Ingenious Old Windmills
Whenever I am driving across western Iowa on I-80, I try to time my trip so that I am near Elkhorn, Iowa at lunch time. After taking advantage of the delicious and reasonably priced Danish buffet at the Danish Inn, I always make time to take another look at the old windmill next door. This mill was built in the early 19th century in Denmark. Then, in the 1970s, A group of Americans of Danish descent from Elkhorn, Iowa bought it and carefully dismantled it, numbering every piece. They took it back to Iowa and re-assembled it and lovingly restored it. It stands as a museum, and it works perfectly. For a nominal fee, you can tour the entire structure.
If you do tour this mill, walk through the upper floors and see all of the working parts. At first everything looks crude, but after you think about it a while, you come to appreciate the ingenuity of the whole design. All of the huge gears have the following arrangement: one solid cast iron gear turning against a larger gear with wooden teeth fitted into a cast iron wheel. The teeth have conical shanks driven into conical sockets, about like a human incisor. They can be installed with a blow from a hammer. If they had used two solid iron gears, sooner or later the teeth would be worn and the whole gear set would have to be replaced. Since the larger gear would weigh several hundred pounds and be several feet in diameter, this operation would involve tearing the top off the mill and using a huge crane. But with hardwood teeth wearing against iron, the iron part will never wear away---all the wear would be on the wooden parts. Any wooden tooth can replaced in a few minutes, and the miller himself can carve as many new teeth as he needs.
Another ingenious design element is the tail wheel. This small turbine wheel sits behind the main turbine blades and perpendicular to them. It can turn in either direction, but will not turn at all when the main blades are facing directly into the wind. Through a deep reduction gear, (probably with a ratio of several hundred to one ) the little tail wheel spins and slowly rotates the mill to face the into wind. The whole top of the mill can rotate, being mounted on iron rollers and a huge bull gear. Whenever the wind changes, the tail wheel starts spinning in whatever direction is needed to reposition the mill. Couldn't they have just made a huge tailfin to position the mill turret, as we do on old farm windmills? Yes, they could have. But if they did, then on a day with gusty crosswinds, the mill would be slamming back and forth, shaking it to pieces, and never being pointed toward the average wind direction.
Another word about the Danish buffet at the Danish Inn: I have lived in Iowa most of my life, and the traditional Danish food served at this buffet is some of the best food in Iowa, and is reasonably priced. For about the price of a jumbo sized fast food hamburger, fries, and a malt, you can have the whole smorgasbord. It's only 7 miles off the interstate. If you are ever traveling across western Iowa, don't pass up the chance to pig out on this buffet, or tour this fascinating old mill.