BS ISO 230-1:1996 download free.Test code for machine tools — Part 1: Geometric accuracy of machines operating under no-load or finishing conditions.
2 General considerations
2.1 Definitions relating to geometric tests A distinction should be made between geometric definitions and those designated in this part of Iso 230 as metrological definitions.
Geometric definitions are abstract and relate only to imaginary lines and surfaces. From this it follows that geometric definitions sometimes cannot be applied in practice. They take no account of the realities of construction or the practicality of geometric verification.
Metrological definitions are real, as they take account of real lines and surfaces accessible to measurement. They cover in a single result all micro- and macro-geometric deviations. They allow a result to be reached covering all causes of error. without distinguishing among them. Such distinction should be left to the manufacturers.
Nevertheless, in some cases, geometric definitions [e.g. definitions of run-out (out-of-true running), periodic axial slip, etc.] have been retained in this part of ISO 230, in order to eliminate any confusion and to clarify the language used. However, when describing test methods, measuring instruments and tolerances, metrological definitions are taken as a basis.
2.2 Test methods and use of measuring instruments
During the testing of a machine tool, if the methods of measurement only allow verification that the tolerances are not exceeded (e.g. limit gauges) or if the actual deviation can only be determined by high-precision measurements for which a great amount of time would be required, it is sufficient, instead of measuring, to ensure that the limits of tolerance are not exceeded.
It should be emphasized that inaccuracies of measurement due to the instruments, as well as to the methods used, are to be taken into consideration during the tests. The measuring instrument should not cause any error of measurement exceeding a given fraction of the tolerance to be verified. Since the accuracy of the devices used varies from one laboratory to another, a calibration sheet should be available for each instrument.
Machines under test and instrumentation should be protected from draughts and from disturbing light or heat radiation (sunlight. electric lamps too close. etc.), and the temperature of the measuring instruments should be stabilized before measuring. The machine itself shall be suitably protected from the effects of external temperature variation.
2.321.2 Tolerances of form Tolerances of form limit the permissible deviations from the theoretical geometric form (e.g. deviations relative to a plane, to a straight line, to a revolving cylinder, to the profile of a thread or a gear tooth). They shall be expressed in units of length or of angle. Because of the dimensions of the stylus surface or of the support surface, only part of the error of form is detected. Therefore, where extreme accuracy is required, the area of the surface covered by the stylus or support shall be stated. The stylus surface and shape should be suitable for the microgeometry of the surface to be measured (a surface plate and the table of a heavy planing machine are not measured with the same stylus surface).
2.321.3 Tolerances of position Tolerances of position limit the permissible deviations concerning the position of a component relative to a line, to a plane or to another component of the machine (e.g. deviation of parallelism, perpendicularity, alignment, etc.). They are expressed in units of length or angle. When a tolerance of position is defined by two measurements taken in two different planes, the tolerance should be fixed in each plane, when the deviations from those two planes do not affect the working accuracy of the machine tool in the same way.
NOTE I When a position is determined in relation to surfaces showing errors of form, these errors should be taken into account when fixing the tolerance of position.
2.32 1.4 Influence of errors of form in determining positional errors
When relative positional errors of two surfaces or of two lines (see Figure 1, lines XY and ZT) are being determined, the readings of the measuring instrument automatically include some errors of form. It shall be laid down as a principle that checking shall apply only to the total error, including the errors of form of the two surfaces or of the two lines. Consequently, the tolerance shall take into account the tolerance of form of the surfaces involved. (If thought useful, preliminary checks may ascertain errors of form of lines and of surfaces, of which the relative positions are to be determined.)
When displayed in a graph (see Figure 1) the different readings mn of the measuring instrument result in a curve, such as ab. It is to be accepted, as a rule, that the error be determined using line AB instead of this curve, as stated in 5.211.1.
2.325 Conventional definition of the axes and of the movements
In order to avoid using the terms transversal, longitudinal, etc., which are liable to create confusion, the axes of the displacements and rotations of the machine parts are designated by letters (e.g. X, Y, Z. etc.) and signs, in accordance with ISO 841.
3 Preliminary operations
3.1 Installation of the machine before test Before proceeding to test a machine tool, it is essential to install the machine upon a suitable foundation and to level it in accordance with the instructions of the manufacturer.
3.11 Levelling
The preliminary operation of installing the machine shall involve (see 3.1) its levelling and is essentially determined by the particular machine concerned. The aim of the levelling is to obtain a position of static stability of the machine which will facilitate subsequent measurements, especially those relative to the straightness of certain components.
3.2 Conditions of the machine before test
3.21 Dismantling of certain components As the tests are carried out, in principle, on a completely finished machine, dismantling of certain components should only be carried out in exceptional circumstances, in accordance with the instructions of the manufacturer (e.g. dismantling of a machine table in order to check the slideways).
3.22 Temperature conditions of certain components before test
The aim is to evaluate the accuracy of the machine under conditions as near as possible to those of normal functioning as regards lubrication and warm-up. During the geometric and practical tests, components such as spindles, which are liable to warm up and consequently to change position or shape, shall be brought to the correct temperature by running the machine idle in accordance with the conditions of use and the instructions of the manufacturer.
Special conditions may be applied to high-precision machines and some numerically controlled machines for which temperature fluctuations have a marked effect on the accuracy.
All of these deviations will affect straight-line motion. When measuring the straight-line motion of the trajectory of a representative point, the measured results include all of the effects of angular deviations, but the effects of these angular deviations are different when the position of a point of the moving component is different from the representative point, and a separate measurement must be made. The value of each angular deviation is the maximum angle turned through during a complete traverse of the moving component.
5.232 Methods of measurement
5.232. 1 Methods of measurement of linear deviations
To plot the trajectory of a functional point of a moving component, the following methods are used.
5.232.11 Method with a straightedge and a dial gauge (see 5.212.112)
When using a straightedge and a dial gauge, it is usual to fix the straightedge to the component used as a reference (work tables of milling machines, machining centres, grinding machines, the bed of a lathe, etc.). The dial gauge is connected to the tool location point with its stylus situated as near as possible to the active zone of the tool
(see A.2 and A.7).
5,232.12 Method with microscope and taut-wire (see 5.212.12)
This is the same situation as a straightedge and dial gauge, with the taut’wire representing the straightedge and the microscope representing the dial gauge (see A9).
5.232.13 Method using an alignment telescope (see 5.2 12.13)
When using an alignment telescope, the reticle is connected to the reference line, the target is connected to the tool post and its centre is situated as near to the active zone of the tool as possible (see A.1O).
5.232.14 Method using a laser (see 5.212.14 and 5.212.15)
When using a laser (direct measurement using a straightness interferometer). the devices defi fling the measuring reference must be firmly fixed to the component chosen as reference. The moving element is fixed to the tool holder and its centre is situated as near as possible to the active zone of the tool (see A.13).