Now Offering CMM Training Courses

We are now offering 10% off CMM training courses when booked April though May.This course will cover level 1 & 2 training. It is structured to introduce users of coordinate measuring machines to PCDMIS involving a practical hands on approach to learning. Through the course you will gain skills that allow you to undertake a wider variety of work and become more effective and efficient, allowing for improvement in ability to adapt and use new advances in technology.

Contact us for more information on participating in these informational courses: https://qci-group.com/contact/

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Quality Inspector Vacancy

We are looking to add to our highly professional and experienced team to meet our expanding customer contracts.

We are looking for an immediate start.

Please follow the hyperlink to our vacancies page for further information and to submit your CV/Resume

QCI Inspector checking a fleet of london underground trains

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We are Expanding our Midlands Metrology Centre

metrology lab with sub contract measurement

Due to ongoing contracts within the automotive sector and recently acquired contracts within the aerospace sector, we are expanding our midlands metrology centre. We have acquired preferred supplier status for subcontract CMM measurement services. In order to supply our customer base with our industry leading services we will be increasing our measurement capabilities by introducing:

  • A new coordinate measurement machine, featuring a laser scanning probe head. (This will be our largest machine to date).
  • A new vision system, featuring the latest Axel Software.
  • A brand new applications engineer.

This will allow us to efficiently continue to provide top quality service.

For updates or queries regarding our subcontract measurement services, visit our contact page operator measuring parts with an optical inspection machine. The optical inspection machine has 400x zoom to ensure maximum accuracy while inspection the parts. The screen shows a live image of the components.

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Why Non-Contact Optical Measurement Systems are Crucial for the Quality Inspection Industry.

Introduction

Selecting the appropriate measuring technique in your given environment is crucial in producing the most definite results. To increase throughput and effectiveness of one’s company the integration of non-contact optical measurement systems should be considered due to its certain advantages over contact measurement instruments and how both machines can be used in conjunction. 

Measurable Materials

There exists a multitude of materials that can be measured to its most absolute accuracy on a non-contact optical measurement system that would otherwise not be able to be easily measured on a contact measurement instrument, things such as pliable matter e.g plastics, foams, etc… and very hard components e.g unpolished metals, abrasive paper etc… as well as dependant on what one’s inspection needs are it can also produce measurements for instances that involve materials measured at a required magnification, high resolution and multi-axis work. With exceptional surface illumination and range of zoom lens vision, systems collect numerous points simultaneously factoring waviness, feature size, and location calculation, measuring the edge directly to form a feature rather than having the feature be created through multiple separate point by point measurements that contact measurements instrument would create. Blind holes, milled slots, and other edges that are shadow less when illuminated form behind can also be easily measured. 

hexagon
Hexagon with Five-Milled Slots
Materials Sensitive to Damage/Pliable Materials

Non-contact optical measurement systems aid a company with increasing sampling rates and measuring batches of miniaturized pieces as computer, medical, and electronic industries progress in making components smaller and smaller, eliminating any damage or contamination these pieces are prone to. 

Concurrence with Contact Measurement Instruments

In conjunction with contact measuring devices, some types of non-contact devices are unable to write repeatable programs, however they can be thought out and measured then written on a contact machine making it easily repeatable. Measurements taken of a product separately, on a contact and non-contact machine can differ due to the way they take measurements, but can be used together to compare specifications of the original drawing of the product.

Contact Probe

Considerations

The use of non-contact measurement systems is ultimately up to a company’s needs and discretion. Bases on conditions present it is always worth considering non-contact measurements systems to optimize performance, accuracy, and throughput as non-contact systems are taking care of increasing workloads across many sectors of the quality inspection industry. 

 

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Maintaining Your CMM Machine

QCI CMM inspection operator using a DEA CMM machines to conduct subcontract inspection on some aerospace components for a customer. The operator is manually adjusting the CMM program to be able to inspect the aerospace parts on the CMM machine. The parts are fixted to the granite surface using a specialist CMM fixture.

In order for your CMM to continuously operate in a safe and accurate way, then then the following maintenance schedule should be followed:

WARNING

Be sure to turn the main disconnect switch to OFF when making adjustments, removing or replacing covers, guards, components, and when making inspections which require physical contact with the machine. Some inspection and adjustments requires the MAIN DISCONNECT SWITCH to be in the ON position to provide necessary power. In such cases, use extreme caution prevent personal injury. 

subcontract inspection being carried out on aerospace parts. precision subcontract inspection being completed in a temperature controlled inspection environment using a DEA CMM and PCDMIS software.

