Monday 9 July 2018
My Corian bowls have been a great success in my wife's art gallery. Their contemporary design, tactile finish, and the fact they are made from a durable material, has made these unusual bowls very popular. I was aware of expensive kitchen worktops in Corian – I just could not afford them – but it was only last year that I was introduced to it as a material for turning. The owner of a local kitchen worktop manufacturer offered me his Corian off-cuts just before I visited the AAW Symposium in Albuquerque where I saw it being used for the first time for bowl turning.
I must admit that my first attempts were based on my experience with segment construction – it was only later that I realised there was an easier and more elegant way to use this very pleasing material.
Corian is a hard resin-based material that is supplied in 6mm (1/4in), 12mm (1/2in) and 20mm (3/4in) flat sheets. It cuts well on a circular saw and bandsaw, but does not plane. Negative-rake scrapers and tungsten-tipped tools work well, but bowl gouges do not. Unless you are an approved Corian fabricator, you are not allowed to purchase Corian directly from the distributors. However, most main towns have a kitchen worktop manufacturer who normally has a lot of off-cuts available. Alternatively you can buy these off-cuts on eBay. I bought as much as I could take away in my car for Â£40. There is a wide range of colours available; I prefer the solid colours rather than the granite look-alikes.
Tools used: 5mm (3/16in) diamond parting tool, miniature parting tool, internal tear-drop shear scraper, negative-rake flat scraper, 20mm (3/4in) negative-rake round scraper, tungsten-tipped ring tool
We are using 12mm (1/2in) Corian sheet for this bowl – a mixture of Glacier White and Marine Blue. In order to get a 150mm (6in) cube you will need to cut six blue squares 150mm (6in) square and six white squares 150mm (6in) square from 12mm (1/2in) Corian sheet. Cut the squares on the circular saw with a fine tungsten-tipped blade
Then, cut out the middle sections – as shown in the diagram – first of all vertically using a small parting tool and then at varying angles, as shown. Use large button jaws for your chuck which will take both square and round work
It is easier to cut away the waste now, before gluing up, rather than trying to turn the waste later. You can save these centre segments for future projects. Stack the levels up to ensure the cut-outs match the round internal shape
Corian will accept instant glues – Cyanoacrylate adhesives – but you can see the join. DuPont, the manufacturers of Corian, make a Corian two-part resin adhesive which is colour matched to the colour of Corian being used. It dries like Corian and, other than the occasional air bubble, it is completely invisible. I use white Corian adhesive, so all of my work has a white component. The Corian glue is initially quite thick but soon starts to run, so gluing two large surfaces together can be problematic – both with air bubbles and uneven thickness of glue. Like tile adhesive it cannot be cramped – only a small amount of pressure is required before it starts to run away. By trial and error I have evolved a process of building up the composite and gluing that now seems to work in most cases. Each layer is cleaned with an alcohol-type cleaner before gluing to eliminate any grease or dirt – methylated spirits is good. Squirt the glue in a circular motion around the area to be glued – the air bubbles gradually even out – and also apply to the corners to give it horizontal support
Pop any stubborn air bubbles and then add the next layer. Build a corner jig out of 20mm (3/4in) MDF to hold the cube squarely. Repeat for each level to complete the cube. When the glue has cured, after about four hours, remove it from the jig and cut the cube diagonally on the bandsaw
The opened up centre will still have wet glue inside, so leave the two halves for at least eight hours to fully cure before cleaning up
Remove as much of the waste material before mounting on the lathe. Firstly, cut a base using the bandsaw fence to position the top enabling a 50mm (2in) wide base to be cut
Mark the rough shape of the outer rim of the bowl with a pencil and cut off the corners on the bandsaw. Take slow cuts – it will not blunt the bandsaw – but don't push too hard as it will overheat
Use a conical jam chuck made from MDF to centre the inside of the bowl on the lathe, using a small steb centre to centre the base on the tailstock. Use the tungsten-tipped tool to remove the sharp corners from the sides and shape the base. Wear gloves and a visor as the cuttings are very sharp. Corian is non-toxic at normal temperatures so normal dust extraction will work effectively. True up the base ready to accept the chuck plate
Clean up the base by removing the pip left by the steb centre. Reposition on the lathe and glue a sacrificial wooden base that will fit the chuck jaws on to the bowl, using thick instant glue. Revolve the bowl slowly to ensure it is centred on the sacrificial base
Let the instant glue set for four hours before continuing to rough out the outside shape of the bowl
Once the outside shape has been roughed out turn the bowl round on the lathe and mount it on its sacrificial base in the chuck to enable the inside to be turned. If you have one, use a large bowl steady to ensure the bowl is safe whilst roughing out the inside. The base is only small and a snag could easily shear the glue and break it away from its base
As before, use the tungsten-tipped ring tool to rough out the inside shape
As the shape gets closer to the finished design, test it with a simple plastic template that you can make to fit the inner radius. With an offset design, the inside has to be quite precisely cut otherwise inaccuracies will show up in the circular features of the bowl
When the inside of the bowl is close to its final shape clean up the inside with a tear-drop scraper on its side at a 45 degree angle, to remove any ridges
Use a round scraper, cut with a negative-rake, to clean up the inside bottom. A normal scraper can be used but they tend to grab; by bevelling the top edge of the scraper on the grinder to make it a negative-rake scraper, it will not grab and will cut the Corian smoothly. Test the final shape with your fingers. Fingertips are more accurate than your eye at finding undulations in the shape. When the inside shape has been finalised, sand with Abranet discs. These have a coarse texture which allows the dust to escape without clogging the sanding disc. Start at 80 and work up to 1,000 grit. Polish with Webrax and then with Auto Glym car polish on a sheepskin mop head to get a deep, luscious shine. There is no need to oil or lacquer the finished piece as Corian has a very high natural lustre
Once the inside is finished, part the bowl off from the sacrificial base and turn it round on the lathe, mounting it on the MDF jam chuck again. Centre it on the tailstock using a small steb centre, which does not mark the base of the bowl
Rough the outside to an almost finished shape with the tungsten-tipped ring tool and then a negative-rake flat scraper to even out the ridges. Take it off the lathe and check the wall thickness – again, fingers are more accurate than callipers for small bowls. When you are completely satisfied with the wall thickness – I prefer around 3mm (1/8in) – finish off the base and sand the outside for the inside, as before. Polish with Auto Glym and finally remove the centre support pip from the base