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Mitutoyo Surftest SJ-210 contact profilometer

The correct name is Mitutoyo Surftest SJ-210. It is a portable contact-type surface roughness tester, often called a contact profilometer. It measures the microscopic peaks and valleys on a manufactured surface using a diamond stylus that travels along the surface.

It is commonly used in machining inspection for turned shafts, ground surfaces, milled faces, bores, EDM parts, bearing journals, and other precision components.

The SJ-210 is primarily a surface roughness instrument, rather than a full form-measuring profilometer. It reports roughness parameters such as Ra, Rz, Rq, Rt, and others according to selected ISO, JIS, ANSI, or VDA settings.

Mitutoyo’s SJ-210 product brochure lists the model configurations and specifications.

1. Working principle

The SJ-210 operates through stylus tracing:

A fine diamond stylus is placed on the workpiece surface.
The drive unit moves the stylus across a defined traverse length.
As the stylus rises and falls over the surface irregularities, a detector converts this vertical movement into an electrical signal.
The instrument filters the profile to separate roughness from longer-wavelength features such as waviness or form.
It calculates the selected roughness parameters and displays the result and, where selected, the profile graph.

Simplified concept

[ \text{Surface profile} \rightarrow \text{stylus movement} \rightarrow \text{electrical signal} \rightarrow \text{filtering} \rightarrow \text{roughness value} ]

The actual measurement is a two-dimensional line trace. Therefore, the result applies to the specific line measured, not necessarily the entire surface.

2. Main parts of the SJ-210

Display unit

The handheld display unit contains:

LCD screen
Control keys
Battery and charging connection
Parameter and standard selection menus
Storage and output functions
USB interface on suitable versions/configurations

The display can show numerical results, the traced profile, bearing area curve, and other output formats depending on the selected function.

Drive unit

The drive unit moves the stylus in a straight line along the surface. It can be mounted to the display unit for portable work or separated for access to difficult features.

Stylus and detector

The stylus is a precision diamond-tipped probe. Two common configurations are:

Detector version	Measuring force	Stylus tip
Fine-force type	0.75 mN	2 µm radius, 60° cone
Standard-force type	4 mN	5 µm radius, 90° cone

The 0.75 mN / 2 µm stylus is better for fine surfaces and for reducing the chance of marking soft materials. The 4 mN / 5 µm version is more suitable for general industrial roughness measurement.

Skid

Most SJ-210 measurements are skidded. A skid rests on the workpiece and acts as a local reference as the stylus traces the surface.

This makes the SJ-210 useful and fast for roughness inspection, but it is not ideal for precise measurement of large-scale form, waviness, or contour. For those tasks, a skidless profilometer or dedicated contour measuring system is preferable.

Calibration specimen

A certified roughness specimen, often around Ra 1 µm or Ra 3 µm depending on the supplied configuration, is used to verify and calibrate instrument performance.

3. Key technical specifications

The exact specification depends on the selected drive-unit version and model number. Key published SJ-210 specifications include:

Feature	Typical SJ-210 specification
Measuring principle	Contact stylus tracing
X-axis traverse range	16.0 mm for standard drive unit; 5.6 mm for certain alternative drive units
Z-axis detector range	360 µm, approximately -200 µm to +160 µm
Vertical resolution	0.02 µm at 360 µm range; 0.006 µm at 100 µm; 0.002 µm at 25 µm
Measurement speeds	0.25, 0.5, or 0.75 mm/s
Return speed	1 mm/s
Stylus options	0.75 mN with 2 µm R / 60°; or 4 mN with 5 µm R / 90°
Standards	JIS 1982, JIS 1994, JIS 2001, ISO 1997, ANSI, VDA
Assessed profiles	Primary profile and roughness profile

These values are from the Mitutoyo SJ-210 specification sheet.

4. Drive-unit types

The SJ-210 may be supplied with different drive units for different access conditions.

A. Standard drive unit

This is the general-purpose arrangement for flat faces, external cylindrical surfaces, and easily accessible work.

Typical uses:

Turned shafts
Ground plates
Flat machined surfaces
General shop-floor inspection

B. Retractable drive unit

The stylus is retracted at rest and extends for measurement. This reduces the chance of stylus damage when entering features whose geometry is not clearly visible.

Typical uses:

Blind holes
Internal features
Recesses
Restricted access locations

C. Transverse tracing drive unit

This configuration is designed for measurement across narrow or shrouded surfaces.

Typical uses:

Crankshaft journals
Narrow shoulders
EDM features
Areas near obstructions

5. Important roughness parameters

The SJ-210 can calculate several surface texture parameters. The drawing or quality plan determines which one is required.

