an analysis of

materials and plant in current use

in the furniture industry

by T. G. DOYLE, A.M.I.Prod.E.

Sub-Group Manager, Remploy, Ltd.

Wallsend-on-Tyne

UP to the early years of the 19th century, themanufacture of furniture was carried out by local

craftsmen working in small workshops with little orno equipment other than a kit of hand tools.

The tremendous increase in population whichtook place last century brought about an increaseddemand for furniture far in excess of the capacityof the small workshop craftsmen. Factories conse-quently mushroomed into being to form the embryoof the furniture industry of today.

There are today more than 2,000 furniturefactories in the country, but there are now strongindications that this total represents a greatermanufacturing potential than is capable of beingsold. A steadily increasing number of small manu-facturers are finding it extremely difficult to remainsolvent, and, indeed, there is a proportionatelysteady increase in the numbers of manufacturersgoing into liquidation. The primary reasons forthese conditions are :—

(i) The Chancellor of the Exchequer has im-posed severe restrictions on Hire Purchasewhich, for the last 40 years, has been themain outlet for furniture sales.

(ii) The growth of monopolies in the retailfurniture trade makes it extremely difficultfor the smaller companies to trade onreasonable profit margins.

(iii) The development of high output multi-operation machinery presents a furtheracute problem for the small manufacturer,not only because of the comparatively highcapital cost involved but also because

such machinery will be capable of pro-ducing far more furniture than he canhope to sell and will subsequently requirefar more productive space than he hasavailable.

Thus it is inevitable that the industry must gothrough a period of adjustment before consolidationcan be effected, with the smaller companies beingprimarily affected and the larger companies —particularly those with direct interests in the retailmonopolies — strengthening their hold on thecountry's markets-development of machine tools, materials, andmethods

The machine tool section of the industry hasmade quite remarkable strides in the past 50years, and has produced a range of machinerywhich today can manufacture a batch of pieceparts in a fraction of the time taken by the fore-runners of the late nineteenth century. Theprincipal machines of the trade are described inmore detail in the section dealing with Plant andEquipment, but it is worthy of note that themachine tool makers have not only endeavoured tooperate at high feed rates, e.g. at 120 feet perminute, but have equally endeavoured to developmachines which will perform a series of operationsin one combined operation. In each case they havesucceeded brilliantly, but it is to be regretted thatthe users of these machines do not always operatethe machines to the best advantage. The mostoffending factor in this respect is the usage, sharpen-ing, and setting of cutters. Only a minority of

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furniture factories have operative toolrooms and inall too many cases the shaping, sharpening, andsetting of cutters is carried out by hit-and-missmethods with little more equipment than a grindingwheel, a rule, and a square. Further, the use oftipped cutters is a rarity, the predominating mediumbeing high speed steel. Thus, having shown excel-lent development in the design of high outputmachinery, it is now incumbent upon the machinetool manufacturers to educate the users fully into athorough appreciation of the advantages to begained by the use of better quality cutting mediums,and by the provision of accurate tool sharpeningand tool setting equipment.

The basic manufacturing materials in furniturehave always been timber and timber products, e.g.,plywood and veneers. The same combination stillholds today, but it is not improbable that themonopoly of these materials will undergo somereversion during the next two decades.

The development of plastics must inevitablybecome one of the main factors in the reversion,since the tremendously varied range and propertiesof such materials must ultimately show economicand other advantages over timber or plywood.Indeed, the melamine type of plastic, such asFormica, has already established a firm hold on thekitchen furniture market; and it can be anticipatedthat extruded plastics may oust, in some measure,the use of solid timber sections in the carcase con-struction of sideboards, wardrobes and dressingchests.

