Contact Juggling

Date: 05-21-02 20:12

This is addressed to GReg and everyone else who are atempting to float a 1" sphere within a 3" acrylic.

I have been contact-juggling for 1 1/2 years now and have been experimenting with making my own balls for nearly as long. It is not impossible to suspend the smaller sphere at the exact center of the larger one, however, it is very difficult to pull off. We are talking three dimensions here, you can't just spin the mold as if you were making a hollow silicone ball and expect everything to come out all right. There is only one practical way to accomplish what you plan with acrylic; (Tip: Experiment with acrylic casting first so you know the rate of shrinkage involved, and always pressure cast as it is the only sure way to avoid bubbles.)
1: Pressure cast your smaller ball and polish it.
2: Cast 6 clear acrylic rods 1/2 cm across and 1 3/4" long.
3: Contour and polish one end with the reversed arc of the 1" ball.
4: Map out the six axis of the ball, marking them with a small scratch from an exacto (This will not be visible in the final product).
5: Afix said rods to the ball exactly centered on the scribed marks with a bit of clear epoxy.
6: Place resulting form in a 3" ball mold that has been modified with dimples for the ends of the shafts (The measure of the form tip to tip being slightly more than 3")
7: Slowly and carefully fill the mold with clear acrylic resin and place in a pressure chamber under 60 psi for at least three hours, allow to cure naturally.
8: When removed from the mold, the resulting ball will have six nipples which must be ground off (A wooden sanding block conforming in shape to the outside curve of the ball will do nicely, use at least 600 grit sandpaper, no heavier.)
9: Polish the ball.

There is, however, a much easier way to get the effect you are trying for. The main problem inherent in doing this work with acrylic seems to be that the rate of shrinkage is too variable. If trying this method I recomend using a clear urethane compound like CrystalClear 204 (Available from www.smooth-on.com), it has much the same durability as pure acrylic and IS water clear (Unlike the poly-carbon compounds some people use.). These should also be pressure cast, for directions on doing so cheaply and easily e-mail me at Tare@boxfrog.com.
1: Make three molds, one being a 1" ball (Exact measurement of mold as CC 204 has neglible shrinkage when pressure cast.) and the others being matching hemispheres so that when fitted together they form a 3" sphere with a 1" spherical hollow in the center.
2: Cast all three and cure (If you used a mold coating agent like pre-cote (smooth-on.com) you will not even have to polish at this stage.
3: Afix small sphere to the inside of one hemisphere with a thin and even coat of epoxy, always making sure to cover ALL of the glueing surface, clamp together with a Quick-clamp, and allow to cure.
4: Affix second hemisphere to resulting form with thin and even coat of clear epoxy, clamp together with a Quick-clamp, and allow to cure (If your epoxy coats were truly even you should have no air bubbles or distortion at the joint).
5: Polish.

These methods do work, I have suceeded with both, though in all honesty I must say that the second is by far the easier for the nocice mold maker.
It is also possible, using the second process, to make a ball with a suspended object inside that will always remain upright no matter how the ball is turned. (Instructions are for a 4" ball.)
1: Make three molds, one being for a 3" ball and the other two being for hemispheres that ,when attached, form a 4" ball with a 3" hollow inside (1/2" walls)
2: Cast the 3" ball with whatever object you wish inside, also encase a small lead plug near the bottom of the sphere:(Attempt to hide it in or behind whatever you are encapsulating.) this is so the 3" sphere will be bottom heavy (Very important).
3: Cast your hemispheres and wipe down the insides with a thin coat of clear sillicone lubricant, making sure to coat all of the inner surface but not the parts of the hemispheres that will touch.
4: Apply a thin coat of epoxy to both glueing surfaces ending 3/16" from the inner edge, fit hemispheres together (With 3" sphere between them.), clamp together LIGHTLY, and allow to cure. Because the lead weight will always seek the bottom of its enclosure and because of the lubrication, whatever you have encased therein will always remain upright.
Well, looking back, that seems to sum it up... If you have any questions or would like to know if something is possible merely e-mail me (Tare@boxfrog.com) and I will respond as soon as I may. I will be moving to Boston, MA in early July and will soon after start giving free CJ classes for beginers and making custom balls on a first come first served basis as well as fire juggling equipment (Poi, fans, staff, etc.), anything is possible. If you would like more contact information other than my e-mail address, please wait untill after the move and I will be happy to oblige those who ask. Till then.

Marz Kelly

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Robin Spehar

05-17-02 01:13

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