Eccentric Turning, Using Chucks:
Richard Findley tries out eccentric turning chucks.
I am taking a look at a couple of eccentric turning chucks that are currently on the market. I received a parcel from Robert Sorby and another from Axminster, two of the biggest players in the woodturning supplies game in the UK. I should make it clear right from the get-go that this is not a product test and with the limited space I have to write an article there is no way I can use either product to its fullest potential, but I wanted to have a play with each and see what I could do with them.
These two chucks allow a work piece to be moved and adjusted in orientation and in a number of other ways within a set range allowed by each chuck. A little research shows that any number of variations and shapes can be made in both spindle turned and faceplate type work. In theory, the cuts should be no different from any other form of turning, the challenge is working out how to position the work in the chuck to create attractive and useful or decorative items. Can I do it? We shall see!
Having never done this sort of thing before – which is the whole point of this series of articles – I feel like I should do a little research into what can be made and exactly how it is done. Bearing in mind I made a box with a finial last month, I feel a slight change is in order, so my thought is to make a bowl of some sort and something else on the other chuck, but what? A dilemma like this will either inspire or confuse and unfortunately, for a while at least, I am at something of a loss as to what exactly I should make until I realise that in the box from Sorby is a DVD with instructions and a couple of step-by-step projects using the chuck.
The DVD is informative, if a little slow, so I skip through some, making sure I have the gist of it. This helps give some understanding of how the chuck works but none of the projects really inspire me. I decide to search for videos relating to the Axminster chuck and immediately something comes up that catches my attention. An Axminster video shows the lid of a box being made that looks, at first glance at least, to be turned on an Ornamental lathe. I’ve always had a fascination with Ornamental turning and to be able to achieve this look without making a Holzapffel-style lathe really speaks to me.
My decision is made, I will try to use the Axminster chuck to produce a design that looks similar to an Ornamentally turned pattern. I will stick to my original plan and use the Sorby chuck to turn a bowl with perhaps three separate dishes, which could be used as a nibbles bowl for a party.
Before I begin the projects I will take a quick look at the chucks themselves. It should be pointed out that these are not the only eccentric chucks on the market, but they are certainly the most readily available, from two of the biggest UK manufacturers.
The Axminster chuck is sold as an ‘eccentric spiralling chuck’ and is relatively small and lightweight, comprising of three parts: a steel faceplate ring that fits onto their standard ‘C’ jaws, this is drilled with threaded holes which allow multiple positioning. There is an aluminium section that fits to this and also fixes to a smaller aluminium boss which is drilled like a faceplate to allow fixing to the work piece and is fitted to the main chuck in such a way that it can be rotated through 12 indexed positions, allowing further adjustment. It comes with the necessary Allen keys and an instruction sheet. There are a number of online videos showing how to use it but these aren’t pointed out on the literature.
The Sorby chuck is a much larger and heavier chunk of metal. Sorby explain that this helps to counteract the unbalancing effect of offsetting the workpiece. The kit is supplied in a plastic carry case, complete with instruction booklet and DVD. Like the Axminster chuck it has a faceplate fixture, but also a screw chuck and a kind of ball and socket connector, which adds a huge variation to the possibilities of work holding and with a range of movement more akin to the technique I used last month, but with a wider choice of options, variations and movement. The fixing attaches to the main chuck body that screws directly to the lathe (an insert to match your lathe is available, there was even one to fit the odd ball spindle thread of my old Wadkin lathe) and can easily be set to actual centre by adjusting two grub screws and through a small viewing window where a very clear number shows how far from true centre you are; 0 being dead centre, and marked adjustments are easily made at 5, 10, 15, 20, 25, 30 and 35mm from actual centre.
The fixing method itself can then be rotated as it is positioned though a 12 section hole, allowing easily indexable rotation.
Before actually starting my projects I mount a scrap of timber in each chuck and make some adjustments to draw circles on the face of the wood in an attempt to better understand how exactly these chucks work. My difficulty with this kind of work has always been understanding and visualising the effect that the adjustments have on the work. Trying a series of positions and making what may appear to be a series of random circles on the piece of pine (Pinus sylvestris), I feel I have at least some understanding of how these chucks work.
You will see a series of circles, which interlink and curve out from the centre. It was clear that by adding rotation to this, something both chucks have the ability to do, interesting patterns will emerge.
Spiral pattern – Axminster chuck
I should say before I begin, I chose to do this pattern with this chuck, purely because this was shown on the Axminster YouTube channel. I am certain this or a very similar pattern can be made on the Sorby chuck too.
