This is a really cool retractable key-chain holder that looks very similar to a real tool holder worn by astronauts in space. An Engineer from the Johnson Space flight center in Houston came to my High school and told us about his job and brought some show and tell items, one of which was a belt loop that had a retractable cord to a carabiner. They beauty of the piece was that once you placed it around your belt it would not come off, and the carabiner was then attached to a tool, preventing tools in space from simply floating away. I thought, gosh that would be perfect for people who don't want to lose their keys, but the NASA one is made out of titanium and costs somewhere in the tens of thousands of dollars. This project shows you how to make a 3D printable version with some hands on work so that you never lose your keys again, and they will always be easily accessible. The reason I really like this project is that this key chain can by printed and then is practical item that can then be used. Using a spring coil, the keys can be retractable. But before it is a physcial item, a 3D model must first be made. Autodesk 123D Design tool is a very simple tool that can be used to make the model for printing.

The first picture is me actually wearing it. It is the same one actually worn by astrounats.
The picture below shows the Key-Chain after being fully assembled using Autodesk 123D Design tool

Step 1: Main Shell

**Note: Change the Units in the bottom right hand corner to inches before proceeding.**
-Start off by sketching a square that is 2inX2in using the rectangle function and extrude it .15in using the extrude tool. (all functions are located on the top ribbon)
-Now we are going to sketch two squares on top of the one just made, that are all concentric. Using the Polygon tool, change the number of polygon sides to 4, and the distance to 1.131in. Repeat this one more time, but use 1.272in as the distance.
-Sketch a rectangle starting in the lower left hand corner of the  largest square and give it dimensions of .86inX.1in.
-In the lower right hand corner of the rectangle just made, sketch another rectangle with dimensions .08inX.1in. (See FIG A)
-Now make three concentric circles, concentric with the squares with diameters .185in, 1.1in, and 1.2in respectively.
- In the smallest circle we are going to make 4 rectangles with dimensions .1inX.013in. The rectangles are made about the center point. (See FIG B)
- Now we get to extrude all we made so far. See figure C for a picture on what to extrude. The circle is brought up .2in, and the rectangles .75in.
-The circles are designed to fit a flat coil spring so that the cord is retractable. The center circle is split for the coil to lock into. See the picture of a flat coil to understand how it fits. The circles could be modified based on the flat coil spring available. The front panel is missing a sliver so that the string can go to the outside.
-Flip the part upside down so that the slit is still facing you
-On the bottom left hand corner of the square make a rectangle .5inX.2in, and one .25inX.2in directl  to the right of that one. Then repeat of the right side of the object. ( See FIG D)
-Extrude the two inside rectangles .673in
-On the right rectangular prism, sketch a rectangle in the lower left-hand corner .1inX.2in
-Then make two concentric circles with centers on the rectangles right side, with diameters .2in and .075in respectively. (see FIG F)
-Extrude the corners and the center of the circle, then change the settings to cut in order to remove those sections.
-Fillet the tops of the rectangles to .01in. This to make that joint stronger.
-Fillet the outside edge of the piece to .025in. This is to make it easier for pieces to fit together.
-And that is the end of the first piece. Whew

Step 2: Shell Cover

This is the cover piece that we house the inside and make it look complete.
**Note: Change the Units in the bottom right hand corner to inches before proceeding.**
-First start out with a 2in square.
- In the bottom left hand corner make a .098in square. See FIG A
-On the upper right corner of that square make another one 1.804in. The distances are odd, but they give a clearance between the parts so that they can be pushed together.
-Then extrude the area between the squares .74in. See FIG B
-Then turn the piece over and extrude the entire bottom .1in. FIG C
-Turn the piece over again and make a rectangle on the upper right hand corner .457inX.27in FIG D
- Create two concentric circles on the upper left hand corner of the rectangle just made with diameters .075in, and .2in respectively
-make a rectangle that starts at the right tangent point with dimensions .2inX.27in, See FIG E for better idea.
-Extrude the sketches as seen in FIG G to .47in
-make a rectangle on either side of the extruded part just made .11inX.37in, and then another one with dimensions .25inX.37in.(SEE FIG H)
-Extrude the center rectangle so that it cuts all the way through.
-Fillet all the square edges according to FIG I. The larger radius ones are .125in, and the smaller ones are .025in.
-On the opposite side make a hole .1in diameter on the top edge centered (See FIG J) This hole allows for the string to go through the part.
-And this part is done, only two more parts to go, but no worries they are easy.

Step 3: Loop

**Note: Change the Units in the bottom right hand corner to inches before proceeding.**
- Begin by creating a rectangle that is 2.05inX.2in.
-At the very bottom create a .2in diameter circle on the center of the bottom edge
-On the upper left hand corner create another rectangle with dimensions .961inX.1in (See FIG A)
-Extrude the sketch out except for the smallest circle (See FIG B)
-Then round all the edges to .05in diameter
-Looking at the top view create a rectangle in the upper right hand corner .168inX.198in
-Create another rectangle off the lower left hand point, .1inX.25in respective (See FIG C)
-Extrude the last rectangle up .15in
-Round the top of the feature .04in, and the base of the feature .02in (See FIG D)
-That is the Loop piece

Step 4: Lock

**Note: Change the Units in the bottom right hand corner to inches before proceeding.**
-To begin this piece make a sketch of a rectangle with dimension 1.25inX.2in
-On the center of the left edge make a circle with .2in diameter and another concentric circle with .075in diameter (see FIG A)
-Extrude the sketch, except for the small circle, .25in
-Round all the edges .05in diameter (See FIG B)
-Turn the piece over and create a rectangle with dimesnions .412inX.09 on the bottom left hand corner
- Create another rectangle on the upper right hand corner of the one just make with dimensions .25inX .1in
-using the extrude tool cut the center rectangle .142in deep
-Round the edges of the cut just made to a .05in diameter

Step 5: Final Assembly

The parts are designed around inserting a coil spring from a retractable name tag, into part 1. The circle in part 1 can easily be adjusted based on the coil at hand.
To assemble the pieces into a function item, cut a 1in. and .5in copper with a diameter small enough to fit in the hole. Then the ends of the wire would be glues to prevent them from falling out, careful not to glue the pieces from moving around the joint. Then it can be spray painted a metallic color to make it look more authentic.
<p>An STL would be wonderful! Thank you!</p>
<p>Any chance you could make the files available for download? I would love to make one of these for my keys.</p>
<p>I could. what file type would you like, I can do .stl if you want to print, or .ipt for Auto desk Inventor if you would like to edit it.</p>
That's awesome. Did you submit to the I Could Make That contest?
No I did not I will have to look into that one. <br>Thanks
NASA knockoffs definitely qualify. Keep up the good work, and good luck in the contests.