Ra: Arithmetic mean roughness

Ra is the most common parameter.

It is the arithmetic average of the absolute vertical deviations of the roughness profile from the mean line over the evaluation length.

[ R_a = \frac{1}{L}\int_0^L |y(x)| dx ]

Where:

(L) = evaluation length
(y(x)) = profile deviation from the mean line

A lower Ra generally indicates a smoother surface.

Example:

Ra = 3.2 µm: relatively rough machined surface
Ra = 1.6 µm: typical machined finish
Ra = 0.8 µm: fine finish
Ra = 0.2 µm: very fine ground or polished finish

Ra alone does not describe the shape or spacing of surface peaks. Two surfaces may have the same Ra but behave differently in sealing, friction, fatigue, lubrication, or coating adhesion.

Rq: Root mean square roughness

Rq gives greater emphasis to large peaks and valleys than Ra.

[ R_q = \sqrt{\frac{1}{L}\int_0^L y^2(x), dx} ]

Rq is useful where occasional high features are important.

Rz: Maximum height of profile

The meaning of Rz can vary by standard. Under ISO practice, it generally represents the average maximum peak-to-valley height across the sampling lengths within the evaluation length.

Always ensure the selected standard matches the engineering drawing because older JIS, DIN, ANSI, and ISO interpretations may differ.

Rt or Rmax: Total profile height

Rt is the vertical distance from the highest peak to the deepest valley across the entire evaluation length.

It is very sensitive to scratches, burrs, dust, and isolated defects.

Rp and Rv

Rp: maximum profile peak height
Rv: maximum profile valley depth

These may be relevant where surface peaks cause wear or valleys retain lubricant.

RSm

RSm is the mean spacing of profile elements. It helps describe the horizontal spacing between surface features.

Rsk and Rku

Rsk, skewness: indicates whether the profile has relatively more peaks or valleys.
Rku, kurtosis: describes peak/valley sharpness and distribution.

These parameters are useful in functional surface assessment, especially for lubricated or wear-critical surfaces.

6. Cutoff length and evaluation length

Correct selection of cutoff length is one of the most important factors in obtaining a meaningful result.

Cutoff length, λc

The cutoff separates short-wavelength roughness from longer-wavelength waviness and form.

Typical selectable cutoff values for portable roughness testers include:

0.08 mm
0.25 mm
0.8 mm
2.5 mm
8 mm

The correct value should normally be taken from:

The component drawing
Customer specification
Relevant ISO/JIS/ANSI standard
Material and manufacturing process requirements

Evaluation length

The evaluation length is usually a multiple of the cutoff length, commonly five sampling lengths.

[ \text{Evaluation length} = 5 \times \lambda_c ]

For example, with:

[ \lambda_c = 0.8\text{ mm} ]

the conventional evaluation length is commonly:

[ 5 \times 0.8 = 4.0\text{ mm} ]

Do not choose a cutoff merely because it gives a desirable Ra value. The selected cutoff must agree with the applicable inspection standard or drawing requirement.

7. Basic procedure for measuring roughness

Step 1: Inspect the workpiece

Ensure the surface is clean and free from:

Coolant
Oil
Chips
Loose abrasive particles
Burrs
Dust
Fingerprints

A small particle can significantly affect the result, particularly Rz and Rt.

Step 2: Place the part securely

The workpiece must not move during tracing. Use a stable table, fixture, V-block, magnetic holder, or suitable support.

For a cylindrical shaft, use V-blocks or a dedicated fixture so the surface remains stable.

Step 3: Choose the correct stylus direction

For machined surfaces, trace perpendicular to the main lay direction.

Surface process	Preferred tracing direction
Turning	Perpendicular to circumferential tool marks, usually axial direction on the shaft
Grinding	Perpendicular to the grinding lay
Milling	Perpendicular to the dominant feed marks
Lapping/polishing	Direction is less critical, but maintain a documented consistent direction

Tracing parallel to the lay may produce an artificially low roughness value.

Step 4: Select the correct settings

Set:

Measurement standard: ISO, JIS, ANSI, VDA, etc.
Parameter: Ra, Rz, Rt, or as specified
Cutoff length
Number of sampling lengths
Measurement speed
Filter type, if selection is available
Unit: µm or µin

Step 5: Position the stylus

Place the drive unit so:

The skid rests properly on the surface.
The stylus is not on a burr, scratch, edge, or deep isolated defect unless that defect is intentionally being assessed.
The tracing path remains completely on the surface.
The stylus does not hit a shoulder or obstruction.

Step 6: Run the measurement

Start the trace and allow it to finish without touching or moving the instrument.