Daily Maintenance

Visual Inspection:

Cleaning:

  • Damaged, broken, or loose probes.
  • Damaged or twisted cables, especially to the jogbox.
  • Loose guards or covers.
  • Note any unusual noises when machine is running.
  • Any burnishing to the bearing ways could be an indication of a major mechanical fault.
  • Wipe both the bearing ways and the granite table with a lint-free cloth and clear solvent.
  • Clean the guideways of all axes using a dry lint-free cloth.
  • Clean the probe module and extension using a dedicated cleaning kit.

Monthly Maintenance

Visual Inspection:

Cleaning:

  • Inspect the machine for any loose, worn, or damaged parts.
  • Check that cable insulation is not damaged.
  • Check condition of of pneumatic air filters and drain if necessary.
  • Clean and replace the electrical cabinet filters on the intake and exhaust (if applicable).
  • Clean the machine structure and painted guards with industrial detergents that are soluble in water. Be mindful not to touch guideways, optical scales, belts, or measure head.
  • Clean guideways of the Z axis.
  • Wipe the optical scales.

Quarterly Maintenance

Visual Inspection:

  • Conduct a full visual check of the machine.
  • Check all guards and covers.
  • Visually check all push buttons/switches.
  • Check to ensure that all of the axes are functioning correctly.
  • Check that all air pipes are intact and that noticeable air leaks are present.
  • Visually check all electrical switches and pushbuttons to make certain that they are functioning properly and that there are no broken, cracked, or loose components.

The Calibration Artifact.

CMM calibrating using an artifact

One of the most important parts of your system is the calibration artifact or sphere. Before any operator attempts to calibrate a probe, please ensure that the following instructions have been carried out:

Visual Inspection:

Cleaning:

  • Check for damaged, broken, or loose probe head components (tip & module).
  • Check that calibration sphere is fixed tightly to the cmm table.
  • Clean the probe and extension using a dedicated cleaning kit.
  • Clean the tip using IPA alcohol and a dry lint-free cloth.
  • Clean the sphere using IPA alcohol and a dry lint-free cloth.
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Geometric Dimensioning and Tolerancing (GD&T) Symbols Explained

Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances. It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describes nominal geometry and its allowable variation. It tells the manufacturing staff and machines what degree of accuracy and precision is needed on each controlled feature of the part. GD&T is used to define the nominal (theoretically perfect) geometry of parts and assemblies, to define the allowable variation in form and possible size of individual features, and to define the allowable variation between features.

All Around Symbol:

This indicates that a tolerance is applied to all surfaces around the part.

All Over Specification:

As well as surface tolerance noted above, this symbol specifies that the tolerance all over on the field of the drawing.

All Around This Side of Parting Line:

To apply a requirement to all features all around one side of a parting line. This symbol will be indicated on the leader line.

All Over This Side of Parting Line:

To apply a requirement to all features all over one side of a parting line. This symbol will be indicated on the leader line.

Angularity:

This is the condition of a surface, axis, or centerplane, which is at a specified angle from a datum plane or axis.

Arc Length:

This symbol will be placed above a dimension and indicates that a dimension is an arc length measured on a curved outline.

Basic Dimension:

This symbol is used to describe the exact size, orientation, profile, or location of a feature. The basic dimension will always be associated with a feature control frame or datum target.

Between:

This indicates that a profile tolerance applies to several contiguous features and letters may designate where the profile tolerance begins and ends. These letters are referenced using the between symbol (post 1994), or the word “between” (pre 1994).

Concentricity:

This describes a condition in which two or more features, in any combination, have a common axis.

Conical Taper:

This symbol is always shown with the vertical leg to the left, and indicates the taper for conical tapers.

Continuous Feature:

This can be in either symbol or note form, and is used to identify a group of two or more features of size, where there is a requirement that they be treated geometrically as a single feature of size.

Controlled Radius:

This creates a tolerance zone defined by two arcs (min max radii) that are tangent to the adjacent surfaces. Where a controlled radius is specified, the part contour within the crescent-shaped tolerance zone must be a fair curve without flats or reversals. Also, radii taken at all points on the part contour shall neither be smaller than the specified minimum limit nor larger than the maximum limit.

Counterbore/Spotface:

This symbol is used to simply indicate a spotface or a counterbore. This symbol will precede the dimension of the spotface or counterbore, with no space.