During the past 50 years the methods used inthe industry have been revolutionised in themachining and in the polishing of the finishedproduct, through the introduction and developmentof mechanical aids. The methods used in assemblyhave not undergone the same radical change, how-ever, and the same basic operations still obtain,although there has been a very considerable reduc-tion in the time-cycle taken on most operationsthrough the introduction of quick setting adhesives,the use of pneumatic equipment in jigs and fixtures,and the greater precision and better quality ofmachined piece parts.

design in relation to production economyAlthough there are, at any time, a myriad

different designs of furniture to be seen, the samebasic methods of construction will be seen in almostevery piece. For example, the joints of the maincarcase will almost invariably be morticed andtenoned, the drawers will be dovetailed, and thepanels will be set in grooves or in rebates. In thisrespect, design has shown little advancement sincethe days of Chippendale or Sheraton, and theadherence to these methods of construction hasbecome very deep-seated indeed.

As indicated in the preceding paragraph, theassembly methods have not improved in the samedegree as either machining or polishing, and thisfactor is entirely due to this adherence to traditionalconstruction in design. There can be no doubt that

a more virile and more imaginative approachto the overall subject of construction would in-evitably yield results which would be of the utmostvalue — particularly to the small manufacturer —in that reduced assembly costs would lead to areduced selling price which, in turn, would help toovercome the sales resistance created by high depositpayments on Hire Purchase selling.

material economyThe material content of the average piece of

furniture averages about 60% of the selling price.All furniture manufacturers are, therefore, veryconscious of the need to minimise wastage inconversion and machining. However, despite thisconsciousness, it cannot be claimed that everypossible means is explored to limit wastage to theminimum.

For example, in the section dealing with Materialsit will be seen that a very large proportion of thetimber used in this country is bought by themanufacturers as sawn logboards, i.e., with the waneand heartwood included in the boards. Both thewane and the heartwood are useless for furnituremanufacture, and both finish up on the waste pile.The only use to which such offcuts, sawdust andchippings are put, is to feed them into the factoryheating system. When it is considered that wastagesuch as this occurs in greater or lesser proportionevery day in every factory in the country, it doesappear that a golden opportunity presents itself toa mechanical engineer to design a compact, in-expensive piece of plant which can convert thiswaste timber into a usable product such as chipboard, i.e., wood chips mixed with a bondingmedium and pressed into sheets of £ in. or 1 in.thickness. The principle of wood reduction, mixing,and pressing is already established in factoriesespecially designed for the mass production of suchmaterials. The plant used in these instances is, ofcourse, purpose-built and is both very large and veryexpensive, and results in such products as Weyrocand Bartrev. If a compact plant, such as thatenvisaged, were designed and made available, itwould thus provide even the small manufacturerwith a functional outlet for every scrap of wasteand would thus again lead ultimately to reducedoperating costs and to reduced selling prices, witha consequent improved selling potential.

plant economyPrevious paragraphs have indicated the strides

which the machine tool manufacturers have madein developing machines which combine in oneoperation the function of several smaller individualmachines.

In the largest, most up-to-date factories, suchmachinery is operated on relatively high efficiencylevels. Loss of running time through re-setting, forexample, is at a minimum because of the productionvolume inherent in such factories which, in turn,permits the machining of large batch quantities ofpiece parts.

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The same favourable circumstances do not applyto the other sections of the industry since thesmaller the factory, the more restricted the batchquantity must be, with a proportionate increase inthe amount of re-setting time required. This loss ofmachine time in the average factory affects thefurniture industry to a much more appreciable degreethan in, for example, the normal medium engineeringfactory, since the time cycle per piece part operationis so very much smaller. This can perhaps best beillustrated by the fact that the complete machiningtime for the average piece part amounts to not morethan two minutes and will include, on average, notless than six operations.

The basic problem of setting time cannot, ofcourse, be entirely eliminated, but it could certainlybe reduced by a more determined effort on the partof the designer to create standard piece parts forframes and drawers, for example, and ring thechanges in design around a standard construction.In this way more operations would be standardised,greater batch quantities would be made possible,and loss of machine running time would be pro-portionately reduced. Again, a better appreciationby the manufacturer of the advantages of bettercutting tools and sharpening equipment would pro-long the life of the tool and subsequently reduce thetime lost by resharpening.

materialsbasic types in common use

Timber species are broadly divided into twocategories, hardwoods and softwoods. Hardwoodsare those trees which are deciduous and which arebare of leaves in Winter. Softwood is the namecommonly applied to those cone-bearing coniferoustrees which retain some form of leaf throughoutthe whole year.

