The CCI Channel Crate: Making a Lightweight, Reusable Crating System – Canadian Conservation Institute (CCI) Notes 20/1

List of abbreviations

D

depth

H

height

HTS

handling-transportation-storage

N

number of skids

W

width

Introduction

When museum objects and artwork are transported by specialized art handler networks, the use of lightweight containers (such as corrugated cartons, mirror boxes and triwall containers) may offer adequate protection for some items of light to medium weight. The channel crate described here adds one more option to these crating choices. It is strong, reusable and can be broken down into a fraction of its assembled volume for storage.

Overview

The crate structure is made of four plywood channel sections that are easy to fabricate with straight-cut plywood parts, wood screws and glue. The channel sections are joined together using M8^{Footnote 1} (5/16 in.) nuts, bolts and washers. An inventory of several vertical and horizontal channel sections of the same depth permits the assembly of several channel crate sizes.

The front and back covers are made of triple-wall corrugated cardboard (triwall). This material is a strong, lightweight wood substitute that is inexpensive and can be easily recycled or reused. The cover edges are finished with reinforced kraft paper tape. Two cover fastening methods are described here. Option 1 is a closure with wood screws; option 2 is a closure with machine screws that engage with threaded inserts permanently installed in the channel rails (Figure 9).

Channel crates for paintings

The channel crate and a handling-transportation-storage (HTS) frame offer a flexible solution for shipping paintings of various sizes (Figure 3a). An HTS frame can contain one painting or several. Two or more HTS frames can also be joined together face to face using draw latches or other suitable hardware.

Thermal insulation

If additional thermal insulating ability is required, rigid polystyrene insulating panels can be added externally, inside the channel’s recesses, and internally, underneath the two cover panels.

Shipping and return for reuse

After the outbound shipment, the plywood channels and protective cushions can be returned to the sender for reuse in a compact form that can be shipped at low cost by common carriers. The corner pads can be packed neatly inside a fitted corrugated box that is flat-packed inside the channel crate on the outbound shipment.

The condition of channel crate parts returned to date suggests that the channel sections can provide long service life if they are stored and shipped with reasonable care. Wrapping the channels in polyethylene or shrink wrap or packing them in light cardboard can help protect them during their return shipment.

Two additional features can also help extend the service life of the crate. The first is replaceable skids to protect the base channel from wear and damage (consult Channel parts and skids). The second is the application of paint or a clear coat finish to help protect the channel sections from moisture.

The material and fabrication costs of a high-quality plywood crate plus the cushioning required for a medium-sized painting can approach $1,000^{Footnote 2}. The cost of a channel crate and cushioning for the same painting is approximately $450, plus triwall cover material at a cost of $20 per sheet. This can reduce packaging costs by as much as 50%. For a scenario where the sender supplies the crate on a loan basis and the recipient covers the cost of the cover panels plus return shipment of the major crate parts back to the sender, the savings can approach 80% or more.

Constructing a channel crate

The crate can be constructed with typical workshop tools, equipment and supplies. All of the wood and corrugated cardboard part sizes are derived from the required interior dimensions (consult Tables 1 and 4).

Note: CCI has created a channel crate design tool as an Excel workbook. The tool calculates the dimensions of each plywood and corrugated cardboard part using the same equations shown in the sections on Channel parts and skids and Cover panels and fasteners. It also calculates external crate dimensions, crate weight, construction and cover fastener spacing, vertical and horizontal rib count and spacing as well as the total quantity and cost of materials and hardware.

Channel parts and skids

The preferred channel material is high-quality industrial poplar plywood, good on two sides, 19 mm (3/4 in.) thick, but other types of plywood may also be used. The plywood part dimensions are derived from the interior crate dimensions using the equations in Table 1. Drill two holes on both ends of the horizontal panels (part 4 in Figure 6). The holes should be 10 mm (0.375 in.) in diameter.

Skids can be added as an option. Each skid is made of two plywood parts (part 7 in Figure 6) laminated together. The ends can be bevelled, as shown, or rounded.

Channel construction

Use wood glue and 4 mm × 40 mm (#8^{Footnote 3} × 1 1/2) wood screws to construct the channel sections. Spacing between screws A, B and C in Figure 7 is approximately 178 mm (7 in.). Add reinforcing ribs (part 6 in Figure 6) when unreinforced channel sections exceed 500 mm (20 in.) in length. Construct handles with two ribs. Accurately align the channel section corners, clamp them together temporarily and use the horizontal channel holes as guides to drill the vertical channel end holes.

Channel assembly and skids

Assemble channel sections with M8 (5/16 in.) nuts, bolts and washers. Install skids, if used, using 50 mm (2 in.) screws.

Assembly hardware to fasten horizontal and vertical panels consists of M8-1.25 × 50 mm (5/16-24 in. × 2 in.) bolts and M8 (5/16 in.) washers. The bolt passes through the horizontal channel, then through the vertical channel, followed by a second M8 (5/16 in.) washer and one M8 by 1.25 mm pitch (5/16 24 thread per inch) nut.

A detail of the optional skids shows that the skids are attached to the horizontal base channel using 50 mm (2 in.) wood screws, adjacent to the stiffening rail and placed inside the channel recess. The first screw is spaced 50 mm (2 in.) from the inner vertical panel surface and driven from the inside panel surface. The second and third screws follow in line and are spaced 152 mm (6 in.) apart.

Cover panels and fasteners

Two cover fastening options are shown below. The cover fastener spacing for F and G in Figure 9 is approximately 229 mm (9 in.) along the rail centreline. If insulation is added or if a different cover panel thickness is used, select screw length accordingly. Cut a 6 mm (0.25 in.) strip off the bottom of the triwall covers if skids are not used to prevent direct contact between the cardboard edge and the ground surface. After the covers are cut to size, finish the edges with reinforced kraft paper tape (Figure 2).

Final comments

The channel crate is a lightweight and durable crating option. However, as a light duty container, it may not be an adequate substitute for a more durable wooden crate in some distribution networks. When matched to the object weight and distribution network, it can offer a good assurance of safe shipment for some items while making good use of resources and helping to reduce packaging costs.

Bibliography

Snutch, D., and P. Marcon. Making Triwall Containers. CCI Notes 1/4. Ottawa, ON: Canadian Conservation Institute, 1997.

By Paul Marcon
Revised in 2024

Originally published in 2020

© Government of Canada, Canadian Conservation Institute, 2024

Cat. No.: NM95-57/20-1-2020E-PDF
ISSN 1928-1455
ISBN 978-0-660-34550-5