Method for immobilizing a frame structure in its free state to establish a net datum position

An apparatus for finding and immobilizing a chassis frame in its free state, despite within-tolerance variations in size or location of said chassis frame, so as to establish a net datum position of said chassis frame to enable net datum features to be fabricated net to a fixture and in design-intent position on said chassis frame, said apparatus comprising:

• a pair of opposed hydraulic units, each hydraulic unit of said pair of opposed hydraulic units being disposed on opposite sides of a portion of said chassis frame such that said portion of said chassis frame is between said pair of opposed hydraulic units, each hydraulic unit of said pair of opposed hydraulic units comprising:
• a plunger mounted displaceably therein and terminating in a pad, said plunger being normally biased toward a retracted position clear of said chassis frame;
• means for advancing said plunger from said retracted position to an advanced position, such that said pad contacts said chassis frame without measurably displacing said chassis frame;
• and
• means for locking said pad in said advanced position, so as to immobilize said chassis frame in its free state between said pair of opposed hydraulic units.

An apparatus for finding and immobilizing a chassis frame in its free state, despite tolerance variations in size or location of said chassis frame, so as to establish a net datum position of said chassis frame to enable net datum features to be fabricated net to a fixture and in design-intent position on said chassis frame, said apparatus comprising:

• a pair of fixed platens comprising one platen and an opposite platen mounted opposite said one platen, said opposite platen being spaced a predetermined distance apart from and substantially parallel to said one platen;
• a plurality of guide bars extending between said pair of fixed platens;
• a pair of displaceable pads mounted about said guide bars between said pair of fixed platens, said pair of displaceable pads comprising one pad and an opposite pad mounted opposite said one pad, said opposite pad being mounted about said guide bars a spaced predetermined distance apart from and substantially parallel to said one pad, said pair of displaceable pads being displaceable from a retracted position distal from said chassis frame to an advanced position in contact with said chassis frame;
• displacing means, positioned between said pair of displaceable pads, for displacing said pair of displaceable pads between said retracted position and said advanced position into contact with opposite reference surfaces on said chassis frame without measurably displacing said chassis frame so as to find said chassis frame;
• and
• locking means, positioned between said pair of fixed platens and said displaceable pads, for locking said pair of displaceable pads in said advanced position so as to immobilize said chassis frame in said free state.

A method of finding and immobilizing a workpiece in its free state despite within-tolerance variations in size or location of said workpiece so as to establish a net datum position of said workpiece to enable net datum features to be fabricated net to a fixture and in design-intent position on said workpiece, said method comprising the steps of:

• mounting said workpiece in its free state atop said fixture;
• advancing an opposed pair of pads from a retracted position to an advanced position in contact with opposite portions of said workpiece without measurably displacing said workpiece despite said tolerance variations, such that said opposite portions of said workpiece are between said opposed pair of pads;
• and
• locking said opposed pair of pads in said advanced position against said opposite portions of said workpiece so as to immobilize said workpiece in said free state.