How a wooden shipping crate is built

Start with the skid base

The skid is the crate's foundation. It is a set of heavy lumber members laid on edge and running the length of the crate, with deck boards or a plywood floor fixed across them. Forklift tines enter between the members, so the skid sets how the crate can be lifted. Its size is chosen from the gross weight and from the span between supports.

For a heavier load the builder uses larger members, spaces them closer, or adds a third runner under the middle. Bolt-down loads usually sit directly on a reinforced floor, and the lag bolts or threaded rods that hold the machine go through the floor into the skid members. A floor that is only nailed will pull apart under that stress.

Step by step

The order below is how a typical sheathed or cleated crate goes together on the bench. A slatted or open crate leaves out the sheathing, and a knockdown crate is built as panels that are assembled later.

1. 01
   Build the skid

   Cut runners to length, set them on edge at the spacing the weight calls for, and fix the floor boards or plywood across them with nails or screws. Add chamfers on the leading edges so forklift entry is clean.

2. 02
   Frame the walls

   Build side and end panels as frames of lumber cleats with sheathing or slats fixed to them. Corner cleats are sized to resist racking.

3. 03
   Set the load

   Place the load on the floor and fix it. Machines are lagged or strapped down, then blocked at the base against sliding in every direction.

4. 04
   Brace and cushion

   Add bracing to tall members, strongbacks across wide spans, and cushioning at contact points. Wrap or bag the load first if it needs VCI, a barrier bag or desiccant.

5. 05
   Close the walls

   Raise the panels around the load and fasten them to the skid and to each other through the cleats.

6. 06
   Fit the top

   Add the top panel, with a strongback across wide crates so the lid does not sag. Handling marks, the centre-of-gravity mark and the export stamp are applied to the outside.

Walls, cleats and sheathing

Walls are panels built on a frame of cleats, which are narrow lumber strips that stiffen the panel and give the fasteners something to bite. Sheathing, usually plywood or boards, fills the frame. A sheathed wall is a closed box that keeps out weather and dirt. A slatted wall leaves gaps and trades weather protection for a lower weight, better airflow and a view of the contents.

Corner cleats and edge cleats tie the panels together and keep the box square when it is dropped or strapped. For heavy loads the builder adds diagonal members or doubles up the cleats so the crate resists racking, the sideways distortion that opens joints and lets the load shift.

Fasteners and joints

Nails hold most of a wooden crate together because they resist shear, the force that tries to slide one board over another. Screws and bolts are used where a joint may need to come apart or where it carries a pulling load. Lag bolts hold a machine's feet to the skid, and carriage bolts with washers pass through bearing members where a nail would split the wood.

Fastener placement is as important as fastener type. Nails driven too close to the end of a board split it, and a split board does not hold. A crate for export carries the same rules, with the added requirement that every lumber member is treated and stamped. The fasteners are metal and are not subject to the wood treatment.

Where heavy loads need more

Weight changes the crate's proportions more than it changes the list of parts. A heavy casting needs a stiffer floor and runners that carry the load straight down. A load with a high centre of gravity needs a wider footprint, diagonal bracing, and lag bolts in the skid that resist tipping. A long, narrow load needs a strongback at mid-span so the floor does not bow.

Lifting method matters too. A crate that will be slung from the top needs sling points and a top that can take the lift, and a crate that moves by forklift needs fork entry on the sides the carrier will use. Cranes and sea transport add lashing points. The builder sets each of these from the load's weight, size and route, which is why the quote asks for them.

Building for export

Lumber in an export crate is heat-treated and stamped under the ISPM 15 program, and the stamp is applied on two opposite sides, per the NELMA program requirement. Plywood panels are exempt from the treatment, but the lumber skid, runners and cleats on the same crate are not. The ISPM 15 guides on this site go through the stamp and the exemption in detail.

If a crate is built for a lane we have shipped before, the crate spec on file is reused so the second crate matches the first. That includes the skid layout, the blocking pattern and the marking. A new load gets a new spec, written from the numbers you send on the quote form.