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The specification of drawing data and associated tolerances for involute gears
DUCOP.01
Scope
This Code of Practice lays out a system for the specification of involute gear teeth. Its use is recommended for all drawings of components that comprise one or more such gears. The Code covers the specification of gear geometry, material, accuracy and accuracy standards, and profile and helix modifications.
In some organisations, for example where the data is computer-generated, it is usual practice to incorporate gearing production information such as stage thicknesses onto the design drawing. Since this is only an acceptable practice in the special circumstances of the precise manufacturing route being known to the designer, the additional production engineering data is not covered by this Code, and the information described here all relates to the design drawing (i.e. applies to the finished component).
Introduction
Good drawing practice generally requires that all data needed by the manufacturer (and the inspector) should appear explicitly on the drawing and that no piece of information should be duplicated. The nature of gear geometry and the multiplicity of manufacturing and inspection processes makes it difficult, if not impossible, to follow these precepts fully. They also create difficulties in attempting to completely standardise either the layout of the information on the drawing or the content. As a way round this difficulty the data required has been divided into sections; each section is covered by one of the clauses below.
When the code is invoked, then it becomes mandatory that the drawing covers each section. An entry must be included for each section even if it is a null entry. (See, for example, the note on profile and/or helix modification.) There is, however, flexibility within each section both in the means of presentation and in the detail of the data.
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The specification of the accuracy of blanks for involute gears
DUCOP.02
Scope
This Code of Practice is concerned with the selection and adequate specification of the reference axis, the datum surfaces which define it, and other associated datum surfaces
Introduction
The numerical values of the parameters associated with gear tooth accuracy (profile error, adjacent pitch error, etc.) are only meaningful relative to a particular axis of rotation. If the axis about which the gear is rotated during measurement is changed, then the measured value of these parameters will change. It follows that the gear drawing must define an axis which is to act as the reference axis for the specified tooth tolerances, and in fact for the gear geometry as a whole.
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Involute gear measurement
DUCOP.03
Scope
This Code of Practice specifies the methods for measuring lead, profile and pitch errors on involute gears so that measuring errors introduced during the inspection process are minimised
The Code covers the requirements for measuring gears of BS 436, 1970 accuracy grades 3 to 12 and ISO 1328-1 accuracy grades 3 to 12. Master gears, gear artefacts and gears to ISO 1328-1, grades 0 to 2 require special techniques which are outside the scope of this document.
Introduction
This Code of Practice is intended to formalise the procedures used for measuring lead, profile and pitch errors in involute gears using dedicated gear measuring machines and CMM's with gear measurement software. It should be used when gear tolerances are specified in accordance with existing gear standards (e.g. ISO 1328, BS 436) and assumes that basic background knowledge of involute geometry and the measurement techniques are familiar to the reader. ISO Technical Report TR 10064-1 1992 : 1 background information is recommended for those who are new to this field.
It has also been assumed that the appropriate information is available on the gear drawing to ensure that sound measurements can be made. Codes of Practice DUCOP.O1 and DUCOP.O2 specify these requirements.
When this Code is invoked all the sections within the Code should be implemented
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Checking the reproducability of a gear measuring machine
DUCOP.04
Scope
This Code specifies the accuracy requirements, test methods and gear artefact requirements for testing the reproducibility and stability of a gear measuring machine or CMM with gear software.
The procedures in this Code are applicable to all gear measuring machines, which measure lead, profile or pitch error on involute gears.
Introduction
It is very important that the accuracy of gear inspection equipment is assessed frequently to ensure that it is suitable for the final inspection of gears: the quality and accuracy of the gears being manufactured depend on its accuracy. DUCOP.O5 parts 1, and 2 specify the accuracy requirements and procedures for verifying the measuring machine accuracy. However, these tests are time consuming and it is not practical to carry them out at a frequency which will ensure that measurements taken on a daily basis continue to be accurate.
This Code specifies simple routine tests to enable the gear inspector to verify that the accuracy of the machine is maintained. The tests check the reproducibility and stability of the machine between the full accuracy verification tests specified in DUCOP.O5.
The tests require the company to obtain traceably calibrated lead, profile and pitch artefacts, to enable traceability to National Standards be demonstrated on a daily basis.
If this test programme is not implemented, the accuracy verification tests carried out in accordance with DUCOP.O5 are invalidated.
When the Code is invoked it becomes mandatory that all sections within the Code are implemented.
