Patent ID: 7748718

Claim:
An improved expandable mandrel having, a shank terminating at a distal end and a proximal end, having a shank length (L) and having a longitudinal shank axis, the shank having, a plurality of radial slots extending longitudinally therein, each of the slots being bounded by a slot bottom surface and a pair of spaced-apart parallel slot sidewalls, the slots initiating in a spaced apart relationship from the proximal end and extending in the direction of the distal end of the shank, the slot bottom surface of each of the slots being inclined with respect to the shank axis such that the bottom surfaces converge as they traverse the shank, a plurality of keys slidably insertable into the radial slots, each of the keys being bounded by, a proximal end approaching key end, a distal end approaching key end, a pair of spaced-apart key sidewalls configured so as to slidably engage the pair of spaced-apart slot sidewalls, a key bottom surface configured so as to slidably engage the slot bottom surface, and a key upper surface having at least a portion which is generated by one or more line segments that each extend parallel to the shank axis when the key is engaged with one of the radial slots such that the slot bottom surface is slidably engaged with the key bottom surface, and each of the keys having an extension positioned in the vicinity of the proximal end approaching key end, a collar configured to slidably engage the shank and having a series of passages each configured and positioned to slidably engage one of the extensions when the keys are slidably engaged with the radial slots, spring means for maintaining the keys radially engaged with the radial slots, and means for maintaining the spring means at a set position from the extensions, the improvement comprising: a platen having, a part-engaging surface, and key passageways radially aligned with the shank axis and of sufficient size to accommodate the keys; means for affixing said platen longitudinally on the shank; and means for limiting rotational motion between said platen and the shank so as to avoid interference of the keys with said key passageways.