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Stylus Manual
Introduction: This is how a stylus system is built up.
The correct stylus choice
The basis for accurate measurement is the stylus and accessories that are suitable for optimum solution of the measuring application. The task in question varies:
- point measurement for highest accuracy level
- scanning in series measuring operation
- scanning of special materials
- necessity for longer styli
- construction of complex stylus systems
The entire system
The deciding factor is the entire system with all its constituent parts. The stylus, extensions, adapters, knuckle joints etc. as a whole make a contribution as to whether a stylus system is suitable or not. Stylus systems must be designed so that as few elements as possible are included, because each item contributes to measurement uncertainty. This contribution must be as small as possible.
The most important selection criteria for the individual elements are shown below.
Styli selection: What does a stylus consist of?
What does a stylus consist of ?
A stylus normally consists of three parts:
| Legend | DK | Ball diameter in mm |
|---|---|---|
| L | Length Range in mm | |
| ML | Measuring length in mm | |
| DS | Shaft diameter in mm | |
| DG | Diameter of base element in mm |
The stylus tip can be a sphere, a disc, a cylinder or a derivation thereof, such as a hemisphere, a cylinder with a spherical end, etc.
Optimum stylus stiffness
The fact applies to all styli, that they should be as bend-resistant as possible to be able to take up the measuring force as far as possible without deformation, the so-called „stylus deflection“. The shaft structure and the transition to the adapter into which the shaft is fixed is decisive in this matter.
Styli selection: Advantages and disadvantages of different shaft materials?
Shaft structure
We differentiate between a full-length shaft and an offset shaft. The offset shaft has the advantage of a slightly greater shaft thickness DS, that reduces towards the stylus tip. Disadvantage is the reduced available measuring range MLE with the shaft thickness DSE (As compared with DS and ML on a non stepped shaft stylus).
| Legende | DK | Ball diameter in mm |
|---|---|---|
| L | Length range in mm | |
| ML | Measuring length in mm | |
| DS | Shaft diameter in mm | |
| DG | Diameter of base element in mm | |
| MLE | Stepped measuring length in mm | |
| DSE | Stepped shaft diameter in mm |
The shaft material
The material used for the shaft and the cross-section (solid material is stiffer than tubes) have a great influence on the stiffness of the stylus. For its standard styli, ZEISS uses tungsten carbide shafts that represent a good compromise
The optimum
The diagram provides an overview of the various different material properties of styli. As you can see, Zeiss ThermoFit styli represent an optimum of the three significant properties:
- Stiffness
- Weight
- Thermal expansion in length
Styli selection: What influence does the thread adapter have?
The adapter
The adapter is the connection between the connection thread and the shaft. It is important that the adapter is designed in such a way that it can withstand the measuring force that is introduced via the shaft in an optimum manner. Otherwise there will be an increased scatter of the probe determinations. In addition, the connection point to the extensions is always undercut to make sure of optimum force fit.
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Caution:
The connection points must be clean!
Which connection thread is there?
Depending on the measuring system being used, Zeiss use M2, M3 and M5 connection threads.
Important!
On XXT stylus systems you must not use normal M3 styli, but rather the optimized M3 XXT styli for passive scanning. As a result of the 1 mm bigger diameter of the XXT adapter body, and the high-strength titanium alloy used, significantly higher stiffness is ensured, when compared to conventional M3 styli.
Styli selection: Which ball material is suited to which application?
The stylus tip
The most often used stylus tip is the stylus sphere. Significant properties are
- the form accuracy of the stylus sphere
- the stylus material and
- possibly the stylus weight.
The shape accuracy of the stylus sphere
The deviation from the ideal spherical shape is generally quoted as the „Grade“. The following qualities are common:
| Grade | max. deviation from spherical shape in µm |
|---|---|
| 3 | 0,08 |
| 5 | 0,13 |
| 10 | 0,25 |
| 16 | 0,40 |
| 20 | 0,50 |
Zeiss uses Grade 5 styli as standard and also has, for special requirements, such as with extremely accurate roundness tests, Grade 3 spheres in their range.
The ball material
The most common ball materials are shown below, together with their main application areas and limitations.
| Material | Application area | DK in mm |
|---|---|---|
| Ruby | Standard for virtually all applications. Inadequacies with certain materials in combination with continuous scanning (wear or material build-up possible). | 0,12 - 12 |
| Sapphire | Same properties as ruby, but larger ball diameters are possible. | 8 - 15 |
| Silicon nitride | Use in the same way as ruby, but possibly less material build-up when scanning aluminum. | 1 - 12 |
| Ceramic (aluminum oxide) | Is used with large ball diameters and disc styli and for scanning rough surfaces, e.g. castings. Weight-optimized hemispheres are possible. | 8 - 45 |
| Zirconium oxide | When compared to ruby, it is a softer material that is used on styli in hand-guided measuring machines. | 1 - 10 |
| Tungsten carbide | Makes possible special sizes of ball diameters, e.g. when measuring gear teeth. Can be made-to-measure. Very high weight. | 2 - 30 |
| Steel | Used mainly for disc styli. Is considerably softer than tungsten carbide but is available in larger diameters. | 30 - 100 |
| Diamond | Hardest material in the world, virtually no wear and no material build-up when scanning. | 1 , 3 |
Styli selection: These errors can arise if the styli selection is incorrect.