The description is one which is generally acceptedbut which, in actual fact, is not entirely accurate,since the hardest and heaviest softwoods are heavierthan the softest and lightest hardwoods.

In general terms, however, in the range oftimbers in common use in this country, the types ofsoftwoods used are most certainly softer and moreliable to bruising and wear than the traditionalhardwoods such as oak, beech and walnut. Thus,the furniture industry with few minor exceptionsuses hardwoods throughout in the manufactureof its products.

hardwood species and sourcesThe traditional types of hardwood such as oak,

beech, walnut and elm, formed the backbone offurniture materials for many, many years prior tothe Second World War. Between the two WorldWars the more popular, cheaper ranges of furniturewere largely produced from American oak, whichwas imported into this country in vast quantitiesand at a considerable price advantage when relatedto the price and quality of homegrown oak. Theeconomic situation of the country after 1945prevented large scale importation of timber from

dollar countries, and the timber trade had to searchelsewhere for suitable hardwoods. The situation inthe other European countries at that time wassuch that large quantities of timber were not readilyavailable for export, nor was their basic pricewholly attractive to the British market.

Attention was therefore directed towards the vasttracts of forest in Nigeria and the Gold Coast, andhitherto little known species of African hardwoodsbegan to be consumed by the furniture industry insteadily increasing quantities. The most populartypes which were developed from that situation areabura, limba, agba and idigbo, and it is likely thatthese species will continue to be largely used formany years to come, principally because of theireconomic advantage over timber from other sources.

From an aesthetic point of view it is perhapsregrettable that the use of these substitute hard-woods has become so commonplace and so acceptedas part of the material structure of the industry, forno matter how cleverly such timbers are stainedand polished they can never equal the naturalbeauty of a piece of fine-grained oak, walnut orbeech. Several reputable manufacturers still endea-vour to give the buying public pieces of furniturewhich contain a proportion of solid oak but theseare relatively few and, in any case, it is virtuallycertain that the solid oak is only utilised on the out-side faces of the piece of furniture and that one ofthese substitute hardwoods is used for every interiormember.

conversionThese African timbers are shipped to the U.K.

either as logs or as sawn square edged boards. Theproportion of logs imported is, however, alarminglyhigh and provides a factor which could well standfurther consideration by both importer and manu-facturer.

The logs are, of course, cylindrical in section and,as such, are wasteful of shipping space. Sawn,square-edged boards can be stowed with a muchmore efficient space factor. Further, up to 20% ofthe average log is lost as waste in the sawing andconversion of each log. This can perhaps be bestillustrated by Fig. 1, which shows a log converted bystraight sawing into square edged boards.

Each saw cut removes between £ in. and ^ in.of timber as sawdust. The black areas around the

Fig. 1.

191

Fig. 2.

periphery represent the bark or wane areas whichare useless for furniture production, and the blacksquare shows the area of heartwood which, again,because of its spongy texture, is also unsuitable forfurniture.

Further wastage occurs when each board ismachined into the different sections required for thefinished product. Fig. 2 shows the conversionof such a board into typical section.

If square edged boards of a suitable nominal size,e.g., 3 in. X 1 in., were used, the machining wasteinvolved is markedly reduced. Additionally, the useof this type of timber permits savings in labourcosts since the size of board eliminates rip-sawing towidth and, in this form, allows much greaterefficiency in handling.

conditioningOne of the main constituents of a living tree is

water. The water is contained in the myriad cellswhich lie axially along the tree trunk and the weightof moisture in relation to the overall weight of thetree can be as much as 50%.

