Backwards Compatible Rotary Indexer

Adding 4-axis capabilities to 3-axis robotic mills

While working at Shopbot Tools, I developed a kit that allows existing owners of 3-axis robotic mills to add a 4th-axis rotary indexer, enabling them to machine larger and more complex parts. A rotary indexer works like a lathe, but rather than spinning at a set speed, it rotates by controlled amounts, “indexing” to a new position. This allows the machining of non-axially symmetric 3D shapes.

Previously, customers wanting 4-axis capabilities needed to purchase a custom-built machine, which was prohibitively expensive, particularly since many customers only realized they wanted 4-axis capabilities after already purchasing and learning to use a 3-axis robot. To address this gap, I developed a kit that allows users to extend the length of their tool and add a 4th-axis indexer onto one end. A key challenge was keeping the kit simple enough for users to install by themselves while sturdy and accurate enough to withstand the stresses of production machining.

This kit is now sold as a standard accessory for Shopbot’s 3-axis robotic mills.

Carving a tiki log using the 4th-axis rotary indexer

(above) The additional 4th axis allows users to machine complex 3D shapes not possible with a 3-axis tool