Tambour: Designing them is a trick, you cannot simply design them and see them work because that cannot account for the intricate movement of the sheet as it bends and turns. A full sized mockup must be tried and adjusted to get the kinks out. To start the design you must choose the shape and size of the door slats. This will determine the diameter of the curves the slats will turn verses the amount of area the slats can span. Draw out the curves the tambour will make first, than design the contents of the cabinet it covers. A tambour door has three parts - the slats, a
canvas (or rubberized vinyl) backing and a thicker
rail or
stile at the bottom to move the whole assembly in its slot and stiffen it. A tambour can run up and down or side to side, and
pass through either an S-curve or a simple-radius C-curve.
An S-Curve gives strength: A
roll top
desk with sides curved in the shape of a lazy S is a familiar icon in furniture. The tambour runs down behind the pigeon holes and false back into a essential part of all tambour design. Without it, you’d see the
canvas backing of the tambour. Moreover, without the
return slot, the materials stored in the
desk might
block the tambour from opening all the way. The pleasing curve has two
practical benefits: bending the tambour into a reverse curve actually stiffens it, which prevents the slats from drooping in the center of a wide
desk. Also the slats in an S-curve tambour can be thinner and lighter in weight than those needed to stiffen a tambour that isn’t curved. Yet another feature of an S-curved tambour is that it’s less likely to come crashing down when you close it due to the extra
track length and curves and added friction from it. A tambour has to flex both forward and backward to
pass through an S-curve. Half-round and Bevel-edged slats are traditional designs that can accomplish this. Both types are just as effective in curving
Sizing S-curve Slats: Design your
roll top tambour on a full-scale drawing. Use a piece of paper as large as the end of the
desk to work out the shape of the S-curve, the size of the pigeon hole section and the placement of the false back. Draw the
groove parallel to the curved side. It’s easiest to make its width the same size as a
router bit. Then make the slats a little
bit thinner than the
groove so they can move freely along it. The
thickness of the slats depends on the distance they have to span. Slats range from a
bit less than 3/4" thick for a 60" opening down to 5/16" thick for a 24" opening. How wide should the slats be? Their width is limited by the sharpest turn the tambour has to make. In a
roll top, that turn is hidden. It’s at the back of the
desk, behind the pigeon holes. On
convex curves, make the slot a little wider than the
track, this is needed for the slats to follow the curve. In this way a wider slat can be allowed to make the curve without pinching, and the bottom
rail can also fit through the S-curve. In the rear curve, this wider slot is important because of the 90° slot. It allows the arc of the curve to be as small as possible so it does not waste space inside the cabinet, yet allows for larger slats to make the corner. If however the slot is too wide, the tambour will bind in the curve. This is why it is hard to design the
track layout without much testing to find the best mix between sharpness of curve and width of slat.
Build a Model:
Sizing the width and
thickness of the slats can’t be done on paper alone, however. You have to test the real thing. Rout a
groove into a piece of plywood, following a
template to prevent the
router from freehand wiggles. Make a few short tambour slats and glue them to a piece of canvass. Try running the mock tambour through the
groove. If it’s too loose, your tambour will make an unpleasant rattling sound. If it’s even a shade too tight, the tambour may not move in humid weather. The right fit can be elusive, but the only way to find it is to
build a model. As for the slats themselves, beveled slats with at least a 10° bevel work as well as half-round ones. On the backing, leave some space between each slat to allow them to
bend inward or
concave. This will have to be tested, narrow slats will allow for a tighter
concave curve, but in the case of a need for wider slats, given they can round the
convex corners designed, a steeper angle on the beveled slats will allow for tighter turns, or making the half rounds a little less round on the edges will also do the trick. Also a little more space between the slats will add a little more flexibility to the bending radius and smooth in turning. No more than 1/16" however should be between slats or they will bind when pushed to open the door.
