Bore diameter measurement gage

An apparatus for measuring the diameter of a rotor's cylindrical bore at any axial position, said apparatus comprising:

• a housing structure having means for indicating the axial depth of insertion of said housing in said bore,
• three legs each of which has a free and a restrained end, said restrained ends being circumferentially equally spaced and pivotally mounted to said housing structure, said pivotal mountings restricting said legs' movements to the radial direction, said legs' free ends being engageable with said bore's wall,
• a push rod having a yoke portion on one end thereof,
• a plurality of rigid linkage arms each of which has a first end pivotally mounted on said yoke and a second end pivotally mounted on a leg,
• a piston element joined to said push rod portion for axially displacing said push rod and yoke in both axial directions, said piston element being slidably disposed in a cylinder element which is attached to said housing structure,
• means for providing a signal indicative of the axial movement of said push rod;
• means joined to the rotor for axially inserting said housing structure a desired depth of insertion in the rotor bore and for preventing axial movement of said housing structure when said legs are pivoted into engagement with said bore wall;
• and
• means for converting said push rod's axial movement signal into a signal indicative of said legs' radial positions and said bore's diameter to accurately indicate said bore diameter and to accurately indicate the axial position of said indicated bore diameter.