Dempster Windmill Conversion

Learn how this old Dempster windmill was refitted and upgraded, taking it from a rusty bit of scrap to a working bit of history.

| December 2019

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Salvaging a damaged mill for an upgraded classic

Sometimes, accidents are a good thing.

I bought a standing windmill, a 6-foot No. 12 Dempster, for fair money. Then, before I retrieved it, a farmer hooked the tower with his corn planter, causing rapid depreciation! I paid $40 for the fan, motor and tail, and then helped him cut up the rest for scrap.

Later, last winter, a teacher brought me a Dempster Annu-Oiled direct-stroke No. 15 that he wanted rebuilt. This would cost way more and he still would have nothing.

A bit about self-oiling direct-stroke mills. Early mills required your presence up high to grease them on a regular basis; self-oiling eliminated that chore. So, No. 1 son Matt and I took the damaged one apart, straightened the fan blades, and mounted his tail on the “new” mill, rebuilt the swivel and tower bearing, making it substantially better.



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Looking at his old mill, I figured it would make a nice display for “show and tell” in our museum, especially for the younger set. I built an expanded metal guard to set over the working parts, thus keeping small fingers out of harm’s way. A wood pulley on the front will allow one turn to see how a windmill works.

Dempster employed a set of Timken bearings on the main shaft with automatic tensioning, via a spring that compressed when the front hub is installed. A spool between the bearings has, as it were, a “thread” on it, which leads oil to the front bearing, from which it drains back into the motor to repeat the cycle.

I had done several of these, and those with oil remaining in them never had a loose fan shaft. Oiling all the parts on a direct-stroke mill is basically the same as on the later, back-geared No. 12, which stayed the same for the duration. After all, it worked well, so why change? So it goes. FC

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1. Detail of the mill’s fan shaft, showing the spring and hub that tensions bearings, keeping them tight. This photo also shows the “thread” that carries oil to the front bearing.

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2. Oil delivery to the upper works on the direct-stroke mill.

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3. Oil delivery to the upper works on the No. 12 back-geared mill, pretty much the same as on a No. 15.



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4. Working parts of the No. 15. Note the lack of wear, as well as a nice brazing job on the upper end.

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5. The bearing assembly, allowing the windmill to follow the wind. Nothing fancy, but functional.

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6. Oil delivery system to front bearing and upper works.

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7. Oil dropped in the bottom tray works its way up the sides to the top, oiling the top works. Nothing happens fast with a windmill.

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8. The direct-stroke mill, set up for our museum.


Jim and Joan Lacey operate Little Village Farm, a museum of farm collectibles housed in 10 buildings at their home near Dell Rapids, S.D. Contact them at (605) 428-5979.



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