From Make via BoingBoing:

This guy worked out how to scratch-build (punny!) functionally retractable Wolverine costume claws. Warning, you will need a bandsaw and some skill with aluminum, but anybody who has done any fair amount of auto body repair should be able to whip up a SNIKT-o-riffic pair of faux-adamantium pigstickers with relative ease. Instructions to be found here.