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left: Photo i Pine blanket box showing grain direction around sides

How to allow for movement when making pieces of furniture

A MAJOR CAUSE of dispute and disappointment in custom-made solid wood furniture is movement occurring after a piece is made — sometimes with disastrous results!

In the past, I have looked at how and why wood moves and how to minimise that movement in timber selected for cabinetmaking. Now I will turn my attention to making allowances for the movement which will inevitably take place when the furniture is made.

The suitability and characteristics of solid wood furniture must be discussed with clients, who must have its limitations explained so as to prevent blatant mistreatment —

like standing the piece in front of a radiator or in a conservatory in full sun!

With the advent of stable sheet materials people tend to forget — or perhaps have never learned — how to look after solid wood.

Shrinkage cracks which may verify antiques — and even increase their value — will not be accepted in modern solid wood furniture. Part of a modern designer-maker's skill and responsibility is to allow for central heating.

Principles

In spite of all precautions taken to select, store, and condition wood properly it will still move as its moisture content changes to match that of the surrounding air.

This movement is an irresistible force; it cannot be prevented or restrained, and must be allowed for in the making. In a normally heated domestic environment wood will tend to expand across the grain — not along it — in the summer, and shrink in the winter.

This means that while the length of a board will not change, the width and, to a smaller extent, the thickness will. The problem really is that simple — it's finding the solutions which can give the headaches!

Grain direction

I have chosen a simple pine blanket box, see photo 1, with which to illustrate a number of methods to negate the effects of movement.

"Clients must have limitations explained so as to prevent blatant mistreatment — like standing the piece in front of a radiator or in a conservatory in full sun!"

ABOVE! Fig 1 Oversire hole for screw with washer

Firstly all four sides should have the grain running the same way, around the box. As the potential movement will be across the width of the grain, the only effect of shrinkage will be a slight difference in the height of the box which will probably go unnoticed.

Dovetailing the joints to prevent any bowing or cupping will ensure this part of the carcass is sound and stable.

It can also be seen from this photograph that the boards used in the top, chosen deliberately for their nice figure, are tangentially sawn and so liable to cupping.

Timber tends to have a different moisture content on the outside faces than core due to its greater exposure to the surrounding air's moisture content, so while thicknessing these pieces I would be careful to take the same amount off each face to keep the balance even and reduce the tendency to cup. I would also leave them to stabilise for some time in stick under a weight.

Clearance holes

Braces fitted under the top will help keep it flat, see photo 2. The grain in the braces is, however, running across the width of the top boards, so that although the top will expand and contract across its width, the length of the braces will remain unchanged.

To prevent the top from cracking or buckling, the braces are screwed to the top through double-countersunk holes. These give clearance to allow the screw to move from side to side with the top movement, while still above right: Photo 3

Underside of pine box showing frame grain direction

ABOVE! Fig I Double countersunk hole for screw and brace

ABOVE! Fig 1 Oversire hole for screw with washer

ABOVE! Fig I Double countersunk hole for screw and brace

  • Countersunk holes
  • Countersunk holes
ABOVE: Photo 4 Frame and panel door

holding it flat, see fig 1. Of course the braces must not be glued to the top.

The holes are plugged with matching pine to improve the appearance. A suitably oversize hole, or a slot, could also be used with a round-headed screw and washer if movement is likely to be considerable, see figs 2 and 3, but this method is unsightly.

Fixed panel

Problems would ensue if the base of the box was of the same construction as the top — and needless to say it isn't. The underneath, see photo 3, reveals a frame and panel. With no movement in the sides relative to the base, the latter shouldn't move either.

The frame is arranged in such a way that the grain runs virtually in the same direction as the sides. The centre panel is ply and, as it will not move, it is glued in all round for added stability. The base can be glued, screwed and plugged directly to the sides.

"Frames with the grain running across carcass sides, for instance those accommodating drawers, must allow for side movement without distorting the frame or the side"

Floating panel

Photo 4 is of a framed and fielded panelled door. The grain runs through the length of the frame components so it will move very little in its perimeter dimensions, retaining its fit in the carcass. The panel is not glued but fitted in a groove in the frame, allowing free shrinkage across its width without adverse effects.

