Economy of Scale

Economy of Scale:
Andrew Lapthorn’s Tripod table captures the appeal of a bespoke piece through clever batch production

The Tripod table was designed primarily for exhibiting purposes. It was intended as an introductory piece not only to my work but also to the world of bespoke furniture. The idea was to take as many cabinetmaking skills as possible and condense them into a single affordable and practical, easily portable piece of furniture. The result was a distillation of the art of cabinet/furniture making that was both affordable for the client and for me to make.

Wood and materials used
• 9mm black MDF for the table top
• 100mm square stock for the boss in sycamore (Acer pseudoplatanus), oak (Quercus robur), walnut (Juglans regia) or other suitable timber
• Three lengths of straight grain timber for the legs
• 1.5mm square ebonised stringing
• Oak dowels

The top
Made from 9mm MDF, the top takes the form of a doughnut 400mm in diameter with a 75mm hole at the centre. The hole at the centre facilitates the leg structure, which comes through and is flush with the radially veneered top. The reason for using MDF (other than for stability) is that you can buy it in sheet form already stained black. This is consistent right through the thickness so it can be machined and polished to give an ebonised finish to the edge.
First, machine the centre out with a router using a profile guide or a profile cutter in conjunction with a template. Then turn a disc that is an engineered fit and drop it into the hole. Fixing the beam of the router to this disc means you are then able to machine out the top thereby perfectly aligning the two circles one within the other.
The top is radially veneered so as to give more impact to the piece. This shows the wood to greater effect and shows off another classic cabinetmaking technique found in high-end furniture. It also gives the table
a more considered look.
In this case I divided the top into eight (though six would work equally well, if not better), using crown cut veneers. Using a mirror to explore the variety of patterns possible from the veneer, a scalpel and a clear acrylic template, each segment is cut out and taped together using clear parcel tape.

The beauty of the design is that you don’t have to be so precise in getting the points of your veneers to meet at the centre. A millimetre or two here or there won’t matter as the centre will eventually be trimmed away, although this should not be an excuse for not striving for perfection.
Ensuring the centre of the veneer is at the centre of the hole, it is then pressed. Four bits of tape are added around the outside edge to prevent slippage and also to prevent tears when removed from the press. Once done the excess is trimmed away and the procedure is repeated. A small radius is routed on the outer
edge, top and bottom, a small 1.5mm chamfer on the top edge of the inner ring. Finally, a rebate 10 x 6mm is routed on the underside.

I have recently invested in a polyurethane vacuum bag from Airpress. Though more expensive than the vinyl ones I had previously, it is definitely an improvement and has made the vacuum pressing process altogether more pleasurable. While it maintains the transparency of the vinyl bags it is more pliable, despite being thicker, making it easier to manage. Another big plus is that the bag is seamless. With the vinyl bags this proved to be a weakness in the long term. So far so great, now it is only the test of time that will prove it’s durability.

An alternative to black MDF
Rather than having to buy a whole sheet of black MDF you could just use regular MDF and stain it. Making full use of the absorbent nature of the material, during the prototyping phase, I used a Morrells light fast stain to stain the outer and inner edges of the doughnut.

The boss
The central hub or boss is turned from 100mm square stock. This is best turned from a single piece of timber as the top end is seen. Being the focal point of the top any glue line or poorly matched end grain will be conspicuous. As 100mm timber is not readily available in most woods, sometimes there is no option other than having to make up the thickness by laminating two or more pieces together. I tend to veneer this with, for example, a roundel of decorative veneer of the same species, more often than not a burr. Again it adds, in a modest way, to the layers of interest to be found in the finished table.
The stock is turned down to an even cylinder 94mm in diameter with a 9 x 6mm rebate at the top end and a cone at the other at a 45° angle leaving a stub on the end, this gets ‘sharpened’ to a point later.
If turned from a single piece then at the top end I usually add three 1mm ‘V’ shaped grooves at 9mm spaces, which are ebonised later. These concentric rings add to the geometry/dynamism of the work and highlight yet another skill incorporated in the construction of the piece, that of turning.

Once you’re satisfied with the turning the boss can be removed from the lathe, the stub cut off and the end sharpened to a point using a 11/2in paring chisel, finishing off with a fine paper.
At this stage the top end can be veneered as previously suggested, or indeed if the ‘V’ grooves have turned out uneven or unsightly (very easily done) rather than lose the work, it can be veneered. Use an expanding polyurethane glue as this will prevent the rings from telegraphing through.
The final process in making the boss is to machine the dowel holes to take the legs. This is a relatively straightforward process but it does require a pillar drill and a sturdy accurate jig to hold the work at the required angle. A band cramp is the approved method in this case for holding the work firmly in place.
Positioning is key as the boss must be centred exactly in the pillar drill. There is a degree of trial and error here, but when fitted the outside point of the leg should not go beyond the rim of the boss when glued in place. If anything, it’s better to be a fraction under. Once you’re satisfied with the setting, the holes are then drilled to a depth of about 50mm. Slacken the band cramp and rotate the work through 120° to drill the next hole until all three have been done.

