The Stansbery “Tripod” is based on the “positional” concept of recording mandibular movement. “Positional” articulators are intended to record the relational positions of the mandible and maxilla without regard to the condylar hinge. These are the border positions, centric relation and right and left lateral, and in addition, protrusive position. Stansbery assumed that within the limits of a tooth, a straight line is as accurate as a curved path. The “Tripod” has three guide slots on the mandibular member and the maxillary member has vertical rods that travel within the slots. Each articulator guide slot is maintained in position by one of 3 vertical set pins, each of which is set to a selected horizontal and vertical number for each border position. The positions of the guide slots are determined by utilizing the Stansbery check-bite appliance. This tracing device has intraoral recording plates with a central bearing point and an extra-oral upper stylus and lower graph-plate. Plaster is injected between the recording plates to create a record wafer for each position. The “Tripod” as well as the Stansbery “Dental Orient” had rotary grinding devices on the lower members that produced elliptical patterns when milling denture tooth occlusion.
Weinberg LA: An evaluation of basic articulators and their concepts, Part II. J. Prosthet. Dent. 1963; 13: 645-663.
Dr. Edgar N. Starcke's articles in the Journal of Prosthodontics have more information on the history of articulators.