Deconstructing Carlton House Desk Fluted Legs archive
Thursday 9 June 2011
John Bullar combines modern machines with old world ingenuity to produce tapered fluted on tapered legs
Tapered fluted legs, where the flutings themselves are also tapered, are the subject of this article. Neither a scratch stock nor a conventionally guided router produces this effect directly but a combination of techniques is used, as you will see.
The leg design is based on the Carlton House Desk, but similar techniques can be used to create radial flutings on other furniture, whether the style is classical or innovative.
Architecturally soundWhat is it about antique furniture that is so enduring? One of the answers for me is that there are certain 'signature features' that are fundamental and visually satisfying. The fact that each item is made to a well researched set of proportions is very helpful, but even those items which break the rules of proportion can be lifted by the presence of one of these signature features. In this series we will show what we think are some of the most interesting examples.
The original Carlton House Desk was designed for George IV when he was Prince Regent. He lived at Carlton House, which no longer exists, but Carlton Terrace does. The superstructure of the desk is said to resemble the architectural curvature of a terrace of buildings.
After the Prince Regent's desk was made there were other examples made, but this desk is not a common piece of Regency furniture. It requires a rather large room and ideally to be in the centre of the room not against a wall.
Such a grand item offered the maker the chance to show off. The result were elegant downswept wings in fancy veneer, a curved outline and amongst other features, the difficult to make tapered flutes.
Reclaimed mahoganyUsing re-claimed mahogany seems to me desirable. This process recycles a valuable resource and gives you access to practically unobtainable material in a well conditioned state.
The best quality dark red mahogany (Swietenia mahogani) (Khaya ivorensis) used in Georgian furniture was felled in vast quantities from mature forests on the island of Cuba. This was followed by closely related woods from Central America. As over-felling depleted these, unrelated paler species from Asia were often sold as mahogany as well as some re-planted Asian Swietenia mahogany from young trees.
Wood you might obtain from a discarded 'mahogany' tabletop, could vary enormously in properties and appearance. For thicker sections, straight-grained mahogany can easily be laminated up without obvious joint lines. A viable alternative for this type of work is to select walnut (Juglans) heartwood, much of which is in sustainable production.
Tapered legsThe narrow tapered ends of the legs on this piece are sized to fit the cups on brass castors. Precise fitting comes later but at this stage it's important to ensure there is no shoulder or gap at the top of the cup.
Some makers use jigs or wedge-shaped shims to guide the wood while rip- sawing a tapered length. I prefer to mark out the taper with a pencil line then follow it by eye, steering the wood through the bandsaw table.
The final shape of the taper can be planed on a jointer, but mahogany is such a pleasure to work I wouldn't miss a chance to use the hand plane. Increase the taper angle by planting the plane down near the narrow end, making a series of longer strokes. Reduce the angle by lifting the plane partway through the stroke. Finish with full-length strokes to remove steps in the surface.
Fluting jigThe fluted grooves on the leg are cut using a 3mm diameter round-nosed cutter in a small hand-held router. This requires a long jig consisting of a base-plate and a pivot arm, both made from MDF. The arm will steer the cutter along the flutes so they converge at a focus point where the pivot is. The same point where the lines
Mark lines following the sides of the leg on to the base-plate face. Use a straight edge or long steel rule to find the point where the lines cross. Drill this point and secure a long steel bolt to it as the pivot pin.
Drill a metal plate (I used half a butt-hinge) with a hole so that it fits over the bolt with no slack. Screw the plate onto the MDF arm so the pivot hole is just over the edge.
Screw and glue a narrow MDF guide fence to the arm. Position the fence so that when the router base runs against it, the router cutter follows a line passing through the pivot hole.
The base-plate has a side rail fixed on the edge of it with screws and glue. The tapered leg is clamped between this fixed rail and a free side rail on its other side. These hold the tapered face of the leg flush with the tops of the rails and the underside of the pivot arm.
An additional rail fixed at the edge of the base-plate provides extra support to improve the stability of the arm.
Marking outThe fluted lines on each leg finish at the top end in a semi-circular stop. This will need to be hand cut later but it is marked out before routing so the router can be plunged just clear of it. I used a shaped steel cabinet scraper of convenient radius to mark the line but you might for example use a suitable tin lid or else mark an exact radius with a compass.
The centres of the fluted lines are carefully marked out just below the stop line. I first drew a line, 1mm from the outer side of the leg. This extra millimetre provides space for the increased width of the flutings at the top of the legs.
I set the dial calliper to one fifth of the width of the leg at this height and then marked out four equal spaces from this line for the positions of four flutings.
In principle, the process of fluting is simple enough, but the work is fine and needs careful control of the router to avoid any wobble or slippage.
I like to check out the alignment and rehearse the process on scrap material before using a newly constructed jig like this for the first time. That way, any teething troubles will not result in my wasting a carefully prepared piece of prime wood.
The pivoted arm is clamped onto the face of the tapered leg so as to position the cutter on the first of the centre lines. A single pass of the router produces a parallel-sided U shaped groove.
In order to taper the groove itself, the arm is re-clamped one millimetre to the side of the centre line and a second pass of the router is made. This results is a groove 4mm wide at the top, tapering to just over 3mm at the foot.
Scraping flutesThe next stage is to clean out the fluted grooves. The base of each groove, having been made by two U shaped cuts, will have a slight W section to it. There are also chatter marks left by using a rotating cutter. A normal scratch-stock is unsuitable, both because of the varying widths of the grooves and their varying positions relative to the tapered sides of the legs.
I used a small elliptical scraping tool to finally shape the section of each fluted groove. The radius of the scraper was slightly bigger than the groove at its widest point. To fit the scraper into the groove I twisted it at an angle, first in one direction to scrape one side, then in the other to scrape the second side. As I ran the scraper down the groove I increased the angle so that it continued to gently scrape the base and narrowing sides of the grove.
Work like this is largely done by feeling, as you can't hope to see the cutting action until the scraper has passed. Keep the pressure gentle to avoid damage if the scraper catches. Ensure that the simple tool produces long, fine shavings rather than dust by having it sharp. It's not necessary to hook the edge as you would with a straight cabinet scraper, a right-angled arris will cut cleanly.
Stopping flutesAt the top end of each fluted groove is a stop where the router was plunged, just ahead of the arc line marked out in pencil. The top end of each fluting needs to be hand worked to continue up to the pencil line.
I made a miniature round-ended paring tool by re-grinding an old square shafted bradawl. This improvised gouge, together with a fine-ended carver's knife, enabled me to continue the flutings up to a tidy stop on the arc line.
Fitting castorsObtaining a good fit between castor and the end of the leg is essential if the castor is not to work loose with time, floor motion or wood movement. Make a cast of the inside of the cup on top of the castor using modelling dough. That way you can shape the leg end to match, being confident that the angles and dimensions are accurate.
Drive the castor cut securely onto the leg, either with a long cramp or a mallet, before boring pilot holes and fitting the brass screws to secure it in place.
MorticingThe upper part of the leg has square section parallel sides, the tapered section finishing just above the stop lines of the grooves. This provides straight-sided shoulders for mortise sockets to take tenons on the horizontal rails of the desk. Chopping mortises in mahogany by hand is very satisfying if you can spare the time. Itâ€™s also less likely to crush the fibres around the socket than a hollow chisel mortiser.
Flutings on this fine scale are clearly a Georgian or Regency feature, but by varying the proportions you might choose to adapt this technique to other periods, or possibly your own innovative designs.