Occasionally one finds projects which require the insertion of two or three skewers or knitting needles through the middle of a Styrofoam ball. (For example the building of an anemometer or a weather vane as described in the book A Guide for Using the Magic School Bus® Inside a Hurricane in the Classroom.) Strictly speaking, this is impossible because the diameters of skewers and knitting needles occupy a finite volume and thus cannot all intersect at the center. Once one skewer is placed through the center of a Styrofoam ball the path of the second skewer moving towards the center of the ball is obstructed by the first skewer.
This Instructables provides a method for having skewers as close as possible at right angles to each other so that they appear to come from the center of a Styrofoam ball. The Instructables is as an extension of an earlier one entitled How to insert a skewer into a Styrofoam ball without using woodworking tools (located at: https://www.instructables.com/id/How-to-insert-a-s...). As many of the steps in the present Instructables are identical to those presented earlier, instead of illustrating and describing all the steps, only modifications to them are described and images given where necessary to illustrate these modifications. It is assumed that you are familiar with all the steps described in the earlier Instructables.
The materials required are the same as before except that now 5 or 6 bamboo skewers are required. If all skewers are to meet at the center of the sphere then 6 skewers are needed. Only 5 skewers are required if one of the skewers passes directly through the center of the ball and remains in the ball for whatever project you wish to carry out.
Step 1: Construct Cardboard Boxes
Construct two cubic cardboard boxes as described in the previous Instructables. This time however, draw diagonals on all 6 faces of the fixture cube and pierce holes at the intersection of these diagonals.
Step 2: Insert Skewers
Each time, before inserting a skewer into the fixture cube containing the ball, the skewer is inserted into the jig cube as described in the earlier Instructables.
Insert the first skewer into the fixture-and-ball as described previously. However, this time push the skewer all the way through the fixture-and-ball so that the tip of the skewer passes a few centimeters through the hole on the opposite face of the of the cube.
With the first skewer remaining in place in the ball slide the jig away from the fixture and remove the jig from the skewer while keeping the skewer inserted in the fixture-and-ball.
Keep the first skewer inserted into the fixture-and-ball when inserting extra skewers (as described below) in order to minimize any movement of the ball.
With the fixture cube sitting on a firm surface, line up the pointed tip of a second skewer with one of the central holes on the fixture cube that is at right angles to the face through which the first skewer was inserted. Then lower the jig so that it sits directly on top of fixture-and-ball
While holding the jig and fixture, push the second skewer through the fixture-and-ball until resistance is met due to the tip of the second skewer reaching the first skewer. Then, slide the jig along the second skewer away from the fixture and remove it from the skewer while keeping the second skewer inserted in the fixture-and-ball.
Keeping both skewers inserted in the fixture-and-ball, repeat this procedure with the remaining three central holes on the fixture cube that are at right angles to the face of the cube through which skewers are inserted.
If a skewer is being inserted into a face of the fixture cube that already has a skewer inserted in its opposite face, then ensure that just under half of the fixture cube is sitting on a firm surface before inserting the skewer into the fixture-and-ball.
Step 3: Removing the Skewers and Ball
Once all 5 skewers are inserted into the fixture-and-ball, remove the last 4 skewers from it so that the ball can be removed from the fixture as described in the earlier Instructables.
Reinsert the remaining 4 skewers back into the ball.
With this procedure only one skewer can be inserted all the way through the ball, allowing the ball to slide up and down the skewer. The remaining skewers can only be placed just under half way through the ball. As noted in the Introduction, if all skewers are to meet at the center of the ball, then the skewer passing all the way through the ball can be replaced by 2 skewers meeting at the center of the ball. In order to have these skewers remain firmly in place, they can be glued into their holes.
Step 4: Testing
You might like to carry out the test described in the earlier Instructables to see how close the skewer is passing exactly through the center of the ball. A further test relies on the necessity of having the newly made pairs of opposite holes being in line with each other. This can be checked by inserting a skewer through one of the pairs of opposite holes and seeing whether it readily passes through its corresponding opposite hole.