Rough Turning and Finishing Bowls
Colwin Way gets hooked on rough turning on a small scale, and achieves a fine finish on his dried blanks
In this article I will focus on small scale rough turning; although I will also show how to finish off the dried blanks too. I want to approach the subject from the hobby turners’ perspective and look at techniques that we can all tackle.
I have fond memories of rough turning as an apprentice, with shavings mounting up as high as my shoulders around me and the delight of turning wet wood as it ribbons off the gouge! At that time we used to convert whole trees at a time, mainly into salad bowls as that was the scale of the operation in which we worked. We timed our rough turning by the seasons: we wanted to do most of this work in the autumn so the bowls could dry during the winter and spring. For larger pieces this process is really important, as the shock of the summer sun would dry the bowls out far to quickly and cause a lot more losses in terms of splitting.
The hobby turner is unlikely to have the ability to convert large trees, have access to kilns, band or chain mills and large scale storage is not an option. The scenario I’m looking at is this: you’re in the right place at the right time, you’ve driven past a council workman as he’s pollarding cherry trees or a friend has heard you’ve got into turning and dumped some logs on your drive! These are typically small logs of timber that you can lift easily and quickly.
What is rough turning and why is it needed?
Rough turning is the process of part turning a piece when the timber is green, i.e. wet, in order for that piece of timber to dry more quickly without stress build up and the potential for splitting. In this article we’re looking at bowl blanks. When most people start out in turning, they don’t realise that timber can be turned wet, which part of the tree a bowl blank comes from, nor the processes needed to dry a piece ready for use.
The general rule for drying planks is 25mm per year plus one year. This means for example that a board of 75mm thickness will take roughly four years to dry and a 100mm board five years. Boards much thicker than this however won’t really dry out in the core. So if you want to turn large salad bowls or don’t have storage space, then rough turning is the way forward.
There’s also a financial reason for rough turning: wet timber is often very cheap or free compared to seasoned bowl blanks, which can be the most expensive way of buying your timber. I would also argue that the process of turning wet wood is such fun that you will be hooked after your first bowl.
Before we start cutting, splitting and turning, it is important to consider possible hazards that lie within the timber you are working on. This picture (below) shows a stunning piece of brown oak (Quercus robur) which was hiding a fist-sized piece of flint, completely concealed within the timber. The flint only revealed itself when my bandsaw blade began to screech at me in severe pain. It’s not uncommon to find barbed wire, nails, shrapnel or stones that have been enveloped in the tree over the years of growth. Inspect the logs before you start work on them.
Can I rough turn any timber?
The answer to this question is yes, however your success with some timbers will be better than others. Ash (Fraxinus excelsior) tends to rough turn extremely well, giving you very few failures. At the other end of the spectrum is eucalyptus (Eucalyptus spp.), which is very difficult to dry successfully. Most of the common timbers like beech (Fagus sylvatica), sweet chestnut (Castanea sativa), ash, sycamore (Acer pseudoplatanus), walnut (Juglans regia), elm (Ulmus spp.), oak and plane (Platanus x hispanica) all dry well. Fruit timbers on the other hand can be a little more unreliable and your failure rate may rise.
Have a plan
The timber I’m using here is a small oak tree measuring 200mm diameter at its largest point. It’s nice and straight with a striking contrast between the heart and sapwood as well as having a highly figured grain. I like to have some sort of plan as to what I’m going to get out of the lumps I’m about to split. This will largely depend on what you like to turn: natural edge or standard bowl shapes, hollow forms or tall vase shapes. Due to the lovely contrast between the sap and heart wood, I’m going to make sure we have a good selection of natural edge and standard bowls. I’ve marked the end of this log to show you where the two types of bowls come from, the one on the left of the log being a natural edge and on the right a standard bowl shape.
