Packaging a machine is a structural engineering problem wearing a carpentry disguise. The forces are large, they arrive from directions people do not expect, and the failure modes are expensive. A few principles cover most of it.
The base is the component that matters
If you take one thing from this article, take this: the bottom of a heavy-duty box is its most important part, because it absorbs forces from both directions — stack pressure from above, and forklift forks, slings and chains from below.
Design consequences follow directly:
- Fork pockets and lifting points must sit symmetrically about the centre of gravity. Not the geometric centre — the centre of gravity. An asymmetric machine in a symmetric crate will tip during handling no matter how strongly it is built.
- The contents should be bolted to the base, with screws running through into the skids. This is what prevents shifting and tipping inside the box. Items that cannot be fixed have to be restrained by tight fit and blocking instead.
- Narrow standing areas need load distribution. Where a machine rests on a small footprint or on legs, crosspieces spread the load across all the skids. Without them you get point loads that punch through floorboards.
For sizing, the governing variable is not weight alone but the weight-length value — the item's weight multiplied by the unsupported span between its base contacts and the skid. A light machine on widely spaced legs can load a base harder than a heavier one sitting flat.
Crate, box, or sled?
Three different products, often used interchangeably in conversation:
- A crate is an open framework of boards and battens, usually with diagonal bracing. The ratio of closed boarding to open space is roughly 1:1 up to 500 kg of contents and 2:1 up to 1000 kg. Above about 1000 kg, crates stop being appropriate — they no longer provide sufficient stability, and a fully sheathed box is used instead.
- A box is fully sheathed, and is what most machinery ships in.
- A sled is a base structure only, with the item fixed to it and no walls. For large, rugged items — machine tools especially — a heavy skid and cross-member assembly is often all that is needed, and it saves considerable volume and cost.
Do not default to a full box because it feels safer. If the machine is weatherproof and robust, a sled with edge protection may be both cheaper and easier to handle.
Bracing: the 45-degree rule
Diagonal bracing is what resists racking — the parallelogram deformation that destroys square structures under lateral load. The research here is unusually specific:
- Diagonals should meet the horizontal members as near 45° as possible, and never outside 30–60°. The closer to 45°, the greater the racking resistance.
- Two crossing diagonals are considerably stronger than one.
- Adjoining diagonals should slope in opposite directions, with a strut between them.
- All faces should be braced unless the item itself resists torsion. When they are, and the item is properly supported, the contents cannot rack until the crate itself has failed.
- The more nearly cubic the crate, the more evenly stresses distribute through its members.
Above 1500 mm internal height, diagonal bracing stops being a design choice and becomes a requirement.
Walls and lid
Wall boarding should run vertically, because vertical boarding absorbs vertical forces better than horizontal. Each side and end wall needs an upper and a lower longitudinal batten, and on side walls vertical batten spacing should not exceed 1000 mm.
The lid is where an avoidable mistake happens repeatedly. Lid boards should be set back, or positioned against the side boarding, so that a hoisting rope passing over the crate cannot catch a lid board and lever the boarding loose.
Lid girders resting directly on the longitudinal battens create point loads that cave those battens in under stack pressure. The alternatives are internal vertical posts — very strong, but they consume internal space — or purpose-made connectors driven into the lid girder and nailed to the side wall, which is nearly as strong without the space penalty.
Lifting
Every crate except small light ones should have provision for slinging designed in. Typically that means a notch at each end of the skids so a sling can pass under without crushing the structure.
If no sling provision exists and cables are simply passed around the ends and sides, the ends get crushed. A short cable is worse than a long one: it concentrates crushing forces on the base, sides and especially the top panel. If you know the receiving crane is short-slung, reinforcing joists should be positioned where the cables will actually bear.
Container limits people discover too late
Heavy items meet limits that are nothing to do with the crate:
- Line load is capped at roughly 4.5 t/m for a 20 ft container and 3.0 t/m for a 40 ft. A 16-tonne machine spread over 4 m gives 4.0 t/m — fine in a 20 ft, not permitted in a 40 ft. The fix is to enlarge the bearing area with dunnage or a sled, and the sled's skids must run lengthwise in the container so they bear on several bottom cross members.
- Centre of gravity position is limited for safe handling: no more than about 0.60 m from the container's lengthwise centre in a 20 ft, or 0.90 m in a 40 ft, and centred crosswise.
- Wall strength is limited. End walls are designed for 0.4 g of the payload and side walls for 0.6 g — and these apply to large-area loads. Point loads damage walls readily.
- Never place anything on the container roof, which is rated for only about 200 kg over a small area.
- Forklifts entering containers are limited to about 5460 kg axle load. A 2-tonne forklift laden is acceptable; heavier trucks, and battery-electric ones in particular, frequently exceed it.
Standards worth knowing
If you receive specifications referencing ASTM: D6039 covers open and covered wood crates for net loads up to 1814 kg; D6256 covers wood-cleated boxes with skidded, load-bearing bases. There is also a heavy-duty sheathed crate specification for loads up to 13,607 kg, though its status should be checked before citing, as it has been withdrawn.
Notably, we found no EN standard covering wooden boxes or crates as a product. European practice relies on generic package test methods, insurer guidance and ISPM 15 rather than a dedicated product standard — which is precisely why the design conversation matters more here than in more standardised product categories.
Send us the machine's drawing, weight, centre of gravity and lifting arrangements, and we will design the packaging around how it will actually be handled.
