Monday, July 2, 2012

Tennis Balls

Inasmuch as one can summarise the matter, the purpose of a Blog is to whine about the cruelty of the world in not behaving as the television advertisements would have us believe it behaves. Endless happiness, we are taught, will result from effecting the purchase of a mock-leather sofa and two mock-leather armchairs on easy credit terms. - Come to think of it this may be true, since I have never tried the experiment of actually buying any TV crap although the advertisers' job is rendered a bit harder by the fact that I do not own a television. If I want to see a film it necessitates a car journey, and if the film is The Age of Stupid, the concomitant guilt as I drive home afterwards. And then I fall to thinking about First World Problems and whether one really should complain - as this morning - about a blunt table knife when 24,000 third world children die of starvation every day. (Though why do we all tolerate the daily frustration of pressing a blunt knife through a piece of bread to divide it in two?) - Actually I keep a table knife, repaired with a gross epoxied wooden handle, sharpened on a stone and finished with one of those cheap plastic diamond files that I don't know how we ever managed without, and it cuts closed cell polyurethane foam like nobody's business, and the reason it needs to is because I've just been making frames to go in the windows to hold insulating sheets of 3mm cast acrylic which I was going to do several years ago and which thought received no follow-up until the recent stunningly cold weather. You need the foam to block the cracks. And you need to carve it thinner afterwards because it isn't as compressible as you think when planning the venture.

My wife's First World Problem concerns tennis balls rather than blunt knives or faux leather sofas. Motueka Tennis Club, like all clubs, is riven with faction and secret hatred, half the committee leaving in a huff and the other half insisting that Slazenger balls are no longer bought and the club switches to Wilson on the grounds that the NZ Tennis Association has received corporate sponsorship. Unf. it seems that Wilson balls are a bit flabby, which my wife's tennis coach has now proven by dropping them on concrete and seeing how high they bounce. (Not as high.)

The reader of this blog - when I remind him, there still is one - is already aware of my addiction to perverse uses of compressed air, and is also aware that one of my brothers is an engineer who designed an enormous machine for one of the companies who makes tennis balls. Resulting from his research he - the brother - told me how tennis balls are pressurized, which of course is one of those problems you never think of until someone points it out. - A tennis ball has no valve: how do you get compressed air into it? - Well my brother told me how, and it's done like this: you get a tennis ball and put it into a sealed chamber filled with compressed air. And in the reverse of the process whereby your tyres go flat if you leave a bike for a month in the garage, the tennis balls become compresseder inside the sealed chamber. Which is why tennis balls are sold in pressurized tubes. Which fact I didn't know because I never buy tennis balls.

So in order to further irritate the remaining members of the Committee (my wife is of the Slazenger faction) I have hit on the plan of taking Wilson balls and pressurizing them to Slazenger standards, and if they'll stand it, beyond. It would be fun to see some elderly biddy - all the Committee are biddies, mostly elderly - pat a ball with what is termed a Lollipop Serve (we are now familiar with senior citizen sporting slang) and be startled to see it shoot out of the courts onto the roof of Motueka Library.

Experiment 1. Cut a car tyre and insert it into the leg of a pair of trousers, a button-hole sewn for the extrusion of the valve. Fill with balls. Clamp ends in wooden clamps to seal. Pump.
Result. At about 18 psi the entire seam of the trouser ruptures.
Conclusion: Du'n't work.

A burst trouser

Experiment 2. Take Golden Syrup tin and solder Schrader valve into base. Insert tennis ball. Pump.
Result. Hissing.
Conclusion. Needs a seal round the lid.

Experiment 3. Cut up whoopee cushion (did my wife really give the children one for Christmas? What was she thinking?) to make a sheet of latex. Put between tin and lid. Pump.
Result. Lid comes off.
Conclusion. Of course it does, stupid. High pressure x Big area = Huge force.

Experiment 4. Repeat, with tin contained between clamped wooden supports.
Result. Lid distends in the unsupported middle, and hisses.
Conclusion. Lid needs support in the middle.


A distended syrup tin lid. And a Mappin and Webb knife, sharpened, with a not-very-Mappin and Webb handle.

Experiment 5. Cut circle of plywood to support new (obv.) lid.
Result. 100 psi! - But after one hour, it was down to 0 psi.
Conclusion. I shall have to do the job properly and sew a helical tube of strong nylon webbing to contain the pressure, which I secretly knew all along because that's what happened when I was playing with this idea yonks ago. Which I don't want to do because I hate sewing. And which my wife won't do - I guarantee this - because she doesn't engage in tennis ball sabotage.




And no, since you ask, I haven't done any more on John's High racer. Too cold. And the West Bank Road, in permanent winter shade, is now a sheet of black ice.

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1 Comments:

Blogger Barry Mulder said...

look at pressureball.com

April 15, 2013 at 3:44 PM  

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