Does anybody know how to create a wrist mounted spring-loaded blade that will come out from the bottom and lock into place and then go back from triggered again?
It sounds complicated.

The basic mechanism already exists in the form of a "double action, out the front" switchblade knife. You'd just have to come up with a trigger mechanism that worked for you. I don't have a picture of the mechanism, but you could buy a cheap one and take it apart, most flea markets have them.

I if remember correctly, there was a recent topic of a (possibly) similar nature, concerning the retractable wrist-mounted blade featured in the game Assassin's Creed. If you're thinking of something along the same lines, I believe there was some discussion about the mechanisms involved. I don't know if that would help, but I thought I'd mention it...

I've moved this from the Historic Arms forum to the Off-topic forum. Please note that the Historic Arms talk is for "Discussions of reproduction and authentic historical arms and armour from various cultures and time periods." Movie, video game and fantasy weapons should are more appropriate for the Off-Topic forum. Thanks!

Please see this topic for more info: http://www.myArmoury.com/talk/viewtopic.php?t=11354