Cylindricity:

This symbol describes a condition of a surface of revolution in which all points of a surface are equidistant from a common axis.

Datum Feature:

This is the actual component feature used to establish a datum.

Datum Target

This is a specified line, point, or area on a part that is used to establish the Datum Reference Plane for manufacturing and inspection operations.

Depth/Deep:

This symbol is used to indicate that a dimension applies to the depth of a feature. This symbol will precede the depth value with no space in between.

Diameter:

This symbol indicates a circular feature when used on the field of a drawing. If a feature control frame is used then this symbol will indicate that the tolerance is diametrical.

Dimension Origin:

This symbol signifies that the dimension originates from the plane that is established by the shorter surface, and dimensional limits apply to the other surface.

Feature Control Frame:

This is a rectangular box containing the geometric characteristics symbol, and the form, runout, or location tolerance. Datum references and modifiers applicable to the feature or the datums are also contained in this box if necessary.

Flatness:

This is the condition of a surface having all elements in one plane.

Free State Variations:

This is a term used to describe distortion of a part after removal of forces applied during the manufacturing process.

Least Material Condition (LMC):

This implies that condition of a part feature of size wherein it contains the least amount of material, examples, largest hole size, and smallest shaft size. This is also the opposite to Maximum Material Condition.

Independency Symbol:

This is applied to the size dimension in order to invoke the principle of independency to regular features of size and override Rule #1.

Maximum Material Condition (MMC):

This is a condition of a part feature wherein it contains the maximum amount of material within the stated size limits. That is; minimum hole size and maximum shaft size.

Moveable Datum Targets:

This symbol may be used to indicate movement of the datum target datum feature simulator.

Number of Places:

The ‘X’ is used along with a value to indicate the number of times a dimension or feature is repeated on the drawing.

Parallelism:

This is the condition of a surface, line, or axis, which is equidistant at all points from a datum plane or axis.

Parting Lines:

These are depicted on forging/moulded/casting part drawings as a phantom extending beyond the part in applicable views, with the parting line symbol added.

Position Tolerance:

This defines a zone within which the axis or centre plane of a feature is permitted to vary from true position.

Profile of a Line:

This is the condition permitting a uniform amount of profile variation, either unilaterally or bilaterally, along a line element of a feature.

Profile of a Surface:

This is the condition permitting a uniform amount of profile variation, either unilaterally or bilaterally on a surface.

Projected Tolerance Zone:

This applies to a hole in which a pin, stud, or screw etc is to be inserted. It controls the perpendicularity of the hole to the extent of the projection from the hole and as it relates to the mating part clearance. This tolerance zone extends above the surface of the part to the functional length of the pin, stud, or screw relative to its assembly with the mating part.

Radius:

This creates a zone defined by two arcs (min and max radii). The part surface must lie within this zone.

Reference Dimension:

A dimension usually without a tolerance which is used for informational purposes only. It does not govern production or inspection operations.

Regardless of Feature Size (RFS):

The condition where the tolerance of form, runout, or location must be met irrespective of where the feature lies within its size tolerance.

Roundness:

This describes the condition on a surface of revolution (cone, cylinder, or sphere) where all points of the surface intersected by any plane.

Runout:

This is the composite deviation from the desired form of a part surface of revolution through a full rotation of the part on the datum axis.

Slope:

This symbol is used to indicate slope for flat tapers. This symbol is always shown with the vertical leg to the left.

Spherical Diameter:

This shall precede the tolerance value where the specified tolerance value represents spherical zone. Also, a positional tolerance may be used to control the location of a spherical feature relative to other features of a part.

Spherical Radius:

This precedes the value of a dimension or tolerance.

Square:

This symbol is used to indicate that a single dimension applies to a square shape. The symbol precedes the dimension with no space in between.

Statistical Tolerance:

This is the assigning of tolerances to related components of an assembly based on sound statistics. By applying statistical tolerancing, tolerances of individual components may be increased or clearances between mating parts may be reduced.

Straightness:

A condition where an element of a surface or an axis is a straight line.

Symmetry:

This is the condition in which a feature (or features) is symmetrically disposed about the centre plane of a datum feature.

Tangent Plane:

This indicates that a tangent plane is shown. The symbol is placed in the feature control frame following the stated tolerance.

Target Point:

This indicates where the datum target point is dimensionally located on the direct view of the surface.

Total Runout:

This is the simultaneous composite control of all elements of a surface at all circular and profile measuring positions as the part is rotated through 360 deg.

