Eccentric turning can produce some fun and interesting results, but many turners are put off trying by not understanding the potential of using an off-centre turning device. Here we give an introduction to the basics and the potential of the Sorby RS60 eccentric turning chuck. Before attempting off-centre work, a beginner should of course master the basic skills of woodturning, then when these are understood the way is open to explore the fun of eccentric work with problems such as occasional cutting and imbalance of work not raising a problem to the open door of this odd and intriguing area of work. That said, the Robert Sorby RS60 eccentric chuck allows anyone with a modicum of skill to produce bizarre bowls, wobbly goblets, contorted candlesticks and complicated cabriole legs. And, of course, there is plenty of scope beyond. It will be patently obvious to anyone who already owns the RS60 chuck that the booklet supplied with it, although running to 12 pages, does little more than touch on the subject of eccentric turning. However, a more expansive booklet would likely cause the reader verbal indigestion. When demonstrating this kind of work I am often asked by prospective purchasers if Sorby have any literature on the chuck and I am always worried that, if I was to supply such a booklet, it would probably put them off buying because it sounds too complicated — it really isn't. As Darwin said, when he propounded his famous theory: "Evolution is only a problem of the imagination". So it is with off-centre turning, especially if combined with indexing as the Sorby device allows. Let's start with a look at the chuck itself. The RS60 allows wood to be turned in infinite increments up to 35mm off-centre, and there is a window in the side through which the graduations (marked in 5mm increments) can be seen.The eccentric boss can be locked in any position by the two locking screws in the side of the body, and the workpiece can also, if required, be indexed in any one of 12 positions. Each workholding adaptor has a hexagonal base which fits into a double hexagonal hole in the eccentric boss and locks into position with a screw from the back. There is a datum mark on the bi-hexagonal hole and an indicator mark on one corner of the hexagonal adaptors. This allows you to imagine the bi-hexagon as a clockface so that you can always keep track of your indexing. The workpiece can be fixed to the chuck in any one of three ways.The first is with the screw chuck adaptor which requires just one hole to be drilled into the wood. Second, there is the faceplate adaptor requiring four screws. Lastly, there is the ball and socket adaptor.This latter method, unique to the RS60, is used in conjunction with the tailstock, and allows the workpiece to be set so that only one end of the wood is off-centre, and this facility opens up a whole new range of possibilities. For example, a piece could be turned which has, say, two or more sides at the headstock end, blending into round at the tailstock end. It is a method that can also be used to produce cabriole legs. Before commencing any eccentric project, I would always recommend that you draw an end on view of what you propose to do, using a pair of compasses.This will tell you the size of the timber you require, which is often bigger than you would think. Alternatively, draw the cross-section of your blank, and use the constraints of the timber size in which to contrive a design. For anyone whose geometry is not so hot, Fig. 1 shows a simple project. This should help make everything clear. For this you would need a blank of wood 200mm (Sin.) in diameter, SO to 100mm (2 to 4in.) thick. Open a pair o^ compasses to 100mm and draw on a piece of paper, a circle 200mm in diameter. Now set the compasses at 3Smm and with the same centre and draw another circle in the centre of the first one to represent the maximum offset available. Without altering the setting, place the point of the compasses on the circumference of the inner circle and draw an arc, cutting the circle. Place the point of the compasses on this intersection and draw another arc cutting the circle. Do this four more times and you will have divided the circle into six. Mark off three alternate divisions. Open your compasses to 5Smm and place the point of the compasses on one of the marked points, and draw a half- circle outside the inner circle. Repeat with the other two points.Your drawing should now look something like a clover leaf. Open the compasses to 120mm and, using the same three points, draw three arcs across the furthest edge of the outer circle. From the completed drawing, it now becomes obvious that this is a bowl or platter you could produce with the RS60, using the full 35mm offset and indexing every fourth division. (Remember to mark them with a felt tip pen before you start.) Once you have tried for yourself the project shown in Fig. I, you might think it would be a simple and logical progression to produce a bowl or platter to the design shown in Fig. 2. However, try drawing it first. You will very quickly discover that it is not quite as straightforward as it appears. It could still be done, but you would need to use the faceplate adaptor and, after first completing the outside, you would then have to remount the workpiece to do the inside. I suggest that only by drawing the design first would you discover this. The drawing will also make something else apparent. After mounting the blank to the chuck, set the chuck to zero so that the blank is not off-centre.The bulk of the waste material can then be removed as in Fig. 3.This will greatly reduce the weight and therefore the imbalance when the off-centre work is commenced. I should point out that the foregoing is not suggested as a project, especially for a beginner on a small lathe, but is rather intended to show the importance of drawing the proposed item first so that you have a clear picture in mind of what it is intended to produce before going to the lathe. Off-centre inevitably means out of balance. The degree of imbalance is directly proportional to the weight of the workpiece plus the amount of eccentricity, and this is relative to the total revolving weight or, more simply, the centre of gravity of the total revolving weight. It stands to reason then that the heavier the chuck, the nearer to the axis will be the centre of gravity or, the heavier the chuck, the less the imbalance and therefore the less stress to the bearings of the lathe and your nerves! Weighing in at 2 1/2 kgs (5 1/2 Ib), the RS60 is good in this respect. Included in the price of the chuck is the thread adaptor to suit the shaft of your lathe. If you change your lathe, you simply change the adaptor. The Robert Sorby RS60 Eccentric Chuck is a truly advanced system for off-centre turning and I hope that prospective eccentric turners can now more readily visualise the concept and have a go. Expand your horizons!