Why Coating Thickness Readings Change Near Edges, Corners and Curved Surfaces Malaysia
Why Coating Thickness Readings Change Near Edges, Corners and Curved Surfaces Malaysia
Content
Your coating thickness gauge measures 105 μm in the centre of a metal panel but gives 128 μm near the edge.
Move the probe to a curved section and the reading changes again.
Does this mean the coating is uneven?
Possibly — but not always.
Edges, corners, curvature, component size and probe positioning can influence coating thickness measurements.
Understanding these effects is important when using a coating thickness gauge such as the UNI-T UT343A for powder coating, painted metal, automotive and factory QA/QC applications in Malaysia.
Why Are Flat Surfaces Easier to Measure?
A large, flat metal surface provides a stable area for the probe.
The probe can normally sit:
Flat
Perpendicular to the surface
Away from edges
With consistent contact
This creates favourable conditions for repeatable measurements.
Once the probe moves toward an edge, corner or tight curve, the measurement geometry changes.
What Is the Edge Effect?
Coating thickness gauges rely on a measurement field between the probe and substrate.
Near the physical edge of a component, that measurement condition can differ from the condition on a large flat surface.
As a result, a reading taken very close to an edge may differ from a reading taken farther inside the same component.
This does not automatically mean:
The coating is thicker near the edge.
Before reaching that conclusion, repeat the measurement at different distances from the edge.
Example: Powder-Coated Steel Panel
Suppose a QA inspector gets:
Centre: 102 μm
100 mm from edge: 103 μm
50 mm from edge: 105 μm
Very close to edge: 128 μm
The last reading should not immediately be treated as proof that the coating suddenly becomes 25 μm thicker.
The inspector should check:
Measurement position
Probe contact
Surface geometry
Repeatability
Instrument guidance for edge distance
Then compare nearby measurements.
Why Corners Can Be Difficult
Corners introduce both geometry and coating-process variables.
First, the probe may not sit as consistently as it does on a flat surface.
Second, the coating itself may genuinely vary around corners because of the application process.
Therefore, an unusual corner reading can have more than one possible cause:
Measurement geometry
or
Actual coating variation
or a combination of both.
The correct response is to investigate rather than immediately classify the component as pass or fail.
Curved Surfaces
Curved components can also affect measurement conditions.
Examples include:
Pipes
Cylinders
Round tanks
Automotive body contours
Curved brackets
Small-radius fabricated components
The tighter the curvature, the more important it becomes to confirm that the instrument and probe are suitable for the geometry.
Example: Measuring a Coated Pipe
Imagine a coated pipe produces:
Top: 145 μm
Side: 147 μm
Bottom: 144 μm
These readings are reasonably close.
But another pipe produces:
Top: 145 μm
Side: 210 μm
Bottom: 142 μm
Before concluding that one side has excessive coating, repeat the measurement and check the probe position and curvature.
If the higher readings remain repeatable around the same area, investigate the actual coating condition.
Small Components Can Be Challenging
Another common question is:
"Can I measure coating thickness on a very small metal part?"
The answer depends on the component geometry and the instrument's measurement requirements.
A small component may not provide enough suitable surface area for the probe's normal measurement field.
This is particularly relevant for:
Small brackets
Thin strips
Screws
Narrow metal sections
Small automotive components
Tight corners
Do not assume that because the probe physically fits on the part, the measurement is automatically valid.
Probe Position Matters
For better repeatability:
Place the probe perpendicular to the surface.
Avoid deliberately tilting the probe.
Do not slide it across the surface while taking a reading.
Allow stable contact at the selected measurement point.
If a reading looks unusual, lift the probe and repeat the measurement rather than continuously moving it around until a preferred number appears.
Establish Consistent Measurement Locations
For factory QA/QC, repeatability becomes easier when measurement locations are defined.
Instead of:
Operator A measures wherever convenient.
Operator B measures near the edge.
Operator C measures the centre.
create an inspection procedure such as:
Point A – Centre
Point B – 100 mm from left edge
Point C – 100 mm from right edge
Point D – Defined upper location
Point E – Defined lower location
This makes measurements between operators and production batches easier to compare.
Do Not Chase a Specific Reading
An operator should not repeatedly reposition the probe until the instrument displays the number they expect.
The purpose of measurement is to identify the actual condition as reliably as possible.
If results vary, determine why.
Possible causes include:
Actual coating variation
Surface contamination
Edge effect
Curvature
Probe positioning
Different substrate
Instrument verification issue
Unsuitable measurement location
Fe and NFe Substrates
The UNI-T UT343A supports both:
Fe – Ferrous substrates such as steel
and
NFe – Non-ferrous substrates such as aluminium.
This makes it useful for many metal coating applications.
However, substrate type is only one factor.
The size, thickness and geometry of the component should also be considered when determining whether a measurement is reliable.
What Should You Do When an Edge Reading Looks Wrong?
Use a simple troubleshooting sequence:
1. Repeat the measurement
Check whether the result is repeatable.
2. Move farther from the edge
Compare the result.
3. Check the probe position
Keep it stable and perpendicular where possible.
4. Clean the surface and probe
Remove contamination.
5. Compare nearby points
Determine whether the variation follows a pattern.
6. Verify the instrument
If readings remain suspicious, check the gauge according to the manufacturer's procedure.
This approach helps separate a genuine coating issue from a measurement-condition issue.
UNI-T UT343A for Metal Coating Inspection
The UNI-T UT343A provides:
0–1750 μm measuring range
Fe/NFe substrate support
Automatic substrate recognition
Single measurement
Continuous measurement
MAX/MIN/AVG
199 data storage
μm/mil units
Upper and lower limit settings
Potential applications include:
Powder coating | Painted steel | Aluminium coating | Automotive inspection | Metal fabrication | Manufacturing QA/QC
Coating Thickness Measurement Troubleshooting Malaysia
If your coating thickness gauge gives normal readings in the centre but unusual readings near an edge, corner or curved surface, do not immediately assume the instrument is faulty.
Send MTM Precision:
Instrument model + Substrate + Coating + Component shape + Example readings + Photos of the measurement position
This information makes troubleshooting much easier.
MTM Precision Sdn Bhd
Showroom & Service Centre: Puchong, Selangor, Malaysia
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my
For coating thickness gauge enquiries and measurement applications across Selangor, Kuala Lumpur, Johor, Penang, Melaka, Negeri Sembilan, Perak, Pahang, Kedah, Kelantan, Terengganu, Perlis, Sabah and Sarawak, contact MTM Precision with your application details.
22 Sep 2026
