Tech Tip of the Month
A little over two years ago, I added the CamCalc page to the Model Engine News website to assist builders produce tables of lift figures for machining harmonic cams by tangential milling. A number of readers have used this program and emailed their thanks, including the Model Engineer's current IC columnist, Nemett (designer of the NE15S that has been serialized in volume 196 of the ME over the past months).
By coincidence, I've been casually reading through volume 121 of the ME (the second half of 1959). These issues contain a series titled Workshop Hints and Tips by Geometer. This alias, I have on good authority, belonged to Ian Bradley, who also wrote prolifically in the ME under his own name. The use of a nom de plume by writers in the ME has been an honoured tradition and a way of preventing over-exposure of valued authors. Many authors had multiple aliases, Bradley, for instance, teamed with Dr Norman Hallows to write extensively under the Duplex by-line. Their styles were sufficiently similar that readers of their Drill Sharpening Jig, Power Hacksaw, and many other construction series believed they were the work of a single individual. In all, Geometer wrote 424 articles, Duplex 212, and Bradley a further 106 under his own name.
But I digress; Geometer's Workshop Hint on page 241 of volume 121, issue 3039, discusses machining harmonic cams in the lathe using an offset jig for the flanks, then worrying away the base circle by hand rotation of the chuck. Although rather labour intensive to my way of thinking, the explanation of the effect of valve clearance prompted me to revisit the text that accompanies the CamCalc program to explain why relieving the base circle is a Good Thing™ to do. Click the thumbnail to be taken to the added text, or visit the CamCalc page for the big picture. Members can view Geometer's original article on the new Geometer Page (And to answer the question before you ask it: you become a member by buying the CD of this site. Sales of the CD are what pays for keeping Model Engine News on-line).