A 2D Model
RETURN TO JUNK BOX ENGINEERING
Students can build a simple 2D plotter model with limited materials and expertise. Start collecting foam meat trays so you can do this with your students. It is a great deal of fun making something like this with so little cost and material. Watch this video to get an overview:
Materials required
Glue Gun/glue
Soldering iron/solder (you can have 1 for whole class and help with each group)
scissors
wire
2 D or C cells and holder
2 small hobby motors
small pieces of rubber tubing
long threaded screw 4" or largest you can find 6/32 or 8/32
Two DPDT switches
Two push button switches
Foam meat trays
Plastic card from hotel lock or similar
Plastic beads
Roller pen
Paper
Bamboo skewers or dowels (or hanger wire)
Starting
It is important for students to understand much of what engineering is all about in doing this modeling. 1) We do modeling to prove a point. It may not be the prettiest or best outcome, but if it works, we know we can design a better one and we have proved the concept. It is much better to attempt something with flexible and modular materials before you buy expensive parts and really don't understand what you are doing. If you can make this model work and understand it, then chance are you can understand all the issues confronting CNC and 3D printing design. 2) Engineers get their hands into the junk box and try things. They do not always live in a computer generated world where every design works the first time. Much of engineering is trying something, learning from it, and then adjusting the model. Somehow we have taught this generation of students that science is composed of experiments that work every time because we have them so well oiled that they are basically "plug and play." Alas, often science and engineering require lots of fiddling with materials and equipment to achieve the purpose. Teaching students that engineering requires persistence and problem solving is important. No one said this will be a cinch! But, when you get something to work after multiple iterations and trial, there is a great deal of satisfaction and appreciation for how other things are engineered. The model in this segment took five iterations to get it to a point where it is now. With others working on the project, the design will be certainly upgraded, simplified and improved. That is the nature of engineering.
STEP 1
Grocery stores often sell meat, chicken and fish on foam meat trays. These can be cleaned and used in this model. The material cuts easily, is rigid and can be reinforced, and can be hot glued. For this firs step use a sharp pair of scissors or craft knife to cut two squares, 2 inches square (2" X 2").
STEP 2
Cut another piece of foam 2" X 3 1/2". Glue 4 plastic beads as shown on one end of the piece of foam so that they are 1 1/2' apart. It is best to glue the beads with a wooden skewer holding them parallel. The beads will stay in position if you first press down on them into the foam so it makes a little depression. Then they can be glued easily.
STEP 3
Turn over the piece you just made and place two ends of the wooden skewers on top of one of the 2" X 2" squares. To locate where to place the glue, press down on the stick. It will leave an impression. You can then lift the skewer, place glue in the impression, and then replace the wooden skewers on the glue.
STEP 4
Repeat the process in STEP 3 so that the skewers are glued to the other end as well. The completed rail system should move back and forth easily on the bead bearings. Test it to make sure it glides easily. If not, inspect for glue remnants.
STEP 5
Cut two pieces (1" X 3 1/2") and glue them to the center sliding platform as shown. Cut a 2" X 3 1/2" piece and glue it on top of these two strips.
STEP 6
Take a piece of wire insulation and slip it on top of the motor shaft. It should be very tight. Attach it to a long machine screw with a larger size piece of insulation or rubber tubing. This can be hot glued. The machine screw can be connected to the insulation by twisting it inside the tube or insulation.
STEP 7
Once the motor shaft is secured to the machine screw, the motor can be mounted on the left side of the rail system. Cut two small pieces of foam to elevate the motor on top of the pad. Glue the motor to the pad.
STEP 8
Take a small piece of plastic card (the kind used as a credit card, ID card or motel entry lock) and melt a hole that is just smaller than the machine screw thread. Run he screw through the card so it makes a thread. If the hole is too big, use the tip of a soldering iron to melt the plastic around the screw. This will make a thread. Then position the machine screw so that it is parallel to the base and mark the slider by pressing the screw against the foam. After you have made a mark on the slider box, bore a hole with a craft knife or melt one with a soldering iron tip.
STEP 9
Use a 9 volt battery to test the motor and the screw activator. Reverse the battery to reverse the motor. Check for smooth operation. If there are stops in movement, check for glue or some other obstruction. If all is well, you are ready for PART II!
GO ON TO PART II To add the second dimension to the plotter.