The Lift
Rail: A large
roll top tambour needs a heavy duty, multi-purpose lift
rail. The lift
rail absorbs the
shock of the tambour closing on the desktop. Its extra width and
thickness help the tambour glide through the grooves without buckling, give you enough room to install a mortised lock and provide a surface large enough to hold a comfortable handle. Design the handle and buy the lock before choosing the size of your lift
rail. They’re generally 2 to 3 inches wide. Cut a tongue on the ends of the
rail so it can slide through the grooves. The tongue is thinner and wider than the slats. Try running a mock lift
rail through the S-curve. It doesn’t have to negotiate the tight turn behind the pigeon holes because you can install the completed tambour from the front of the
desk. If it does not negotiate the turns well enough, instead of making the
rail smaller, it can be shaved down more into an hourglass shape to make the curves or made into two pegs on each end of the
rail which will correspond with the size of the slats in distance but with middle ones removed. For example: given a
rail with tongue four slats wide, the pins would need to be the size and approximate shape of slats one and four and slats two and three would be missing. This space between pins is especially needed to be the same as the slats because if the slats work well in a curve than these pins given proper and proportional
spacing will also make the curve.
Turning Tight C-curves: Lets turn to the Federal
desk, where the tambour moves across the
face of a cabinet to make two C-shaped turns at each end. This tambour disappears like magic into a cavity between the outer cabinet and the inner box that contains pigeon holes or shelves. Because it only bends
in one direction, the tambour can have
flat faces. It does not need to have bevels because it will not be making a any
concave turns. It can even have slight tongue and
groove shaped edges if wished with the tambour only linked at the top and bottom. When closed, square edged slats it will look like a
flat panel, unlike the ribbed surface of the
roll top
desk tambour. Often the trick here is to design a tambour that can make a very tight turn. A wide turn would require large awkward-looking stiles at the sides of the cabinet. The secret is to put small, invisible tongues on all the slats. The smaller the tongue, the tighter the radius the tambour can turn. Unequal shoulders to the tongues are important for the tambour to glide smoothly through its horizontal grooves. The back shoulder should be very narrow or eliminated altogether to bring the
canvas backing in
line with the curve. This back shoulder could cause the slats to bind as they go around a curve because they are out of axis with the curve of the
track. The tambour rides on the end of its tongues, not on the shoulders so that the opening and closing the tambour won’t wear down the finish on the cabinet. Cut the tongues just a
bit longer than the
groove is deep. You may dispense with the lift
rail, because you’re not fighting gravity. However, if you want the door to lock or need more room for a handle, you can make a lead strip that’s larger than the slats. It doesn’t have to negotiate the tight C-curves. Insert the finished tambour from the rear of the cabinet and attach a two-part lead strip to the tambour after it has passed through the turns. The smaller the space between the slats, the better on this type of Tambour, as it will cause the strips to bind less and form a tighter joint when closed. On this horizontal sliding type cabinet however there is a disadvantage in that there must be an inner cabinet all around the sides and back of the space to prevent the contents from
blocking the tambour
groove. While the top is now able to be touched by the pigeon holes, the sides are lost for things like mail slots and more effective storage across the width. The inner cabinet and the
groove around it can be masked by a deeper shouldered lead strip as it will be all by itself and thus can make corners without binding. This lead strip which is installed after the tambour is pushed in from the rear, is attached by an extra flap of fabric backing being left on the front
edge of the tambour which can later be attached to the lead strip when in place.
Rolling Garage Doors: a final type of Tambour
track layout is the most efficient use of space in the cabinet as it does not require false backs or sides, but still has all of the advantages of the C-curve design featuring the square edges or beveled
edge slats. It might however require an even stiffer backing yet if not a rolling mechanism as per window shades to help the tambour
roll up out of the way. Given a small enough door, and enough room, the smaller slats can simply
roll into a scroll form of
track without any need for winding mechanisms. But for larger doors it is best if the tambour has a tensioning mechanism to keep it rolling and tight into a spiral instead of flowing out into the cabinet when it leaves the
track, or binding because it is too loosely wound. This tight rolling mechanism will also help to keep the amount of space needed to store the tambour as small as possible. These mechanisms are commercially available with the doors, but can otherwise be as simple to some extent as a shade mechanism’s spring or counter-weighted to draw the tambour in. It can also be engineered to the extent of a
roll drop given the want for such complexity, however the essential part of this concept is the idea that the
roll is put either at the back or front of the cabinet either instead of the first turn or behind it and to the back of the cabinet behind the top/uppermost row of pigeon holes. Both places out of the way for storage and structural strength on the vertically traveling door, or in the same relative position and space savings. The vertical traveling door can even make the S-curve if desired, given the added friction and
track length is accounted for in the rolling spiral or winding mechanism.
(B.Ship. With idea the idea from American Woodworker, Dec. 1999. “Tambour Doors” by Tom Caspar p86-92)