Step 7: Review and record

Record:

Part identification
Surface or feature measured
Direction of trace
Roughness value
Parameter used
Cutoff and evaluation length
Standard selected
Date and operator
Calibration status

For critical work, measure several locations and report the agreed method, such as individual values, average, maximum, or all readings.

8. Calibration and verification

Calibration should be performed:

At the beginning of a shift or inspection session
After transport or impact
When the stylus is changed
When readings appear questionable
According to the laboratory or quality-system schedule

General calibration method

Clean the certified roughness specimen.
Place the SJ-210 carefully on the calibration specimen.
Select the specified calibration parameter and cutoff.
Run the calibration trace in the correct direction.
Compare the measured value with the certified specimen value.
Accept the instrument only if it meets the permitted tolerance defined by the manufacturer or internal procedure.

A calibration specimen is itself a precision reference. Avoid touching its measuring area with fingers or dragging the stylus unnecessarily across it.

9. Sources of error

Incorrect direction of travel

If the stylus travels parallel rather than perpendicular to machining lay, roughness can be understated.

Wrong cutoff

Different cutoff settings can give different results on the same surface. A result is incomplete without documenting the cutoff and standard.

Unstable workpiece or instrument

Vibration, hand movement, or a part that shifts during tracing can produce unreliable values.

Dirty surface

Oil, swarf, dust, and particles can create false peaks and valleys.

Damaged stylus

A worn, chipped, contaminated, or bent stylus can produce incorrect readings. Stylus condition should be checked if results become inconsistent.

Edges, shoulders, grooves, and holes

A standard skid may not sit properly near an edge or inside a narrow feature. Use an appropriate accessory, transverse drive unit, retractable unit, or special stylus.

Excessive curvature

A small-diameter cylinder may require proper support or an accessory. Incorrect seating can distort the trace.

Surface outside the instrument’s capability

Very rough, highly curved, highly soft, sticky, or complex surfaces may require another instrument or a specialized probe.

10. Advantages

Portable and suitable for shop-floor inspection
Fast numerical roughness measurement
Useful for checking production parts near the machine
Supports common standards and roughness parameters
Can display profiles in addition to numerical values
Suitable for flats, shafts, many bores, and accessible machined features
Detachable drive unit assists measurement in restricted locations
Uses interchangeable accessories for special applications

11. Limitations

The SJ-210 is excellent for routine roughness control, but it has limitations:

It measures only along a single trace line.
It can scratch very soft surfaces, although the low-force stylus reduces this risk.
The stylus cannot enter features smaller than its geometry allows.
It may not adequately characterize large-scale waviness or form because of the skid-based measurement method.
A 2 µm or 5 µm stylus tip cannot reproduce every extremely narrow valley.
Incorrect setup can cause significant variation between operators.

For advanced 3D texture, non-contact optical measurement, precise waviness, contour, or form analysis, consider a different system such as a skidless profilometer, optical profiler, contour tracer, or coordinate measuring system.

12. Typical applications

The SJ-210 is used to inspect:

Turned shaft journals
Bearing surfaces
Sealing faces
Ground machine components
Hydraulic and pneumatic components
Milled die and mold surfaces
EDM surfaces
Automotive crankshaft and camshaft features
Medical-device metal components
Aerospace machined parts
General production quality control

13. Practical example

Suppose a drawing requires:

[ Ra \leq 1.6\ \mu m ]

A suitable inspection setup could be:

Parameter: Ra
Standard: As specified on drawing, often ISO
Cutoff: 0.8 mm, if specified or appropriate
Evaluation length: 4.0 mm, using five 0.8 mm sampling lengths
Trace direction: Perpendicular to machining lay
Measurements: Three positions around the functional surface

If readings are:

Location	Ra
1	1.21 µm
2	1.34 µm
3	1.48 µm

The component meets an individual-value requirement of Ra ≤ 1.6 µm, assuming the drawing does not impose another acceptance rule.

14. Maintenance and handling

Keep the stylus protected when not in use.
Do not touch the diamond tip.
Store the instrument in its carrying case.
Clean the skid and stylus area carefully with suitable clean air or a soft brush.
Avoid dropping the drive unit.
Keep the calibration specimen clean and protected.
Verify calibration routinely.
Replace damaged stylus assemblies through an approved Mitutoyo service route.
Follow the specific manual for battery charging, data transfer, and accessory installation.

The most important rule is: never force the stylus into a hole, groove, edge, or workpiece feature. The stylus is delicate and expensive.

For the exact model number, accessories, and current regional configuration, consult the Mitutoyo SJ-210 brochure and the operation manual supplied with the instrument.

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