After felling it is therefore necessary to allow aperiod of several weeks to elapse before sawing since,as soon as the trunk is severed from its roots, thecells begin to lose their moisture and they shrink inminute proportion. If the log is sawn into boardsimmediately after sawing, the moisture loss andsubsequent shrinkage is accelerated, thus causingexcessive splitting and distortion of the sawn boards.

The resultant moisture content is still too high forfurniture manufacture, and must be reducedfurther to a moisture content approximating to thatof atmosphere to prevent shrinkage and distortionof the finished product. It will be readily seen thata piece of furniture such as a wardrobe would bedrastically affected by such conditions, since theframework or carcase is composed of solid timbermembers firmly secured to each other by, usually,mortice and tenon joints. Shrinkage in any or allof these members will most certainly cause seriousdistortion, and may even result in the breakage ofa joint or in the splitting of a member should theshrinkage action set up a torsional stress.

The reduction of moisture in the sawn boards tothe required moisture content can be achieved byboth natural and artificial means. The natural,traditional, method is to stock the sawn boards insuch a manner as to permit the maximum circula-tion of air around each board, as illustrated in Fig. 3.

This method, known as air drying, is not whollysuitable for present day needs, particularly in the

larger types of factory where mass productionmethods are applied, the principal deterrents beingtime and storage space. On average, a period of 12months is required on 1 in. timber to reduce themoisture content to that approximating to outdooratmosphere. It is then necessary to stack the timberinside the factory for a period of between approxi-mately three to six weeks to reduce still further themoisture content to that of the atmosphere of anormal house or office. Thus, those manufacturerswho utilise air dried stocks must contend with thefollowing disadvantages :—

(a) an excessive capital outlay since stocks mustbe carried over a period of several months:

(b) excessive storage costs since storage yardsmust be proportionately greater in size :

(c) loss of productive space since stocks must beretained in the factory for between approxi-mately three and six weeks.

The artificial method of seasoning or dryingtimber is known as kiln drying. The kilns arespecially constructed brick structures with equip-ment to control both heat and humidity within thechambers. In operation, the timber is stacked on amovable trolley in much the same way as the stacksare prepared for air drying. The trolley is moved intothe chamber and the doors are closed to seal offthe contents from normal atmospheric temperaturesand humidity. Streams of moist air are then force-circulated through the timber stack with atemperature initially slightly higher than the normal.The temperature is then steadily increased and thehumidity proportionately reduced. In this way, thecell fibres are made to yield their moisture at agreatly accelerated rate, so much so that a 1 in.board of abura, for example, can be dried out to arequired moisture content within a period of two tothree weeks.

The advantages of the use of this method areobvious in relation to the practice of using air-driedstock, but all too many of the smaller manufacturersin the industry fail to grasp the ultimate financialadvantage which this method must yield. Naturally,the smaller manufacturer cannot afford to buildand maintain these expensive structures, but thereare a very considerable number of timber importerswho already have this equipment and who carryout the work involved at rates which are on anational agreed basis.

WOODEN SPACING LATHS

AIR -^STREAMS

Fig. 3.

192

plywoodPlywoods are secondary only to timber in

importance to the furniture industry. Indeed, thesurface area of any piece of domestic furniturenormally contains very much more plywood thansolid timber. For example, a wardrobe has a totalsurface of about 53 square feet. Of this quantitythere will be not more than 12 square feet oftimber with 41 square feet of plywood.

In very many respects plywood is superior tosolid timber, particularly in stability, in strength,and in price. The latter factor is of primary im-portance, since the entire basic price structure offurniture in this country would be increased by atleast 25% if plywood was replaced by solid timber.

The physical advantages of plywood over timberof similar dimensions are not generally appreciatedsince, unfortunately, a large section of the popula-tion still thinks of plywood in terms of tea chests.However, plywood as opposed to solid timber is anextremely strong and stable material. Its strengthcan be very simply illustrated by comparing a loadtest on a piece of solid timber £ in. thick by 3 in.wide with a piece of plywood of similar dimensions.As the load is applied to the timber the fibres ofthe concave face are in compression, whilst those ofthe convex face are in tension. As the load increases,the deflection of the plank is proportionate to theload until a critical point is reached when thedeflection increases more rapidly than the load andfracture occurs on the convex face (Fig. 4).