If required, the panel can be spot glued at its top and bottom centres to locate it in the frame and ensure equal movement on each side, see fig 4.

Drawer frame

Frames with their grain running across carcass sides, for instance drawer runners, must allow side-to-side movement of the carcass to avoid distortion. This can be achieved by leaving the rear mortices and tenons of the frame dry, and allowing an expansion gap, see panel and photo 5. If the sides of the frame are then fixed only at the front of the carcass,

RUNNING FREE

THE ABILITY of the runner to enable free movement of the drawer is an important feature of solid carcass construction.The ends of the front and back rails are glued into the sides, but the side rails are fitted dry into locating housings in the carcass sides, so allowing the sides to expand and contract by means of the expansion gap, see fig 5.

Colin Eden-Eadon adds: One other way of accommodating carcass movement for drawer runners is to construct solid dividers, always ensuring that the grain direction follows that of the rest of the carcass work. An alternative, less expensive timber may be used, the front edge being lipped to match the finish timber of the piece.

above' Photo 5 Drawer frame showing expansion gap f Grain direction • Washer t Slot • Screw

ABOVE! Fig 3 Screw and washer in slot

Glue area

I Side nail dry in housing

Spot glued to locate panel in centre and equalise

movement tt,

Floating fielded panel let into groove in frame but not glued all round •'

BARRIER CREAM

Sealing its surfaces can slow down the movement of moisture in and out of wood, but completely sealing all the surfaces without total immersion of the finished piece is difficult, so it will eventually stabilise to the average moisture level in its immediate environment.

I have had some success with oil on burr elm ((Jlmus sp).The burr can be quite porous; because of its wild grain, and by keeping the first coat wet as long as possible, the oil is encouraged to penetrate deeply.

I think this fills a layer of cells under the surface, which then, instead of absorbing the moisture, becomes a barrier to moisture pick-up, helping to even out sudden peaks and troughs.

RIGHT: Photo 6 Carcass with drawer frames

RIGHT: Fig 4 Frame and floating panel construction

' • Expansion gap • Side nail Fig 5 Drawer frame showing gap and dry joint

Glue area

End of back nail glued in housing •

• Dry mortice and tenon

They are fixed to the frame directly with screws through countersunk holes, and to the top through slots — again allowing the necessary movement while holding the top flat.

The two slots at are right-angles to each other — be sure to put the screw into the right one!

Precautions

A number of precautions should be taken to minimise movement in the timber used in the making of furniture. While clients must also be told what constitutes suitable conditions for solid wood furniture, they must also accept that the wood will move as it adjusts to its environment.

All my suggestions are based on the premise that wood moves across but not along the grain. With that in mind all sorts of ingenious solutions can be devised to solve design problems.

Spot glued to locate panel in centre and equalise

movement tt,

Floating fielded panel let into groove in frame but not glued all round •'

Frame <

shrinkage of the carcass sides can occur without problems.

Fixed tops

Solid tops on tables must be allowed to expand and contract across their width, but be held flat to prevent any twisting or cupping.

The simplest solution is for the underside of the top to be held flat by wooden buttons which have a tongue located in a slot in the underframe. The body of the button is screwed directly to the underside of the top, allowing the top to expand and contract across its width while being held flat to the frame.

Set the slot slightly low to pull the top down as the buttons' screws are tightened up.

Photo 6 shows detail of the same top with one of the buttons removed and replaced by an expansion plate for demonstration purposes.

These plates can be used instead of the wooden buttons.

I Side nail dry in housing

Part Two

PROJECTS

Traditional in style with clean simple lines - and eminently practical

Three in one

Nest, or stacking, occasional tables are useful in providing maximum table-top area when required, while occupying minimum floor space when not in use. They are usually of simple construction, but still require a range of basic making operations and techniques, repeated a number of times. They are useful practice pieces - that give a little more satisfaction than the ubiquitous woodwork-class stool!

