It's 2011, and I am in charge of choreographing a bunch of children in a "ninja" skit to be played out on stage in front of their friends and families.

I decide to finish the skit by having the two most experienced kids have a battle on stage. In the beginning of the battle, the Ninja would bow, and suddenly, one would whip out a shuriken (AKA Ninja Star) and throw it at her opponent. Fortunately, the other ninja had a table nearby to grab and block the weapons with.

Of course, being children and on stage, no real stars would be used. Nothing would really be thrown, but it had to look - and sound - real. That's just how I roll. ;-)

I decided to create a variation of the apparatus magician's use in their knife throwing bits. Magicians have assistants behind a big board to trigger the knives. I would have an 11 year old child both holding the prop, acting with it, and activating it. I needed a simple, quick, stable illusion. This is a chronicle of what I came up with.

In the end, I managed to freak out the stage manager and the guy in the booth during the dress rehearsal, and not only did several parents ask me how long the kids practiced to throw the stars so accurately, but a couple people backstage dove for cover when they thought ninja stars were coming their way. That was a satisfactory reaction.

I want to give a big thanks to the people at HeatSync Labs in Mesa for their help. http://www.heatsynclabs.org/
I LOVE the hackerspace / makerspace concept!

Thanks to my friends at AZHaunters.com for putting up with me doing this when I should probably have been making monsters.

Step 1: The Stuff

I made the table from scratch, though I probably could have used one from Ikea.

I needed the table to have one leg right in the middle with the triggers on it. I used:
Plywood - 1/4", maybe 1/2", whatever was cheapest.
a 1 1/2" dowel rod, as long as the table will be high
3 small binder clips
3 nails with large heads - like furniture nails. Alternatively, short screws with large heads, or washers.
3 mousetraps - NOT from the dollar store! Geez, spend a couple bucks and save yourself the frustration.
Heavy fishing line. Strong twine would do.
Eye screws
Stiff cardboard, such as from a pizza delivery box
Black fabric
Hot Glue, screws, staple gun

To make the stars, I used:
Thin sheet metal,
Tin snips,
JB Weld 2=part epoxy, and
Pliers.

You'll need tools to cut the plywood, maybe drill some holes, and of course to screw the screws and/or hammer nails.

Step 2: The Table

I'll start right off by saying I could have made the table more stable. In the end, it was a circle of plywood screwed to a dowel, screwed to a small square of plwood as a base. It was not very stable.

I began by deciding how high I wanted the table to be, and how large I wanted the tabletop to be. Then I simply cut the dowel to size. I made the circle by simply using a piece of string 1/2 the diameter I wanted the finished table to be. I tied a crayon to one end and a nail to the other. Put the nail where the middle will be, and use the crayon as a compass to make the circle.

I cut the circle with a jig saw. It was about 18" in diameter
I cut a square for the base with a table saw. It was about 12" to a side

You will need enough stiff cardboard to make a 3"-4" skirt around the table. You will NOT want to put it on yet, though. You have a lot to do first.

Step 3: The Mechanism

The mousetraps needs to be cut in half. The part where the bait is set will be removed. All you want is the death trap part, and enough wood to attach it to the table. There is an arm that holds the deathtrap part in place when set. You do not need the arm, but you WILL need the metal loop that it is hooked to. Leave that in place.

Cutting them is a little tricky, since you have to hold the trap in the "loaded" position and cut away the other part.
I pulled the unnecessary parts out with pliers first, then cut the mousetrap with my tin snips.
I hope my high school shop teacher does not find out. You probably have more appropriate tools - like a saw of some kind.

For those of you who cannot stand the suspense, the way this is going to work is you will screw the mousetraps to the underside of the table, hold them in the loaded position with the fishing line, and secure the line with binder clips.

For the stars, I got some thin sheet metal from Lowe's.

I made a cardboard template kind of like the one pictured here. I used this template to mark out two points of each star on the metal. I only cut out a little of the other two points to have a way to attach the stars to the spring. I cut out the shapes with the snips.

I have included a very rough diagram here of the star. The important part is the tab on one side where the star's points would have been. There is a kind of dotted line where I bent the metal. If I had welding equipment, I would have welded the things on. As it is, I bent the tab, put in my JB Weld 2-part epoxy, and pinched the whole thing together as tightly as I could with pliers. I let them cure at least 24 hours. The stars are fixed so that when the mechanism is set, they stick up 90 degrees from the bottom of the board, and when it is sprung, they stick up 90 degrees from the top of the board.

In the pictures you can see I covered the edges of the stars with masking tape and painted them sliver. This was just in case of accidental contact with the blades. Though they were not sharpened, they were thin enough to possible cause injury. My actors were children, after all.

Step 4: The Holes

This is probably a good time to figure out where the stars will pop out. You don't want them too close to the middle, or the leg will interfere with the mechanism.

I wanted mine popping out at different angles - not all oriented in the same way at all. I could have made them oriented with the table leg like spokes on a wheel and maybe made it easier on myself without sacrificing the effect at all. Make sure at least one is far away from the center, so the actor's hand never comes into contact with any of the stars as they are triggered.

The actor pretending to throw the shuriken was using a prop star that was 5 inches across - 4" from tip to tip. I cut spaces in the table 4" long and about 1/2" wide. This is not a precision instrument. The stars bend or twist, and there is some play in the movement of the mousetrap too. You need more than a little slit for the stars to pop out of.

Figure out where you want the holes, and take the spring mechanism and make sure it will have room to load and to spring forward too.

