How to Choose a Roundness Tester: Key Selection Factors

Choosing a roundness/cylindricity tester starts with the workpiece and the features that need inspection. Small bearing rings may require basic roundness checks, while shafts and commutators may also need cylindricity, straightness, flatness or runout measurement. This guide compares three INSIZE models by measurement functions, workpiece capacity and setup requirements.

Define Your Measurement Requirements

Before comparing models, establish three things:

1. Workpiece size and mounting: maximum diameter, measurement height, weight, and whether the part will be held by its internal or external diameter. Note any interrupted surfaces, e.g. commutator segments.

2. Inspection items: whether you need roundness alone or additional measurements such as cylindricity, coaxiality, flatness and total runout.

3. Installation and operation: whether the instrument will be used in a measuring room or production area, whether compressed air is available, and whether repeated automatic measurement is required.

These requirements help determine the appropriate measuring range, stage capacity and level of automation.

Basic Roundness Inspection: RCT-RA260

The RCT-RA260 roundness measuring machine suits small shafts, bearing rings, precision sleeves and small mold components requiring roundness, concentricity, flatness and radial runout checks.

It uses an air-bearing spindle, an adjustable centering and leveling stage, a manually positioned horizontal arm and a motorized vertical column. The software includes four roundness evaluation methods, Gaussian filtering, spectrum and waveform analysis, and automatic gap and burr removal from measurement data.

It is a suitable starting point when cylindricity analysis and automatic centering and leveling are not required.

Combined Form Measurement: RCT-300

The RCT-300 roundness/cylindricity tester suits motor shafts, gear shafts, sleeves, bearing raceways and commutators requiring several inspection items on one instrument.

Its six modules cover roundness, cylindricity, straightness, single- and multi-section flatness, commutator measurement, and related parameters including coaxiality and runout. Automatic centering and leveling reduce manual setup, while the horizontal and vertical axes are motorized.

Cylindricity analysis supports 2–10 sections. The system also supports measurement of interrupted surfaces, making it applicable to parts with gaps or notches.

Heavy and Long Components: RCT-500

The RCT-500 provides greater capacity for components such as spindle bushings, shaft cores, gear shafts and crankshafts. It supports loads up to 80 kg and has an 800 mm vertical measuring range, with automatic centering and leveling.

Its maximum measuring diameter is 320 mm, while its maximum workpiece rotation diameter is 500 mm. The latter describes clearance for the rotating workpiece; it is not the maximum diameter that can be measured.

The RCT-500 offers the same measurement-module categories as the RCT-300. An air dryer is included.

INSIZE Roundness/Cylindricity tester Comparison

Match the Stylus and Chuck to the Part

All three models include a 2 mm ruby stylus, with optional diameters of 0.5, 1, 4 and 8 mm. Choose according to the surface geometry and access needed, particularly for small internal features.

The standard precision chuck grips external diameters of Ø1–81 mm and internal diameters of Ø31–70 mm. Optional chucks offer alternative ranges. Check mounting requirements separately from measuring capacity: a part within the instrument’s measuring range may still need a different chuck.

A reference block is included with each model for calibration.

Select According to the Inspection Task

For basic roundness and related checks, consider the RCT-RA260; for combined form measurement with automatic centering and leveling, consider the RCT-300. Choose the RCT-500 when greater load capacity or vertical measuring range is needed.

Contact INSIZE expert with your part dimensions, weight, mounting method and required inspection items to discuss a suitable configuration.