Styli build-up
Specific material combinations of styli and work pieces can be problematic, because of their surface structure, that a material layer builds up on the stylus ball during constant scanning mode. A typical example is ruby balls in combination with soft types of aluminum.
Stylus wear
In continuous scanning of rough surfaces, such as ceramics, a stylus may suffer „flattening off“. The consequence of the wear is a flat section. The stylus is then unserviceable. Often this can only be detected by an optical increase in size or an increased standard deviation when calibrating.
Diamond styli
A solution to this is the diamond stylus Diamond!Scan. It is suited to all surfaces and materials. The main advantage is the maximum service life when scanning hard ceramic surfaces. On soft materials there is no material build-up on the stylus ball.
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Extensions: This is needed to scan quickly and with repeatable accuracy.
Diameter and material
In order to achieve the highest possible scanning speed at the lowest possible form deviation, we must choose extensions with a large diameter, low weight and high levels of stiffness. The following diagram shows that the highest speeds are achievable with ZEISS ThermoFit extensions.
Form deviation on ring Dmr. 15 mm
Stylus DK=4 mm, Z=100 mm, Y=500 mm
Thermal torsion
In the longitudinal direction all CFK extensions are stable with regard to thermal changes, but not to torsion about the longitudinal axis. The special structure makes the ThermoFit have the additional advant-age over conventional CFK extensions from other manufacturers of torsional security during temperature changes. Especially on long stylus systems with elements which have collars out to the side, there are decisive advantages in the environment close to manufacturing.
Recommendation:
If you have any problems, please contact us - there‘s always a solution.
Extensions: How can the gluing gap make the measurement inaccurate?
Hysteresis
We refer to hysteresis if the stylus, after making contact, does not return to its starting position. This always occurs if, on carbon fiber stylus extensions, the connection between tube and adapter is only realized by adhesive with an adhesive gap. ZEISS ThermoFit extensions, in addition to the adhesive, have undercut threaded adapters for optimum connection between the tube and the adapter.
This effect makes itself felt by an increased standard deviation, e.g. when calibrating. In contrast to the competition, Carl Zeiss exclusively uses a combination of both connecting methods in order to ensure the optimum force fit. This is demonstrated clearly in the following sectional views.
Comparison:
Comparison under the microscope clearly shows that the thread does not cut in and thus does not create a force fit with the carbon fiber tube. The connection is only produced by the adhesive.
Important:
We can scan more quickly with a stiffer structure of the stylus system, for example by the use of ThermoFit® extensions.
Extensions: How does the material of the extensions affect the measurement?
Which extension is best suited?
The table below describes the various different extensions.
| Material | Diameter | Plus points / negative points |
|---|---|---|
| Aluminum | 11 20 |
Plus point: low weight. Negative points: large length expansion even with slight temperature variations. Application: Only in a measuring room with very good climate control. |
| Titanium | 18 11 |
Plus point: low weight. Negative points: reduced stiffness as a result of thin wall thickness and large thermal expansion in length. Application: Only in a measuring room with very good climate control. |
| Stainless steel | 11 |
Negative points: heavy weight and large thermal expansion in length. Application: Only in a measuring room with very good climate control. |
| ThermoFit Silver | 5 11 20 |
Plus points: low weight and thermal stability with maximum stiffness. Application: can be used in all applications. |
| ThermoFit Pro | 11 20 |
Plus points: as per ThermoFit silver. In addition: Twisting resistance and reduction in interfaces, producing another weight saving of up to 25%. Application: can be used in all applications. |
ThermoFit® Pro
You can quickly create high-quality stylus systems with ThermoFit for use in production. Twist-secure plug connections and our ThermoFit technology provide optimum application security. Using our pre- fabricated ball blanks you can even quickly manufacture your own special angle blocks.
Important for all CFK styli and extensions
After a hard collision you must carry out a visual check and must re- calibrate to be on the safe side. Even if no visible damage is evident, the fibers on the inside may be damaged, which can only be determined by checking the standard deviation of the calibration process.
Connecting elements: Unlimited possibilities for building-up styli.
