How to Find the Centre of Timber


How to Find the Centre of Timber

Philip Greenwood looks at finding the centre of timber

Some by people new to turning and others who have been turning for a while ask about finding the centres of pieces of timber. I show how here, with methods I use on a day-to-day basis. Yes, there will be more ways than I have explained here. However, some of the conventional methods don’t work with the odd shapes of timber I use. How accurate does finding the centre have to be? This depends on the project and how much spare capacity you have over the lathe bed.

This is the method that can be used on both square and round timber and all you need is a pencil. On square section timber, hold the pencil in your fingers with the pencil protruding so the pencil tip is more or less on centre. Slide a finger along the timber side so you have a pencil line on the timber end. Rotate the timber 90° and repeat for the other three sides. It is important to make sure the distance of the pencil is the same on all four sides. You should be able to see the centre. On round blanks, hold the pencil in the same way and draw an arc. Repeat this several times around the blank until you can see the approximate centre. 

Corner to corner
This method is used on square timber using a ruler and a pencil drawing a line corner to corner and repeating on the other two corners. One main point to bear in mind is to offset the ruler by the thickness of the pencil point or where the two lines cross each other will not be in the middle, this is very easy to forget. The second photo shows this with the true centre being marked with the hole. If you’re using a piece of timber to make a spindle with squares ends on, this offset would show up when mounted on the lathe, especially if turning a pommel or a bead which may have a flat on one side.

Plastic jig
This is a plastic centre-finding jig and is very useful; these can be found in most turning supply shops and online. The jig can be used on both round and square timber. They are good for smaller round blanks but larger rounds call for different methods, which we will look at below.
For round section timber we place this on the blank and draw a line with a pencil then rotate the centre finder 90° and draw a second line. I normally draw at least two more lines, and then mark this with a bradawl where or as close to where all the lines intercept. If you are marking a very large blank use a ruler to extend the lines to the blank centre. For square section timber we use the jig on at least two corners, we then use a pencil to draw a line and then rotate to the next corner and draw a second line, repeat for the other two corners. Why bother with the two other corners? Well if the timber does not have 90° corners, the two lines may not join in the true centre.

Hardboard disc
This is a method I use most of the time. I have several discs of different sizes going up in 25mm stages. All you need to make these is some hardboard or even thick card. The first stage is to draw a circle with a pair of compasses, then cut the circle out very carefully on the line you have drawn, and then push a bradawl through the centre where the compass point was. To use these discs, pick a size that fits the blank size, or one that is just smaller, and line the disc up on the blank so you have an equal space all around the edge. Now use a bradawl though the hole in the centre and press into the blanks to mark the centre. This can be used on the end of branch timber to find the centre. You can use this on planks as well to mark out bowl blanks. Unless you want all the blanks to be the same size you can lay different size discs on to get the most out of the plank. This system works very well on natural edge bowl blanks; this is the method I use mostly on this type of timber.

Plastic disc to find centre
This is used to find centres on larger irregular shaped pieces of timber. Simply, this is a large piece of plastic sheet – acetate in this case – with circles drawn on it. You could use polycarbonate sheet too: this is strong and withstands a lot of abuse without breaking. I used a pair of dividers to score circles on the disc: the reason I wanted to score is so I can mark the circles with a marker pen, and using different colours makes lining this up easier. You can set the rings at fixed sizes sat every centimetre or inch, but have enough marked rings to make life easy for yourself. Then drill a small hole in the centre of the disc so you can use a bradawl to mark the timber surface.  Place the disc on the timber and adjust until you have found the centre of the timber or as near as possible and mark. This will help you visualise where you may wish to hold very irregular pieces like burrs, logs and so on. Don’t be fooled though as it can be used for working on other pieces too.

Odd legs/callipers
These are a compass type of equipment; the difference is one leg has a step which you can place on the edge of the blank, then roughly set the other leg to the centre of the blank. As you can see this is a homemade pair made from two pieces of timber joined with a bolt and wing nut, with a pencil taped to the straight leg. To use these, place the step on the edge and open out so the pencil is around halfway across the blank, lock this setting. Now draw an arc then move round the edge of the blank drawing arcs until you can see where the centre of the blank is, then mark this. These are mainly for round blanks.

Finding the centres of work helps by enabling you to minimisise vibration and also wastage  of timber. That said, a log or burr can be so irregular in shape that finding the true centre is very difficult, but getting close is important. No one wants to work on material that is heavily off-centre or out of balance, unless it is something we have to do. We really don’t want to have the lathe vibrating all over the place for longer than necessary.Given that we work with timber from a variety of sources and in various shapes, even if we buy pre-prepared blanks, they are rarely truly round when we buy them.  There is no one perfect way to find the centre of something and there are certainly more methods available than those shown here. However, these are cheap and easy to use ways that form the backbone of the majority of methods used. Absolute accurancy is rarely required, so ‘close enough’ is often good sufficient for the majority of work.

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