Plywood, on the other hand, is built up oflaminations in such a manner that the grain of eachlamination is at right angles to its neighbour. Thecrossing of the grain in this manner thus gives thematerial the greatest possible strength in bothdirections of the grain. Plywood is, in actual fact,many times stronger than the strength of thelaminations measured individually, through :

(a) the cross-graining of the laminations; and

(b) the adhesion through gluing of eachlamination.

The same load test applied to the timber specimenabove would thus not create any fracture whatso-ever in a similarly proportioned plywood specimen.Furthermore, the plywood, by virtue of its lamina-tion strength, would regain its original position whenthe load was removed.

The tendency to shrink or expand is also verymuch more restricted than that of a solid piece oftimber, since its movement is controlled by twofactors :

(a) the laminations are dried out to a very lowmoisture content before manufacture;

(b) the laminations are fully bonded to eachother

Thus, from a purely physical point of viewplywood is undoubtedly superior to timber for

FIBRES IN COMPRESSION

FIBRES IN TENSION

Fig. 4.

work which requires large areas to be covered bymaterial of relatively thin section. Unfortunately,most of the commercial types of plywoods do nothave attractive or decorative figure characteristics.A piece of furniture in which plywoods are used istherefore made attractive and decorative by the useof veneers on these plywood panels.

veneersAs has been indicated in preceding sections, the

furniture industry depends largely upon "substitute"hardwoods and on plywood for the current manu-facture of modern furniture. Neither of thesematerials — in the normal commercial grades —can compare with the beauties of, for example,finely figured oak or walnut, which, apart frombeing in short supply, are extremely expensivematerials in relation to the other two commodities.The manufacturer therefore employs the practice ofveneering in order to enhance the quality of hisgoods, and to make them attractive in the home tothe ultimate buyer.

Again, a large section of the general publicdeplores the practice of veneering and feels that it isallied to shoddy manufacture. It must be admittedthat there are limited grounds for this supposition,because undoubtedly a great deal of shoddy workwas turned out during the slump years and duringthe early part of the War. Veneering, however, is aneconomic necessity in this day and age and, further-more, is a medium which does provide a definiteattraction in the appearance of the finished product.

Veneering is by no means a modern innovation.The practice was used as far back as the day of thePharaohs and has been continually in use by mastercraftsmen in Europe for the past 300 years.

The veneers are cut from the rarer types of woodin the form of logs, roots, stumps, boules or burrs.It is perhaps interesting to note that the greaterthe disfigurement of the tree through bends ortwists, the more magnificent is the figure obtainedwhen the veneer is cut. Many different methodsare used to cut the veneer in such a way as topresent the most attractive figure and amongst themore popular means are slicing and half-roundcutting. Fig. 5 illustrates how these operations arecarried out.

The veneers are normally imported into thiscountry in a ready cut condition and, after purchaseby the manufacturer are fixed to the plywood

193

NOSE BAR

VENEER

KNIFE

HALF ROUND CUTTING

CLAMP

NOSE BAR* _ KNIFE

CLAMP

HORIZONTAL SLICING

Fig. 5.

panel by gluing under pressure. The gluing of thisveneer to a piece of plywood upsets the "balance"of the forces in the cross-grained laminations of theplywood. In order to avoid the resultant twisting,the furniture manufacturer compensates this actionby simultaneously gluing a cheaper "backing" veneerto the other face of the plywood.

blockboardBlockboard is a material akin to plywood in its

physical attributes, but which is cheaper than ply-wood in thicknesses of | in. or more. Briefly, block-board mainly consists of two outer laminations witha centre core made of strips of softwood. Thematerial is normally used in the doors of wardrobesand sideboards and, occasionally, in the manu-facture of dining room table tops (Fig. 6).

laminated ^YoodThe term laminated wood is normally applied to

timber laminations which have been glued andpressed to a predetermined shape. An example ofthe use of this medium is illustrated in Fig. 7, andits advantages both in strength and in cost can bereadily appreciated if one considers the comparativecost of producing the same shape from solid timber.