General points
There is a wide variety of different connecting elements for building up stylus systems. A detailed description can be seen in our web-shop or in the relevant styli catalogs. Recommendation:
Connecting elements for XXT stylus systems:
Recommendation:
For series measuring operation, fixed connections, such as angle blocks or the system ThermoFit Pro is preferred, so that the angles do not move in continuous mode.
Calibration elements: Which reference sphere size is suitable for my stylus?
Climate-controlled measuring range
Carl Zeiss offers the reference sphere holder RSH for the measuring machine in various different heights (214, 364, 514 mm). The reference sphere holder can be fitted with the suitable sphere, depending on the application, and is used in the climate-controlled measuring room.
It is particularly important with small stylus ball diameters to use a suitable reference sphere in order to avoid contact with the shaft. The following table provides an overview of the recommended reference sphere for the specific stylus ball diameter, where, in principle, all combinations are possible.
| Reference sphere DK | Application area of recommended stylus ball diameter |
|---|---|
| 8 | until aprox. <1 mm |
| 15 | until aprox. 1-2 mm |
| 25 / 30 | until aprox. >2 mm |
Production-like environment
For applications under fluctuating ambient temperatures we use reference sphere holders made of ThermoFit or Invar, because they have very high thermal stability levels.
Styli mounting: This must be taken into account when assembling a stylus system.
Handling and auxiliary materials
There are suitable auxiliary materials for mounting the styli and exten-sions, that will prevent damage if used properly and which ensure safe deployment. The following are the most important auxiliary materials and tools.
Setting the adapter plate MT/VAST correctly
The rotary position of the MT/VAST adapter plate can be adjusted using three screws on the top. These must be tightened with a max. torque of 2 Nm, and this is best achieved using a torque wrench. This prevents over-tightening of the screws.
Mounting the extensions and styli:
The extension and the stylus should be hand-tight. There are suitable hook wrench and pin wrench available. Hook wrenches are available for base bodies having a diameter 5, 11 and 20 mm. Pin wrenches 1,1 and 2,9 are used in the pin holes having a diameter of 1.2 mm and 3 mm. Always make sure that you tighten directly on the thread.
Important: Never apply torque via an extension and only use hook wrenches for tightening!
Styli mounting: How do I align the stylus correctly?
Mounting XXT extensions
The XXT styli assembling aid is used to hold an extension whilst you screw in a stylus with a pin or hook wrench. The assembling aid is pushed against the side of the extension when doing this.
Aligning the XXT star stylus
The set up device for the star styli M3 XXT can be used to adjust the star styli or side styli to the desired angle before fitting. To do this, the XXT stylus plate is placed in the cut-out at the bottom, and the displacement unit is pushed against one of the side collar styli with the prismatic guide placed at the side, thus fixing the rotation angle. This then allows the stylus system to be tightened in this position.
Set up device for knuckle joints
This adjustment aid can be used precisely to set the knuckle joints, diameter 11 mm, to the desired angle before installing.
Styli mounting: Fitting the stylus quickly and simply with FixAssist.
Angle setting with FixAssist
FixAssist is a stylus pre-setting unit for stylus systems with MT/VAST adapter plates and is used independently of the MMC. With the FixAssist you can set the rotary angle of the adapter plate and the rotation of a second side collar extension can be aligned.
Aligning the XXT star stylus with the FixAssist
The adapter set for the FixAssist Linear is provided for setting of XXT stylus systems. It consists of an adapter for the XXT adapter plate and a magnetic prismatic adapter. These adapters are used in the FixAssist. Styli mounting Fitting the stylus quickly and simply with FixAssist.
Threshold values: Threshold values for XXT probe heads.
Threshold values for XXT stylus systems
The table shows the permissible ranges in which styli for the XXT systems TL 1 to TL 3 can be built up.
The gray area is permitted; the light-blue area is also possible, with limitations in the dynamics of the measuring machine. The white area is not permitted.
The weight
In the weight of the stylus systems you must also take careful account of the threshold values, since otherwise there may be a malfunction of the XXT probe head. The following threshold values are stipulated:
| Stylus system | Maximum weight including adapter plate |
|---|---|
| TL 1 | 10 g |
| TL 2 | 10 g |
| TL 3 | 15 g |
Threshold values: Thresholds of other ZEISS probe heads.
