Step 1: Ingredients
This whole blade was pretty cheap. Price breakdown:
Drawer sliders (2) @ $3 for 2 sets (Axmans surplus store!)
Ring @ $1.50 each (Target clearance shelf)
Rubber bands @ practically free...
Letter opener (AKA blade) @ $1 each (Office Depot)
Cotter pins (2) @ ~$0.20 each (Hardware store)
brass ones (11) @ $0.09 each (Hardware store)
steel ones (~12) as filling on long bolt @ $0.08 each (Hardware store)
size 10 brass @ $0.25 each (Hardware store)
size 6 (8 of them) @ $0.08 each (Hardware store)
size 10 (8 of them) @ $0.08 each (Hardware store)
tiny size 6 (8 of them) @ $0.08 each (Hardware store)
2" long size 6 @ $0.08 each (Hardware store)
L-brackets (8 of them) @ special discount, I got 100 for 35 cents :)
That adds up to about $10.50
Step 2: Assembly Step 1
Grab one of the drawer sliders and slide it as far apart as it will go. Measure on your arm about how long you want the casing of the hidden blade to be. (mine is about 7~9 inches, i forget exactly how long).
Grip the slider firmly and saw off the extra slider (the wider part)
You should be able to slide the thinner slider part out of the wider one. Do so. We are going to throw away the thinner part, but first we need to get the other smaller piece attached to it.
Bend down the piece shown in the 3rd picture with a pliers. Carefully (and close to the ground) slide off the piece with the ball bearings. Keep this piece along with the ball bearings.
Refer to picture 5 to see what we are keeping.
Go to next step.
Step 3: Assembly Step 2
Pick up that smaller piece that used to have the ball bearings on it.
Cut it so that it is only six holes long (as in picture).
Estimate where you will want the blade to be fastened.
Drill holes through blade and slidy thingy so that you can put bolts through them both along with nuts to tighten them.
Tighten the nuts and bolts securely (as tight as they go!).
Then, put 8 of the ball bearings back on, on the back / bottom 4 holes on each side (see picture 6). Slide the whole thing back into the large slider (picture 7).
Examine its beauty and try it out :) just don't lose the ball bearings!!!
Step 4: Assembly Step 3
Alright, this is a short step.
We are working on the side of the blade casing with the butt of the blade. This is to keep the blade from sliding into your elbow / arm / face / whatever. It is the back of the casing. NOT THE POINTY END!!!
Drill a small hole (just wide enough for your size 6 bolt) through the L-bracket just above one of the other holes already in it, and near the bend. (picture 1)
Drill another hole to match this one on the casing (not the blade or the slidy thingy we attached it to), the wide casing.
Attach as shown in pictures 2 and 3.
Tighten a bolt / nut. (tight!)
Easy! Next step!
Step 5: Assembly Step 4
Make another one of those L-brackets have an extra hole in it. Attach it onto the other L-bracket as shown in pictures 2 and 3.
Since this step is so short, I will add another part to this step... (also, I forgot to document it with pictures, kinda, but its easy anyways!)
Remember that wider slider thing from the first assembly step? get another one of those, exactly the same length, through whatever means necessary!
Thats all. Its shown in picture 4 also as the wide slider below the one we just made. We will also be using it in the next step!
Step 6: Assembly Step 5
Another easy step. Drill a hole in the other wide slider to attach to the last L-bracket attached. Pretty easy to see in the pictures.
Step 7: Assembly Step 6
The key. This is what allows you to open and close the blade.
This step uses the 2" long size 6 bolt with a whole jumble of nuts and washers on it to hold everything in place. You will also need the longer of the two cotter pins that you have. Along with 2 more L-brackets.
Add a size 10 nut to the cotter pins before bending them so that they will remain together while the blade is in use.
Bend the cotter pin to have one end be the pin that sticks into the casing and the other end form a loop to tie a string to. (do this part at the very end of the whole assembly)
Have the L-brackets facing each other.
Have the cotter pin in the middle.
Maybe have larger washers around the cotter pin (?).
Just follow the pictures, easier than words!
Step 8: Assembly Step 7
In this step we will attach the "key" from the last step and mount it onto our casing. It will go on the back of the second wide slider that we cut.
Drill two holes appropriately spaced to fit the "key" into the wide slider.
Hold it on and judge about where the pin will need to go through the casing. Drill a long and wide gouge into the casing there. (Picture 3)
To place it in the right spot, you must have the key already bent how you want it. The tip of the key's cotter pin must fall onto the first wide slider when the blade is all the way out. The key's cotter pin tip should be designed to catch the blade when it hits something and tries to go back. This is what locks the blade!
Continue to the next step once you are satisfied with this.
Step 9: Assembly Step 8
Grab 2 more of those L-brackets. And a pliers...
Bend the L-brackets flat to start. Then bend them as shown in picture 1 on the right. Bend both sides to look like this.
After looking at the next step you might have a better idea of how to do this...
Step 10: Assembly Step 9
Last step!!! Woot! (I never thought I would ever type that)
Even better, half this step is optional!!!
They don't do anything, but if you want to know how I made mine exactly, then read... I'll tell you when to listen again for real.
Grab two more L-brackets and fold them over themselves.
Hold the "key" in place and hold the previous step along with this step in place too while you carefully push a small bolt through the holes (all the way through the key's L-bracket holes) and attach a nut from the key's side. Tighten as tight as it can go. Then fold and crimp the L-bracket on the bottom over the bolt head. (Picture 4)
Alright, Listen again. You DO have to follow these instructions...
Fit the two wide sliders together as shown in picture 5.
...I must admit, I forgot one picture... You should have one cotter pin left over, right?
Well, it simply goes right through those holes of the L-bracket. (Picture 6). Then bend the ends of the cotter pin so it can NEVER get out :)
Ok, I also lied, there is one small step left.
Attach rubber band over the cotter pin (look at finished pictures) of the key.
Also, tie a string (I used kevlar thread, use whatever you want) to that loop on the key's cotter pin. Have the string attach onto a ring that goes on one of your fingers (tie it to the ring). Tune the length of the string so that the hidden blade operates as you like!
To open or close blade, pull on string and hold the blade either up or down, or fling it open / shut. Release tension in string to lock it into whatever mode it is in! The key catches underneath to keep it open, and pushes against the blade to keep it firmly still when closed.
Step 12: Strap-on :)
Here are just a few pictures of the blade with the straps and glove attached. More pictures can be seen at the link at the top of the page!