First Woodworking Project- a Bed of Nails Is Better Than a Bird House!

Building things is fun!  Building a bed of nails with your kids is awesome. Okay, before you decide that this is a crazy, bad idea, let me explain.  The bed of nails is a science demonstration that teaches force, pressure and Newton’s third law of motion.  This project uses a balloon, not a person to demonstrate the concepts.  It is also really COOL for kids to build it and then show it and explain it and show it and explain it and show it and explain it.  Really, they will want to demonstrate it a thousand times, which is why it is a better first woodworking project than a bird house.  

Wood- plywood or 1X12

2 Wooden dowels (36 inches)

4- Eight foot 2 x 3 boards 

Nails (100+)

Sandpaper (various grits)

Paint - optional

Wood glue

Cheap balloons

Tools 

Safety goggles

Hammer

Nail punch

Ruler

Drill /drill bits

saw

Paint brushes/small rollers (optional)

This project is perfect for kids because it is forgiving and adaptable to what you have. 

Base- Cut the plywood  into 3 squares (12” x 12”)  

Weights- Cut the 2x3 boards into 11 inch pieces this length allows the pieces to be stored in a standard milk crate.  These wooden blocks can also be used to play a large-scale yard Jenga style game, so technically this is two great projects in one. (Tip- painting  the board before you cut is quicker but optional)

You will need three pieces of wood the same size.  I had some scraps of 1X12 board left over from a project, however plywood scraps work well too.  Sanding is often drudgery to adults but kids love to sand. While your young builder is sanding is a perfect time to talk about friction. Friction is caused when two surfaces rub against one another.  If you have several different grits of sandpaper you can let them feel the different amounts of friction produced. Sandpaper with a lower number has larger, coarser grits or abrasive particles and produces a lot of friction. High numbers or fine sandpaper has very small abrasive particles.

The project requires four equal lengths of ½ inch dowels . Cut into 18 inch pieces.

Two of the squares will need ½ inches holes. Each square will need four holes, From each ½ inch hole center to hole center should be 5 ¾ inches.  This distance allows two wooden 2x4 weights to fit between the dowels.  It is helpful to have the young builder put the wooden weights on the base before drilling and hold the dowels next to them. One square will have ¾ inch holes.  This is the middle square that slides up and down on the dowels.

Painting produces a nice finished product, but it is an optional step. I recommend just a base color at this point.  If your builder wants to paint a design, wait until the end because it is possible that the wood may crack during the nailing process and losing a detailed design is sad.

We were building two beds of nails at the same time, one cracked, which is why the pictures are not the same throughout the Instructable.

Between the holes, draw a 10 cm x 10 cm grid in Sharpie marker. At the intersection of each line, use a nail punch, this will make drilling the holes easier. Drill a small hole at each intersection. An inexpensive corded drill is lighter and easier for a younger builder. Drilling 100 holes is great practice and very fun for young builders. The small holes make nailing easier. 

Hammer 100 nails! Hammering 100 nails is fun and provides a lot of bragging rights.  Hands down it is the best part of the project.  Start in the middle of the grid and work to the outer edges. One hundred nails! What fun!!

Twist the dowels into the holes of the base with the nails.  This may require gentle persuasion. Add the middle square.  Finally, add the top square.  Adding the top square can be tricky, if you need to tap them in with a hammer, be sure to put a wooden block to diffuse the force and avoid cracking the bases.  (Tip- rub a little bit of bar soap on the end before twisting or if the  dowel fits loosely add glue or wood filler and allow to dry)

A bit of theatrics is very helpful.  Ask the audience, what they think this marvelous thing is?

Then lift the middle board to reveal the bed of nails.  Have a volunteer touch the nails to prove that they are real and sharp. Inflate a balloon and ask the audience to predict what will happen, then place the balloon on the nails.  Bounce the middle board on the balloon for good measure and dramatic effect. Pass out a wooden weight to each member of the audience, tell them that each wooden block weighs about a pound. Ask for predictions of the number of blocks it will take to pop the balloon.  Add the wooden weight, one at a time. Stack them “Jenga” style.  Pause after each layer to add up the total amount of weight.  Let the tension build.  A cheap balloon should pop at about 25- 35 pounds!!!    (tip- if the balloon will not pop, pull out two blocks on each side and add more weights or have two audience members push down)

The bed of nails is an excellent first woodworking project.  It provides opportunities for sanding, drilling and hammering and produces a show worthy project.  However, it is also a good  science demonstration. The nails are pushing up against the balloon and the balloon and the weights are pushing down on the nails because of gravity. Each is exerting a force, a push or pull on the other.  This is an example of Newton's third law of motion that states that when two things  interact, they apply forces to one another that are equal in strength  and opposite in direction. The third law is also known as the law of action and reaction.   Pressure is the application of force over a particular area. In mathematical terms, pressure is equal to force divided by area. With more force comes more pressure, and with more area comes less pressure. So what that means is if you only had one nail the area of the nail tip would be very small, so the pressure would be very great and the balloon would pop as soon as the middle board was dropped on the balloon.  However, since the bed of nails has 100 nails the area of the points touching the balloon is much larger, so the pressure is much less and the balloon resists popping even when lots of weight is added.