Datum Translation Symbol:

This symbol indicates that a datum feature simulator is not fixed at its basic location and shall be free to translate.

Unilateral and Uequally Disposed Profile Tolerance:

This symbol indicates that a profile of a surface tolerance is not symmetrical about the true profile. The first value in the feature control frame is the total width of the profile tolerance. The value following the symbol is the amount of the tolerance that is in the direction that would allow additional material to be added to the true profile.

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Effects of Temperature on Dimensional Measurement

Introduction

A common phenomenon well-known to engineers and metrologists alike, is that everything changes when temperatures change. Although these subtle changes are usually invisible to the naked eye, the need for expansion joints when constructing bridges presents a more noticeable example, as a bridge’s span length increases and decreases due to the current seasonal climate. In industrial measurement where tolerances are low, and a small difference in size becomes critical, then these small, subtle changes in temperature can become very important.

Thermal Expansion

Whenever a material is subjected to heat, then the distance between the individual atoms will change. This distance is dependable on the material used, although the most common change to occur is an increase in distance. Since this heat effects all atoms in the material equally, then the change in length is proportional to the original length. So, a constant of proportionality can be observed as the length change is proportional to the temperature change, thus coining “The Coefficient of Thermal Expansion”, though over large temperature ranges, problems can still occur.

Because of the above coefficient, to define the size of a piece of material, we must also state the temperature reading at the stated size. This is where standardization comes into effect, as ISO 1 states that all dimensional measurements should take place when the material is 20˚C (68˚F), unless otherwise stated.

Above is a table showing a number of common materials, along with how they respond to changes in temperature. The CTE numbers in the second column are averages, as many different material types can still use the same names (e.g Stainless, and High Carbon Steel). The third and final column represents an estimate regarding the importance of temperature in measurements. A very high accuracy measurement would be a length measurement that has an uncertainty of around 1ppm.

100mm Samples & 5C Expansion

The above graph illustrates another example of how to think of thermal expansion. If all samples shown have a length of 100mm, then raising a temperature by 5˚C increments will result in the lengths changing as shown. This provides a rough template for how close a metrology laboratory should be to 20˚C, depending on what type of material is being measured. Also, the graph shows two types of steel gage blocks (25nm & 500nm), this is due to the peculiarity within steel gage blocks, in that the CTE is dependent on the length of the block.

Conclusion

Ultimately then, an understanding of thermal expansion is needed to provide highly accurate measurement results. Here at QCI, our laboratory is set at a constant 20˚C resulting in the perfect environment to provide customers guaranteed precise metrology solutions. Our Midlands based metrology centre uses the latest technology, offering a full range of measurement, reporting and programming services. Customers receive the measurement information they need for product verification and quality control to the highest degree of accuracy. We operate a temperature controlled clean room environment to help minimise factors that contribute to measurement uncertainty, such as thermal expansion which is covered above.

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Micrometer Types and Usage Guide

Introduction

Over a past number of years more sensitive measuring instruments have been developed due to the need of satisfying requirements for higher accuracy. These newer types of instruments however, are of the comparator type and require a setting master. Also, the measurement range can be rather small. Micrometers have an advantage over these gauges as they can measure absolute lengths over a much larger range. Smaller micrometers are widely used due to their versatility, although the larger micrometer types have been replaced for applications with tighter tolerances. In comparison to other measuring instruments, micrometers are relatively cheap and their operators require very little training. The digital micrometers, rather than the analogue, are much more reliable as they eliminate parallax error and are easier to read. Internal micrometers use the same scale and mechanism but are used to measure large bores.

Types of Micrometer

Digital Micrometer
Analogue Micrometer
Depth Micrometer
Internal Micrometer
Ball Micrometer
Disk Micrometer

Environmental Requirements

  • The frame of the micrometer can be warmed by the hands which can result in significant measurement errors on the larger types of micrometer. Therefore, gloves or insulation on the frame may be used to minimise the heat transferred from the hands to the frame.
  • The micrometer should always be used in an environment with adequate lighting. A minimum of 700 lux is appropriate.

    Usage Guidance

     

  • The user of the micrometer should be conscious of any changes that could indicate possible errors with the gauge.
      • The thimble should run evenly and not stick.
      • The ratchet should turn smoothly.
      • The zero line on the spindle should align with the index line that is on the micrometer sleeve.
      • The end of the thimble should be aligned with a graduation line on the sleeve and not cover it.

