As I'm sure most everyone has seen at this point that crayons can be lit on fire and stay lit for 15 to 25 minutes. Any of you who don't know this, prepare to see crayons in a whole new light! It has been shared by many people across the internet as a good way to have light in an emergency. I do it because it's awesome. However, I like to do it outside but the wind where I live is brutal. On a lovely night perfect for sitting I cannot light my crayon in some sort of a tuna fish or olive can that I found in the garbage because the wind would blow it out! So I set about on a design for a "crayondle stick holder" that could be cast out of Rapid Set Cement All and would keep my crayon's large flame bright and mesmerizing in a stylish and novel sort of way.
Step 1: Design Your Chimney
When starting this project I had a good idea of what I wanted this chimney and holder to look like. I based my design on a chimney that people use for wood fires in their back yards. I used Rhinoceros 3D modeling program to design and model the two pieces; the chimney and the holder.
*crayons have a diameter of a hair less than 3/8" and a height of 3-5/8"
1.) Design half of the profile of both the holder and chimney. I drew the holder with a hole half the diameter of the crayon so it will be the full diameter of the crayon when revolved. The hole had walls 1/4" high to hold the crayon up as seen in the second picture. I gave everything a thickness of 1/2". That is the smallest thickness I would recommend for this cast.
2.) A simple revolve 360 degrees around the center axis will give you the basic shape of your chimney and final shape of your holder.
3.) I wanted to make two ways of viewing the crayon burning. I gave it a traditional opening at the base like an outside wood chimney and a slot that is slightly wider than the crayon that ran the rest of the way to the top of the chimney. Both are done with simple extrusions an Boolean Subtraction operations. This part of the step can be seen in the pictures 4 through 8.
Step 2: Make the CNC File
Next, I designed the mold by subtracting the designed object from different masses to obtain the inverse. Keep in mind when designing the mold that the CNC machine cannot cut undercuts and the mold will have to be made in several pieces. Also keep in mind that rigid insulation foam is the material that is going to be milled and usually has a thickness of two inches. This means that the mold cannot have pieces that cut deeper than two inches.
1.) The outside part of the mold for the chimney will be designed in two pieces to avoid undercuts and for easy mold assembly and dis-assembly. I made sure one side of the mold had the inverse of the openings centered in it as seen in the second picture.
2.) To make sure that the object is hollow when cast, make an object that fills the inside of the chimney by revolving the inside contour. Split this object in half so it can be cut on the CNC and then be glued together later before casting
3.) The holder is cast as a separate piece. The mold is made by just subtracting the object from a mass to obtain the inverse
The third image shows all the pieces of the mold 3-D modeled and ready to be milled on the CNC machine. There are 5 pieces in all. 4 pieces for the chimney and one piece for the holder. The final image shows the milled foam that will be used in the casting process.
Step 3: Assemble Your Mold
Once you have your foam milled, it's time to cut out the pieces and put the mold together.
*make sure that you do not get to close to the foam when using spray adhesive so that the aerosol doesn't melt the foam.
1.) a hot wire or band saw will work best for cutting the pieces apart. You can sand the foam smooth or let the texture of the milling process show in your cast. I chose to keep the texture from the milling.
2.) take the two inside pieces of the chimney mold and glue them together with a some spray adhesive to make one piece
3.) Take the outside piece of the chimney mold that has the inverse of the viewing slots and center and glue the inside mold piece inside with spray adhesive to hold it in place. Secure these pieces together with screws through the back. This can be seen in the 5th and 6th image.
4.) Take the other opposite outside piece of the chimney mold and secure it to the other side with screws. Make sure that they match perfectly. It should look like the last image when completed.
5.) The holder is already ready for casting.
Step 4: Casting
Casting is sometimes the most tricky part of the process and with foam a lot of the time you only get one shot. I chose to use Rapid Set Cement All for my casting process. Cement All is a grout mixture of Portland cement and sand. There is no course aggregate so it is ideal for thin casts like this. It can capture a lot of detail, be poured relatively thin, and be very strong when fully cured.
1.) I just used a small bucket and a dowel to mix the grout in. I mixed to a consistency that was a little thinner than pudding. It has to be a consistency that can easily be poured into the mold. The best way to get a feel for how thick to mix should be is just through practice. The consistency can be seen pretty well in the 4th image.
