Now you should be ready to finish of your sphere. However, a sphere is only created in the details of the finish. Any inconsistencies in the curvature of the item, and it is strictly speaking, not a sphere. So at this point you may think you are on the home straight – alas, there are still many process between your carefully crafted ball and the perfect sphere!
Wooden mounting cups
To achieve this secondary holding method, we need to turn some wooden cups to hold the sphere securely without marking it. I chose two pieces of tulipwood (Liriodendron tulipifera), a relatively soft hardwood of around the same density as the redwood I used for the balls. One is simply held in the chuck and turned to a cup shape, the other needs to fit onto your live centre. I am fortunate that I own a Oneway live centre which features a threaded portion, designed to hold various attachments and homemade holding devices such as the wooden cup needed here. These centres are acknowledged to be one of the best on the market, but have a price tag to match.
There are now some very similar versions available. To make accessories for this style of live centre, you need to buy a tap that matches – in this case a ¾in x 10tpi UNC, but check your centre to find the correct size. Any wood can be tapped; I have used this soft tulipwood here, but you need to select a piece of side grain – like a bowl blank, rather than like a spindle – as this will hold the thread. Threads cut into an end grain blank will just crumble, unless you use a very dense wood. I cut a square of timber, oversized in all directions, pilot drilled a hole and tapped out the thread. I’m sure an engineer would wince at my tapping technique, but it does the job! With the thread cut, I fit the block onto the live centre. With a drive centre in the headstock, I bring the tailstock up and engage the centres until the block spins and I turn it to a cylinder. This can then be removed from the live centre, reversed, and held in the chuck to turn the cup shape into the face.
What if I don’t own a fancy live centre?
If you don’t have this sort of centre, it isn’t a problem because you can turn a similar version to sit over your live centre to do the same job. The process is similar to making a box, in that you hold the blank in the chuck and turn out the inside, deep enough to accommodate the live centre and to a diameter that is a tight push fit over the parallel section of the live centre. At this point you can mount it and drive it between centres as I described for the threaded version. The main difference here is the grain direction – the threaded version is cross grain, which means turning it needs a little more care and the use of a spindle gouge. Conversely, the standard push fit version will be end grain and can be simply turned, as a spindle, with a roughing gouge.
Once the fitting is made and turned true, mount it in the chuck and turn a cup shape into the face. Again, the grain direction is relevant here, as the cross-grain version will need turning from the rim down to the bottom, like a bowl. The end grain version will need drawing out from the centre to the rim with the wing of the tool like a box. The exact shape of the cup is important here; too deep and only the rim will drive the ball, which will certainly leave ring-shaped dents in the sphere. You need to turn the cup slightly too shallow, which means that a good proportion of the bottom of the cup will drive the sphere, but importantly the rim won’t come into contact, leaving the sphere blemish free. To achieve this, I cut out the same radius curve on the other side of the template and turn the cup to suit, ensuring the rim doesn’t come into contact with the template, and so the sphere.
With the cups turned the sphere can be remounted. It is important to understand the grain direction of the sphere before starting to turn it. You need to ensure the poles of the globe are directly up and down, or north and south, to ensure a clean cut. When turning the blank initially, it was a standard spindle blank, so the cuts ran from the equator, down to the poles. Now, with the blank mounted between cups, it becomes faceplate work, so the cuts will be drawn apparently uphill, but still from the equator to the poles, and so still working with the grain of the wood.
What you can’t do at this stage is mount the sphere with the poles running diagonally, because then you won’t be cutting consistently with the grain; at some point you will be working against the grain. I’m not one to say this will never work, but it will be making life difficult for yourself when it comes to achieving a good, even surface finish.
Turning between cup centres
With the sphere held at the equator by the cups, and the poles running directly vertically, you can finish turn the sphere. Light cuts with the wing of the tool in a shearing cut work really well here. This is when it becomes clear just how simple this all is, because as you turn in this new orientation, the waste marks will be removed and, because the lathe simply spins the sphere, you will automatically be removing anything that wasn’t perfectly spherical from the earlier operation. Because you are using a light shearing cut, working with the grain of the wood, it cuts cleanly and a sphere is formed almost effortlessly. Check the sphere regularly and reposition it in the cups occasionally, but only by rotating it around the equator, so a different portion of the sphere can be turned. Once it is all turned and the cut off marks are gone, the sphere is ready for sanding.
The completed spheres
The sanding process is even more simple. I worked from 120 grit to 240 grit on these softwood spheres, but you might choose to go finer. You can sand in any direction, so now you can feel free to mount the ball in whatever orientation you like between the cups; just try to ensure every surface is worked evenly. Very quickly, you will find you have a perfectly smooth and spherical ball.
Summary
If you’ve never crafted a sphere from wood before, the process can seem quite daunting. Such is the consistency required that one could easily believe that such a challenge is for CNC machining only. I hope this article has shown that this is not the case. With this step-by-step process, carving out a sphere by hand is perfectly achievable. Just make sure you take your time, check your work regularly and make accurate measurements and cuts. If you do, you will end up with a perfect sphere.