In this instrutable I will be showing you how to replace a piece from a toy. More specifically from a Nerf gun. This method can be applied to more then just toys. You will need a general knowledge of a 3D modeling software.
Step 1: Take the Toy Apart
There were only about 8 screws holding this Nerf gun together. After taking them out the two halves separated. Be careful with toys with small pieces or springs, they might get lost. After separating it you want to take a picture to know where all the pieces go. Put all the screws and small pieces into a safe place like a magnetic holder or zip lock bag.
Step 2: Identify the Broken Piece
Identify which piece is broken and remove it from the toy. The piece that was broken on this Nerf gun was the hammer. It was held to the other parts of the gun with a few pins. Remove them with a small screwdriver. After that trace the broken piece on a piece of graph paper. The smaller the grid the more accurate your part will be when you transfer it into a 3D model. After tracing it put dots along the traced shape that are easily recognizable. What I mean by that is if its in an intersection on the graph paper.
Note: If I did this again later I would have used atmost 1/16" grids and not 1/8" grids.
Step 3: 3D Model!
I used Autodesk Inventor the same could be done in Google Sketch Up.
First thing to do to make life easier is make a rectangle that can fit your piece inside. Then make a grid the same as your graph paper in the program. In Autodesk there is a point feature where you can make a reference point. Make all the dots from the tracing into Autodesk. Then erase the lines leaving only the points. Most parts can be made with connecting lines and semi-circles. To make semi-circles, make a line from the two points you want to have a semi circle on then go to the midpoint of that line and draw a circle from the midpoint to one other points. then trim the half of the circle you don't want and delete the middle line. For more fancy parts you can connect the points together with a spline. After creating the shape extrude it to the thickness you need.
Step 4: 3D Print It
The next part depends on whether or not you have a 3D printer.
If you do not then there are 2 options for getting your piece printed, Shapeways and 3D Hubs. They are both 3D printing services.
If you do have a 3D printer then you can export your 3D model as a ".stl" file. With your .stl file you can use a program, like Repetier Host, in conjunction with a slicing program to create gcode. The gcode tells the printer what to do.
The settings I used were:
-Layer height 0.13 mm
-Horizontal Shells 5 upper 5 lower
-Extruder Temp.: 190 C
-Bed Temp.: 50 C
Step 5: Your Done
I had to to print 3 different models before I got it to work properly. I also had to sand it down a lot. Then I reassembled the guns. It actually preforms almost exactly the same as the gun that wasn't broken.
Step 6: Test Video
All the darts landed pretty close to each other between the two guns.
Also if you happen to have the same broken piece on your Nerf gun here's a link to the .stl file I used - http://www.thingiverse.com/thing:853796