Preparing your blanks
The first approach we’re going to take is the simplest and is especially good if your log is a bit to big to take to the bandsaw, or indeed if you don’t have a bandsaw. Inspect your log section to see if there are any natural cracks you can follow and align your axe or wedge to these. It is important that you spread the load when splitting, moving the wedge along the line you want to split. If you don’t do this, you may find that the split veers off to one side. If you’ve ever split a concrete block with a bolster, this is the correct technique to adopt. Once the split has started, chase it down with the wedge to keep it on the right track. A second wedge may be needed to keep things straight.
In the picture below you can see the log has been split nicely down its length, showing the two toned hart and sap wood and ready for the bandsaw. If you’re unsure what you want to make or you’re short of time, this is the first thing to do with all of your logs. At this point, the end grain can be painted with paint or PVA and the logs left to dry. Halving the logs likthis takes away a lot of the stress and movement is able occur whilst keeping the full width of the tree intact.
Now that the logs are in a manageable state, we can cross cut them to size, checking the end grain for any splits and cutting back if required. Measure the width and cut to the same length using the split flat section on the bandsaw table for stability.
You can clearly see where we can take our bowls from. If making a standard bowl, nature has helped us in providing a natural curve. Turn the piece upside down and you have a wavy natural edge with
a white sap and dark hardwood running through the middle.
Choosing the right blade
The correct blade for the job is very important and especially so when cutting wet timber. I tend to go for fewer teeth of around 4tpi, which gives more clearance and is less likely to clog with the wet dust and sap. For all the straight cuts in cross cutting and ripping, use a wide blade (in this case 13mm) which helps to keep the cut straight. For curved cuts such as cutting out your round bowl blanks, my preference is for a narrower blade of around 6mm. You also need to clean the blade and bearings regularly with resin cleaner as you will quickly build a coat of resin and dust.
Crosscutting logs on a bandsaw or with a chainsaw can be very hazardous and must be done with extreme care. I would not encourage anyone or advise anyone to use a chain saw to do this unless they have had full training. Crosscutting round log sections on the bandsaw must not be done free hand as the log will spin, potentially taking your fingers or hands into the blade. To crosscut our log section, we’re going to use a large cradle which will support the log preventing any movement. The cradle is made up from a piece of 9mm plywood and several wedges secured with screws. For extra security, a strap clamp can be added around the cradle and timber. Your hands need to be placed at either end of the log and well out of line of the cutting area. If you are unsure or nervous of this process, go back to splitting with the wedges and do not take any risks.
Crosscutting on the bandsaw
I’ve measured the diameter of the log and I am cutting a series of billets to the same length. This will give me the option later to do any of the bowl designs mentioned. You can clearly see in the picture how well the cradle is gripping the log and how I can position my hands out of the way. Ensure that the upper guide of your saw is as close as you can get it to the top of the timber: this will give less wander to the blade and cover any unused areas of the blade for safety. I’m using the same 13mm 4tpi blade here, helping to keep the cut true and minimising clogging.
Cutting your bowl blanks
Now that the billets have been prepared, we can start cutting out our bowl blanks. I’m firstly going to stand the billet up and cut through the heart of the log. This will help to minimise any splitting radiating out from this point. This gives us two bowl blanks ready for shaping, with a nice flat face to use on the bandsaw. To cut the bowl blanks into a round can be difficult with sections of this shape, so I use different sized plywood discs to position over the blank. These give a great guide and size to cut to.
Protecting the blanks from splitting
As soon as your wet timber is prepared, it’s a race against time to stop the timber drying out too quickly and splitting. When the blanks are converted for turning, this is a crucial moment and where most blanks can be lost through damage. If you leave the timber for any length of time, make sure it is covered or bagged up, especially if left over night. Better still, you can seal the end grain with paint or PVA.
Preparing the blanks for the lathe
Mounting the blanks onto the lathe is slightly different between natural edge and standard bowls. For a natural edge, I tend to create a flat on the natural edge face with a Forstner bit. This flat should be big enough to take a large four prong drive. Give the drive a couple of good taps into the blank, using the drill point as a centre. The blank is held between the two centres using a tailstock ring centre for extra security. The bowl can now be turned to shape, leaving a foot as a hold point for the chuck. This foot can be removed later, when finishing the bowl after drying. When happy with the outside shape, reverse the foot and remove the inside, leaving the bowl about 20mm thick.
