Andrew Potocnik lets nature take the lead with this project
For so many of us, the process of turning begins with dry wood that stays stable and ‘behaves’ as we trim away unwanted material to fashion a shape we envision in our minds – and expect it to stay just as it was when it left our lathes. However, in reality wood moves, some species more than others, especially as diameter increases and internal tension is released.
Working with ‘green’ or unseasoned wood provides a whole new adventure riddled with positives and problems, depending on how you see them. I love the idea of salvaging a tree that was cut down in the morning, turning it in the afternoon and drying in the evening to have a completed bowl, the shape of which is determined by nature, rather by me.
There are ways of drying turned bowls. I prefer to allow the wood to dry either in the heat of a summer’s night or in the warmth of a winter’s heated interior while I sleep, ready to see what nature has determined as I was off in slumber land. The joy of seeing what nature has added to my efforts is something to behold, providing it hasn’t taken too much control and twisted the bowl into something that is beyond use. There is plenty of material available in books and online describing how to cut logs to get the most of your material and predict, to an extent, how it will distort as it dries. Alternatively, you could use a technique referred to as ‘twice turning’, or ‘rough turning’, where a wet blank is rough turned with over-sized wall thickness, allowed to dry and then turned again. This requires a turner to have numerous roughed blanks set aside to dry, taking up time and space.
Turning a bowl in the method described in this article will ensure you can capture the most vibrant colour available from your timber, and you’ll also have the tactile pleasure derived from running fingers over undulating growth rings and grain changes. And, depending on the species you’re working with, you may find nature has a few surprises in store.
1. There are many ways you can mount your blank to ensure safe turning. On this occasion I used a ring that then fits into the expanded jaws of a scroll chuck. This blank had been rough cut with a chainsaw some time ago and kept wrapped in plastic shopping bags in a shady spot for when I was ready to turn it. You could cut it into a circle on a bandsaw before mounting, or use a faceplate screwed to the blank ready for mounting on the lathe2. Ready to begin turning, you could add extra support by bringing up the tailstock, however I was confident the mounting method I used was sufficient and would ensure my toolrest could be brought into place with ease. You can see a ripple pattern on the blank’s surface, which indicates there would be substantial movement in the wood as it dries3. Roughing the blank down involved both my larger bowl gouges, one with a swept-back grind, and the other with a fingernail profile. I like to trim down the face of the blank and then work my way around to the edge so the weight is more evenly balanced and I can increase the speed of the lathe slowly. You can see that these cuts disclosed some cracks and imperfections in the wood, which I’d need to take into consideration in shaping the bowl4. As the blank’s edge was roughed, I could see just how deep the cracks were, and how much discolouration there was. I needed to true up the top of the blank and see what the wood had to offer there. I could now increase the lathe’s speed again and remove unwanted material more rapidly5. Time to cut a tenon and begin to establish the overall shape of the bowl. The bulk of cracked material was removed by this stage, so I was confident that my imagined shape would accommodate the imperfections still left in the blank6. I like to use a flat curved scraper to refine the outer shape of the bowl, in this case aiming for a fairly traditional ‘Roman ogee’ profile7. Time to establish how far the burnt border will go and cut a narrow groove with a 9.5mm detail gouge. This cut is only temporary and will be refined after scorching has been completed. Its secondary role is to prevent the torch’s flame from reaching too far into neighbouring wood that is not meant to be burnt8. You can see how the groove allows for severe scorching of the border with only mild burning of wood that will later be ‘cleaned’. Depending on the effect you seek, you could leave the charred surface and seal it to retain the crackled surface, but I haven’t tried this and cannot advise on the process. It is important to follow safe working procedures whenever burning wood in an environment that has many flammable materials. It is advisable to do your scorching outdoors, preferably well away from flammables and with water on hand in case anything goes wrong9. I use a brass wire brush to remove charred material. This, or a stiff nylon brush, will remove residue without leaving marks on the surface as a steel wire brush would. You can also see how the edges of cracks in the wood are ‘softened’, blending with the texture and exposed grain of the wood. Remember to use dust extraction and a face mask to protect your lungs10. To create a crisp definition line between charred wood and the remainder of the bowl’s surface, use a fingernail-shaped spindle gouge or a round-nosed carbide cutter. This groove should be deeper than adjoining surfaces as it will later form a shadow line. A flat curved scraper is used to remove material that was burnt to the right of the shadow line, lowering the surface for two reasons. Sometimes surface material is discoloured by the heat generated in the burning process. The second is to allow the burnt border to stand proud of the overall bowl. Surprisingly, this will not interrupt the visual flow of the ogee shape11. To reduce sanding and add an element of textural sensitivity, the area from foot to burnt rim was treated with a series of incised grooves cut with a 6mm bowl gouge held on a steep angle to create cleanly cut scallops of about 4mm width. These lines also help to accentuate movement that happens later as the wood distorts in the drying process
Fire Safety
When using a blow torch to scorch or burn work it is always advisable to do this away from the workshop, outdoors for preference, and to have a bucket of water or water fire extinguisher close to hand.
