Router Guide Pt 3
Wednesday 22 October 2008
Andrew Lawton continues looking at routers for furniture making
This, the third instalment of the series, will look at some further applications of the router as a hand-held machine in the pursuit of fine furniture-making, including a few typical uses for some of the various types of cutter described in the first part of this series.
Rebating with a bearing guided cutterIn many situations, it is easy enough to cut a rebate with a simple straight cutter, using the router fence to keep the cutter parallel to the edge of the workpiece, always being mindful of the chances of spelching and taking steps to avoid this, as described in my previous articles.
There are situations, however, when it is awkward to work with a fence - for example when rebating a convex edge such as a circular table top to allow stringing to be applied. Or it can be impossible - as is the case when a rebate has to be worked on a concave edge. We had just such a problem recently on some glazed cabinet doors which had a curved top rail. An effective way of performing these kinds of operations is to use a bearing guided cutter, such as one from Trend (C040), which has comes with three alternative diameter bearings as standard to give rebate widths of 7.9mm, 9.5mm and 12.7mm, with other diameter bearings available to order.
In use, the bearing simply follows whatever shape the inside edge of the workpiece is and the cutter obviously cuts a rebate parallel to this. If a deep rebate is being cut, it should be done in several passes, and backfeeding is recommended to prevent spelching.
Groove cutting for inlaysSmall cutters with diameters of 2mm, 2.5mm and 3mm are great for cutting fine grooves to accept inlays, or stringing, of a contrasting coloured wood, which, if not overdone, can be a wonderful visual device at the furniture-maker's disposal. Such small diameter cutters tend to leave a channel which is clogged with frass on a single pass, necessitating a second pass to clear the debris. This second pass can be done in two ways: either by working in a series of short forward cuts followed by backfeeding to clear the waste, or, the method I prefer, in which the full length of the cut is made, then the cutter retracted clear of the timber, followed by the second pass. Neither method is ideal: the risk of the router running away when backfeeding can damage the workpiece and both methods add time to the job.
I was intrigued, therefore, to learn from Mark Applegate's experience with what I believe is a fairly recent innovation, the up-cutting spiral cutter, which he used on his oak chest of drawers.0. The spiral design of these cutters makes them very efficient at clearing the waste and leaves a clean, accurate groove after just the one pass - see photos for comparison. Unfortunately, the smallest spiral cutter available at the time of writing has a diameter of 3mm, which is too wide for very delicate stringing.
Freehand routingSo far, we have looked at the router as a hand-held machine, guided either by its own removable fence, some form of guide or straightedge, or with self-guiding cutters. As well as in these modes, it is useful to be able to use the router entirely freehand on occasions. This calls for a greater degree of control and should not be attempted until one is thoroughly at home with and familiar with one's particular machine.
Generally, I find I use the router freehand in the following situations: when cutting wide housings and large mortices in carcasses. In both cases the reason is to work with greater speed. For example, if the two outer, or defining, cuts of a wide housing are machined first, using a fixed guide, then the waste portion in the middle can sometimes be removed more quickly by working without the need to keep repositioning a guide, though I would say there is less of a time advantage in this now, since the advent of the various proprietary clamp guides. Secondly, it is often useful to be able to cut big, but relatively shallow, mortices in carcass sides by carefully guiding the router by hand, then squaring up afterwards with a chisel. In these situations, the router is much more controllable if held by its base instead of the handles, but since one's fingers are that much nearer to the cutter, a good deal of experience with routing, along with great concentration are essential.
Edge mouldingMoulded edges, often based on classical moulding, feature prominently in traditional furniture and the less ornate profiles still have a place in contemporary work. At one time all of this would have been done, laboriously and expensively, by hand, using wooden-bodied moulding planes, but the router has liberated us from all that - or at least given us a choice! In my experience, most furniture-makers rarely, if ever, need a spindle moulder to get the right results. If anyone is in any doubt, look at what Paul Richardson has achieved with a router in his book Making Classic English Furniture.
The three types of cutter which are used for all the various moulding work we do, whether on the edge of a workpiece or its face are the shaped, pin-guided and bearing-guided cutter. Shaped cutters must be used against a straightedge or in combination with the router fence, which allows them to be used anywhere on a furniture component, not simply along an edge, as is the case with guided cutters.
At the time of writing, I am making a TV and video cabinet of MDF, later to be dyed and lacquered, the design of which calls for no applied handles. Instead, a cove moulding has been worked along the top edges of the doors to provide finger-grips, using an 18mm radius cutter guided by the fence. The resulting moulding has been stopped at an appropriate point rather than having to be run right through as would have been the case if a moulding plane had been used. As in previous operations, backfeeding gives a cleaner cut.
Pin-guided cutters follow the profile of the workpiece, whether straight or curved, but the fact that the guide-pin is an integral part of the cutter and rotates at the same speed, is a drawback; since the router must be held firmly against the component to prevent a ridged or uneven finish. The friction caused by the pin rubbing against the timber all too often leaves a scorched edge. When the component is straight, it is good practice to use the pin in conjunction with the router fence, so that there is scarcely any pressure between pin and workpiece, thus preventing scorching.
Bearing-guided cutters are much more satisfactory. Not only is friction eliminated but alternative bushes can be fitted to change the profile of the moulding, in a similar way to the rebate cutters described earlier. Note in the photograph how the same cutter can produce a roundover moulding and an ovolo simply by changing the bearing.
Next time we will investigate some simple jigs and router tables, which open up a whole range of new possibilities. Keep routing and stay safe!