The most common errors in dimension specifications – and how to avoid them

Dimensions are the basis of every successful order of aluminium sheet cut pieces. Even small ambiguities or mix-ups lead to parts not fitting, having to be reworked or even being unusable. These 7 mistakes occur particularly frequently in practice – and can be specifically avoided with a little care.

Typical sources of error in dimensions

1. Length and width swapped

A classic in practice: the terms "length" and "width" are not clearly defined. Particularly with rectangular cut pieces or with sheets that have a machining direction, this can lead to serious deviations. Often the problem lies in drawings that have not been agreed or order forms without orientation (e.g. no arrow for the longitudinal direction).

Solution: Always state length and width in the context of the application. If in doubt: attach a sketch with a direction indicator.

2. Thickness forgotten or swapped

When ordering, the thickness of the alu sheet is often forgotten. Yet it is precisely this that is decisive for stability, weight and fit. A missing or misunderstood specification (e.g. "2 mm" instead of "20 mm") can make the component unusable.

Solution: Always state dimensions in three parts: length x width x thickness (e.g. 300 x 200 x 5 mm).

3. Wrong or missing units of measurement

In technical drawings or in international projects, inch specifications and millimetre specifications are sometimes mixed up or misunderstood. Particularly tricky: decimal and comma notation (e.g. 0.8 mm vs. 0.8 inch).

Solution: Always use uniform metric units (mm) and label them clearly. No specifications without a unit.

4. Fixed size or tolerance not defined

With many cutting services, customers can choose between a fixed size (exact edge length) and production with a tolerance. Anyone who does not know this difference or does not state it may receive a cut piece with deviations in the tenth-of-a-millimetre or millimetre range.

Solution: Decide deliberately: is a fixed size necessary (e.g. for insert panels), or is a standard tolerance sufficient? If in doubt: state a fixed size and have it confirmed in writing.

5. Installation clearance not allowed for

Particularly with close-fitting constructions (e.g. frames, cut-outs), installation clearance must be taken into account. Without this small amount of play, the component jams or cannot be fitted.

Solution: Allow for 0.5 to 2 mm installation clearance depending on the application. For large sheets or thermal load, possibly more.

6. Technical tolerances unknown

Even with CNC cut pieces, small deviations can occur, particularly with long or very thin sheets. Anyone expecting a 100% exact edge must order this explicitly – and safeguard it technically (e.g. by milling instead of shearing).

Solution: Ask about the supplier's technical tolerances. With tight requirements (e.g. -0/+0.2 mm), special machining processes must be selected.

7. No technical drawing attached

Many orders are placed purely in writing (e.g. "please send 3 sheets of 1 m x 0.5 m each"). Without a technical drawing or sketch, misunderstandings are inevitable. A wrong interpretation of the position (e.g. storage side, visible side) can also have consequences.

Solution: Always attach a simple sketch or drawing, ideally with dimensions, view and direction indicators.

Ordering aid: how to avoid dimension errors with alu sheets

Stating dimensions correctly – overview table

Specification	Description	Recommendation
Length & width	Note the aspect ratio, clarify the direction reference	Attach a sketch with an arrow
Thickness	Influence on stability and weight	Always state it
Unit of measurement	Millimetres instead of inches	Name the unit clearly
Fixed size vs. tolerance	Define dimensional accuracy	State fixed size for a precise fit
Installation clearance	Play for assembly	0.5–2 mm (depending on application)
Technical drawing	Clarifies view, dimension reference and positions	Always attach (handwritten is fine too)

Anyone ordering alu sheets should be aware that every specification counts. Even small errors in length, width, thickness or fixed size can become expensive in a project. Our recommendation:

1. State all three dimensions: length x width x thickness in mm
2. Define fixed size or tolerance clearly
3. Attach a sketch or technical drawing
4. Allow for installation clearance
5. Clarify technical queries with the supplier

This way you avoid expensive mistakes – and receive exactly the aluminium sheet cut pieces that your project requires.

FAQ – Technical details and planning

What does "fixed size" mean for alu sheets?

A fixed size is an exactly cut dimension without tolerance play. It is produced to millimetre accuracy, e.g. 300.0 mm × 200.0 mm.

Why is thickness so important when ordering?

The thickness influences load-bearing capacity, weight and installation height. Wrong values can make the cut piece unusable.

How much installation clearance should I allow for?

Depending on the application, 0.5 to 2 mm is usual. For large surfaces or thermal expansion, possibly more.

What should I do about differing tolerances?

Ask specifically about the production tolerances. With tight requirements (e.g. <0.2 mm), CNC milling should be used.

Can I attach a handwritten sketch?

Yes, a simple sketch with clear dimensions is often enough to avoid misunderstandings.