Ruth A. Walker
Hunter College City University of New York and Louise F. Davis Worthington Corporation Harrison, New Jersey
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Jig for Removing Accurate Spherical Segments -
A jig whose main feature is a V-shaped
trough with sides a t an angle of 71° was proposed by Lambert' for positioning the tetrahedral cuts on the styrofoam components of Fisher-Hirschfeld-Taylor type models. Two basic modifications of this structure have greatly increased its accuracy and versatility. The trough instead of being tiltable is mounted horizontally and sawing slots are placed a t an angle of 71 to the base, and a backstop is inserted in the trough. The backstop consists of a smaller trough2 with one end cut so that the triangle formed by closing this end with a board will have edges that parallel the cutting slots. Both troughs are slotted near the top so that the backstop can be secured in position with a nut and screw (Fig. 1).
' LAMBERT, F. L., J. CHEM.EDUC.,30,503 (1953).
This method of supporting the backstop wae suggested by Gaetano D'Angelo, a Hunter undergraduate.
U Figure 1. Side view rhowing backstop and cutting slot in relotion to the sphere.
The segment to be removed from the sphere lies between the backstop and the cutting slot, a distance which can he measured accurately as follows: Place a model of a tetrahedron in the trough with its edges a t the cutting slots. Insert in between the backstop and the face of the tetrahedron a block of wood the exact thickness of the segment to be removed (Fig. 2). Secure the backstop in position. Replace the tetrahedron and the spacer with the sphere, and cut. To obtain cuts a t the tetrahedral angle keep turning the cut face as indicated in Figure 3. The position of the backstop can be marked on the trough so that precisely the same cuts can subeequently be made. Thus, accuracy and reproducibility are obtained more easily from this jig than from those previously described. This jig is easy to construct because it can he built around a tetrahedron, thus eliminating the need for careful measurement of angles. Construction details are available on request.
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Figure 2. Side view rhoring how to parition backstop with a tetrahedron ond o spacer the sire of the segment to be removed.
Figure 3. End view. Sphere ready for second cut in the formation of o tetrohedrol atom.
Volume 42, Number 8, August 1965
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