Found trampled in a field, rare 12-foot windmill is restored and becomes a permanent fixture at a South Dakota museum
Last summer, we were hired to locate a site for an irrigation well northeast of South Shore, S.D. This is some rather grim country, sort of a poor soil, hard-scrabble area. My wife, Joan, agreed to go along and witch for the best place to dig test holes, so she went ahead and I followed in the big truck. We went up a narrow, two-lane gravel road that turned into a one-lane dirt road and then a field approach before finally ending in a horse pasture.
We drilled test holes, located a couple well sites and were leaving when Joan returned, telling me to look at a windmill she’d spotted buried in the grass. Not much was visible, but we could tell it was open-geared, meaning it was old. We made a deal with the property owner and returned the next day to retrieve the windmill. This all took place 100-odd miles from home, so we were lucky to find a neighboring farmer with a loader to lift the mill after we dug it out and set it on our trailer. After it was loaded, we could see the bevel gearing and then figured out it was a “power” mill, 12 feet in diameter, built by Aermotor Co., Chicago. But that’s about all we knew about it.
When you need advice, it’s best to go to a good advisor. In this case, we turned to T. Lindsey Baker, who wrote the Field Guide to American Windmills. Paging through my copy that night, I found mention of the power mill, mostly in passing. It appeared that, at least in 1985 when the book was written, power mills were considered rare. I wrote Baker, telling him of our good luck. He responded with a copy of a sales brochure on this mill, a 1900 Model Power Aermotor.
A 12-foot fan produces very little power at low wind conditions, only making 0.2 hp when working a 10 mph breeze. With more wind, it gets better, slowly; at 25 mph, the mill will generate 3.12 hp. However, if you get winds of 35 mph, and can keep the mill loaded, it can generate 8 hp. One wonders how the 3/4-inch shaft coming down from 50 feet or so can handle that much power. As a safety feature, a slip clutch was located at the bottom of the downshaft, above whatever was being driven, so if something stuck, one would not have to climb “upstairs” in the middle of winter to take the mill apart.
These 12-foot mills were touted as being able to provide enough power to grind 70 or 80 bushels of grain a day, plus pump all the water, shell all the corn and saw all the wood needed on a large farm. The 14-foot and 16-foot units would do somewhat more work.
Looking at gearing, you can see the gears are reversed. That is, the large gear is on the fanshaft, speeding things up quite a bit. When the unit runs at normal speed, the downshaft turns at 500 to 600 rpm. Given the nature of the lubrication system, it is a wonder that these held together at all. A couple of oil cups, with a thimble-full in each, fed oil via capillary action through a wick to some bearings. Another cavity, filled with cotton waste, was also kept oiled. Any servicing required a climb to the very top. In all honesty, it is a neat piece of early technology.
We were fortunate in that the gearing was not damaged. The fan itself, though, was pretty much gone, the result of cattle walking over it for many years. I went to Dakota Windmill down at Hurley, S.D., where Larry Rechnagel generally has used pieces available. We were able to buy a very nice set of fan sections for $240. We bolted them on and painted them in the shop. Luckily, the main shaft carrying the fan was tight, so we only had to make four bronze bearings and a couple new short shafts here at home. Joan painted lettering on the unit and we picked a quiet morning to hoist the mill into place on a tower near the museum, where it can look out over the surrounding country for years to come. So it goes. FC