EDITORIAL MISFIRES DEPT

A regular reader, I purchased your August 2016 issue primarily for the article on the Ping Pong cannon.

We obtained the materials needed according to the list in the article and one of my grandchildren and I built the gun while my wife was out shopping. Her list included the required ping pong balls.

Oh well, I am sure you might have heard the story from other disgruntled readers. The internal diameter of South African 40mm PVC pipe is approximately 36 mm, whereas a ping pong ball is about 40 mm! We discovered this after expending money and time on the project.

Maybe I have missed something from the instructions and got something wrong? Or maybe I didn’t, as a closer look at the accompanying photos seem to indicate that the article might originate from America, one of the few countries in the world that remains with the Imperial measuring system, and a gremlin could have crept in with the translation to Metric. COLIN ADDIS HILLCREST

(Firstly, our abject apologies to you and the other frustrated readers who contacted us with the same problem. The article does indeed originate from our American parent edition and that’s where the confusion arose. According to Imperial measurements used as standard in the US, 1½-inch pipe refers to inside nominal diameter. In the Metric system that we use, our equivalent 40-mm pipe refers to outside diameter; as pointed out, the required ball won’t fit. The next biggest pipe size locally is 50 mm, the specs of which indicate a wall thickness of 2,2 to 2,6 millimetres, resulting in an internal diameter of about 45 mm. We plan to construct a prototype using 50 mm pipe, if necessary shimming to narrow the bore, and will report back on how things worked out. – Editor.)