GB2045159A - Method of bending wood - Google Patents

Abstract

After pre-treatment the solid wood 1 is bent using a woven strap 4 which is substantially inextensible longitudinally. The strap may be made from carbon fibres, high tensile steel wire or aromatic polyamide fibres. <IMAGE>

Description

SPECIFICATiON Method of bending wood This invention is concerned with improvements in or relating to the bending of solid wood and is of particular relevance to the field of furniture manufacture.

The art of bending solid wood has been practised by substantially the same method since the 1840s.

The successful production of bends is partly dependant upon the selection of the timber to be used and the manner in which it is treated prior to bending but principally upon the fact that solid wood can be compressed but not stretched.

The conventional technique for bending solid wood is described in "Wood Bending Handbook" (Stevens and Turner, HMSO 1970). After pretreatment (by means of moisture and/or heat) the wood is compressed to an extent such that, after it has been bent, the convex face of the wood is required to extend to no more than the original length of that face of the timber.

The actual step of bending is effected by firstly laying that portion of the wood which is to be bent on an inextensible strap. The strap and the wood are then bent around a tool having the contours that it is desired that the concave surface of the wood should have. The material of the strap is required to be very resistant to stretching either elastically or plastically.

"Wood Bending Handbook" suggests a strap in the form of a strip of spring or high tensile steel, wider than the timber to be bent and 1 - 2mm thick for 11/2" thick timber.

It is a disadvantage of the technique that such a metal strip is springy and, especially when making a three dimensional bend, it can be difficult to prevent the strip from sliding sideways off the work. In addition, after repeated use, the strip may workharden, become brittle and snap when under ten- sion, which can be dangerous to the operator. These problems are especially severe with timber which is round in section.

We have now discovered that, if a woven strap of fibres which is substantially inextensible longitudinally is substituted for the metal strip used hitherto, bends of a tight radius and occupying more than one plane (i.e. three dimensionai bends) may be produced with advantage.

According to the invention therefore there is provided a method of bending wood which includes the steps of compressing the wood longitudinally and bending it by means of force applied to what becomes the convex face of the bend using a woven strap of fibres which is substantially inextensible longitudinally.

The woven strap may be composed of any of a variety of materials thus, for example, carbon fibres or high tensile steel wire may be used. As a practical matter some straps, for example one composed of woven steel wire may bite into and disfigure the surface of the wood but this disadvantage can be easily overcome by interposing a suitable liner between the strap and the wood prior to bending. It is not necessary for the weft to be of the same denier or of the same composition as the warp; greatest strength is needed in the warp but it is advantageous to use fibres which have a high tensile strength and high Young's modulus.

The method according to the invention may be used with particular advantage in the bending of solid wood having a cross section which is curved especially wood which is round or substantially round in section.

We particularly prefer to use a strap woven from an appropriate synthetic organic fibre and have found that one woven from fibres of an aromatic polyamide may combine the advantage of being substantially inextensible longitudinally with the quality of being sufficiently supple to wrap around enough of the surface of the wood as not to slip off of the workpiece when the wood is being bent.

The character of the fibres and the use to which the strap is put may cause rapid wear due to abrasion of the fibres against one another. According to a preferred feature of the invention therefore we subject the fibres of the strap to an anti-abrasion treatment prior to use. Such treatment may conveniently take the form of coating the fibres prior to or subsequent to their being woven to form the strap with a tough but resilient material such as an elastomer. Alternatively, the fibres or the woven strap may be treated with an oil such as paraffin which acts as a lubricant where the fibres rub against each other.

In order that the invention may be well understood one preferred embodiment thereof will now be described by way of illustration only with reference to the accompanying drawing.

A length of freshly sawn (about 2 weeks old) timber 1 which is round in section is subjected to steam at atmospheric pressure for about 45 minutes.

The wood which may be intended to form part of the back or an arm of a chair is then placed on a strap of woven high tensile strength, high elastic modulus aromatic polyamide fibres 4 and compressed longitudinally by applying force through end stops 3 at each end of the length of wood. The force is designed to achieve a desired degree of compress ion and will vary according to the nature of the bend to be produced.

The compressed wood is then abutted to a forming tool 2 which may be a jig or simply a surface having the contours that it is desired to give to the wood. The arrangement is such that the strap covers that portion of the wood which will became the convex surface after bending. The wood may now be bent and force is applied to the strap through the end stops 3 and frame 5. The bend may occupy a single plane or, if a more complex bend is required, the strap can twist out of the plane of the first bend moulding itself laterally to the timber to continue to apply force to the wood as it is bent out of the first plane through whatever contour is desired.

When once the wood has been bent it is placed, while still being subject to force through the strap, in an oven at about 150"F for 24 hours to dry out whereafter the force may be removed to leave the bent timber ready for subsequent working.

Claims (6)

1. A method of bending wood which includes the steps of compressing the wood longitudinally and bending it by means of force applied to what becomes the convex face of the bend using a woven strap of fibres which is substantially inextensible longitudinally.

2. A method according to claim 1 wherein the strap is woven from fibres of an aromatic polyamide having a high tensile strength and high Young's modulus.

3. A method according to either claim 1 or claim 2 which comprises using a strap which has been subjected to an anti-abrasion treatment prior to use.

4. A method according to any one of the preceding claims wherein the timber is round or substantially round in section.

5. A method of bending wood substantially as described herein with reference to the accompanying drawing.

6. Wood whenever bent by a method according to any one of claims 1-5.