Clamshell Box Part 3: Cover Tray Construction


Clamshell case construction is a step-by step process. The size of the fine binding defines the size of the clamshell’s base tray. The finished base tray defines the size of the top tray that is the clamshell cover.

  1. Use the covered base tray to measure for the cover tray.
  2. Square the mill board by cutting a selected corner to be 90 degrees. Mark the corner that has been “squared”. By starting with squaring the first corner, it  will ensure the other corners will be squared more easily. Be sure the “grain” of the cover tray millboard is parallel to the long side of the board. Match the base tray’s “grain” direction.
  3. Overlay the base tray on the millboard. Align the tray to the squared corner. Mark off the width and height of the overlaid tray onto the millboard. This will become the bottom of the cover tray. Essentially, the the width and height of the cover tray equals the width and height with the 3 walls of the base tray. Allow about 1/16″ for the bookcloth fabric (dependent on the thickness of the bookcloth)
  4. Overlay the cover’s bottom on the base tray and measure the depth of the combined two.

Tray construction helper

  1. Cut the back side panel the length measure of the base panel and the depth measure of the combined base tray + the bottom of the cover tray.
  2. Cut each side panel the width measure of the base + 1 millboard thickness. Pay attention to the “grain” direction of the side panels.
  3. A box making support is a handy helper in making a tray. It keeps the sides perpendicular to the tray base. The bottom and 2 sides of the support is covered teflon laminate that prevents glue from sticking.
  4. Place the side into the box maker support. Glue the vertical edge of the back panel and place against the millboard side panel in the box maker support. Apply PVA glue to the side and back edges of the cover’s millboard base. Lay the base on the box maker base and align it to the back and side panels.
  5. Glue the remaining back and base millboard edges. Place the final side against the back and base panels. Place a weight on the bottom of the tray and allow about 20-30 minutes for the glue to set up and harden.

Construction of clamshell hinge panels

  1. When the glue dries on the cover tray, place the base tray into the cover tray to test the fit.
  2. Cut a millboard panel with 1/8″ added to the width and length measure of both sides(short measure) and the back(long measure). This panel will align flush with the cover tray’s open side.
  3. Cut a second clamshell hinge panel the same size for the base tray.
  4. Cut the clamshell spine length(long measure) the same length as the 2 hinge panels (with 1/8″ additions on each side) and width that equals the height of the 2 trays stacked inside each other.
  5. Cover the clamshell cover tray with the bookcloth material.

Covering the clamshell hinge panels

  1. Align the millboard panels with the spine panel centered between the 2 larger panels. Space 1 + 1/2 board thickness between the center spine and 2 panel on either side for the folding hinge. Measure the width and length of the aligned panels. Cut the bookcloth material adding a minimum of 3/4″ extra fabric all the way around.
  2. Position the panels on the cut bookcloth backing side facing up. Pay attention to including the 1 + 1/2 board thickness between the center spine and 2 panels. Pencil guidelines on the bookcloth backing for the spine and 2 side pieces. The pencil guidelines will help position the panels after the glue application.
  3. Remove the millboard panels and brush on PVA glue to the bookcloth backing. Align the clamshell hinge panels to the pencil marks on the backing. Allow the glue to dry fixing the panels to the backing.
  4. Position the 90-degree square against the millboard edge and align the 45-degree angle point to the panel’s corner. Pencil 45 degree guidelines on each side of the corners. Be sure there is 1 board thickness of bookcloth fabric stand away from the corner point. This ensures there is enough material to cover the corner point.
  5. Glue down the long side turn-ins first. Use the bonefolder to crease and smooth the fabric over the board edges. Run the bonefolder over the fold spaces between the spine and large millboard panels to crease and flatten the fabric. This will lock the panels into place. Smooth down the miter corners last.
  6. Glue the turn-ins on the short sides.

Clamshell hinge

  1. With the bone folder, tuck in the fabric at the corner point.
  2. After tucking the corners, fold the short side turn-ins over the millboard edge and crease the edges with the bonefolder. Smooth the short turn-ins onto the flat-side of the millboard. Be sure the mitered corners meet.
  3. Apply PVA glue to the bottom of the smaller base tray. Align the tray’s open edge to the edge of the large panel toward the spine. The corners of the tray will align with the mitered corners of the hinge panel. There should be equal distance measure of the bottom panel showing on the back and 2 short sides of the tray.
  4. Lay the top cover tray on top of the smaller base tray with the bottom side facing up. Apply PVA glue to the inverted cover tray’s bottom side.
  5. Fold the spine hinge panel over the open edge of the stacked trays keeping the larger panel vertical making sure the spine piece is flush to the tray’s open edge. Then let the large panel fold down on top of the upturned cover tray. Press the panels firmly to the tray bottoms.
  6. Be sure the trays and hinge panels fit snugly on the spine and open to test the hinge action.If all pieces fit well together, close the clamshell. Place bag weights on the top of the clamshell to press the hinge panels to the tray bottoms until the glue dries.

Read more in Clamshell Box Part 4: Lining the Clamshell Interior

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