Torpedore-Tambour

With there being two tambours a means was required to prevent either of them going beyond the centre point at the front of the cabinet. This was achieved simply by stopping the grooves that guide the tambours just before the centre point of the cabinet top and bottom, see below.

At about the same time as the 54 staves that make up the tambours were machined up, plus about ten extra staves to allow for rejection due to unacceptable warping, appearance, etc, the two central locking staves were made, carved, shaped and test fitted to the tambour grooves, below.

Dying and Polishing
With all the tambour staves made, they were hand planed to remove machine marks, then scraped, the sharp arris on edges knocked back, and sanded ready for dying and polishing. The purpose of polishing at this stage are threefold:

Firstly, because the intention was to effect a graduated colour change from the white of the hard maple at the centre of the cabinet through yellow, to orange, to red, to purple, to blue, and a blue black at the outer edges, the way chosen to accomplish this was to use Morrells 'Light Fast Dyes', which are spirit soluble, and apply them with a spray gun.
Secondly, all the staves are eventually linked together using canvas glued on to the back face of the staves. So, with the show face and edges of each stave polished, any glue seeping between the staves during application of the backing canvas won't cause them to stick together.
Thirdly, it's just hard to properly polish every part of an assembled tambour, so doing the job prior to assembly makes sense.

To start, two base boards of MDF were cut and all the staves of each tambour were temporarily stuck, show face up, to the MDF with double sided tape, spacing each stave roughly 18-25 mm apart, see below. To help prevent air pressure from the spray gun moving the staves around on the base boards the tongues on the end of each stave were also taped together with masking tape. This had the dual purpose of preventing polish getting on to the tongues that run in the grooves already worked in the cabinet.

The series of images below illustrate the dying procedure. At the left in the first image is an L shaped shield made out of two pieces of MDF simply tacked together which, as can be seen, lies over one of the tambour staves. Underneath the long leg of the L a piece of brown paper extends further to the left to protect staves hidden under it. This prevents any dye overspray from the spray gun landing directly on any wood that should not be coloured during the colouring up of the exposed staves which, as can be seen had already been partially coloured up. The methodology was relatively straightforward: put a little dye into the cup of the spray gun, and add a lot of cellulose thinner, aka lacquer thinner, reduce the air pressure entering the gun, and mist the dye on evenly. Then let this first application dry, perhaps adjust the concentration of the dye in the gun and mist on another coat, etc.

Moving on from the image above which showed the first dying stage, it can be seen in the image below that the protective L shaped piece of MDF and pieces of brown card were rearranged whilst additional dying had been undertaken. As you scroll through the subsequent images this method of moving protective card and L shaped MDF pieces as the dye colour is adjusted continues until the job is complete. The method used to adjust the dye colour was simply to assess what effect each application of dye had on the wood and adjust colour as required. For instance, I wanted to change from yellow to orange to red so, employing those proven methods of ultimate control in work, sometimes known as "by the seat of the pants" method (sic), I used my instincts and a 'best guess' technique which informed me when to add a bit of red to the yellow already in the gun, and when to get rid of the yellow altogether, etc to achieve the graduations in colour.

Finally, in the image below all the staves had been dyed and polished with two coats of 30% sheen pre-catalysed lacquer, rubbed down between coats with 400 grit abrasive paper to remove nibs and dust specks. Here, they are simply laid out on a flat surface to indicate their final appearance.

Tambour Assembly and Final Fitting
After polishing the tambour slats they have to be assembled, and to do this an assembly board was made out of MDF. Assembly boards need to be exactly square in one corner, and two battens are screwed on to the two edges that lead into the square corner, see below. In reality the other two edges of the assembly board don't need to be square or particularly accurate, but with a sliding table saw it's simple enough to just make the whole board square.

How an assembly board works is that all the tambour staves are jammed into the square top right hand corner as shown in the image underneath. On the left hand side there is another batten fixed firmly to the assembly board and six folding wedges provide pressure that clamps all the staves tightly together. As long as the staves are tight in the right angled corner of the assembly board (up against the screwed on battens) then, all else being equal, the stave assembly is square and ready for the attachment of the canvas backing. Note the cabinetmaker's triangle marked in pencil on the back face of all the staves. The purpose of this is to ensure they are assembled in the right order. For instance, if all the parts had been moved around for some reason and become disordered, then reordering them is easy through just putting the triangle back together correctly. With two tambours in this cabinet, and a lot of staves, one triangle was needed for each assembly. Ensuring the position of the triangle on one assembly is quite different to the position and form of the triangle on the other, if staves do become muddled up it's relatively easy to sort everything out if necessary.

Attaching the canvas to the staves required spreading glue onto the wood, in this case PVA glue, but other glue types are just as good, placing the pre-cut canvas carefully in place, and applying gentle heat with an iron through a protective cloth. This protective cloth -- blue here, prevent possible burning of the white canvas backing.

After gluing on the canvas to the tambour staves, a test fit of the tambours followed, see below. All worked well at this point and construction of other parts of the cabinet continued until final fitting of the tambour near the end of the job.

A means is required to operate the tambours, ie, to open and close them, and various types of finger friendly profiles, shapes, or holes, etc are suitable. A typical method is to make use of a canvas locking stave and create a protruding profile that can be grabbed or pushed with the hand. The locking stave is the last stave attached to the canvas backing which holds together all the rest of the staves in the assembly. The finger friendly mouldings used on the locking stave protrude towards the open front of the cabinet, and because of this protrusion these staves can't pass all around the tambour groove, especially where the groove passes close to the cabinet side (in this case). The method of attaching the locking finger stave is illustrated below. The inside of the stave is machined to create a rebate into which a bead is screwed into place. This can be seen on the right side of the picture and it can also be seen that the canvas backing is trapped in the rebate by the bead. To the middle left of the picture is the unassembled second locking stave and bead for this specific cabinet.

All that remains to do is to remove the screwed on bead from the locking stave, slip the tambour into its groove at the back of the cabinet, and push the tambour around to a convenient spot. Next, working from the back of the cabinet, the locking stave is reattached to the rest of the tambour by refitting the bead and trapping the canvas, and the canvas cut flush with the back of the locking stave to leave a clean finish on the inside.

The last small job is creating and fitting stops to prevent the tambour opening too far, and in this case, four small T profiled maple blocks were fashioned and screwed into place. The lower leg of the T profile fits into the tambour groove, and is simply a means of eliminating the very small chance of the blocks rotating in use. They are held in place with a single screw making them easy to remove and replace if the tambour assembly requires maintenance of some sort in the future.

Richard Jones Furniture

Making a Tambour