Design

Many different arrangements are possible, from the Long John side table with two free-standing tables under, to a nest of up to five - four suspended under the main table, sliding in and out on bearers.

For this project the primary use was as a side table, so the dimensions of that table were the starting point.

The design specified traditional construction, with stop chamfered, rather than turned, legs.

The overhang of the tops and the thickness of the legs reduced the size of the smaller tables by considerable steps. By the time I got to the third table it would only just hold a bottle and a glass, so a fourth table was obviously not required!

Increasing the size of the top of the largest table, and/or reducing the top's overhang, and replacing the legs with thinner, solid sides, would allow larger tops and/or more under-tables.

Timber selection

The timber of choice was elm, and I had some English or common elm, Ulmus procera, which had been air-dried for some years. The wood was hard, and dark in colour, with a course texture and some nice figuring.

Timber preparation

As of all the elms English is the most unstable, it must be thoroughly conditioned to its end-use environment. Select what you require, and mark out the various components about 10% oversize. The pieces for the table tops are cut from the best figured boards, choosing the very best wood for the largest table, as this will be in permanent full view.

I stacked and sticked all the pieces and put them in my conditioning cabinet

How to make a nest of tables

Traditional in style with clean simple lines - and eminently practical

Recessed expansion plate

Tenons

Best quality boards chosen for outside table

Bearer screwed to spacer

Butt joints have loose tongues

"They are useful practice pieces -that give a little more satisfaction than the ubiquitous woodwork-class stool!"

Mortices

Stopped chamfers

Stretcher rails

559mm 432mm 300mm

22mm

FRONT

19mm

395mm

406mm

438mm

63mm

75mm

32mm

22mm

228mm 330mm 432mm

SIDE

ifer o

6mm rr

12mm

32mm

"As of all the elms English is the most unstable, It must be thoroughly conditioned to its end-use environment"

clamped up, checked to ensure they are flat, and left to set.

for a month. If you do not have access to a conditioning cabinet the pieces should be placed, similarly stacked and sticked, for as long as possible, in the room in which the tables will eventually live, or a similar environment.

The selected boards are faced and thicknessed, and matched for the most pleasing figure and colour, trying to ensure that the figure runs through the joins to disguise them. The grain in my elm was pretty wild, so alternating the cupping tendency of the boards was irrelevant. I am not convinced about the value of this practice anyway -1 prefer to address the likely movement in one direction rather than the corrugated iron effect!

The joining edges are machine-planed on the jointer, then hand-planed to remove the machine ripples which would weaken the glue joint.

The fit of the joining edges is slightly concave, touching at each end with an approximately 1.5mm (Msin) gap at the centre. This helps the clamps pull up right, and allows for extra shrinkage at the ends, if there is any further drying out.

The joining edges are then slotted for a loose ply tongue to add strength. The boards are marked where they will be finally cut to size, and the slots stopped 25mm ( lin) short of those marks so that the final trimming will not expose the tongue. Cascamite glue is applied to the slots, edges and tongues, the tops are

The legs are cut to length, and dimensioned to 38mm (IMin) cross section. The mortises are cut for the top frame and bottom rails -1 used the morticer on my planer, although a router would also have been suitable. The floor-end of the legs is rounded over to ¡4 radius to prevent splintering and aid sliding on carpets.

The stopped chamfers were cut on a router, all starting 75mm (3in) in from the ends, and finished with a sharp scraper.

The pieces for the top frames and bottom rails are dimensioned and the tenons cut to fit the mortises in the legs. These are dry-fitted to check accuracy. It

A cabinet scraper Is used to clean up the stopped chamfers

Elm varieties

Elm can vary considerably in colour, texture, figure and stability depending on which of the sub-species it is. Dutch elm is not as dark and has straighter grain than English, with less figure, and is more stable. Wych elm is even straighter grained, paler in colour, often with a green streak, and the most stable of the three. Beware when buying to match previous work!

Although all three types are affected by Dutch elm disease there are still reasonable supplies of timber available, mainly from the North. It is being replanted in the South.

"It is particularly important that the joints on the bottom rails of the two larger tables are a really good fit"

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