Building a Model Windmill

The first step was to decide on the dimensions of the new design; the diameters of top and bottom of the main structure, height to turntable, sail-span and total height, being the crucial measurements from which the rest would flow.

                                            Height to turntable 39 inches
                                            Diameter at base    21 inches
                                            Diameter at top (to turntable) 13¹/₂inches
                                            Span of sails 48"
                                            Total height to top of capping  - approx 48"

SOME MATERIAL FACTS

Timber/Wood Strip  
2"x 3" - 7ft.     
1¹/₂"x 1" - 8ft.     
1"x 1" - 3ft.       
³/₄"x ¹/₂" - 31ft.      
2"x ¹/₄" - 8ft.      
2"x ³/₁₆" - 15ft.     
³/₁₆"x ³/₁₆" - 6ft.

The above is not completely exhaustive, as I had a little wood lying around, some approximating to the above dimensions, which supplemented purchases,  and saved me some pennies. 

MATHEMATICS  FREE ZONE - ALMOST!

Above I said that the base of the windmill would be 21 inches diameter, giving a circumference of 66 inches. The structure was actually to be twelve sided (to appear as near round as possible without going to ridiculous lengths) so that meant the base of each side being  slightly less than the 5¹/₂" which would be the measurement if the sides were curved and fitted exactly on the circumference.

These sides would however be flat, forming twelve chords with each side only touching the circumference of the 21 inches diameter at two points; but some vaguely remembered 'school' geometry provided the method used to obtain the sizes by marking and measuring, as set out below.

The base was made from half-inch board - I used plywood - starting off with a square a little over 21 inches each way.

The approximate centre was found and marked, a circle drawn of 10¹/₂^" radius and a line drawn through the mid point to touch the circle at opposite sides.

Using these points, enough of two more same-size circles were drawn to touch the circumference at four further points.

As can be seen in the diagrams below this produced six equidistant points on the circumference, from which six further points could be identified, to enable 12 equal length chords to be marked.