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BS 939:2007

BS 939:2007

$167.15

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

Published By Publication Date Number of Pages
BSI 2007 34
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This British Standard specifies requirements for engineers’ try squares (excluding adjustable squares), cylindrical squares and block squares of solid or open form.

Section 1 specifies general requirements applicable to all types of square.

Section 2 specifies requirements for 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.

Section 3 specifies requirements for cylindrical squares in accuracy grade AA in sizes from 75 mm up to and including 750 mm.

Section 4 specifies requirements for 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.

Section 5 specifies requirements for 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.

NOTE 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.

PDF Catalog

PDF Pages PDF Title
3 Contents
Section 1: General 1
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Protection against climatic conditions 2
Section 2: Engineers’ try squares 3
5 Designating size 3
6 Recommended sizes 3
7 Material and manufacture 4
8 General features of design 4
9 Finish 4
10 Accuracy 5
11 Rigidity 9
12 Marking 9
Section 3: Cylindrical squares 10
13 Designating size 10
14 Recommended sizes and dimensions 10
15 Material and manufacture 11
16 General features of design 11
17 Finish 12
18 Accuracy 12
19 Marking 13
Section 4: Solid form block squares 14
20 Designating size 14
21 Recommended sizes and dimensions 14
22 Material and manufacture 15
23 General features of design 15
24 Finish 16
25 Accuracy 16
26 Marking 17
Section 5: Open form block squares 18
27 Designating size 18
28 Recommended sizes and dimensions 18
29 Material 19
30 General features of design 19
31 Finish 19
32 Accuracy 19
33 Marking 20
Annexes
Annex A (informative) Notes regarding bevelled edges on blades of grade AA engineers’ try squares 21
Annex B (informative) Notes on the manufacture and testing of squares 25
Bibliography 26
4 List of figures
Figure 1 – Exaggerated illustration of deviation from squareness and squareness tolerance 2
Figure 2 – Engineers’ try squares 3
Figure 3 – Squareness of blade edges to working faces of stock 8
Figure 4 – Lateral squareness of blade 8
Figure 5 – Rigidity 9
Figure 6 – Nomenclature for cylindrical squares 10
Figure 7 – Nomenclature for solid form block squares 14
Figure 8 – Nomenclature for open form block squares 18
Figure A.1 – Using a bevelled edge 21
Figure B.1 – Method of testing squareness of block squares 23
Figure B.2 – Tilting tester 24
Figure B.3 – Testing for rigidity 25
List of tables
Table 1 – Tolerances on straightness of blade edges 5
Table 2 – Tolerances on parallelism of blade edges 5
Table 3 – Tolerances on flatness of working faces of stock 6
Table 4 – Tolerances on parallelism of working faces of stock 6
Table 5 – Tolerances on parallelism of side faces of stock 6
Table 6 – Tolerances on squareness of blade edges to working faces of stock 7
Table 7 – Tolerance on lateral squareness of blade to base of stock 8
Table 8 – Recommended sizes and dimensions of cylindrical squares 10
Table 9 – Tolerances on cylindrical squares 12
Table 10 – Recommended sizes and dimensions of solid form block squares 14
Table 11 – Tolerances on flatness, parallelism and squareness of working faces (solid iron block squares) 16
Table 12 – Tolerances on flatness and squareness of front and back surfaces (solid iron block squares) 16
Table 13 – Recommended sizes and dimensions of open form block squares 18
Table 14 – Tolerances on flatness, parallelism and squareness of working faces (open form block squares) 20
Table 15 – Tolerances on flatness and squareness of front and back surfaces (open form block squares) 20
5 Foreword
7 Section 1: General
1 Scope
2 Normative references
3 Terms and definitions
3.1 deviation from straightness and flatness
8 3.2 deviation from parallelism
3.3 Squareness of two surfaces
Figure 1 Exaggerated illustration of deviation from squareness and squareness tolerance
3.4 tolerances
4 Protection against climatic conditions
9 Section 2: Engineers’ try squares
5 Designating size
Figure 2 Engineers’ try squares
6 Recommended sizes
10 7 Material and manufacture
8 General features of design
9 Finish
11 10 Accuracy
10.1 Straightness of inner and outer edges of blade
Table 1 Tolerances on straightness of blade edges
10.2 Parallelism of blade edges