The main deterrents from the manufacturer'spoint of view are two-fold. The first of these is thatit is necessary to employ high frequency electricheating to accelerate the gluing time required, andsuch equipment is relatively costly. Secondly, theitems of furniture so far produced by these meanshave not been singularly successful from a sellingpoint of view — possibly because of the inherentantipathy towards plywood by the public asmentioned in preceding paragraphs.

Again, as in the case of veneering, the method isnot new since, for example, laminated wood has

been used in the rims of grand pianos for the past100 years. With the ever-increasing costs of timberand the increasing demand for less heavy andequally robust furniture, there is no doubt that thismaterial must steadily gain ground in popularityduring the course of the next decade. The growthof its popularity depends solely upon the ingenuityof the designer to produce more tasteful, attractive,design forms, and the education by the manu-facturer of the retailer and the buying public of theadvantages to be gained from this form ofconstruction.

melamine plasticsThe use of these materials under such household

names as Formica or Warerite has gained tremen-dous popularity in recent years, and rightly so,because of their very definite advantages overtimber, plywood or veneers, in durability and sur-face strength. Their use has been confined principallyto kitchen furniture up to the present, but there isno reason why they should not be incorporatedinto other " working" surfaces such as dining-room table tops or sideboard tops. This practicewill come inevitably when the manufacturers areable to :—

(a) reproduce faithfully a natural timberpattern;

(b) develop a more ductile material which canbe readily moulded to any reasonablyfunctional shape;

(c) reduce the basic price of the commodity toa level more approximately that of decorativeveneer.

LAMINATED ARMS

Fig. 6. Fig. 7.

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POWER FEED ROLLERS SAW1MBER

POWER FEEDROLLERS

Fig. 8.

The manufacture of these plastic materials isbasically a relatively simple operation and consistsof the fusing together under heat and pressure ofseveral layers of paper impregnated with a mela-mine resin, the top paper having the colouredpattern which is evident on the finished product.

plant and equipment(a) machine shop(i) conversion machinery

As has been indicated in the section dealing withhardwoods, the material arrives at the factory insawn boards. It is then converted into the nominallengths and widths of the piece part prior tofurther machining. Each of these operations iscarried out by high speed rotary saws. The opera-tion of cutting to nominal length is carried out on across cut saw which, as the name implies, cutsacross the grain. One machine used has a foot-operated hydraulic feed which permits a board24 in. X 3 in. to be cut in under two seconds cuttingtime.

After cutting to length, the pieces are then passedthrough another saw known as a straight line edger,with a longitudinal power chain feed which forcesthe material past the saw at feeds between 50 and180 feet per minute, depending upon the species andthickness of the boards. Fig. 8 illustrates the operationof the machine.

(ii) basic production machineryThe stock, having been converted to nominal

dimensions, is now ready for succeeding operationswhich, of course, vary according to the finishedsection and shape of the piece part.

The most important of the production machinesis a combined planing and moulding machineknown as a 4-cutter or a 5-cutter, according to thenumber of motorised heads incorporated in itsconstruction. The object of this machine is fully tomachine all four surfaces of any straight stock tovirtually any required section. Fig. 9 gives a broadindication of the operation of the machine andshows the position of the various cutter heads,which are used at speeds of up to about 7,000r.p.m. As in the case of a straight line edger, themachine is power fed and is normally equipped withpower feed rollers which pass the stock through themachine at feed rates of up to 120 feet per minute.

The next most important machine on the mass pro-duction line is a double end tenoning machine. Thepurpose of this machine is basically simultaneouslyto cut tenons and cut both ends of the piece tolength in one operation. It carries out more opera-tions at the same time than any other piece ofwoodworking machinery and may include as manyas two circular saws, four horizontal cutters andeight vertical cutters. Again, this machine is in-variably equipped with a power chain feed whichcarries the work through the cutters at a feed rateof up to 40 feet per minute.