You can see in the picture that the mechanism is right at the base of the hole. If you measured the space from the first tip to the second, you would find it to be about 4" The first point of the star penetrates as shown, and the second point penetrates about two inches or so farther up.

Hopefully the pictures show you what I mean about how the stars move through the holes.

You'll want to cut the holes and then affix the mechanism as shown in the pictures. The stars should move freely through the holes. You can bend the metal if you need too, but it is better to adjust the trajectory of the stars by loosening the screws and moving the mechanism itself until it works well.

Step 5: The Triggers

I used 3 small binder clips for my triggers. They held fast, and triggered easily.
I put them relatively close to the top of the dowel rod because I wanted them hidden by the cloth. Not so close that they might come into contact with the springs or stars though.

I put them on the dowel rod one behind the other as shown. I had some nails with huge plastic heads which I used for this. I think they were intended to be used as feet for a table or chair.

I also hot glued them into their final position. If you look closely, you can see that they are slightly askew from one another. Not too askew though. The actor had to find them easily and reliably without looking and while hamming it up on stage. Which he did.

I fastened the table leg to the center of the table with just screws. I screwed right through the center top of the table and into the leg. If you want to do the same, I recommend drilling 3 or 4 holes around the center and screwing into the dowel through these. Ditto for the foot.

If I were doing this again, I would use something more stable. The table is a bit thin to bore a hole in for the table leg to go into, but a thicker wood could be used. Alternatively, some L brackets might have worked nicely. I am pretty sure there is some kind of cylinder with a flange at one end that one could put the leg into, and screw the flange to the table. Sorry to get all technical on you.

OK, so the mechanisms are in place and the table leg is in place with the triggers. At this point, I tied the fishing line to the crossbar on the traps. I used 50 pound line. You don't want anything flimsy. I ran the line through the convenient loop that the mousetrap's arm used to be attached to. I used eye screws as shown as well. Once I knew where I wanted the lines to end, I simply tied big knots in the line for the triggers to grip. Worked fine.

I arranged it so that the stars closest to the center triggered first. This way, the actor's fingers were well away from them when they were triggered. If you look at the first picture of the stars and triggers in place, this is what you should see:

1. The star "front and center" in the picture triggers first. The line goes from the trap, through an eyehole, and straight up to the topmost trigger.
2. The star right above that one in the picture triggers next. The line goes from the trap, through an eyehole, and actually wraps around the leg a bit and clips into the middle trigger.
3. The star on the far left, well away from the triggers, goes last.

These triggers held very well. They never misfired except in practice when they were actually being whipped around. It is also impossible to know whether they misfired or the actors did. ;-) I can tell you that I loaded the mechanisms and stuck the whole thing in my shed for a year and a half after the performance. It got bumped and kicked and had all kinds of stuff stacked on it as if it were a real table. When I pulled it out, it was still in the loaded position, and all 3 fired perfectly.

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Step 6: Making It Work

OK, at this point, it is time to make everything come together.

Paint the whole thing flat black. This will hide a multitude of sins.

Take that stiff cardboard you had prepared back in step 2 and staple it to the outer edge of the table. You could make this extra wide and use this as the edge all by itself.

I covered it with black cloth, which I stapled around the edge. If you do not have the cardboard under the fabric, it will interfere with the stars and spoil the illusion. Test the mechanisms to be sure this is not happening.

I set the mechanism and covered the tabletop with newspaper and painted that black. If the stars were triggered, I simply spray glued more paper on top and painted it black too.

Everything is painted and set.

Now we need to make it work.

I took that cardboard template and covered it with shiny silver duct tape. Not gray like in the picture - silver. Bam! Instant shuriken.

The two big parts of this illusion are palming and timing. Magicians "throwing" knives palm them and/or drop them into secret pockets to achieve the illusion. I had my actor start with the star in full view, pretend to throw it backhanded so the star disappeared from the audience's view. She then pretended to draw another, throw it overhand, again hiding it from view, and again pretending to draw and attack. At the end, she simply threw the thing away in full view, so there was never a need to build secret pockets.

As for timing, the other actors rehearsed again and again with the actual table, miming the triggering most of the time so as not to wear it out before the performance. Throw, trigger, throw, trigger, throw, trigger. over and over again. We ultimately did practice several times with actual triggering, of course.

In the end, we did it in front of an audience that seemed very appreciative of it. I wish I'd gotten decent video that shows it in action on stage, but I did take some video in the daylight just for this instructable about a year and a half later...

When the mechanisms fire, they not only pop the stars out the top, they also slam into the plywood, making a convincing SLAP! Without this, the illusion would not be as convincing.

As I mentioned before, you can use it again and again. The holes are easy to cover using newspaper, glue, and black paint. If the table will be sitting quietly by until it it picked up and used as a shield, this may not be 100% necessary.

This idea could, of course, be turned into a wall as easily as a table. Unlike the magician's knife trick, these could be triggered from the front by the actor.

I imagine running the trigger line down the wall and under the bottom of the wall, where the concealed triggers could be fired by the actor stepping on them. Then, when a ninja throws the star from one side of the stage, the other could dodge Matrix-like and the stars would slam into the wall behind him.

Obviously, in this case, it would be necessary for you to cover the holes completely before each performance.

There you go!

Thanks again to the great people at HeatSync Labs in Mesa, AZ for their input, help, and workspace while I was making this.
Here's a shout out to my friends at AZ Haunters too! I hope someone can use this to make their next haunted house even cooler!
Oh - and that's not me holding the shuriken in the picture. That's Steve Jobs. Apple, please don't sue!

If anyone builds one of these, please post pictures and video.