Table 2 Tolerances on parallelism of blade edges
12 10.3 Flatness of working faces of stock
Table 3 Tolerances on flatness of working faces of stock
10.4 Parallelism of working faces of stock
Table 4 Tolerances on parallelism of working faces of stock
10.5 Parallelism of side faces of stock
Table 5 Tolerances on parallelism of side faces of stock
13 10.6 Squareness of side faces of stock to working faces of stock
10.7 Squareness of edges of blade to side faces of stock
10.8 Squareness of edges of blade to working faces of stock
a) the outer edge of the blade to the outer working face of the stock; and
b) the inner edge of the blade to the inner working face of the stock;
Table 6 Tolerances on squareness of blade edges to working faces of stock
14 Figure 3 Squareness of blade edges to working faces of stock
10.9 Lateral squareness of blade
Table 7 Tolerance on lateral squareness of blade to base of stock
Figure 4 Lateral squareness of blade
15 11 Rigidity
Figure 5 Rigidity
12 Marking
a) the number of this British Standard, i.e. BS 939;
b) the grade designation, e.g. A;
c) an identification number for grade AA try squares; and
d) the manufacturer’s name or trade mark.
16 Section 3: Cylindrical squares
13 Designating size
Figure 6 Nomenclature for cylindrical squares
14 Recommended sizes and dimensions
Table 8 Recommended sizes and dimensions of cylindrical squares
17 15 Material and manufacture
15.1 Material
15.2 Steel squares
15.3 Cast iron squares
15.4 Granite (diabase) squares
16 General features of design
18 17 Finish
18 Accuracy
18.1 General
18.2 Straightness of sides
18.3 Flatness of ends
18.4 Squareness of cylindrical surface to end faces
Table 9 Tolerances on cylindrical squares
19 19 Marking
a) the number of this British Standard, i.e. BS 939;
b) the designating size and grade, e.g. 450 mm AA;
c) an identification number;
d) the manufacturer’s name or trade mark.
20 Section 4: Solid form block squares
20 Designating size
Figure 7 Nomenclature for solid form block squares
21 Recommended sizes and dimensions
Table 10 Recommended sizes and dimensions of solid form block squares
21 22 Material and manufacture
22.1 Material
22.2 Steel squares
22.3 Cast iron squares
22.4 Granite (diabase) squares
23 General features of design
22 24 Finish
25 Accuracy
Table 11 Tolerances on flatness, parallelism and squareness of working faces (solid iron block squares)
Table 12 Tolerances on flatness and squareness of front and back surfaces (solid iron block squares)
23 26 Marking
a) the number of this British Standard, i.e. BS 939;
b) the designating size;
c) the grade designation (AA or A, as appropriate);
d) an identification number for grade AA squares;
e) the manufacturer’s name or trade mark.
24 Section 5: Open form block squares
27 Designating size
Figure 8 Nomenclature for open form block squares
28 Recommended sizes and dimensions
Table 13 Recommended sizes and dimensions of open form block squares
25 29 Material
30 General features of design
31 Finish
32 Accuracy
32.1 General
32.2 Open form block squares supplied in matched pairs
26 Table 14 Tolerances on flatness, parallelism and squareness of working faces (open form block squares)
Table 15 Tolerances on flatness and squareness of front and back surfaces (open form block squares)
33 Marking
a) the number of this British Standard, i.e. BS 939;
b) the designating size;
c) the grade designation (A or B, as appropriate);
d) an identification number;
e) the manufacturer’s name or trade mark.
27 Annex A (informative) Notes regarding bevelled edges on blades of grade AA engineers’ try squares
Figure A.1 Using a bevelled edge
28 Annex B (informative) Notes on the manufacture and testing of squares
B.1 General
a) cylindrical and block squares;
b) testing of engineers’ try squares; and
c) the rigidity and design of engineers’ try squares.
B.2 Cylindrical and block squares
B.2.1 General
B.2.2 Cylindrical squares
B.2.3 Block squares
29 Figure B.1 Method of testing squareness of block squares
B.3 Engineers’ try squares
B.3.1 Testing an engineers’ try square against a reference cylindrical square or block square
30 B.3.2 Tilting square-tester
Figure B.2 Tilting tester
31 B.3.3 Rigidity of engineers’ try squares
B.3.4 Notes on design of engineers’ try squares
Figure B.3 Testing for rigidity
32 Bibliography
[1] National Physical Laboratory. Notes on Applied Science No. 5: Gauge Making and Measuring. London: HMSO, 1967.

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BS 939:2007
$167.15