Expanable mandrel
View Patent ↗An expandable mandrel for holding a part has a shank with inclined radial slots slidably engaged by keys. The keys are coordinated by a collar which engages an extension on each key. A platen affixes to the shank of the mandrel to provide a stop that will index the position of a part mounted onto the mandrel. The platen has radial key passages to allow longitudinal movement of the keys in the slots. The platen preferably has resilient indexing nubs to engage the part. Preferably, the position of the platen on the mandrel can be adjusted by a set screw engaging one of several indexing holes or engaging a longitudinal guide track. For machining in a wet environment, the slots can be provided with longitudinal rails and the keys provided with transverse channels to remove liquid from between the keys and the slots.
1. 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.
2. The expanding mandrel of claim 1 wherein said means for affixing said platen longitudinally on the shank and said means for limiting rotational motion between said platen and the shank are provided, in combination, by affixing said platen to the shank.
3. The expanding mandrel of claim 1 wherein said platen further comprises:
a central passage of sufficient size to accommodate the shank, and
wherein the improvement further comprises:
means for translating said platen along the shank axis.
4. The expanding mandrel of claim 3 wherein said means for translating said platen along the shank axis is provided by having said central passage configured to slidably engage the shank,
further wherein said means for affixing said platen longitudinally on the shank and said means for limiting rotational motion, in combination, comprise:
a platen set screw which can be tightened to fixably engage the shank.
5. The expanding mandrel of claim 4 wherein said means for affixing said platen longitudinally on the shank and said means limiting rotation motion, in combination, further comprise:
at least one indexing hole on the shank extending normal to the shank axis and configured to accept a portion of said platen set screw,
said at least one indexing hole being positioned on the shank such that, when engaged by said platen set screw, said platen is positioned such as to avoid interference of the keys with said key passageways.
6. The expanding mandrel of claim 5 wherein said at least one indexing hole further comprises:
a series of indexing holes arranged on the shank in a line parallel to the shank axis.
7. The expanding mandrel of claim 4 wherein said means for affixing said platen longitudinally on the shank and said means limiting rotation motion, in combination, further comprise:
a longitudinal platen guide track in the shank, said platen guide track being configured so as to guidably engage said platen set screw.
8. The expanding mandrel of claim 7 wherein said means for affixing said platen longitudinally on the shank and said means limiting rotation motion, in combination, further comprise:
a series of indexing holes arranged on the shank in a line parallel to the shank axis and located within said longitudinal platen guide track, each of said indexing holes extending normal to the shank axis and being configured to accept a portion of said platen set screw.
9. The expanding mandrel of claim 1 further comprising:
indexing nubs resiliently mounted to said part-engaging surface of said platen.
10. The expanding mandrel of claim 9 wherein said indexing nubs further comprise: a first set of indexing nubs located at a radial distance less than a reference radius r from the shank axis; and a second set of indexing nubs located at a radial distance greater than reference radius r from the shank axis.
11. The improved expanded mandrel of claim 1 wherein the improvement further comprises:
a pair of longitudinal rails on the slot bottom surface of each of the radial slots; and
a series of transverse grooves on the key bottom surface of each of the keys.