The legs
For this sculpted joint, positioning is all important. Anything slightly too high, too low, off to the left or right will result in unsightly gaps around the shoulders of the joint. If done with care and attention to detail the result is very gratifying.
The legs are made from three lengths of timber 600mm long x 34mm square. Wherever possible a straight grained timber is employed. This will become advantageous later on. With a 20mm Forstner bit held in the tailstock, the work is centred on the lathe and by winding the tailstock in, a 75mm deep hole is bored into the end.
The legs are then held in a jig on the diagonal placed on the sliding table of a dimension saw with the fence at 24°. The ends are then nipped off. This process removes most of the initial waste from what will be the shoulder line of the joint.

Profiling the shoulder
Turning a cylinder the same diameter, or more, with a conical end at 45°, mimicks the jointing surface of the boss. This is then finished with a sanding sealer or lacquer but not with oil or wax. Cut out a 150mm disc from a sheet of coarse grit (60/80) abrasive paper, and remove the centre with a 25mm hole punch. A segment of approximately one-third is then removed and the remaining two-thirds is backed with double-sided tape. After removing the backing from the tape, the disc is carefully wrapped around the conical end of the lacquered turning so that you end up with a seamless joint. The more seamless the better as it will last longer.

For batch production purposes I have been able to source 150mm x 60 grit self-adhesive sanding discs from Mirka which save a lot of messing around, and I have also made a solid aluminium cone. As it is metal I get good adhesion, a hard-wearing surface and most importantly it draws the heat away thereby giving longer life to the abrasive paper. One can expect to get at least two or three legs from a single disc, sometimes more sometimes less depending on the timber used and how good the paper joint is. In contrast, the hardwood cone shown in the image (above centre) shaped around 30 legs before degrading beyond
the point of usefulness.

A cradle is then constructed, which straddles the lathe and allows the leg to be supported on the diagonal at 21° from the horizontal. Again the important point here is to ensure the centre line of the cradle, thereby the leg, is directly in line with the centre of the lathe.The leg is then introduced slowly into the rotating abrasive cone. By rocking the leg gently at the start the process goes a lot quicker and is less likely to result in friction burn.

Towards the end four sharp points begin to form and a steady, firm, straight push is all that is required to get the finished profile. If the left and right points of the shoulder don’t form at the same time then something is out of line. Once you’re satisfied with the shoulder the legs are then shaped. Marking out the taper on one inside face the waste is removed then finished with a plane and the procedure is repeated for the second inside face. At this stage a stringing line is added. It is not necessary but I think it enhances
the value of the table as well as the design and all for relatively little effort.

Using 1.5mm square ebonised stringing, a 1.5mm square rebate is machined from three of the outward facing corners. Holding a reduced 20mm dowel in a vice so that the leg can be rotated and using a fine plastic coated electrical cable or nylon fishing line, all three stringing lines can be glued in at the same time by winding the line firmly around the leg. It takes two to three minutes and once dry it then takes seconds to remove.Ordinarily I hold the stringing in position with masking tape but for the sake of speed I had to find an alternative means. Having to apply a lot of small bits of tape and then pick them off again is enough to try the patience of a sun-ripened tomato!

The excess stringing is nipped off at the shoulder with a scribing gouge then cleaned up with a nicely sharpened and finely set smoothing plane. This is where a straight grained timber for the legs helps as they then don’t require sanding. This eliminates the inconvenience of getting black dust worked into the grain. The four corners of each leg are then stroked with a finely set block plane and the leg is then cut to length. Finally, a small chamfer around the bottom of the leg is added. If polishing the work then all components are finished at this stage before the gluing of the legs, the oiling is left until afterwards.
To complete the leg joint, an oak dowel is turned roughly on the lathe and is finally sized by knocking it through a dowel plate. Cutting into 80mm lengths, chamfering the edge at either end and adding a couple of ‘V’ grooves down the side completes this task.

Gluing up
The final jig is the gluing-up jig. Gluing up a three-legged anything usually presents its problems with no opposing partner to cramp onto, let alone three tapering legs into one boss at an acute angle all at once. The footprint of the table is set out with a compass and the positions of the legs plotted onto a 600mm square board of 18mm ply (18mm MDF proved not to have sufficient integrity). In the image shown (below right) it has been done with differing table diameters and heights in mind. Holes in which the legs locate are drilled to a depth of 10mm. This holds them in position and stops them splaying out as pressure is applied. Three cutouts are then required towards the centre to accomodate the cramp head of a sash cramp.

The joints are assembled using Cascamite. This lubricates the joint in the initial stages of assembly and gives plenty of time to complete the gluing-up process before setting. While the process is straightforward one must be very aware of the stresses and strains put on the legs as each cramp is tightened in turn, to ensure an even pull all round. If the joints have been fashioned accurately, firm but even pressure should suffice to pull the joint together, though every now and again the extra turn of the cramps can eliminate a hairline gap at the shoulder. Because the joint is on a single dowel quite often any gaps on the shoulder are due to misalignment. To eliminate this possibility, a quick rotation left and right under slight pressure will usually find the joint bedding in. The second benefit of choosing a straight grained timber for the legs becomes apparent at this point.

Because of the narrowness of the leg toward the bottom this is where any bending or distortion will occur as the pressure is increased, so keep a watchful eye at this point. In the past I have returned to the workshop in the morning to be confronted by an unsightly pile of cramps and bits of precious timber where one of the legs have failed. Once set, add a small bead of PVA around the rebate on the underside of the top and place the neat fitting top onto the boss. While pressing down firmly, rotate the top a couple of times to and fro for what is in effect a rub joint. All of a sudden the job is done.

The finished Tripod table will be a great companion piece to any room in the home.