Why Are Your Paper Sheets Not Square?

In paper sheeting production, a sheet can have the correct length and width and still fail to meet the required size.

One common problem is diagonal error.

For example, the sheet may measure correctly at both ends, but the two diagonal measurements are different by 2–5 mm. 

When only one sheet is checked, the difference may not look serious. But after hundreds or thousands of sheets are stacked together,

 the problem becomes much easier to see.

The edges no longer line up properly. The stack may look uneven, and the sheets may cause problems during packing or printing.

    So what causes this?

    It May Be the Diagonal Adjustment System

    When a sheet is not square, operators often start by checking the cutting length, knife position or basic machine settings.

These are worth checking, but they are not always the real cause.The diagonal adjustment system also has a direct influence 

on the final shape of the sheet.

During production, the diagonal motors control the movement used to correct the paper position. If the two motors do not respond

 at the correct speed, the paper position can change slightly during operation.

    The result is a sheet that is correctly cut in length, but not perfectly square.

    This problem can be difficult to notice because the machine itself may continue running normally.

    Three Parts Worth Checking

    1. Diagonal Motor Speed

    The two diagonal motors need to work together correctly.

    If one motor runs faster or slower than the required setting, the diagonal position can gradually change. The difference

may only be a few millimeters, but it can become visible in the finished stack.

    In some cases, simply adjusting the motor speed and recalibrating the diagonal parameters can improve the result.

    2. Potentiometer Wear

    On machines using potentiometers for diagonal adjustment, long-term use can cause internal wear.

    The setting on the control panel may appear normal, but the actual signal can shift slightly because of the worn component.

    This is one reason why operators sometimes find that the machine can be adjusted correctly today, but the same problem comes back later.

    If the error becomes unstable or difficult to adjust, the potentiometer should be checked.

    3. Lead Screw and Mechanical Wear

    The diagonal lead screw also needs attention.

    During long-term operation, the screw may be subjected to side loading. Over time, slight deformation or wear can affect the movement accuracy.

    When the mechanical part itself has changed, continuously adjusting the electrical parameters will not solve the problem.

    In this situation, the lead screw, nut and related bearing components should be inspected.

    Paper Settings Also Matter

    Not every paper grade behaves in exactly the same way.

    Different paper thicknesses and materials can require different diagonal settings. If the machine parameters are 

not adjusted when changing paper, a setting that worked well for one material may not give the same result with another.

    For this reason, when a diagonal error appears, it is useful to check whether the problem started after changing the paper specification.

    How Can the Problem Be Solved?

    The solution depends on how serious and how frequent the error is.

    For a small or occasional error, start with remote adjustment. Check the diagonal motor speed and recalibrate 

the segmented diagonal parameters according to the current paper.

    If the problem keeps returning, inspect the hardware. A worn potentiometer may need replacement. If the lead screw has 

deformation or excessive wear, replacing the lead screw, nut and bearings is a more reliable solution.

    For machines that require a higher level of automation, an automatic diagonal correction system can be considered. 

    The system can detect and compensate for diagonal deviation automatically, reducing repeated manual adjustment.

    A 2–5 mm diagonal error may seem small.

    But in a high-volume paper sheeting operation, a small error repeated thousands of times becomes a real quality problem.

    When a sheet is not square, don't only look at the cutting knife or length setting.

Check the diagonal motors, adjustment signal, mechanical components and paper-specific parameters step by step.

    Sometimes the problem is not with the cutting itself.

    It starts with how the paper is positioned before the cut.