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Cradle Mount for Objects with Rounded Bases

Purpose

This storage mount is designed to support objects that have rounded or conical bases (e.g., ceramic jars and baskets). The rims of these objects often are not structurally engineered to bear the weight of the object, thus they should not be stored upside down or resting on their side. The cradle mount supports objects at the base to avoid placing stress on the potentially weak rim areas (Fig. 1).



Figure 1. Interlocked cradle mount anchored to pH neutral cardboard base with twill tape ties.

 

Author(s)

Brigid Sullivan
Collections Conservation Division
Cultural Resources Center
National Park Service
Bldg. 28, Charlestown Navy Yard
Charlestown, MA 02129 USA
Tel (617) 242-1979
Fax (617) 565-6859

Illustrations: Karen Ackoff after Brigid Sullivan

Publication: 1992

 

Description

The cradle mount is formed from two pieces of polyethylene foam plank carved to the shape of the object’s base, and placed at right angles to each other. Areas that contact the object are covered with softer, thin closed-cell or crosslinked polyethylene foam sheeting to avoid abrasion. For added stability, the outside mount is fastened to a base board with cotton twill tape.


Materials Tools Supplies

  • Corrugated pH neutral cardboard
  • Cotton twill tape
  • Flexible drafting ruler
  • Polyethylene foam plank, 1in or 2in thick, 2 pieces
  • Polyethylene foam sheeting, closed cell, crosslinked (electron irradiated) 1/8in thick, 4 strips or spunbonded olefin tape
  • Utility knife


Construction

  1. Starting from the bottom center of the object, measure the curve from the base up to 1/3 of its height with a flexible drafting ruler (Fig. 2). The rulers can be bent around a form to retain the profile of the object until moved again.


    Figure 2. Measuring the base curvature of the object with a flexible drafting ruler.

  2. Leaving 2in at the bottom of a polyethylene plank, mark the profile of a full cross-section of the object and indicate a center axis. If the shape of the object is not too irregular, one profile can be flipped to provide a full cross-section (Fig. 3).


    Figure 3. The profile of a full cross section of the object is marked on each plank, leaving 
                    2in at the bottom for cutting interlocking notches.

  3. Cut out the complete cross section profile with a sharp utility knife (blade 10 or 11). Repeat the process to produce another cross-section profile to bisect the first.
  4. Cut a 1in x 1in notch in the center of the base of one cross section, and another 1in x 1in notch in the center of the cut-out curve in the other profile plank (Fig. 4). Fit both cross sections together at the notches.

    Figure 4. Notches are cut in the base of each plank for interlocking the two pieces.

  5. Make sure the object fits adequately into the cradle. Pare away foam with a utility knife or file so that the fit is close enough to prevent rolling or pitching of the object, but not tight enough to exert pressure on the walls of the object, or inhibit easy retrieval of the object from the mount.
  6. The cut surface of polyethylene foam plank can be rough. To avoid abrasion of the object, line the curved area with strips of smooth closed-cell or crosslinked polyethylene foam or spunbonded olefin tape. The lining material can be attached with wooden toothpick splints as indicated in figure 5.

    Figure 5. Cut edges of the plank are lined with strips of a soft, smooth material.

  7. Attach the cradle to a cardboard base to increase the stability of the mount. Punch holes in the cardboard and in the base of each quadrant section of the foam planks. Thread twill tape through these holes and tie the cradle to the cardboard base (Fig. 1).


Comments

The thickness of the polyethylene foam plank chosen for the support depends on the size of the object. Thicker planks should be used for larger and heavier objects.

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