When abrading or re-turning scorched or burnt work, a suitably rated dust mask and extraction is advisable; carbon dust is a known carcinogen and, while one-off exposure/inhalation is unlikely to cause any issues, repeated exposure can prove detrimental to health. It is also worth pointing out that a suitable period should be allowed between scorching and abrading so the wood is fully cold; smouldering dust sucked into an extractor is a recipe for disaster.
12. Reversed and held in my scroll chuck, the faceplate ring was removed and the tailstock brought up to the wood to provide extra support while hollowing13. The top of the bowl was scraped to a true, flat surface that slopes slightly down to the centre. This also exposed a wonderful wavy grain that was evident in an earlier photo14. Rather than waste it, I opted to use a centre saver and removed the core for another day. You can simply hollow the inner part of the bowl, keeping the tailstock in place until left with a narrow nub which can be broken free15. I removed some wood from the interior to true up the surface and then power sanded the rim in preparation for burning. The same process was followed as described earlier16. This time it left a lovely undulating surface, enhanced by distortion resulting from the burning process17. I used a 9.5mm bowl gouge to create a sharp entry point to the bowl’s interior and expose the beautiful rich, red colour of the wood, then cut a V-border about 6mm in with a round skew. Definition is key in making visual impact, so make sure all cuts are crisp and precise18. Ready to work on the inside of the bowl; I positioned the toolrest as close as possible to the work surface to provide optimal support for the tool. Remember, the more support you have, the less likely you are to get a catch or chatter, and potentially destroy your work.19. Figure eight callipers were used to check the thickness of both the walls and base. It is advisable to do this regularly so you don’t go too thin, or leave too much wood. I aim for an overall wall thickness of about 6-7mm20. Tools used to complete the interior area were a fingernail profile bowl gouge for the bulk of the final cuts, a swept-back ground gouge for the lower section and a 10mm-thick finishing scraper for the centre portion of the bowl21. If the surface of your wood is quite moist, use a heat gun to gently dry the surface before sanding. If you don’t, the moist dust will clog your sandpaper and prevent the process from going smoothly22. I use a variety of sanding options depending on the situation. A sanding pad fitted to a drill removes lots of wood quickly and can run either clockwise or counter-clockwise. This can be handy if you have some difficult grain to deal with. An inertia sander and hand-held sandpaper were also used as I worked my way through to 320 grit. The bowl will not be sanded after it has dried, so the surface must be perfect at this point. Don’t forget to position your dust extractor chute as close to the area you’re sanding as possible23. Having sanded to a crisp, sharp edge, a light sand with 320 grit takes just enough wood away to leave an edge that is sharp visually, but not to the feel24. To complete the foot, the bowl was reversed and pressed up against a padded carrier fitted to a faceplate and held in position with the tailstock. If you have a vacuum set-up, it would work perfectly in this situation25. The foot was trimmed down just enough to remove chuck marks and the centre hollowed leaving just a small stub. A V-groove was cut with the detail gouge, but you could use a skew. Other tools used at this stage were the bowl gouge and round-nosed scraper, which made easy work hollowing the foot26. The stub was carved away and the surface sanded smooth27. The bowl initially weighed 750g, but after a few days of drying it over the heater indoors in winter, I decided to help the drying process on its way and gave it several zaps in the microwave. I’m not aware of any formula that determines how long to ‘cook’ and at what setting, so I used the medium setting for four bursts of three minutes, allowing the bowl to cool between each burst. The final weight was 670g – a loss of about 11%, but please forgive me for my mathematical inadequacies28. Although this bowl didn’t distort as much as expected, the base need to be flattened, which only took a few passes on a sanding board fitted with 120 grit29. I like quick and easy finishes, so a couple of coats of a food-friendly oil were applied, allowed to soak in and residue wiped off – and that’s it
Conclusion
Turning a bowl is down to personal preferences. Do you like to turn bowls of freshly cut wood that will distort as it dries and be happy to deal with what nature provides, or do you allow the turned form to dry and then turn it down to a true circular form? The choice is yours, but you may well guess where my preference lies.
Examples of distortion
30-32. These show how some species, such as European oak, can distort extremely as they dry and introduce a wonderfully organic aspect not associated with turning. Dimensions are 168 x 156mm, which equals about 8% shrinkage across the grain. The difference between the peak and lower edge of the rim was 13mm31.32.33-35. These show red gum turned from much wetter timber than that used in this article. The bowl contracted much more across its grain than along it but, contrary to the oak bowl, the sides did not pull down and stayed somewhat level. Don’t expect every piece of wood, or even every species, to behave according to your desires, because nature has its own plan in place. Dimensions are 232mm long x 209mm wide, which equals about 10% shrinkage across the grain34.35.36. This shows how things can go wrong and distort in ways that defeat the functional aspect of the bowl and challenge what the majority of consumers see as an item they can use. Some of us can see how this form still has its own element of beauty, but the market generally says otherwise
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