Ōdachis, also known as nodachis, were traditionally made using similar materials and construction techniques as other Japanese swords. The blade of an Ōdachi was typically made from a combination of a high-carbon steel cutting edge and a lower-carbon steel body, which provided a balance of sharpness, durability, and flexibility. This construction method is known as differential hardening or "clay tempering."

The process of making an Ōdachi involved several steps:

1. Blade Core: The core of the blade, known as the shingane, was made from softer and more flexible low-carbon steel. This provided support and resilience to the cutting edge.
2. Cutting Edge: The cutting edge, called the hagane or ha, was made from high-carbon steel. This steel was harder and capable of achieving a sharper edge, allowing for effective cutting.
3. Differential Hardening: The blade was subjected to a process known as clay tempering, where a layer of clay was applied to the blade during the heat-treating process. This resulted in differential cooling rates, with the edge hardening more than the body. This differential hardening technique allowed for a sharp edge while maintaining the necessary flexibility.
4. Other Components: The blade was then fitted with a handle (tsuka), guard (tsuba), pommel (kashira), and other fittings made from various materials such as wood, ray skin, cord wrapping (ito), and metal.

Overall, Ōdachis were crafted with careful attention to the balance between sharpness, durability, and flexibility. The specific materials and construction methods used may vary depending on the time period, region, and the skill of the swordsmith. Today, Ōdachi replicas or modern interpretations may also utilize similar materials and construction techniques to recreate the traditional aesthetic and functionality.