2.) Before you do your casting you have to apply a mold release to your foam mold so the mixture doesn't stick. I usually use WD-40 in this kind of cast and it always comes out great. Be liberal with it. The chimney mold had a lot of curves so it was a little difficult to get the release agent inside.
3.) After pouring, pound on the table to level out the grout and bring the air bubbles to the top. This will ensure a nice consistent cast. This can be seen in the last image.
Step 5: De-molding
In about 6 to 8 hours you are ready to take apart your mold and see what you have created. This is the best part of the entire process.
1.) For the holder just lightly tap the mold on the edge of the table and let the piece fall into your hand as shown in the first image.
2.) Remove all the screws from the chimney mold and pull the sides off. This leaves the middle piece inside the cast.
3.) Try to just push the center piece out of the bottom. I must not have had enough mold release, or had a small hole in the center part of the mold but my inside piece was very stuck. If this happens it is easy to remove with either lacquer thinner or acetone. I would recommend lacquer thinner because it doesn't seem to contain as much acetone and will just eat away at the foam making it easy to pop out of the cast, as seen in the 3rd and 4th images, where full blown acetone will dissolve the foam and leave a bigger mess that is sometimes difficult to clean up. Wear good quality gloves when using chemicals.
The final image shows how the "crayondal stick holder" parts fit perfectly together. As soon as the lacquer thinner dissipates its ready to try out.
Step 6: Design Crayon Cutter
The way that the crayon lights is like a candle in reverse. The wax is on the inside and the paper outside works as the wick. So in order for it to work, the big wax chunk at the top of the crayon that you usually draw with has to be cut off to easily light the paper. You can use a knife of some sort to cut it but I decided to come up with a contraption that would easily cut off the top of the crayon. It sort of resembles a cigar cutter.
1.) I based my design around a straight razor blade and 1/8" plywood pieces that could stack to create the two sections of the cutter.
2.) First design draw up your pieces in Autocad to make a laser cut file. Then to be sure that your design works in 3 dimensions, take the Autocad file and open it in Rhinoceros and quickly model it to see that there are no issues. The second image is the completed lase cut file that was used to cut 1/8th" plywood.
3.) The cutter is made in 2 sections; one side holds the crayon with a hole just big enough to fit the crayon in, as seen in the 5th image, and the other side holds the razor blade that moves across the hole, as seen in the 6th image. Between these two pieces inside I put springs that I took out of mechanical pencils to push against the pieces that holds the razor, as seen in the 7th image. The 8th image shows how the whole thing is capped so it stays together as one object. Assemble your pieces carefully so that the pieces slide easily. Use just a little white glue to allow to easy manipulation when putting it together instead of super glue that will hold instantly.
You can see how the whole thing works in the 9th, 10th and 11th images.
Step 7: Cut, Light, Enjoy
Lighting the crayon in the crayondlestick holder is simple and fun. I would recommend Crayola crayons because they have paper that resembles construction paper that is easy to light where other crayons seem to have a wax paper that is harder to light.
1.) Cut the top of the crayon off with the new cutter.
2.) Hold the lighter to the bottom of the crayon until the wax that sticks out starts to melt a little. Press this side into the holder so it is secured in the hole. Hold the crayon in place for a few second while the wax re-hardens. This is seen in the 1st and 2nd images. Make sure there is no grout dust in the hole so the wax adheres to the holder.
3.) Hold a lighter to the top of the crayon paper until the crayon catches fire. It is usually a pretty big flame once it gets started.
4.) Now put the chimney on the holder to let the flame go nice and big and straight out the top of the chimney with no fear of the wind blowing it out.
5.) Relax and enjoy
Step 8: Cleaning the Holder
For cleaning the holder you have a couple of options to get the wax off.
1.) You can use a heat gun or hair dryer and let the wax just melt and wipe it off with a paper towel. After I heated it up I just scraped the wax out of the hole in one swipe. I just used a mechanical pencil that I probably stole the springs from but you could use anything to pull the wax and paper out.
2.) If you want to light multiple crayons in a row you can blow out the crayon just a little bit early so you have something to grab onto and can pull it back out of the holder. Or you can use the wax from the previous crayon to hold up the new one.
3.) You can submerge the holder in mineral spirits for a while so the wax dissolves. This worked great but I would rather have the safer alternative of the heat gun that is not dependent on chemicals.
I don't worry about any burn marks because it give character to the chimney.