BS 939:2007 - Engineers' squares (including cylindrical and block squares). Specification – BSI British Standards

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BS 939:2007

Engineers' squares (including cylindrical and block squares). Specification

Status : Confirmed, Current, Under review   Published : October 2007

Format
PDF

Format
HARDCOPY



WHY IS BS 939 IMPORTANT FOR ENGINEERS?

The standard BS 939 is the specification for the try squares cylindrical squares and block squares used by mechanical engineers.

Mechanical engineers and engineering designers should use BS 939 to ensure that all users maintain the same level of precision accuracy.

It will save wasted expenditure by mechanical engineers, by ensuring dependable accuracy is maintained in one of their principal tools.

By ensuring that the cross referencing to only current British Standards will facilitate the production of UK designed products by manufacturing resources both within and outside the UK.

BS939 is the specification standard used by industry within the UK that covers this specialist area of measurement.

BS 939 is the British Standard that specifies requirements for engineers’ try squares (excluding adjustable squares), cylindrical squares and block squares of solid or open form. The requirements covered include:

  • General requirements applicable to all types of square.
  • Engineers’ try squares in three grades of accuracy, AA, A and B, with inner lengths of blade from 50 mm up to and including 1 000 mm.
  • Cylindrical squares in accuracy grade AA in sizes from 75 mm up to and including 750 mm.
  • Solid form block squares in accuracy grades AA and A in sizes from 50 mm × 40 mm up to and including 1 000 mm × 1 000 mm.
  • Open form block squares in accuracy grades A and B in sizes from 150 mm × 100 mm up to and including 600 mm × 400 mm.

While the standard provides for squares in various grades of accuracy, it should be noted that their accuracy in use is dependent upon the flatness of the surfaces on which they are used.

Contents of BS 939 includes:

Normative references

Terms and definitions

Protection against climatic conditions

Engineers’ try squares
Designating size
Recommended sizes
Material and manufacture
General features of design
Finish
Accuracy
Rigidity
Marking

Cylindrical squares
Designating size
Recommended sizes and dimensions
Material and manufacture
General features of design
Finish
Accuracy
Marking

Solid form block square
Designating size
Recommended sizes and dimensions
Material and manufacture
General features of design
Finish
Accuracy
Marking

Open form block squares
Designating size
Recommended sizes and dimensions
Material
General features of design
Finish
Accuracy
Marking
Notes regarding bevelled edges on blades of grade AA engineers’ try squares
Notes on the manufacture and testing of squares
Bibliography

List of figures
Exaggerated illustration of deviation from squareness and squareness tolerance
Engineers’ try squares
Squareness of blade edges to working faces of stock
Lateral squareness of blade
Rigidity
Nomenclature for cylindrical squares
Nomenclature for solid form block squares
Nomenclature for open form block squares
Using a bevelled edge
Method of testing squareness of block squares
Tilting tester
Testing for rigidity

List of tables
Tolerances on straightness of blade edges
Tolerances on parallelism of blade edges
Tolerances on flatness of working faces of stock
Tolerances on parallelism of working faces of stock
Tolerances on parallelism of side faces of stock
Tolerances on squareness of blade edges to working faces of stock
Tolerance on lateral squareness of blade to base of stock
Recommended sizes and dimensions of cylindrical squares
Tolerances on cylindrical squares
Recommended sizes and dimensions of solid form block squares
Tolerances on flatness, parallelism and squareness of working faces (solid iron block squares)
Tolerances on flatness and squareness of front and back surfaces (solid iron block squares)
Recommended sizes and dimensions of open form block squares
Tolerances on flatness, parallelism and squareness of working faces (open form block squares)
Tolerances on flatness and squareness of front and back surfaces (open form block squares)

BS 939:2007 replaces BS 939:1977 which has been withdrawn.




Standard NumberBS 939:2007
TitleEngineers' squares (including cylindrical and block squares). Specification
StatusConfirmed, Current, Under review
Publication Date31 October 2007
Confirm Date01 October 2012
Cross ReferencesBS 1134-1, BS EN 1561:1997, BS 3643-1:1981, BS 3643-2:1981, BS 1133-6.2, BS 1133-19
ReplacesBS 939:1977
Draft Superseded By07/30163789 DC
DescriptorsSquares (instruments), Angular measurement, Dimensional measurement, Accuracy, Dimensions, Dimensional tolerances, Design, Flatness (surface), Smoothness (surface), Marking, Steels, Hardness, Roughness (surface), Designations, Blocks, Cylindrical shape, Test equipment
ICS17.040.30
Title in FrenchEquerres d'ingenieur (y compris les equerres cylindriques et en forme de bloc). Specification
Title in GermanRechte Anschlagwinkel fuer Ingenieure (einschliesslich von geraden, zylindrischen Staeben und rechteckigen Vierkanten). Spezifikation
CommitteeMTE/1
ISBN978 0 580 58628 6
PublisherBSI
FormatA4
DeliveryYes
Pages34
File Size415.1 KB
Price£190.00


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