I pick a piece of American black walnut (Juglans nigra) to use as a potential box lid and use a freshly sharpened point tool to cut the groove detail. First I cut an outer border with the chuck set on dead centre. The first adjustment is to reposition the outer ring. There is a choice of four positions either side of centre. The movement range at first appears quite small but has a significant effect on the end result. The downside to this chuck is that to adjust it you need to remove one of the screws, which would be easy to
lose in the shavings. I use a pencil to draw a circle on the wood, working out the correct position for the pattern. With this set I can turn on the lathe and cut my first circle with the point tool. To achieve the desired pattern I now leave the outer ring of the chuck in the same place and make the adjustment by rotating the central boss. This is clearly indexed and locates firmly in each position. I mark position ‘1’ so I can keep track of each movement. I turn circles on each of the 12 positions but could easily have achieved an interesting and, I’m sure, effective pattern by only using every other position.
Once all 12 circles are cut, I re-centre the chuck and sand the surface to remove the remnants of pencil and tidy it up. A coat of oil darkens the walnut and emphasises the pattern. The pattern is far from perfect, but
as a first attempt I am very pleased with how it turned out.
Health and Safety – Turning out of balance work pieces
The off sets that these chucks can produce can create some spectacular results but great care needs to be taken when doing this as off setting the work will introduce vibration to the turning process, depending upon how much you off set the work, your lathe and how it is set up. I use a 1950 Wadkin RS8 which weighs in at around ¾ of a ton, making it incredibly solid and perfect for this kind of work. A mini or midi lathe is likely to struggle with some of this work. As with any work that is new to you, the best advice is to start on a slow speed and gradually build up as you feel safe to do so.
Three dish bowl – Robert Sorby chuck
I sketch my original idea on a scrap of paper, it is to turn a circular bowl with three separate dishes, allowing perhaps a different flavour of crisps or other nibbles to be placed in each. I should also point out that I realised just in time that I would need to fix the bowl with either a faceplate or screw chuck, but as is the norm these days, don’t want holes in the base of my bowl, so glued a sacrificial block to the underside of my maple (Accer saccharum) bowl blank. In hindsight I would have used a block that was just thick enough to hold screws but thoughtlessly grabbed the first offcut of timber that came to hand. This meant that 50mm of pine stood between the chuck and the bowl blank and did add to the distance between the bowl and the spindle bearings. As it is, my large lathe was able to handle this but a smaller lathe could struggle with additional vibrations.
I true up the blank with the chuck set to true centre and smooth the face of the bowl and add a slight curve to the surface, aware that too much curve here can make a bowl look like it droops, so I only cut a slight gentle curve. I roughly sketch the three circles to show where I want the separate dishes. Many of the designs I saw when researching had three dish shapes overlapping, which looks good but isn’t quite what I have in mind. I slacken off the two grub screws that allow the chuck to offset by the maximum 35mm, and draw a circle on the face of the bowl. I then rotate the screw chuck boss, which is divided into 12 positions,
by four ‘clicks’ – 12 divided by four giving the three positions for my dishes. I then draw my second circle, repeating this action to mark the third. It is clear to me that the three dishes are not as large as I’d originally hoped, perhaps being better suited to condiments than crisps, but I continue anyway, re-purposing my bowl as a condiment bowl rather than a nibbles bowl. This issue is less down to the chuck, and more subject to the laws of physics and my imagination running away with itself!
Turning the dishes in the bowl is quite straight forward, using a bowl gouge to cut the shape and sanding it before moving on to the next dish. Once again the mass of my old Wadkin lathe allows this large offset with barely a hint of vibration at 950rpm, but clearly a smaller lathe would struggle with this.
Once all three are turned I return the chuck to true centre – again, easily done thanks to the well thought out design of the chuck – and carefully re-sand the face to remove any trace of pencil lines. The outer shape of the bowl is then turned and finished in the usual way, I decide on a soft curve that fits the hand well and could be passed around at a party. Guacamole, salsa and sour cream, anyone?
As with every project I tackle in this series, the end result is the first of its kind that I have made and as such is full of faults, to my critical eye at least. If I was to do either project again there would be changes and alterations made to improve the end result. The bowl turned out a little differently to my initial plan and is a bit plain but was a good exercise. Making it has opened my eyes and indeed my mind, to a few other options that I would be interested to explore. The ability to turn what appears to be an Ornamentally turned design has really piqued my interest and I hope to be able to use this again in the future.
As far as the chucks are concerned, both are very well thought out and well engineered pieces of equipment. The Axminster eccentric chuck is the more basic of the two, but is capable of doing a variety
of off-centre turnings. The Sorby model is more expensive, but you get a lot more equipment in the box, giving a greater choice of mounting options and position variations. As I stated earlier, there is no way I could do either chuck justice in this article and both are clearly capable of far more than I have shown. If off-centre, eccentric turning interests you, I wouldn’t hesitate to recommend either chuck.