Article 3 - Bias

ARTICLE 3 - Bias

(Originally published in 1997 and revised in 2009)

Bias The Oxford English Dictionary considers the first use of the word, as follows "Originally an adjective, as in PR. "Via Biayssa" - cross or oblique road". The seamstresses amongst you will also recognise the use "on the bias" -being "diagonally, across the textures". The dictionary does say that the word became the technical term at the game of bowls, whence comes all the latter uses of the word.

So we can see that 'bias' comes from the bowl running obliquely to the line on which it was delivered. Again, referring to the Oxford English Dictionary, there are two very good paragraphs which are worth bringing to this article. They are as follows "a term of bowls applied a like to : the construction or form of the bowl in parting an oblique motion..... thus a bowl is said to have a wide or narrow bias. The second makes mention as follows "formally bias was given by loading the bowls on one side with lead and this was itself sometimes called the bias..... ..... they are now made of very heavy wood and the bias given entirely by the shape, which is that of a sphere slightly flattened on one side and protuberant on the other, as if composed of the halves of an oblate and prolate spheroid".

Well that has helped my education !!! but I wonder about the artificial weighting - certainly the story about the Duke of Suffolk's experience in 1522, may support it. Although, I always understood the significance of the story of when he discovered that his hastily cut bowl from the bannister post, having bias was thus able to "go round" the blocking bowls and giving him an advantage. I feel indicating that the other opponents bowls actually ran straight, not having bias introduced by another means..

Just a note, all artificial weighting is illegal - despite this when bowls come in for service, there are still some bowls that people have tried to 'adjust' the bias with loading.

The simplest way to show the bias effect and produce same is to take a snooker ball and produce a flat on one face and then run that ball on the table. Such a ball rolled along the table will turn away from the ''flatten" side, (just as for the Duke of Suffolk) and you have thus produced a biassed ball. Basically the side which has been ''flatten" is now lighter than the other side so the ball falls to the heavier side - the centre of gravity of the ball has been shifted from the centre of the ball.

 

This the simplest method of producing bias as described, obviously has to be modified for the production of a bowl so that the bowl can be comfortably handled.

Originally, with Lignum Vitae, (wooden) bowls the shift in the centre of gravity, used to produce the bias was more easily seen by the bowler. The reason being that as the timber is has a specific gravity of about 1.32 it needs a larger percentage of its mass to be 'off centre' to produce the bias. The more modern phenolic bowls using higher specific gravity material than Lignum Vitae means that that shift in the centre of gravity is visually less obvious, but is still there nevertheless.

 A3_bias _1

However, the bias can also be produced by adjusting the running sole, and any of you that have had your bowls adjusted will know that this in the method used to produce a change in a bowl to a required bias. At the Drake Pride factory, because we renovate large numbers of Lignum Vitae bowls (for the Crown Green players) where basically every set has to be re-biassed during renovation procedures, we therefore, have great experience and skill in the intricacies of hand biasing. However, as we now are producing the modern phenolic bowls on computer controlled lathes, it means that another set of skills is required to ensure that the bowls run as the manufacturer requires.

All manufacturers now use computer controlled. lathes (Drake Pride being the first company to install such equipment) and therefore the modern bowls no longer require hand biassing as the programmes that are used produce the 'total' geometric shape of the bowl. This may incorporate some shaping of the running sole, but all the shape is produced on the lathe, combining with the gravity shift and the mix of how these two basic methods are used is how the different manufacturers produce the different handling characteristics of their models.

From an interesting old book 'The Physics of Ball Games" there is a section on "the path of a a wood" across a bowling green, and this is worth producing as in relatively simple terms it does explain how the curved path of the bowl is produced.

 A3_bias

 THE PATH OF A 'WOOD' ACROSS A BOWLING GREEN:

Fig B.

The fact that a bowls 'wood' which has bias pursues a curved path across the green is a result of the principle of conservation of angular momentum, and its motion is best explained on that basis.

However, it is fairly easy to accept, at least in general terms, why it behaves as it does.

Fig. B is meant to represent such a wood, seen from above, rolling across a green in the direction of the arrow OA.

Since it is rolling, the top of the wood will be moving with a velocity in this same direction. Suppose the bias is on the right; that is to say, the centre of gravity of the wood Is to the right of its centre. Then this bias will tend to rotate the wood over from left to right, and so give the top of the wood a small velocity in the direction OB This, combined with the very much greater velocity along OA will give a combined velocity somewhat to the right of OA-along OC. It is therefore in this direction that the wood will tend to roll. In this way it will always tend to roll slightly to the right of the path on which it finds itself. In the early stages, when it is rolling rapidly forwards, the velocity along OA is very much greater than that along OB, and so the curvature of the path will be slight. Later on, as it slows down, the transverse velocity becomes relatively more important, and the curvature in the path gets greater and greater, until the bowl eventually stops rolling and comes to a halt.

Next Month, I will cover the manufacturing of Lignum Vitae bowls and Phenolic Composition Bowls.

© Peter Clare 2009 - © E.A. Clare & Son Ltd. 2013 - reproduction of article allowed only with permission from E.A. Clare & Son Ltd.