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Verifying the accuracy of gear measuring machines
DUCOP.05
Scope
This Code of Practice specifies the requirements, procedures and subsequent analysis required to estimate the magnitude of the likely errors which will be present in a dedicated gear measuring machine or a CMM with gear measurement software used to measure cylindrical involute gears. The Code is restricted to the measurement of lead, profile and pitch errors on these machines.
The Code is applicable to all gear measuring machines or CMMs but the size of the verified measuring volume depends on whether the tests specified in Parts 2
have been carried out.
The measurement uncertainties which are estimated from the measurement results relate to the expected performance of the machine when measuring gear artefacts, master gears or other high quality gears and do not reflect the lower performance which will be achieved when measuring lower quality gears. A procedure for estimating these uncertainties is given in DUCOP.O3 Annex B.
The tests described in this Code can be applied to measuring machines which are used to calibrate gear artefacts and master gears, but in these cases further tests are necessary and the accuracy requirements are not those specified in this Code.
Introduction
This Code of Practice specifies the general requirements and procedures to be used to verify the accuracy and measurement uncertainty of a gear measuring machine and demonstrate traceability to National Standards. The procedures involve functional tests with traceably calibrated gear artefacts and tests on those individual elements of the machine which are known to cause significant measuring errors.
When this Code is invoked, it is mandatory that the requirements of all sections of the Code are met in full. However, this only verifies the accuracy of the machine at the time it was tested. It is the responsibility of the machine operator to demonstrate that this accuracy is maintained by carrying out regular checks of the machine's measuring reproducibility in accordance with DUCOP.O4 'Checking the Reproducibility of a Gear Measuring Machine'. If these frequent checks are not carried out and correctly documented, the accuracy verification certificate issued for the machine in accordance with this code will be invalidated and traceability for gear measurement cannot be demonstrated.
The Code is divided into two parts, each of which is published as a separate document:
Part 1:
Specifies the requirements and tests which are necessary to verify the accuracy of any gear measuring machine. The principal tests are based on traceably calibrated gear artefacts. These tests limit the size of the traceably verified measuring volume to that of the size of the gear artefacts used for the tests.
Part 2:
Specifies the additional tests necessary to increase the traceably verified measuring volume to allow the measurement of gears of up to twice the size of the largest artefacts used for the tests in Part 1.
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The interpretation of measurements
DUCOP.06
Scope
Annex A contains examples of how to interpret measured results and identifies the possible sources of error during manufacture.
Annex B contains practical hints on gear measurement, highlighting common mistakes which are often made when measuring gears.
Introduction
This code contains informative annexes which support the Code of Practice for Involute Gear Measurement DUCOP.O3.
It must be borne in mind that there is an inherent duality between manufacturing errors and measurement errors. For example, measurements which show runout or swash merely indicate that the measurement axis is not the same as the production axis and can as easily be caused by an error in the measurement set-up as in that of manufacture.
Before diagnosing a manufacturing problem by use of the examples in Annex A, therefore, it is vital that the potential sources of measurement error (as discussed in Annex B) are eliminated.
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Calculation of quantities associated with gear measurement
DUCOP.07
Scope
This Code of Practice is intended for use once a design (or at least a tentative design) of gear has been established; the starting point for each calculation is the basic gear data. The calculations covered are listed in table 1 below. The calculation number appears at the top right of each sheet. For each calculation there is a formula/calculation sheet with blanks for data entry. These may be copied and used as an aid to calculation.
For those new to some of these calculations, worked examples are provided by means of an addition set of sheets. The blank sheets have the letter C after the calculation number at the top right of the sheet; the worked examples have the letter S.
On each sheet there is a reference to the section in DIN 3960 (English translation of 1980 version) which contains the main formula used by that sheet. It should be noted, however, that all these formulae do appear in other publications (albeit sometimes presented differently) and that it is in any case possible to derive all of them by use of basic geometric and trigonometric rules.
Introduction
Good drawing practice generally requires that all data needed by the manufacturer (and the inspector) should appear explicitly on the drawing and that no piece of information should be duplicated. The nature of gear geometry and the multiplicity of manufacturing and inspection processes often makes it difficult to do this. It is inevitable, therefore, that there will be occasions when it is necessary to augment the data which appears on the drawing even if the drawing complies with these Codes of Practice. It is to assist in these situations and to help at the drawing stage those who do not have access to a suitable computer program that Code 7 has been produced.
The formulae which are necessary to perform these calculations already appear in several published documents. Experience has shown, however, that these can be difficult to use for a specific calculation. In this Code of Practice, all the formulae necessary for the calculation of a particular quantity appear together on one sheet. Since some formulae are required in several calculations, the Code of Practice obviously contains several repetitions of those formulae.
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