Preparing the blank for the standard bowl is a little simpler: here I’m using a faceplate in the conventional way (see below). Again, turn the outside of the bowl leaving a foot as a hold method for the chuck. This time the top of the bowl has a flat face as opposed to the natural edge. Once the outside is shaped, reverse the bowl and remove the centre.
When preparing for a session of wet turning, there are a few things to consider. You will make an extreme amount of shavings! These shavings will be very wet and the sap will spray away from the lathe. Cover as much of the workshop with tarpaulins or dust sheets and protect any bare metal surfaces from the moisture. If you leave the job over night, make sure you wipe down, oil or wax your tools, chucks and the bed of the lathe bed to avoid corrosion. Tannic acid is a natural acid found in oak, chestnut, olive
(Olea europaea), yew (Taxus baccata), etc. As you can see from the picture (below middle), this acid will cause your tools and hands to go blue and in some cases cause cracking of the skin. Using a barrier cream on your hands is a wise choice if you have a lot to do. You can also use camellia oil or wax to protect the
lathe and tools.
Drying your bowls
I tend to do all the backs of the bowls first, then reverse them to de-core, leaving them around 20mm thick. As they dry and distort, there should be enough thickness to re-turn the bowl to shape. However, the bigger the bowls become, the thicker you’ll need to leave them. While turning all the backs, I keep the unfinished bowls buried in the damp shavings until they’ve been de-cored. Once turned, I tend to keep them in the open air to dry. Don’t stack the bowls, otherwise they will grip onto each other causing stress to build up and may start to split. Either stand them on their sides or put sticks between them, keeping them apart. If you are rough turning in the summer months, it is wise to dry your bowl in a bag of dry shavings, turning them regularly and getting them back out in the autumn to finish drying. Drying time normally takes around six months to a year, depending on the timber and time of year but the slower you can make this, the better result you will get.
Finishing off the rough turned bowls
Now to start finishing some of the rough turned bowls from last year. See in this picture (above) how I’ve altered the wall thickness depending on the diameter. This is to carry the extra movement of larger pieces. One word of warning at this point: remember that your bowls have moved and are out of balance, so keep the lathe at a low speed to true up and always turn the piece by hand before you start the lathe, making sure that no part of the bowl will meet the toolrest.
Holding the bowl between centres
The first thing we need to decide is a holding method for our bowls, which will depend on the chuck you own. I’m using a medium size set of Gripper-type jaws to hold a wooden drive dome. The drive dome is made from a piece of scrap timber and roughly shaped. This will sit inside the rough turned bowl and act as a friction drive when pressure is added from the tailstock. If the bowl is too large for a dome then a large bowl blank can be used. This way you won’t be wasting any wood as you can use the bowl blank when you’ve finished rough turning.
Truing up the outside of your bowl
Firstly I’m going to clean up the foot of this small Claro walnut (Juglans hindsi) piece. The foot will eventually be re-shaped, but it remains important at this stage and is needed to form a good hold point for shaping the inside of the bowl later. When the foot has been trued up, you can continue to cleanly cut the outside profile, then sand and finish with your chosen polish or oil.
Turning the inside and finishing the bowl
When the outside is complete, turn the bowl around, this time holding the foot in your chuck. True up the rim of the bowl before starting to hollow out the remaining timber. It’s important that you reduce the wall thickness of the bowl by a small section at a time to avoid chatter. In these pictures I’m cutting down about 50mm into the bowl, getting the wall thickness where I want it to be before progressing any deeper. Continue with this method until you have taken out the uneven waste timber and you have the thickness you want to achieve. Finish by sanding and polishing. To finish the bowl, I’ve used a set of button jaws to hold the rim and have cleaned up the foot, creating a small cove and slight recess on its bottom.