SIMS Plumbob

Two years ago my wife told me that she wanted to be a SIM for halloween.  Being the dutiful husband I am I got to work.  I researched for hours the best way to go about this project.  There were ALOT of helpful designs out there.  Unfortunately i'm kind of arrogant, so I looked at all the well thought out, well intentioned designs and thought, I can certainly do that better.  My major gripe was the materials that were being used by others.  To me, the SIM plumbob is a crystal that radiates light from the inside.  The crystal structure breaks up the light in a sparkle kind of way rather than a flat uniform color.  With this in mind I set out to create the awesomness that is before you.

Note:  There are deffinately things I would change with my design if I were to do it over.  Financial considerations played a big role in some of the steps I took.  Please feel free to critique the design.  If I decide to make another one I will take all ideas into consideration.

Materials:

Castin Craft resin (alot)
Castin Craft catalyst
Mold release
26 gauge sheet metal
1/2" steel tube
AWG 3 point tool belt shoulder straps
Double stick tape
1/4" bolts
1/4" nuts
Bicycle safety lights

Unfortunately, because this is an after-the-fact instructable I do not have a picture of the actual forms I used for the 12 sided diamond but I will do my best to describe it. 

1) I used 26 gauge sheet metal because I am a sheet metal worker by trade and I am used to working with it.  There was a two part mold for EACH HALF of the 12 sided diamond.  I made two 6 side pyramids.

2) After looking at the SIMs literature that comes with the game discs I figured that the plumbob has a height to width ratio of about 3:1.  I didn't do any fancy trig calculations to figure the angles out.  With a piece of paper and a compass I played with some dimensions until I came up with a size that looked right.  The dimension I cam up with was a form the has 2 1/4" base widths and 6 1/2" centerline height.

3) Knowing that this was going to be a form that was to be filled with a liquid I then extend the form height a little and scored a line where i would be filling the resin to, so that none of the resin overflowed.  The picture describes the basic layout of each half of the mold.  When bending the metal it is important that you measure the angle of the BOTTOM of the pyramid to 120 degrees.  NOT the angle between the two flat sides.  Put the form upright on a flat surface and lay a compass down next to it.

4) There are two 1 inch flaps on either side so that there is something to help clamp the two halves together.  I applied some silicon to each flap and clamped them together.  The silicon was mostly to prevent the liquid resin from running out of the mold.

I'm sure there are other ways to make a mold this shape but I went with what I was familiar with.  Also, once you add the catalyst to the resin it gets really hot.  I figured the metal would handle the heat well.

This was my first experience with Castin Craft clear resin.  This stuff is mostly used for making little pieces of jewelry, or paper weights with objects suspended inside them.  All of the instructions and tips I found for it only included mixing instructions for castings of up to one inch thick.  This was the biggest hurdle I faced.  The resin cures when you mix in a catalyst that starts a chemical reaction which heats up the resin and causes it to harden.  Too little catalyst and you end up with jello.  Too much catalyst and the casting will crack from the excessive heat.  The casting you will be doing for this is seven inches thick.

I decided to play with the ratio of resin to catalyst first to see if I could get it right.  Pictured is my first attempt, I suspended one of my sons lego men for extra flare.  It came out great.

UNFORTUNATELY, there is no rhyme or reason to the ratio mixing once you add coloring to the resin.  I had to special order some green coloring because mixing the blue and yellow coloring that you can buy at Michael's simply does not work.  Once you add the coloring it throws off the catalyst ratio in unpredictable ways.  That, plus the fact that outside air temperatures will affect the curing process made for alot of attempts.  I wish I could give you a formula but there are just too many factors that will affect the curing.  I personally went through $150 worth of resin until I got it right two times (remember there are two halves of the plumbob).

The last picture in this step is a failed casting.  The apex of the pyramid came out like jello, while the bottom and center cracked horribly.  You can kind of make out the striations in the middle.  I think this was due to poor mixing prior to pouring the resin into the mold.

I was so happy when I finally got two pyramids that had no cracks in them!  The second pyramid required some time under a heat lamp to assist the curing, but it finally cured completely after about 2 days of letting it rest.  After demolding the pyramids i noticed that due to a meniscus affect the bases of the forms had a slight raised edge to them that needed to be sanded flat.

So I had this pretty awesome crystal 12 sided diamond that I needed to figure out how to join it together, light it, and suspend it above someone's head.  Oh yeah, this stuff is heavy!  The plumbob weighs 10 pounds.

From the beginning I knew that plumbob would have to be able to be easliy seperated to replace the batteries for whatever light source I used.  I decided to try neodinium magnets.  Thats the six silvery spots on the bottom of the pyramid.  I drilled 1/4" holes in the bottom of each pyramid and epoxied the magnets flush with the surface.  This actually worked great but there was no protection against shear forces, and once the magnets in each half didnt line up the thing would fall apart.  So the i decided to add stainless steel posts that would keep the two halves alligned.  This solved the shearing problem but I was still not comfortable with it holding together.  In the end, right before my wife walked out the door on halloween night I added double sided tape.

If I were to do this again I would suspend some LED's in the resin before it cured, but because I didn't think of that I had to look for another solution.  I found some saftey lights that you attach to your bike at night.  They click on and click off and are covered in a rubber sheath to protect them.  I cut of the rubber part and was left with something roughly the same size and shap as a small votive candle.  I drilled a hole in the bottom of each pyramid and siliconed the lights in flush.  The silicone holds them in place pretty well and it is easy to scrape out if I need to replace the lights, which don't have replaceable batteries.

As you can see, all of the drilling is pretty visible from the side, which is why I would use suspended LED's and double sided tape next time.  However, in my defense when the thing lights up at night you can't see the drill marks.

The first image shows the basic design for my suspension rig.  As I said before, the plumbob weighs 10 pounds.  I knew I would need a substantial setup to hold it in place.  The rig was specifically designed for my wife's body.  She has much better posture then I do.  The rig consists of 1/2" steel square tubing welded in a sort of "s" curve.  There is a triangular shaped steel centerpiece that is bolted to another triangular shaped piece of steel that sandwiches a three point tool belt harness.  The harness hooks to the belt loops on a regular pair of jeans.  The weight of the plumbob kept leaning the whole thing forward and hitting the back of my wife's head, so I extended the bottom arm low enough to go under her belt slightly.  This keeps the whole thing parallel with her back at all times, even if she bends over.

I know the rig looks rather ungainly on me but it was designed to follow the shape of my wife's back and neck.  She wore it on top of an under shirt, and then put another shirt on over the rig.  She has long braids which completely obscure the part immediately behind her head.  The steel that extends above her collar line is painted matte black to blend in with her hair and make it less visible at night.

To attach the plumbob to the rig I cut off a small section of the bottom of the diamond, drilled a hole for a 1/4" thread rod and epoxied it in place.  The rig has a 1/4" nut welded to the top of it which I just thread the rod into.

All in all, I think it turned out well.  There are deffinately some improvements to be made.  The looks on people's faces were priceless.  You can see the light from a block away so people would come running up to my wife from a couple hundred feet away completely amazed until they got close enough to see the steel rig.  At night you need to be within 3 or 4 feet to see the rig.  Success.