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Specification for

Sizes of hardwoods and methods of measurement

Dimensions des bois durs et methodes de mesure

MaBe von Harth61zern und MeBverfahren

British Standards Institution

BS 5450 : 1977 UDC 674.031.021

Gr3

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BS 5450 : 1977

Contents

Foreword Cooperating organizations

Specification 1. Scope 2. References 3. Definitions 4. Moisture content

Page Inside front cover

Back cover

5. Basic sizes of sawn hardwoods 1 6. Permissible deviations from basic sizes 1 7. Methods of measurement 2 8. Reduction of sawn hardwood sizes by processing 2

Appendix A. Shrinkage on drying 4

Foreword Hardwoods are natural raw materials suited to many purposes and uses. They vary considerably in their working properties, durability, colour and their grain configuration, depending on the individual species and the areas in which they grow.

Most hardwoods in stock in the United Kingdom are in logs or in a standard range of thicknesses sawn square edged or waney edged, each thickness having a random range of widths and lengths. Hardwood can be produced to almost any sizes required, subject only to the restrictions imposed by the sizes of logs or sawn stock available or the particular characteristics of the species and the higher cost and longer time involved.

This is the first British Standard applicable to sizes of sawn hardwoods and it can be applied to the species which are listed in BS 881 and which may be in stock in the United

Page Tables 1. Basic cross·sectional sizes of sawn hardwoods 2. Permissible deviations from basic sizes of

thickness or width 3. Reduction from basic sawn size to finished size

by processing of two opposed faces

Figures 1. Measurement of length for specified widths,

square edged and random widths, square edged

2. Measurement of length for random widths, waneyedged

Kingdom on a commercial basis. It can also be applied to any other hardwood which may become available in the future.

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Stocks in the United Kingdom are in the hands of importers, merchants, producers and manufacturers, and they are not necessarily acquired in accordance with any British Standard. They are normally produced and acquired in bulk quantities in accordance with various grades, rules, methods and customs which this British Standard does not attempt to explain. However, it should be possible for a supplier to select and saw, dry, measure and supply to dimensions which comply with this British Standard.

Although a particular kind of hardwood may be in stock on a commercial basis it does not necessarily follow that it will be available in every possible combination of thick· ness, width and length.

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BS 5450 1977

British Standard Specification for

Sizes of hardwoods and methods of measurement

1. Scope This British Standard specifies a range of basic sizes, in metric units, of sawn hardwood at 15 % moisture content with permissible deviations, and the methods of measure­ment of moisture content and sizes of sawn hardwood. I t also provides a table of reductions by manufacturing processes from the basic sawn hardwood sizes, for some end uses and products.

2. References The titles of the standards publications referred to in this standard are listed on the inside back cover.

3. Definitions For the purposes of this British Standard the definitions in BS 565 and BS 881 and 4.1 of this standard apply.

4. Moisture content 4.1 General. Moisture content is defined as the amount of moisture in timber, expressed as a percentage of its oven dry mass.

4.2 Instrument. Unless otherwise agreed between purchaser and vendor measurement of moisture content by means of an electric moisture meter shall be adopted. The meter shall be recalibrated in accordance with the manufacturer's instructions, or against oven drying tests, at intervals of not more than six months.

4.3 Sampling. Unless otherwise agreed between purchaser and vendor testing shall be carried out on at least 10 pieces or 3 % of the pieces of anyone thickness taken at random, whichever is the greater. The average of the total readings taken shall be the average moisture content.

4.4 Method of measurement. The test shall be carried out according to the instrument manufacturer's instructions, on the wider face of the piece at a point not nearer than 1 m from either end or at the centre of the piece if under 2 m long.

4.5 Permissible deviation of moisture content. For any specified moistu re content agreed between the purchaser and the vendor a maximum deviation of ± 3 % shall be permissible in any piece.

5. Basic sizes of sawn hardwoods 5.1 Basic sizes. The basic cross-sectional sizes, at 15 % moisture content, of hardwoods sawn square on four sides shall be as given in table 1.

5.2 Basic thicknesses. The basic thicknesses, at 15 % moisture content, of hardwoods sawn to random widths, square edged or waney edged, shall be as given in table 1.

