BS ISO 4468:2020 pdf download.Gear hobs — Accuracy requirements.
1 Scope
This document specifies requirements for the accuracy of general-purpose hobs of 0,5 module to 40 module.
These hobs are intended for producing gears which conform to ISO 53 and ISO 54.
This document applies to hobs for spur and helical gears. It applies to solid (monobloc) and inserted blade hobs.
The elemental features of hobs are graded according to accuracy, as follows:
— Grade 4A;
— Grade 3A;
— Grade 2A;
— Grade A;
— Grade B;
— Grade C;
— Grade D.
Grade 4A is the highest order of precision.
In addition to the elemental tests for hobs, this document gives permitted tolerances for composite tests that are taken along the cutting edges on the line of action. The two groups of tests are not equivalent and one can choose between one or the other. If there was no previous agreement, the hob is regarded as belonging to the precision class specified if it satisfies one or the other of the two methods of inspection.
NOTE The tolerances in this document were determined for gear hobs whose dimensions conform to ISO 2490, but with certain precautions they can be applied to hobs not specified in this document.
maximum deviation between any two teeth within any group of consecutive teeth contained in one axial pitch
Note 1 to entry: The number of teeth in one axial pitch is the number of teeth encountered by the measurement probe as it moves parallel to the reference axis during lead testing for a distance of one axial pitch of the hob.
Note 2 to entry: Hobs having one thread:
Measuring distance = one axial pitch = one revolution
Hobs having two threads:
Measuring distance = one axial pitch = 1/2 revolution
Hobs having three threads:
Measuring distance = one axial pitch = 1/3 revolution, etc.
Note 3 to entry: The number of teeth is determined by the number of gashes, the number of threads and, in the case of helical gash hobs, the gash lead.
Note 4 to entry: Test 11A is used for lead deviation in one axial pitch when the line of action test is used.
4 Allowable deviations
Hobs shall conform to the requirements of Tables 2 and 4, as appropriate. The hob sizes shall be in accordance with Annex A.
When prior agreement between the hob manufacturer and purchaser specifies measurement of hobs, the manufacturer should select:
— the measurement method to be used from among the applicable methods described in this document and summarized in Table 1;
— the piece of measurement equipment to be used by the selected measurement method, provided it is in proper calibration;
— the individual teeth to be measured, as long as they are approximately equally spaced.
No particular method of measurement or documentation is considered mandatory. When applications require measurements beyond those recommended in this document, it is recommended to negotiate
special measurement methods prior to manufacturing the hob.BS ISO 4468 pdf download.