Introduction: DIY Timber Model Garden Windmill
1. Drawing Octagonal shapes
2. Making Octagonal Components
3. Tower Central Core
4. Assembly of Tower Central Core and Octagonal Platforms
5. Making Tower Cover Boards
6. Fitting of Tower Cover Boards
7. Bearing Housing Assembly
8. Making and Fitting Shaft in Bearing Housings
9. Making Sails
10. Making Sail Attachment Bar
11. Assembly of Sails on Sail Attachment Bar
12. Fitting Sail Assemblies on Shaft
13. Making Roof
14. Fitting Roof
15. Base Board
16. Weatherproofing Using Yacht Varnish
17. DIY Aid for Making Perpendicular Saw-cuts
18. Swivelling Windmill
This elegant, sturdy and durable timber model garden windmill, with its shaft mounted in low cost miniature ball bearings rotates well, even in light wind conditions. The tips of the windmill sails give an overall height of 50 cm.
It can be made without access to a circular saw or bench drill. Just basic DIY skills are needed, together with tools such as a timber saw, hacksaw, mains or cordless drill, drill bits, workbench or vice, screw-driver and spanners.
Step 17 provides information on a useful DIY aid for making perpendicular saw-cuts, because I don’t have a circular saw.
The requirement for only relatively small quantities of timber and other materials such as screws and nuts and a short length of thin metal bar results in a relatively inexpensive, but attractive, dynamic and durable garden feature.
Whilst the sequence of manufacture and assembly can be varied, the project naturally breaks down into distinct stages. The Step by Step schedule has been formulated on the basis that sub-assemblies will be made once the relevant components have been manufactured. This is not only straightforward, but probably more rewarding than manufacturing every individual item, before attempting to carry out any sub-assemblies.
The stages of the project may be summarised as:
· Making Octagonal Shaped Components
· The Windmill Tower Structure
· The Windmill Sails
· The Rotating Shaft and Bearing System
· The Windmill Roof
The structure of the windmill can be seen in the illustration.
The Tower Central Core, with its Upper and Lower Octagonal Platforms, provides structural strength for attaching the tower cover boards, the octagonal sloping roof and the assembly of the rotating shaft in bearings carrying the sails.
The logically sequenced Step by Step Procedure set out here, is on the basis that the assembly and construction of the windmill will proceed alongside the manufacture of the various components, rather than after all components have been manufactured.
The relatively large number of individual Steps and detailed information is a result of intentionally aiming to produce clear instructions, to make the project as straightforward as possible, and of interest to the widest possible range of people. Some people will need little more than a glance at the photograph of the windmill, to be able to make one. Others will need only parts of the detailed Step by Step information, whilst some will be heavily dependent on the Step by Step fine details. It’s much easier to write a brief set of instructions, but in doing so, there is a high risk that people will experience problems and/or make mistakes.
There are some potential pitfalls which, by use of the carefully prepared documentation, should enable even people with limited DIY experience to avoid. Please bear this in mind, when perusing the information.
The windmill with a double set of sails and swivelling motion refers to the ‘optional challenge’ in Step 18.
2.8 m of 150 x 20 mm (or 18 mm minimum thickness) Planed All Round (PAR) board, either rectangular section or tongue and groove boarding (for Tower Cover Boards)
1 m of 100 x 20 mm (or 10 mm minimum thickness) Planed All Round (PAR) board, either rectangular section or tongue and groove boarding (for Sails)
1 m of 150 x 38 mm timber (or absolute minimum thickness 25 mm) (for Octagonal Platforms and Roof)
0.2 m (off-cut length) of Planed All Round (PAR) spar of square section approx 60 mm x 60 mm (minimum 50 x 50 mm)
2 pieces each approx. 250 x 30 x 2 mm flat steel or aluminium bar (or Flat Structural Restraint Strap available from Builders’ Merchants such as Travis Perkins)
2 lengths (of 300 mm) M6 threaded rod
2 small 90 degree thin angle brackets – available (or suitable material) from DIY stores
M6 Locknuts 1 pack of 20
Woodscrews (40 x 3.5 mm) 1 pack of 50
2 Miniature 6 mm bore ball bearings pre-mounted in Bearing Blocks - Code No 4604-021 (Technobotsonline.com)
£35 Total estimated cost of timber, bearings, metal straps, threaded rod, locknuts and woodscrews
Timber Saw, Metal Hacksaw
Power Drill, Drill Bits, Countersinking Drill
Workbench or engineer’s vice,
Set-square or 90 Degree Angle Tool
Step 1: Drawing Octagonal Shapes
· Octagonal shapes are easy to create using the information in the diagram. Note what the terms ‘Across Opposite Faces’, ‘Face Width’ and ‘Half Face Width’ mean. (The term ‘Across Flats’ is sometimes used instead of ‘Across Opposite Faces’.)
· Start by drawing two lines exactly at right angles to each other, by using a set square or other right-angled object.