     

  • If the micrometer has been subject to any kind of damage, then the checks mentioned above should always be carried out. The parallelism between measuring faces and flatness of the micrometer can also be checked if an optical parallel is available. Do not use a micrometer if there are any doubts in regards to its condition.
  • Before using an analogue micrometer, all the scales should be checked for clearly marked graduations.
  • Different types of anvils can be used to measure different types of features. Some examples of common anvils are pin, ball, or disc anvils.
  • Internal micrometers (also known as inside micrometers) can be used on large diameters when feature tolerance does not justify using a more accurate comparative gauge.
  • Micrometers should be periodically checked for zero error. For micrometers that do not start at 0, (e.g. 25-50mm or 75-100mm), a calibrated length bar should be used to zero the scale.
  • The accuracy of the measurement in analogue micrometers relies on the lead of the screw. The error in the screw is cumulative, which means the error increases with the length of travel. For this reason a micrometer with the closest possible range to the nominal dimension should be used.
  • The zero point of micrometers should be checked regularly. It is possible on a digital micrometer to re-zero the scale. Continued re-zeroing however, may mask any significant changes in the scale, and therefore should be avoided.
  • Micrometer Capability Charts



    QCI Group can assist with any inspection you with any inspection activities across multiple sectors. We carry inspection for some of the largest manufactures in Aerospace, Rail, Automotive, Oil & Gas and Power Generation. We offer subcontract CMM Inspection, optical measurement, FIA & LAI support, ISIR, PPAP, revese engineering and much more. Follow the link for more infomation on our services.


    Inspection Services

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Surface Finish Instruments & Usage Guide

Surface Finish Instrumentation

The functional performance and mechanical properties of materials are all affected by surface finish. A total of 90% of all engineering component failures are believed to be initiated through mechanisms such as fatigue cracking, abrasive wear, or stress corrosion cracking. The functional performance requirements for surfaces vary hugely; those of vehicle brake disks are clearly different to those of bearing surfaces.

The surface texture characteristics are generated by a combination of the machining process, feed rate, tool speed, tool geometry, and also the environment conditions. It is very important to gain an understanding of how the manufacturing process modifies the surface of the material in use when planning any measurement. Specific processes such as the direction of lay (machining marks), and the level of control (e.g. a regular repeatable cylindrical grinding process vs a hand polishing process) should be considered.

The surface texture may be assessed comparative or direct measurement. Comparative methods assess the surface texture by either observation or the feel of the surface. The technique involves dragging the finger nail over the surface to be measured and then comparing the referencing standards. Although this was one of the first methods for surface texture measurement, it is still a popular method today.

Direct measurement of the surface is usually carried out with a tactile measuring instrument that is fitted with a diamond tipped stylus. This form of instrumentation can measure vertical movements down to nanometre values and due to the effects of vibration and shock, these are generally only used in a laboratory environment. The contact pressure applied at the tip of the stylus is very small in order to ensure it does not plough the surface which would result in false readings.

A Surface Texture Machine with Tactile Probe

There are two types of stylus instrument in general use, those that have a skid to support the stylus, and those that do not. In the skidded instrument, the stylus is supported by a curved, metal skid which rests on the work piece surface and acts as a reference. The current ISO standards do not recommend skidded instrumentation, although these are still used in workshops as they are more robust than skidless instruments, and also provide additional filtering to the data.

skidlessandskiddedprobe
Skidless (left) & Skidded (right) Surface Texture Probes

There are many other non-contact or optical measuring instruments which can measure surface texture quickly. However, these non-contact methods depend upon reflections from the surface and these reflections can vary with different materials, depth, and characteristic of the surface. As a result, the only measurements traceable to either National or International Standards are currently made by tactile stylus instruments.

The surfaces to be measured can incorporate waviness or curvature which if not removed from the measurement will go on to affect the final result. Filtering can remove these effects, either automatically by modern digital equipment, or by using a skidded or larger styli. A stylus with a larger 5μm tip radius will filter out troughs that it cannot reach, and a skidded probe will filter out long wavelength waviness as the skid acts as the reference level.

Analysis of the surface requires magnifying the vertical displacement of the styli compared with the horizontal travel. This is known as the aspect ratio which is typically 400:1. The most common sampling length is 0.8mm (cut off length) with the evaluation length being the average 5 such lengths over 4.0mm.

