Segmented Turning by Stan Knowles

Over the last year an influx of new members has joined our club, this is just what is needed. New ideas have given a new lease of life to the Village Turners.

There are a few members now who are producing segmented turnings and hopefully those numbers will swell. With that in mind I would like to pass on some of the
pros and cons of this type of work that I have been engaged in over many years.

Turning from a blank can be very rewarding and apart from your lathe and tools requires little else. However your time at the lathe is short lived, you may spend four or five hours turning and it is finished. But lf you want to extend the time taken to produce that special turning then look towards segmented work. A segmented turning can take many days, sometimes weeks to make, thereby extending your hobby time and the cost of your wood is no more. Results can be staggering with the patterns, colours and shapes that are possible, the extra cost is in the machinery.

First is the wood you will use, colours are limited, but there are just enough to give a contrast.,They are mostly exotics and as such are more expensive than home grown hardwoods. lt is important you get your wood down to 8% moisture content or one or more woods will shrink below another. Then machinery, a table saw will allow you to both rip and cross cut the wood. A thicknesser will finish the wood all-round to the size you require and of course your lathe. Although a chop saw will cross cut your segments you will still have to rip your timber. Cross cutting your segments on a table saw will require a homemade sled to set up your angles of the segments. lt is important you get your angles dead right or problems will arise Anyone with a computer should take advantage of a design program such as Woodturner Pro, downloaded from the USA. This will give you help with your calculations.

Close segment work. This is when all your mitres are joined together to form a ring. Open segment is when each segment is separated by a gap, the method to do this is completely different to the close ring. There are two basic methods for open segment work, one is the use of plastic or wood discs with thin strips fixed to it like wheel spokes. All the ring segments are placed on the discs and glued to the preceding ring. NB see Lloyd Johnson, Stomper on line. The other is the use of an index system on your lathe and a jig to place and glue the segments to the previous ring; this is the method which I use. This gives you more scope in the
number of segments you can have in a ring.

Your design other than a simple spiral depends on the number of segments in a ring. Example, twelve segments would give three patterns of four, four patterns of three or two patterns of six. The more segments in a ring the more different patterns, say thirty six segments in a ring would give 6x6, 4x9,9x4 and so on. You can just about manage as many as 36 on a 12" diameter turning. Both open and closed work will suit any design with one thought in mind, the edge length.

The edge length, to calculate how many segments you can have in a ring. First you start with the smallest diameter of you work, it may be the base or the neck of a vase. You divide that with the number of segments you would like, as follows-3.1416 x the diameter and divide that number with the number of segments, this will give you the edge length of each segment. You have to decide how small you can cut the segments on your saw, any edge length smaller than 10mm you will find them blowing away by the saw unless you are using miniature saws. With open segment work you have to consider the gap.
Say you have a 10mm segment and a gap of 6mm, this only leaves 2mm of glued area either side of the gap, and this is really pushing your luck, so you have to be realistic, the first few rings on a vase would have to be strong enough to support the weight of the rest of your turning. As the work piece increases in diameter your segment edge length gets longer and the glued area becomes greater.

The way I do close segment work is, I cut half the number of segments required out of waste wood put them together dry into a half ring, hold a straight edge along the bottom of the horseshoe and check that it lies flat across the tails, if it is perfect then your saw is set dead on and you may then cut up your expensive hardwoods. The glue I use is Titebond II . I lay all the ring segments in a row, if there is a pattern involved they would be placed in the right order, apply glue to both edges, starting from left to right apply rubbed joints by holding one and rub the next one back and forth until you feel the grab taking place making sure that the mitre points are dead on. Carry on by making two half rings, leave overnight to set. Next day join the two halves together, you may have to lightly sand the ends of the two halves for a perfect fit. Each ring has to be sanded flat on a disc sander before stacking. lf you do not have a electric sander, cut out a MDF disc mounted on a face plate and fix a 9"or 12"self adhesive sanding disc, by using your lathe as a sander you can face off all your rings. When all rings are completed they are glued together in brickwork fashion stacked one at a time, clamping ensuring they are on centre. Titebond will grab in a few minutes and clamping can be removed in twenty minutes. When you have a pattern great care must be taken that you have the coloured segments where they should be before gluing.
Feature rings, normally in close segment work, these are a central focal point to a vase or bowl. They consist of special patterned panels, usually the same number as the segments in a ring. A zig zag or laminated panels between 50mm to 75mm deep depending on the size of your turning. I usually design the feature ring first and then design the vessel around it. The secret of success with these rings is the absolute centring of the feature ring with the rest of the turning and the matching up from one panel to the next. Chevrons can form a zig zag around the turning but it is vital the points of the chevrons come together at top and bottom. Also if you are the slightest bit out with centring, when you start turning the patterns will be out and nothing can be done to rectify this. lf you are unsure of the quality of your feature panels joining up correctly put a thin dividing strip between each panel, this does not alter the bevel of the segment but does increase the diameter slightly. These feature rings are not for the faint hearted and I commend anyone who has a go.