As can be readily appreciated, the speed of out-put from this machine in terms of piece parts isphenomenal and is, to a certain extent, a drawback,in that it has to be far more frequently broken downand re-set for succeeding batches of parts than anyother of the woodworking plant. Fig. 10 shows thebasic operation of the machine.

The machines dealt with above are concernedentirely with straight stock and do not play any

VERT. CUTTERS HORIZ. CUTTERS VERT. CUTTERS

FEED

POWER FEED

ELEVATION

TIMBER

Fig. ?.

HORIZ^CUTTERSPLAN

195

CROSS CUT SAWS CHAIN FEED

CUTTERHEADS

Fig. 10.

part in the finish machining of shaped or curvedstock. The majority of this work is carried out bysingle spindle machines, the two of which in mostcommon use are called a router and a spindlemoulder.

The router has a cutter mounted above thework table in much the same way as a verticalmilling machine. The cutter head works at a veryhigh speed within the range of 18,000 to 25,000r.p.m. It is normally used for shaping, rounding,or moulding both outside and inside curves and canbe used for most forms of carving. Because of itsvery high speed and normally small diameter cutter,the quality of finish obtained is usually very highand requires very little hand finishing.

The spindle moulder is the maid-of-all-work inthe woodworking industry and consists of a verticalrevolving spindle projecting through the centre ofthe work table. It can be used for the machiningof straight or curved, singlesided, or edge mouldingsof all kinds including grooves and rebates. Itsversatility is further increased with the use ofspecially designed attachments which permit workto be dovetailed, or tenoned, on the machine. Thecutter speeds are necessarily lower than the routerbecause of the wide range of work which thismachine undertakes, and are usually within therange of between 4,500 and 9,000 r.p.m.

(iii) finishing machinery

The fundamental principle of wood machining isto cut with the grain and not across the grain. Thus,each of the pieces of production machinery referredto is designed so that the cutter operates with arotary action in line with the grain. In turn, thisaction causes the surface to be rippled as illustratedin Fig. 11.

The rippling action—although not always clearlyvisible to the naked eye—shows up quite clearlywhen the work is polished to a fine gloss finish. Itis therefore necessary to eliminate these ripples andthis is achieved by the use of motorised sandingmachines.

The most important of these is known as a tripledrum sander, and consists of three drums coveredwith sanding paper and mounted above a rubberfaced endless chain belt which automatically feedsthe work under the drums. The height of the drumsabove the work can be finely adjusted and it isnormal for the first drum to take the heavier cut,and the second and third drums proportionatelyfiner cuts. In the same manner, the grade of gritused in the sand paper of each drum is progressivelyfiner. The second and third drums are providedwith an oscillating movement in order to preventany scoring on the finished surface by a " build up "of wood dust on any one part of the rollers (Fig. 12).

For even finer finishing — particularly onveneered panels — a machine known as a beltsander is used. This machine consists fundamentallyof an endless sanding belt running horizontally overthe work table. The table is mounted on rollerbearings running on tracks which enable it to beslid backwards and forwards along these tracks. Thework is placed on the table and moved to and frounder the continuously moving belt, which ispressed down to the sanding surface by a pad whichis manually slid from side to side on steel runways.

TRIPLE DRUMS

OOPPIECE PART

ENDLESS RUBBERCHAIN BELT

Fig. l l . Fig. 12.

196

(b) assembly shopThe basic methods of assembly are still very

much akin to those used by the earlier craftsmenbut their time cycle has been speeded up by

(a) the more accurate machining of piece parts;(b) the development of quick acting synthetic

resin cements;(c) the use of pneumatically operated jigs and

fixtures.

