Popular Woodworking 2002-08 № 129, страница 81
holes in the hand and arm (parts A and B) that will make the tentacles move. Finally, drill the V4" suction cup divots (28 per limb) in the arms and hands with a Forstner bit. Although it might seem a bit obsessive-compulsive, I made a "negative" jig to hold the arms plumb while I drilled them for the 3/l6" arm extension dowels. It worked great, and the jig became a nice addition to my "and-what-the-heck-is-that-for" collection. After gluing the extensions in place, carefully drill the pivot holes in the extension dowels (part C) and shoulder parts. Sea Chest Hides the Works The sea chest, menacingly guarded by the octopus, is a simple bottomless box that conceals and protects the arm extensions, pivot point and rotor cam. Drill the ends of the lid slots with a V4" drill bit and remove the waste between them on the scroll saw. The rotor, drive shaft and cam assembly would probably make a decent science fair project by itself. See the plans and description on the final page of the article for all the mechanical engineering details. Problem: Inertia. Solution? Fishing Gear! If there is a secret ingredient in the octopus whirligig, it has to be the tentacle counterweights. At first I thought all eight arm extensions could simply lean against the cam and the slightest breeze would cause them to be pushed aside by the rotating cam. Wrong! When Sir Isaac Newton said, "a body at rest tends to remain at rest," (his "First Law of Motion") he must have been working on some early version of the octopus whirligig. It was only when I connected fishing sinker counterweights 5 1/2 There are other ways to drill the holes for the arm extensions, but this simple jig holds the arms in place perfectly as you drill the 3/i6" holes for the arm extensions . to the ends of the extensions (11/4 ounces worked for me) that the whole thing came to life. The best way to visualize the arrangement is to think of the extensions as tubes on a wind chime. They want to dangle in space about halfway through their pivoting arcs. No more than two or three extensions should be contacting the cam while it is at rest. Because the greatest problem encountered by a whirligig is overcoming inertia (getting started) the counterweights help lighten the load. The Octo-perch To levitate the octopus and sea chest above the vertical rotor, I came up with an assembly that looked (to me) like something out of a shipyard. It was designed to slip over the top rail of my deck. Because the design is totally arbitrary, I'd be interested to know if anyone can come up with a more elegant solution. Although I'm now the proud owner of the only octopus whirligig on my block, the new staircase still lacks finials. I guess you could say I'm easily distracted. PW Drilling the suckers is just a matter of following the holes on the pattern (above). Sea chest - Half-scale plan 1/2" 3 1/2" 1/2" 1/8" x 1/8" reveal Sea chest -Half-scale elevation 80 Popular Woodworking August 2002 |
