Honeycomb Board Edge Crush FAQ: Cut Edges, Frames and Fasteners

Most crate failures that are blamed on a panel are failures at an edge. These questions cover edge crush, the frame bearing detail and the tests that show whether a panel will hold a stack.

What is edge crush and why does it differ from flat compression?

Edge crush is the load a panel carries at its cut edge, with the load applied along the cell axis. At the cut edge the cells are open and the load passes through the wall thickness only, which is a small bearing area. Flat compression tests the panel with continuous faces, which carry tension and compression. A panel can be strong in the face and weak at the edge, and the crate load arrives at the edge because that is where the frame bears. That is why a heavier panel can perform worse than a lighter one after a substitution.

Why does a heavier panel sometimes fail?

Because a heavier panel is not always a stronger edge. If the increase in thickness comes with a larger cell, the number of walls per metre of edge falls and the edge crush drops. Thickness buys bending stiffness, while cell size and paper weight decide the edge. A specification that compares thickness and flat compression is comparing the properties that matter for a span, not the ones that matter where the frame meets the panel, and the failure appears exactly there.

How should the edge be treated?

Three options: fill the open cells, cap the edge with a denser strip, or place a solid insert at the bearing point. A filled edge restores some bearing area and adds cost. A capped edge gives a defined surface and is easier to control. A local insert is the simplest and most targeted, and it does not change the panel. Try the insert first, because it addresses the load path without changing the material, and move to a smaller cell only if the load is distributed along the whole edge.

How does the frame detail affect the result?

A frame that bears on a continuous member spreads the load, while one that bears at points concentrates it. Corner blocks and a continuous top and bottom member turn a point load into a line, and a line is what the edge is designed to carry. Draw the joint and the edge together, because a joint that relies on fasteners through open cells concentrates the load on a few walls. A crate that fails at a corner is often failing at a joint, not at a panel.

Where should fasteners go?

At least one cell width from the cut edge, with a washer or a plate to spread the load. A fastener close to the edge splits the cell wall and loosens under vibration, and a loose fastener transfers the load to the panel face, which is not where the strength is. Specify the fastener spacing and check it on the first article, because it is a detail that is easy to move during assembly and hard to see after the crate is closed.

How is edge crush tested?

Cut a sample with a defined edge, condition it at the route humidity, and apply the load along the cell axis until it fails. Report the failure load, the sample size and the condition. A test on a dry sample overstates the performance in a humid container, and a test on a sawn edge with crushed cells understates it. Agree the cutting method, because the edge condition is part of the test.

Does humidity change edge crush?

Yes, and the edge is the first place to soften because the cells are exposed. A panel conditioned in a dry room can lose a large share of its capacity in a humid container, and a sealed or capped edge slows the uptake. For a wet route, protect the edge as well as the face, and include a humidity indicator in the crate so the receiver can see whether the pack held.

What does a failure look like?

Crushed cells under the frame, a buckled face, or a separated joint. Each points to a different fix: a crushed edge means bearing area or cell size, a buckled face means bending or support spacing, and a separated joint means fastener spacing or glue. Photograph the failure with a scale, and keep the section, because the mode decides the change and a photograph of the whole crate does not show it.

What belongs in the specification?

Cell size, paper grade and basis weight, edge crush at a stated humidity, edge treatment, frame bearing detail, fastener spacing from the edge and the test method for each. Add a first-article report with a section through the edge and a crush result. A specification that names thickness and flat compression has described a panel; the crate needs a description of its weakest line.

Agree how the sample edge is cut, because the edge condition is part of the test. A sawn edge with crushed cells reads lower than a cleanly cut edge, and a supplier and a buyer can disagree about a panel while using identical board. Photograph the edge before the test and state the method on the report. The same discipline applies to the conditioning: a sample tested straight from a dry store and one conditioned at the route humidity will differ, and the second is the one that predicts the container.

The frame is where the design is won. A continuous top and bottom member, corner blocks that are glued and stapled, and a solid insert at each bearing point turn the load into a line and then into an area. A frame that relies on fasteners through open cells is a frame that concentrates the load on a few walls, and it will fail at a corner in a way that looks like a panel failure. Draw the joint at scale and check it on the first article, because the joint is easier to fix before the first shipment than after the first claim.

Keep the failed section. A photograph of a whole crate shows that something collapsed, while a section shows which mode: crushed cells, a buckled face or a separated joint. Each mode points to a different change, and only one of them is solved by a heavier panel. The section costs a saw cut and it ends the argument about whether the board was at fault, which is the argument that otherwise consumes the most time in a damage investigation.

Lead time matters when an edge problem is found. A change of cell size or paper grade is a new board and a new supply lead time, while an insert or a cap can often be added with a local supplier in days. When a shipment is already booked, plan the fix in two steps: the insert for the immediate lots and the panel change for the next contract. That sequence protects the delivery and still corrects the design.