Surface finish is typically measured using Ra (Roughness Average, also known as Centre Line Average [CLA], Arithmetic Average [AA]). This is defined as the average height from a mean line of all coordinates of the surface over the length of the assessment. This is the oldest and most common texture parameter, though today many new parameters have been derived with similar functionality.

A 2D line profile may be used to define the characteristics of a surface. On its own, Ra does not fully define the properties of a surface as can been seen in the illustrations below, where different machining processes have the same Ra, but the shape of the surfaces differ significantly.

The most commonly used 2D measurement parameters are as follows:

  • Ra: Arithmetic mean of the absolute peak height and valley depth values.
  • Rq: Root Mean Square (RMS)
  • Rv: Maximum valley depth.
  • Rp: Maximum peak height.
  • Rt: Maximum height of the profile (Rt = Rp – Rv) within evaluation length
  • Rz: Ten point height parameter.
  • Rsk: Skewness – a measure of whether the bulk of the material is above or below the mean line.
  • Rku: Kurtosis – measure of the sharpness of the surface.

Environmental/Storage Requirements

Surface texture measurement takes place at the sub-micron level and therefore extra care should be taken in order to:

  • Control the environment. Temperature variation, draughts and vibration will have a more noticeable effect on results taken at the sub-micron level.
  • Keep the part, probe, fixture, and other parts of the measurement system clean. Dust, dirt, coolant and other contaminates will have a big impact on the measurement capability.
  • To protect the styli from damage. Damaged styli will cause measurement errors as shown below.
Effect of a Damaged Probe (left) & A Damaged Diamond Tip (right)

Usage Guidlines

  • It is important to note that if comparative methods are used, it must be with surfaces produced by similar techniques.
  • Dedicated fixtures will improve measurement repeatability. When carrying out repeatability measurements, it is important to measure the same surface as close to the original position as possible. This is because the surface will vary over the part and 2D measurement is only over a very small length. Fixturing will also help prevent misalignment of the stylus.
  • The measurement device should be placed level to the measurement surface. Some measurement devices can be affected when both the device and measurement surface is tilted. If such a situation cannot be avoided, the effects of measuring at the required angle will need to then be assessed.
  • Care must be taken when selecting instruments to measure curved surfaces, such as aerofoil surfaces. With portable skidded devices the supported skids have been found to prevent full contact of the styli with the curved surface. With skidless instruments, the range of movement in the vertical direction can also limit the curvature of the surface that can be measured.
  • Inexpensive hand-held gauges are generally not suitable for measurement of complex free form surfaces such as curved aerofoils.
  • Any stylus/probe can reach the required surface without causing damage to the probe or to the surface.
  • The instrument calibration should be checked regularly using the glass surface roughness standards and the instrument itself should be serviced and calibrated by the instrument OEM.
  • The instrument should first be checked on a surface roughness standard similar to the measurement roughness to be evaluated. The Ra value measured should correspond with the roughness standard. If the desired value is not as expected, then the instrument should be quarantined and the problem investigated.
  • After turning the machine on, time should be given for the machine to stabilise. The minimum time for this is usually documented in the manufacturer’s instructions.
  • The stylus shape will be a cone with either a 60˚ or a 90˚ inclusive angle. Tip radii should be 2μm or 5μm.
  • The 16% rule on acceptance of surfaces is as follows when a surface roughness value is specified in the product definition:- A surface is considered acceptable if less than 16% of the measured values (over the measured length) are over/under the limit specified.
  • Max Rule: when a maximum value is specified, none of the measured values (over the measured length) can exceed the specified value.
  • The measurement direction should traverse perpendicular to the direction of the lay unless otherwise indicated. For aerofoil surfaces the measurement should be taken in the direction of the gas flow.

Common Pitfalls

  • Smaller tip sizes tend to report larger values of Ra, so care should be taken when choosing tip size.
  • In the case of a skidless probe, the stylus tip should be the ONLY part of the probe to touch the part.
  • Although surface roughness measuring instruments apply very little pressure to the surface, a 0.002mm stylus radius can create a small track in the material if the surface is not too hard. This will result in false readings.
  • The use of the correct filter and correct sample length is very important as misapplication can lead to significantly incorrect interpretation of surface parameters.
  • Results of the surface roughness measurements using Stylus instruments are the only true traceable devices to the national standards.
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We now hold the latest AS9120:2016 Standard

QCI Group have successfully completed the transition to AS9120:2016. Did you know we are the only inspection and quality management support company in the UK to hold this standard!

Our standards are constantly maintained and regularly externally audited to ensure best practice.

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