Before Ammnra displayed his design that pretty much summed up what the hidden blade would be, I used to research whatever I could to build one. I tried different prototypes and materials to make this hidden blade. The first Idea that came into my head was to use the drawer slide because it already had the key features of the hidden blade.
After 2 years of researching, planning, waiting, procrastinating, I finally found a tutorial for a hidden blade design that I thought was perfect. My goal with his hidden blade was to design it so it would be "practical" to use, i.e. parts held up together, can withstand amount of weight, etc. Further along the line, I learned the whole idea of a hidden blade as a self defense tool was improbable. However, that did not stop me from wanting to make it. I still tried to make it with the idea of it can be used (in defense, of course).
The tutorial I found that I thought was perfect was on YouTube by a guy with the username Abonude. His design was derived from another YouTube user by the name of TheBserk. Basically, Abonude make the design sleeker without TheBserk's larger front end, making the entire rig bulky.
All in all, with what tools I had (mostly hand tools), I was able to make it. Hope you enjoy!