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


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.


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


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.


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


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


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


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


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


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.


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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