Making A Kaleidoscope



There is so much material on the web about assembling a kaleidoscope, that there's not much point in repeating the same information again. Instead, we thought we would provide some more detailed information to go along with our kaleidoscope video, specifically our thoughts about making kaleidoscopes for a large group of students.

Introduction.

By now you probably know that a basic kaleidoscope consists of three long mirrors, some sort of transparent cell at one end to hold bits of translucent colored glass or plastic, and some sort of basic structure to hold the parts together. So we'll focus on each of these components in turn, with an emphasis on low-cost and quick, simple assembly that can be of particular importance to a student project.

Structure

Most recipes for kaleidoscopes suggest using some sort of tube to hold the whole affair together, the traditional choice for a student kaleidoscope being a standard-sized paper tube. This assumes that one of the key components, the transparent cell at the end, can be made to fit snugly into the end of the tube. So by making the design decision to use a tube, you are simultaneously forcing yourself to find two items that match.

After some thought, we abandoned this design restriction and realized that the tubular design missed the whole purpose of the "structure", which is to connect the cell and mirrors. Think "glue".  More on this later.


Cell

The traditional "cell" is a cylinder with transparent 'windows" that can be filled and sealed. Our choice was to use commonly-manufactured plastic Petri dish and cover pairs (BD Falcon 35 mm Petri dishes, distributed by Fisher Scientific, part number 08757100A.) 

We made this choice because
a) assembly is very fast
b) assembly requires the use of relatively un-sophisticated tools that can be found in the typical elementary school
c) the basic material preparation (teacher time) is essentially zero.

The disadvantage of this choice is that the cost per 'scope can be moderately high (about $0.35 per cell) and that a bulk purchase of parts may be required.

The most common size for a Petri dish is a rather large 100 mm diameter, but with a little efffort, we were able to find 35 mm diameter Petri dish pairs (dish and lid). Our particular choice was not a tight-fitting pair, because the only tight-fitting parts that we could find were of 60 mm diameter and were more expensive. In our opinion, gluing the dish and cover together was so easy that the tight-fitting requirement might not need to be considered except for the most demanding of assembly circumstances (for example: kindergarten). Because our school district received a discount through the distributor, we were able to purchase a bulk quantity of the Petri dishes at a very substantial discount over the price listed on the web.





Cell Filler

The best cell filler is small pieces of broken tinted glass.  This glass needs to be tumbled to smooth off the sharp edges so kids will not be injured.  Fortunately, we have a local supplier of such stuff, a rather odd antique store in Half Moon Bay, CA that goes by the name of "Half to Have It".  They literally have a large yard of smoothed, broken glass bits and pieces.  The material that we used was hand-selected; I doubt that they will do this for you.  One might also check stained glass supply shops for similar material. 

In lieu of stained glass, tiny colored clear plastic beads are available at the typical well-stocked "craft" supply stores such as www.michaels.com.




Cell Assembly

The words "hot glue" say it all. Two blobs of hot glue are placed on the OUTSIDE edge of the dish (the smaller diameter component), 180 degrees apart. When the cover is added (after glass or plastic beads are added), the glue blobs squish between the cover and dish without oozing into the cell volume. The glue stiffens in about a minute.  Alternatively, the cell can be glued from the outside at the seam (see below) but I personally like the former approach.

When testing a prototype, the instructor should experiment with the amount of filler added to the cell. We settled on filling the cell about half-full for the sized particles we used. Smaller beads that tumble more readily in the cell might allow more filling.




Mirrors

The most important components of the whole project are the mirrors. A kaleidoscope is unimpressive unless multiple reflections of the light coming from the entrance port are achieved. And for this to happen, the mirrors need to be of good optical quality. Do not waste your time trying to make your own mirrors by going to an art supply store to purchase cardboard sheet with a laminated "mirror" or "silvered" coating, or do not waste your time buying aluminized mylar sheet which is then adhered to cardboard with spray adhesive or double-stick tape. The experimenter actually should try these techniques, so that when one actually does take the leap to the somewhat more expensive material, one will be that much more amazed by the difference in quality.

Our choice for mirror material was to use .060" thick acrylic plastic with an aluminized mirror back surface. This sort of material is very readily available in the .118" (nominally 1/8") thickness, but we think that you will find this material to be too thick. Our thinner material was purchased from Calsak Plastics (http://www.calsakplastics.com). The material comes in 4' x 8' sheets and is thus obviously not easily shipped. But all plastics vendors provide fabrication services and one should not bother to attempt cutting the material oneself unless one has access to the specialized saw required to cut the material cleanly. We purchased the entire sheet cut into 1-3/16" x 5-1/2" pieces. The 1-3/16" dimension was selected so that when the mirrors were assembled, they would form an assembly that neatly fit the Petri Dish cell.  The 5-1/2" dimension was selected so that when the sheet was cut along the 48" direction, we would have little waste after accounting ffor the saw thicckness. 

The basic sheet cost was $78 and the cutting charge was $38, resulting in over 500 pieces, at a net cost of about $0.65 per kaleidoscope assembly. We required overnight shipping for our project, but ground shipping will save a substantial amount of money and increase the per assembly cost by perhaps 20%.

Here are the raw mirrors, already cut, as they came from Calsak.




The mirror material is supplied with a protective film that may be removed by peeling up the film at a corner, or that may be removed by pulling off the film with the help from a piece of tape. Wait until just before assembly to do this to keep fingerprints off of the mirror surface.




Mirror Assembly

It's hard for small hands to assemble the mirrors together. It helps to place a rubber band around the whole set of mirrors, and then the mirrors can be aligned and held securely while taping. The ends of the mirrors should be adjusted to that they lie in a plane. The assembly will then stand up perpendicular to the transparent cell when stood on end.




Wrap masking tape or fancy "artists" tape around the ends of the assembly, pulling the mirrors tightly together to minimize the space between the edges of the mirrors. The tape should be held back from the ends of the mirrors by about 1/8 inch so that when the mirrors are glued, the glue is actually in contact with the mirrors, and not in contact with only the tape.





Finally, you're ready to attach the mirrors to the cell. Stand the mirror assembly up on top of the cell and center the mirrors onto the cell. Carefully put a blob of glue at the center of each of the three joints between the mirror and cell, being very careful not to move the mirrors while gluing. The hot glue will not leak under the mirrors and contaminate the portion of the cell that is visible if you are careful not to move the whole afffair while gluing. Sometimes it helps to wrap a large rubber band around the whole affair (mirrors and cell) while gluing takes place.