5.3 Basic lengths. The basic lengths of hardwoods shall be any integral multiple of 100 mm, but not less than 1 m.

NOTE. The normal length of imported hardwood will vary according to the spec;es and the origin.

Table 1. Basic cross-sectional sizes of sawn hardwoods Thickness Width (mml

50 63 75 100 125 150 175 200 225 250 300

mm

19 x x x x x

25 x x x x x x x x x x x

32 x x x x x x x x x

38 x x x x x x x x x

50 x x x x x x x x

63 x x x x x x

75 x x x x x x

100 x x x x x x

NOTE. Designers and users should check the availability of specified sizes in any particular species.

6. Permissible deviations on basic sizes 6.1 Thicknesses and widths. For thicknesses and widths the permissible deviations shall be as given in table 2, but minus deviations are permissible only on 10 % or fewer of the pieces in anyone th ickness.

Table 2. Permissible deviations from basic sizes of thickness or width Basic size Minus deviation Plus deviation

mm mm mm

Under 25 1 3 25 to 75 2 6

76to125 3 9 126 to 300 4 12

6.2 lengths. No minus deviation is permissible, but over­

length is unlimited.

6.3 Actual sizes. The actual sizes of any piece of timber

will vary with its moisture content at the time of measure­

ment. The dimensions given in tables 1 and 2 apply at

15 % moisture content. For any higher moisture content up

to 30 % the sizes shall be greater and for any moistu re

content lower than 15 % the sizes may be smaller. Because it is impossible to predict accurately the shrinkage on

drying of most hardwoods, some information on the subject is given in appendix A, but this should be regarded only as

a guide. For any moisture content higher than 30 % no

larger size will be required than at 30 %.

BS 5450 1977

7. Methods of measurement

7.1 Measuring. The characteristics of the three product

groups of hardwood require different methods of

measurement for each group.

The groups are as follows.

(a) Specified widths, square edged. All pieces are of

the same thickness and width throughout the length, in the parcel.

(b) Random widths, square edged. All pieces are of the same thickness; widths are constant in each piece but random in the parcel.

(c) Random widths, waney edged. All pieces are of the same thickness but widths vary in each piece and in the parcel.

7.2 Specified widths, square edged. The units of measu re­ment are:

length: metres; width: millimetres; thickness: mill imetres.

Length shall be measured as the length of the longest piece with square ends and of the same cross section that is contained by the piece, taken to the nearest 100 mm multiple below. See Figure 1.

Length

Figure 1. Measurement of length for specified widths, square edged, and random widths, square edged

Width shall be measured at the narrowest point.

Thickness shall be measured at the thinnest point.

NOTE. Width and thickness are specified to be measured at the narrowest and thinnest points in the piece to allow for uneven dimensional changes caused by changes in moisture content, or for irregular sawing.

7.3 Random widths, square edged. The units of measure­ment are:

length: metres; width: millimetres; thickness: mill imetres.

Wane

Figure 2. Measurement of length of random widths, waney edged

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Width measurement shall be taken to the nearest 10 mm multiple below at the narrowest point.

Thickness shall be measured at the thinnest point.

Length shall be measured as the length of the longest piece having square ends and width and th ickness as measured that is contained by the piece, taken to the nearest 100 mm multiple below. See figure 1.

7.4 Random widths, waney edged. The units of measure­ment are:

length: metres; width: millimetres; thickness: millimetres.

Width shall be measured across the narrow face, including half the wane, at three points along the length of the board and from these the average width of each board shall be calculated. The measure shall be taken at the following points:

point 1: 300 mm from one end point 2: centre point point 3: 300 mm from the other end.

Thickness shall be measured at the thinnest point.

Length shall be measured as the length of the longest piece having square ends and width and thickness as measured that is contained by the piece, taken to the nearest 100 mm multiple below. See figure 2.

8. Reduction of sawn hardwoods by processing 8.1 General. Processing of hardwoods to accurate finished sizes involves reductions of size which vary with the size, the process and the product. The figures in table 3 have been established by experience to be economic, workable and not wasteful.

