De Oudkerkermolen, or Oudkerkemolen (English: Old Church Mill) is a smock mill in Aldtsjerk, Friesland, Netherlands which has been restored to working order. The mill is listed as a Rijksmonument, number 35674.
De Oudkerkermolen was built in 1864. On 13 March 1955 it was badly damaged in a storm. Repairs cost ÃÂ6,734, including new sails at ÃÂ3,200 and a new Archimedes' screw at ÃÂ1,950. The repairs were carried out by millwright De Roos of Leeuwarden. Further repairs were made to the mill in 1963.
The mill drained the Oudkerkerpolder until 1970. A diesel engine formerly provided auxiliary power. It was restored in 1975. Although in working order, the mill just pumps water in a circuit to demonstrate the process.
De Oudkerkermolen is a smock mill whose sails almost reach the ground. The mill has a single-storey brick base. The smock and cap are thatched. The mill is winded by a tailpole and winch. The four Common sails, which have a span of , are carried on a cast-iron windshaft. This was made by millwright H J Koning of Foxham in 1910. The windshaft also carries the brake wheel which has 50 cogs. This drives the wallower (29 cogs) at the top of the upright shaft. At the lower end of the upright shaft the crown wheel (37 cogs) drives the wooden Archimedes' screw via a gear wheel with 34 cogs. The Archimedes' screw has an axle diameter of and is diameter overall. It is inclined at 19ýð. Each turn of the screw lifts of water.
De Oudkerkermolen is open to the public by appointment only.