Editor’s Note: Prell has forwarded another letter from his survivalist friend Karl, whose little group is making more modifications to geodesic domes to make them easier to build. I’ll share pictures when any become available. -John
After all my talk about hubs made of pail lids and tubular hubs made of four inch PVC pipes, I have been taken down several notches! I feel very foolish now because I realize that hubs are not even necessary! I had to be shown a far better, and simpler way to make strut connections.
The obvious question, one that we often forget to ask, is why use hubs at all? I once would have answered, “To hold the struts in place at the proper angle.” But now it has been explained that if you connect the struts to one another the angles are formed automatically. These domes seem to know how they should shape up and do it on their own. But next, the objection is, if you drill holes in these tubes and try to put a bolt through them, you have a monstrously thick tangle of strut ends, unworkable, really.
So, flatten the ends of the struts into blades, and run a bolt through them. Great in theory, but how do you flatten the ends of the tubes?
Doc, (who is seen inspecting the original pail lid dome), came up with the answer. Use heat to soften the PVC, then squeeze the plastic flat. Immediately, some one suggested a heat gun. One online source called heat guns, “hair dryers on steroids”. But good ones are expensive and cheap ones can conk out after a lot of use. Another objection to the heat gun is, it needs a lot of electricity and we would prefer not to do that. Then it was suggested we immerse the struts ends in hot water until they are soft enough to flatten. We tried hot water in a can and used a vise grip plier to squeeze it flat. Crude and not entirely effective. Maybe we didn’t leave the tube in the can long enough?
Again, Doc came up with the idea of putting the tube ends into oil, which gets hotter than water. “Motor oil?” someone suggested, “it can take a lot of heat.” But that idea was not appealing somehow. With additives involved might the fumes be toxic?”
“What about cooking oil? Asked Beth. At this point I want to say that there are enough in our group who want to make domes, that we could almost have a little factory! The cooking oil idea had a lot of appeal and no one could think of anything against it. Soon a small sauce pan of corn oil was heated on a stove and short pieces of 3/4" PVC were placed in it. We did not heat the oil too hot, no boiling or fumes. The tube ends were submerged about three inches in the heated oil. After a few minutes one was withdrawn and found to be nice and pliable.
Doc had the honors, since it was his idea. He placed the end of the softened tube in an old shop vise someone had, and he cranked the jaws shut. After a couple of minutes, the jaws were opened and the sides of the tube were nice and flat, with a slight imprint from the textured surface of the vise’s jaws. The end of the tube was completely flattened–it worked!
Eventually we made six pieces with flattened ends and drilled a hole about a half inch from the end. A 3/8 inch bolt (because it was what we had on hand) was put through the six holes, a washer and wing nut was placed on the end and hand-tightened until it was snug. We all agreed that this six way joint was a success, it even looked nice! The bolt we used was 2" long. The four and five strut joints will be even more compact. The tubes in this first joint had a flattened surfaces 1 ½ inches long and it worked fine. I hope the Fun Saver pictures show up ok. We are all very happy with the results of our experiment. With this system, any size dome only uses 26 bolts! It looks like it can’t be any simpler than this.
What do you think, G.? Is there any value in this?