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Dr Ian Plummer

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Technical
Bouncing Balls

[Letter to U.K. 'Croquet' magazine, August 1993]

Dear Sir

I was interested to note the bounce results by John Beech in a recent edition of 'Croquet'. I would like to comment that the results of a bounce test should include maximum and minimum values before a ball can be graded, or compared. For instance, if a ball bounces an average of e.g. 31 inches, but the height varies by 3 inches above or below that average, the ball can hardly be recommended. It is for this reason that a test apparatus was designed some year ago that allows that ball to fall vertically without any spin. This in turn means that a ball can be dropped onto any one of several chosen spots which can be chalk marked as proof of impact within ±2mm. It is thus possible to repeatedly test a ball on any spot. This apparatus is used locally to test tournament balls. The balls are bounced on each of six spots.

Temperature tests were also made within the range of 5°C to 50°C, using great haste at the extremes. A good ball will give closely comparable results on any position, although variations will occur due to milling.

A rust-proof bond must also be made between the one-inch steel plate and at least 200mm of quality concrete. The concrete area should be a minimum of 350mm across, and the plate set into the concrete while wet with a hard cement. Anything less will give up to two inches less bounce, based on personal experience with a plate set in only 100mm of concrete.

On page 8 of the same issue of 'Croquet', col. 4. par. 1 lines 2 to 9 inclusive, you state that the paint on a Jaques Eclipse ball affects the bounce. Bounce will increase indeed increase as the paint wears off, but the two effects are not connected in any way.

The real reason for the increase in bounce, which may not be well known, is the wear of the milling on the ball. For example a newly-cast ball with milling will bounce a surprising 25 to 30% less than when it is manufactured smooth. Few players will have had the chance to do such tests, but they are very revealing. I even have an old moulded ball, made by the method of covering a core of compressed chips of various materials with a thin bonding layer to which a casing is applied (construction is revealed by sectioning a ball with a band-saw). The ball has some small patches about half-an-inch across which are smooth where the casting has been chipped away by attrition, exposing a shiny, intact, pigmented bonding layer. The rest of the surface is milled, but worn. The bounce on the shiny patches averages 36 inches, some 18% more. Any ball of whatever manufacture will show less bounce on places where the milling is very close, compared to spots where the surface is less cut-up by milling.

The present solid-moulded ball has a casing surrounding a core. External 'paint' only affects the appearance as in the case of the American ball, where the new technology of moulded colouring should overcome this. The increase in bounce results from the fact that the milling of certain balls deforms on hard impact: slowly, with use, it becomes flattened. Bounce increases, and size decreases correspondingly. The ball becomes easier to play with (roquet strokes softer). Because the milling flattens, the wall angle changes, and the 'pull' on the peeled ball decreases, making the peel easier. The game also moves out of the tournament status, since the hoops remain the same. but the balls gets smaller. Apart from American balls, spun-cast balls are homogeneously made with the same resin and pigmentation throughout. There is no casing to split or chip, and the wear rate is so low that the bounce does not vary detectably over long periods, given other conditions constant. This means that peeling is just as difficult when the balls are old as when new.

The following questions are appropriate at this point: What other sport allows a 20% variation in ball elasticity? Could tennis players survive if the balls had to be individually graded and the opponent informed? In croquet, since four balls are in use, would not tighter specifications be preferable to 'matched' sets? The only ways to overcome present problems, compounded as they are by the milling effects, is with modern technology. Modem resins can be modified by additives to change elasticity and make them resist change due to temperature. Other properties, density, hardness, etc. can all be accommodated. What we need to do is to produce the specification.

In many other sports an old ball is discarded because the game becomes progressively more difficult after wear and tear. For example, in cricket the new ball is taken: the balls are changed during tennis tournaments, and so on. For croquet to gain respect, and because of the long life of the croquet ball, we must ensure that its statistics when used in competitions remain acceptable, as is the case of a wood in bowls.

It is fitting that we should pay tribute to the fantastic efforts which have been made in the last ten years by all the manufacturers, and I apologise for seeming to be so critical. It is just that there is too little knowledge of the performance statistics of the various makes of ball on the market today. The technology of modern resins has made tighter specifications very possible as well as desirable.

In conclusion, I just issued another report on croquet balls, this time about bias. I hope that you will get a copy and enjoy it. I think the subject of equipment will continue to harass us until your 'Holy Grail' is properly specified within the wide bounds of possibility, ball, hoop, mallet, the lot.

Yours sincerely,

R. Le Maitre

Author: R. Le Maitre
All rights reserved © 1993


Updated 28.i.16
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