The point regarding piece parts is readily appre-ciated when one considers the great strides whichhave been made by the machine manufacturers inproviding high speed machinery designed specifi-cally for the accurate reproduction of piece parts.Unfortunately, not every furniture manufacturerhas appreciated the need for strict quality controlunder modern circumstances, but the realisation forthis need is growing as the advantages are realised.

The development of synthetic resin cements hasreduced very considerably the time cycle requiredfor the hardening and setting of the adhesive in,for example, a complete carcase assembly. Apartfrom the reduction in time, the synthetic resincements now provide a joint very much strongerthan that of any of the natural traditional glues.Development of these materials is a continuousprocess and it is quite probable that before verylong it will be possible to butt-joint the pieces ofwood together so firmly and so securely that theneed for the traditional types of joint, such as amortice and tenon, may be completely eliminated.Such a development would have a far-reachingeffect upon the furniture industry and, indeed, uponthe ultimate selling price of the product, since itwould then not be necessary to install and maintainsuch expensive machinery as that required at thistime for tenoning and morticing.

The use of pneumatic equipment has grown veryconsiderably in the industry in the last 25 yearsbecause of its suitability for the quick and sustainedapplication of pressure. In most pure assemblyoperations, pressure must be applied firmly to gluethe joints of each piece part in the assembly. Formany, many years the pressure was obtained by theuse of a sash cramp which, in effect, consists of anadjustable bar with a lead screw at one end whichis turned to apply the pressure. Wherever practi-cable the sash cramp has now been replaced bypneumatic cramps, and pneumatically operatedfixtures have now been evolved which permit thewhole of a wardrobe body to be assembled andpressed in one-fifth of the time taken by traditionalmethods.

The smaller sub-assemblies are normally carriedout on a steel cramping table, which has longitudinalgrooves spaced some 8 in. apart and which is equip-ped with between four and eight pneumatic cramp-ing heads. The location jig is secured to the table,and the pneumatic heads are adjusted to apply thepressure at the required points. Other minor assem-blies are carried out on jigs or fixtures equippedwith toggle clamps or simple cam clamps.

(c) polishing shopVirtually no furniture today — particularly in

the popular market — is polished by traditionalhand polishing or "French Polishing" methods. Thebulk of the industry now utilises cellulose-basedmaterials, the finishing coats of which are appliedby spray gun, or other mechanical means. Theoperations sequence on normal polished furniture isas follows :

(i) stain fillerThe stain filler is a paste with a cellulose base

which permits the open grain pores to be filled and,at the same time, stains the whole surface to areasonably uniform colour. (It is necessary to fillthe grain in order to achieve a full gloss finish). Thepaste is applied by hand and is rubbed into thetimber or veneer by a portable machine which con-sists of a motorised spindle fitted with flexibleblades, which rotate against the surface and pressthe filler firmly into the grain material.

(ii) cut downThe moisture in the filler causes the surface

fibres of the timber to lift, and it is necessary forthese to be removed by the application of abrasivepaper. This operation is carried out by anotherportable piece of electrical equipment, which con-sists of either one or two flexible pads operating athigh speed with a reciprocating motion.

(iii) sealingTimber is always affected by changes of moisture

content in the atmosphere. It is therefore necessaryto seal the whole surface in order to prevent absorb-tion of moisture by the finished product. The sealeris a transparent cellulose material and, in thisinstance, is applied by spray gun.

(iv) cut downAgain, the moisture of the sealer coat causes

fibres to rise — albeit in lesser proportion. It istherefore necessary for the whole surface to be verylightly rubbed down — normally by hand — witha very fine grade of abrasive paper.

(v) matchingDue to the differences in density of the grain in

the various members and panels of a piece offurniture, the stain filler shows up some degreeslighter in certain places than in others. In order toobtain a fully uniform colour throughout, it isnecessary to apply a mist of liquid stain to thelighter patches. This operation is carried out byanother finer type of spray gun which emits a veryfine and delicate spray mist.

(vi) lacquerClear cellulose lacquer is then applied by spray

gun and normally consists of a double coat appliedwet on wet.

(concluded on page 205)

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