8.2 Reductions. The reductions appropriate to some end uses and products appear in table 3. Any finished sizes in British Standards covering particular hardwood products and components will take precedence over those in table 3. For other end uses not specifically mentioned, the same figures as one of the end uses listed may be adopted. Intermediate figures would be unlikely to achieve an average of any greater accuracy and would tend to confuse.

8.3 Permissible deviations. For all finished sizes after processing a manufacturing deviation of ± 0.5 mm shall be allowed.

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Table 3. Reductions from basic sawn size to finished size by processing of two opposed faces End use or product Reduction from basic size to finished size

For basic sawn sizes of width or thickness (mm):

15 to 25 26 to 50 51 to 100 101 to 150 151 to 300

mm mm mm mm mm Constructional 3 3 3 5 6 timber surfaced

Floorings, matchingSj 5 6 7 17 7 and interlocked

boarding J 5 6 7 7 7

and planed all round

Trim 6 7 8 9 10

Joinery and 7 9 10 12 14 cabi network

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BS 5450 : 1977

BS 5450 : 1977

Appendix A

Shrinkage on drying

Hardwoods when dried start to shrink when the moisture content falls below about 30 %. Shrinkage expressed as a percentage of dimension is greatest in a direction tangential to the growth or annual rings of the original log from wh ich the timber was sawn, and is usually about twice the shrink­age in a radial direction. Shrinkage in the length is usually negligible. The maximum shrinkage in a piece of sawn hardwood can thus be in any direction with in the cross section depending on how the log was sawn, and this complicates the estimation of the size to which moist

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timber has to be sawn in order to obtain the basic size at 15 % moisture content.

Shrinkage is smaller in woods of higher density but the relationship is not precise and reference should be made to average values for each species of the radial and tangential shrinkages.

For further information reference may be made to 'The handbook of hardwood', Building Research Establishment, second revised edition 1972, published by H M Stationery Office.

Standards publications referred to BS 565 Glossary of terms relating to timber and woodwork

BS 881 Nomenclature of commercial timbers including sources of supply (contained in BS 881,589)

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This British Standard, having been prepared under the direction of the Timber Standards Committee, was published under the authority of the Executive Board on 28 February 1977.

©British Standards Institution, 1977

ISBN. 0 580 09910 5

Copyright Users of British Standards are reminded that copyright subsists in all BSI publications. No part of this publication may be reproduced in any form without the prior permission in writing of BSI. This does not preclude the free use, in the course of implementing the standard, of necessary details such as symbols and size, type or grade designations. Enquiries should be addressed to the Publications Manager, 101 Pentonville Road, London Nl 9ND (Telephone 01-8378801 ; Telex 23218).

Cooperating organizations The Timber Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations.

British Plastics Federation • British Woodwork Manufacturers' Association • Department of the Environment, Building Research

Establ ishment

• Department of the Environment Fibre Building Board Development Organization Ltd.

• Forestry Commission Hardwood Flooring Manufacturers' Association I nstitute of Wood Science I nsti tu tion of Civil Engineers

• Institution of Structural Engineers National Federation of Building Trades Employers

• National Sawmilling Association • Royal Institute of British Architects

Royal I nstitution of Chartered Surveyors

Amendments ·issued since publication

Amd. No. Date of issue Text affected

BS 5450 . 1977

Contract requirements Attention is drawn to the fact that this British Standard does not purport to include all the necessary provisions of a contract.

Revision of British Standards British Standards are revised, when necessary, by the issu 3 either of amendment slips or of revised editions. It is important that users of British Standards should ascertain that they are in possession of the latest amendments or editions.

The following BS I references relate to the work on this standard' Committee reference TI B/ 1 Draft for comment 76/11069 DC.

• The Softwood Agents' and Brokers' Association • The Timber Trade Federation

Timber Packaging and Pallet Confederation • Timber Research and Development Association • Timber Stress Grading Association

The organizations marked with an asterisk In the list above, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard.

Council of the Forest Industries of British Columbia Greater London Counci I Home Timber Merchants Association of Scotland Institute of Building Ministry of Defence Scottish Timber Merchants' and Sawmillers' Association Timber Drying Association Individual experts

British Standards Institution· 2 Park Street London W1A 2BS . Telephone 01-629 9000 . Telex 266933

7702-1.8k-B

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