Threshold values of other stylus systems
There is a wide variety of other measuring systems that are stipulated for the maximum weights and lengths of the stylus systems. The most important are shown in the following overview:
| length in mm | weight in g | tilt torque in Nm | |
|---|---|---|---|
| ST | 200 | 200 | - |
| ST3 | 200 | 200 | - |
| ST-ATAC | 200 | 200 | - |
| XDT-TL3 | 150 | 15 | - |
| RDS/XDT-TL3 | 150 | 15 | - |
| VAST XXT-TL1 | 125 | 10 | - |
| RDS/XXT-TL1 | 125 | 10 | - |
| VAST XXT-TL2 | 250 | 10 | - |
| RDS/XXT-TL2 | 250 | 10 | - |
| VAST XXT-TL3 | 150 | 15 | - |
| RDS/XXT-TL3 | 150 | 15 | - |
| DT | 500 | 500 | 0,3 |
| VAST XT | 500 | 500 | 0,3 |
| VAST XT gold | 500 | 500 | 0,3 |
| VAST | 800 | 600 | 0,1 |
| VAST gold | 800 | 600 | 0,1 |
| HSS | 600 | 600 | 0,2 |
Caution!
The specification in the documentation of your measuring machine is binding
The tilt torque
The tilt torque is created by an uneven weight distribution of the stylus system. This must be prevented by the use of suitable balance weights. The tilt torque KM can be calculated as follows:
| Legend | S | Center gravity of a stylus |
|---|---|---|
| F | Force at the center of gravity | |
| L | Distance from center of gravity to line of symmetry |
For information about this can be taken from the „Sensorik“ operating instructions.
Storage: Where is it best to store the stylus system?
Storage
Stylus systems can be stored securely in our special probe cabinets. There is a wide variety of accessories for the specific styli material that makes the storage more simple. You can find this in our web- shop or in the individual styli catalogs that you can request from us free-of-charge as a PDF file or in paper form.
Installation
The setting table is an ergonomic workplace, adapted to the requirements of measurement technology. It provides a large working area for preparation of devices, assembly of stylus systems and for clean- ing your styli. Drawers and the wall cabinet with styli storage areas promote tidiness and provide storage facilities for your cleaning materials, tools and documents.
Care
Stylus balls and reference spheres should be cleaned to remove contamination at regular intervals. We recommend, in particular, the ZEISS microfiber cloth. If a slight film of aluminum pick-up should have formed on the styli, this can be removed carefully with a cloth moistened with a solution of the cleaning agent (see also measuring machine operating instructions). If this cannot be carried out completely, the stylus needs to be replaced.
Caution:
On thin styli this must be done with extreme care!
Calibration artifacts: This is how to test the accuracy of the machine.
Performance
In order to ensure the performance of your coordinate measuring machine you need to make regular intermediate tests. Your coordinate measuring machine is tested in association with a stylus system, in which the importance of the high-quality stylus and connecting elements are stressed once more.
Recommendation:
For this we offer suitable calibration artifacts, together with the necessary measuring plans, depending on the task involved. These test schedules ensure that the stipulations of the relevant standards for monitoring of coordinate measuring machines are implemented correctly (DIN EN ISO 0360 and VDI/VDE 2617).
As a result you will receive, based on monitoring factors, a clear assessment of the performance of your measuring machine. If the monitoring shows that your measuring machine cannot maintain the required specifications, you have the possibility of reacting correspondingly, e.g. with a service for your machine. This is always more economical than working in series measurement with the incorrect measurement results.
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CMM-Check
The following properties can be evaluated with the calibration artifacts:
- Probing behavior of probing system
- Scanning properties of the probing system
- the CMM as a form measuring machine including filter properties
- Length deviations and four-axis deviations for CMM with Rotary table (optional)
Check
Multi-Feature-Check
The Multi-Feature Check is used for the determination of the measurement uncertainty related to characteristics and inspection process suitability for virtually all deviations in dimension, shape and length that arise in coordinate measurement technology.
The application of this process determines the measurement uncertainties and inspection process suitability under conditions close to reality. This takes into account:
- current local temperature
- material close to work piece material
- workpiece-similar surface influences
Check
Multi-Sensor-Check
The Multisensor-Check is used for standardized checking of coordinate measuring machines with tactile and optical sensors
The following properties can be evaluated with the calibration artifact:
- Probe deviation of measuring head system
- Scan deviation of measuring head system
- Probe deviation and length measurement deviation are tested in a tactile and optical manner
Temperature monitoring: How do we monitor the temperature?
Temperature monitoring
In order to get correct measurement results it is necessary that the temperature of the stylus systems during measurement is virtually identical to the temperature during calibration. Otherwise, errors may arise as a result of the modified geometrical dimensions of the stylus systems. Monitoring of the temperatures of the work piece and measuring room is not only sensible, it is obligatory from the point of view of the obligation of traceability.
In our web-shop www.taster.zeiss.de we therefore offer a wide range of various different possibilities of temperature monitoring, from the hand measurement sensor, up to a complete room montoring system with recording function. We would be pleased to help with the layout of a temperature monitoring system made-to-measure for your requirements.