quality carbon fibre cloth. I will always recommend using unidirectional twill cloth. There are also videos on youtube that show how to lay up layers for areas that need it more.
 

Last but not least, there are frame made from bamboo and fibreglass. I have not first-hand experience with them, but from what I've understood, they are fun to ride and pretty durable.