Many years ago when I started on open segment work I was frustrated with the gluing time and started experimenting with CA or super glues. My worry was how it would it stand the test of time? Would customers bring their purchases back in pieces? I need not have worried. I have never had a failed joint and I have been using it for over twelve years. I use industrial CA medium grade from Star Adhesives. Lincolnshire Woodcraft supplies this brand. One important factor is do not make a mistake in the placing of your segments or you are in trouble. A thirty six segment ring takes me twenty five minutes to glue then face it off ready for the next ring, no setting time. You have to accept that segmented work can be nerve racking at times but that is the fun of it.

How about turning? lf your design is correct, turning is easy. You should have designed your vessel with a wall thickness of not less than 8 to 10mm. This gives you scope to sweeten any curves out, you can take it off but you can't put it on.

As your turning changes in shape the rings form steps, start by removing the steps inside and out. This does not weaken your turning as you are only removing surplus wood, this will also show your wall thickness. Start your turning as soon as you can reach in with your tools, there is no need to complete the vessel, build and turn in stages but always leave the last ring untouched so you can carry on with more rings. On very deep vases you may finish the inside as you go. The outside you finish turning to its final shape and wall thickness, you should not make the wall thickness too thin as you would a solid turning. And always complete the thinning of the walls by starting at the rim and working towards the base leaving the last few lower rings slightly thicker for added strength.

With segment work, you are turning in long grain so your tools will cut very easily, a bowl gouge and side scrapers are the best. A ring tool can be very useful once you get the hang of it. When you are making a vase or vessel with a neck size which is too small to get your hand in you can make it in two halves. You have to be very careful when you do this especially if a pattern is involved. I normally glue the top ring to a temporary base, reverse my drawing and work from top down towards the main turning. This requires dead reckoning on the inside and very careful gluing to eliminate runs. lf you are turning a very deep vessel always bring the tailstock up for support via a jam chuck.

Finishing an open segment vessel. Apart from a large number of segments, you have the same number of gaps, I have found the best finish is oils. There are many different oils to choose from, all of them will work, and I use Danish or finishing oil. Making sure all your sanding is complete; I hold a vacuum close to the gaps and slowly turn the work piece by hand to get rid of any dust. Put a tray on the lathe bed and slosh plenty of oil checking that all the gaps are covered, any surplus oiljust pours out the lower gaps, and I then wipe it off with paper towels. The fact you are covering long grain the oil does not darken the wood. After a few minutes stand well clear and spin the lathe to get rid of any excess oil from the gaps and wipe off immediately, wait about four hours and buff to a high shine. You may need another coat, if so, apply with a cotton cloth. lf you wait a further twenty four hours and apply a good past wax like Black Bison natural, leave for four hours and buff to a high shine.

Close segment work can be done with any finish of your choice.

Laminated work - this is completely different from any of the above. lt involves the gluing up of layers of different woods before turning. Usually starting by gluing strips of different coloured wood about 20mm thick to form a board about 150mm wide, the length depends on the design, it is cut into diagonal strips at a predetermined angle, these are the glued together and cut again and glued together. lt can be very complex and any mistakes in the cutting or in the angles can result in putting it in the bin. There are first, second, third and fourth generation laminates, each generation increases the complexity of the turning and of course errors are multiplied with each generation. A simple form is a goblet , take a piece of walnut say 65mm square by 150mm long , glue a 10mm thick piece of sycamore to each side and simply turn it , you will see four oval or round sycamore panels appear. You must be centred on your lathe or the ovals will be different sizes and the piece is ruined. lt is difficult to explain in words about laminated work as it is very complex and a computer program is really needed to design these pieces. A good program is Laminated Pro from the USA.

l have one or two DVDs in the club showing my laminated work if anyone is interested and several DVDs on segmented work. My largest piece to date is a vase consisting of 1765 pieces and took four and a half weeks to complete. lt was built and turned in one piece without steadies and a lot of anxious moments as the pattern itself was complex.

I hope I have covered as much as possible the complexities of segmented work and not put anyone off, or bored you to death.

Regards, Stan Knowles