· Next draw a square whose centre coincides with the intersection of the two perpendicular lines. The length of each side of the square should be exactly the same as the distance across two opposite faces of the required octagon.
· On each side of the square, measure and mark on each side of the perpendicular centre line where it crosses the side of the square, a distance equal to the Half Face Width of the required octagon. These markings will represent the 8 corner positions of the octagon.
· Join all the adjacent marked points with a line, to create the octagonal shape.
Step 2: Windmill Tower Upper and Lower Octagonal Platforms
· The timber for the Octagonal platforms should be at least 25 mm thick – 30 mm would be better. The larger Lower Platform requires a timber width of at least 141 mm.
· The Lower Octagon Platform has an ‘Across Opposite Faces’ dimension of 141 mm.
· The Upper Octagon Platform has an ‘Across Opposite Faces’ dimension of 99 mm.
· First, using the previous instructions for drawing octagonal shapes, mark out with fine pencil lines on the surface of the timber, the octagonal shapes, leaving a space of at least say 20 mm between the two octagonal shapes. You may wish to use one edge of the timber as one of the final 8 edges of the octagon, or you may prefer to draw the octagon clear of both edges of the timber.
· Before starting to cut the 8 edges, check that the face widths and distances across opposite faces, are all equal and as specified in the table of octagonal dimensions.
· Cut the long length of timber to create two short lengths of timber, one for each octagonal shape.
· Clamp the timber using a workbench or engineer’s vice and, one by one, cut the 8 edges of each octagon. It’s useful to do the cuts just a fraction outside the pencil lines, so that this very small excess can be carefully removed with a fairly course file. Don’t cut along the pencil line itself, because that would result in the octagon being too small. Aim to do the line of the cut so that it leaves the full length of the pencil line intact which can then be used as a guide for filing to finish off the octagon.
· Whilst you should aim to achieve a cut which is perpendicular to the surface of the timber, it isn’t particularly important in this case, because of the tapered nature of the windmill tower. The only aspect which is critical is the upper surface of the octagon, because it is against the upper edges of each octagon that the Windmill Tower Cover Boards are in contact when fixed by screws. For this reason, mark in pencil on the upper surface of each octagon “UPPER SURFACE”, to remind you to have this surface uppermost when attaching the Octagons to the Tower Central Core member. (The upper surface of the finished octagon will be the surface on which you accurately marked out the octagonal shape.)
Step 3: The Windmill Tower Central Core
· The square cross section timber for the Tower Central Core needs to be approximately 60 x 60 mm) with a minimum size of 50 x 50 mm and an absolute maximum size of 69 x 69.
· The central core of the tower needs to be very carefully cut to ensure that the sawn end faces are perpendicular to the four side faces of the block of timber.
· Making perpendicular saw-cuts without a circular saw or device to ensure squareness of cut is difficult.
· If you don’t have access to such devices, you can either make a simple ‘perpendicular saw-cut jig’ (see Step 17) or attempt to achieve reasonable squareness and then use a coarse file on the saw-cut ends to make them perpendicular in both directions, but even then it’s not easy to achieve a surface which is both flat and perpendicular.
· I made a ‘perpendicular saw-cut jig’ (see photo’s for Step 17), which enabled me to make very good perpendicular cuts with a flat surface.
Step 4: Assembly of Central Core and Octagonal Platforms
· Drill clearance holes in each octagon for the woodscrews and use a counter-sinking drill bit so that the screw heads lie below the surface of the octagon.
· The two woodscrews (no shorter than 40 mm in length) should be approximately 15 mm from the centre of each octagon along a line joining two opposite corners of the octagon.
· The upper and lower octagonal platforms can now be secured to the vertical central core square cross section block, using two woodscrews at each end.
· Before fixing the screws make sure that:
§ the face of each octagonal platform on which the octagonal shape was drawn in pencil and marked “UPPER SURFACE” is placed uppermost
§ each octagonal platform is exactly centred relative to the centre of each end of the central core
§ the faces of the upper and lower octagons are also exactly in line with each other.
Step 5: Tower Cover Boards
· Eight cover boards in total are required for the windmill tower, but as explained below, it is important that only FOUR boards are cut initially.
· Board thickness of approximately 20 mm is advised, with 10 mm the absolute minimum.
· Draw the shape of the board on the surface of the timber with a sharp pencil.
· Before cutting each board write in pencil on the surface on which the shape is drawn, “INSIDE SURFACE”, because it’s important that this carefully measured shape is the side of the board which fits against the edge face of the octagonal platform. However carefully you do the saw-cut, the other face of the board is likely to have slightly different dimensions, but this isn’t critical because the outside surface of each cover board is not in contact with anything else. The critical face is the one in contact with the octagonal platforms.
· Straightness of the long edges of the tapered boards is just as important as the width, because the two edges of each board butt up against an adjacent board.
· First cut just one Cover Board and place it against the assembly of the Octagonal Platforms and the Tower Central Core, in a position where the board width exactly matches the width of the Upper and Lower Octagonal faces. Carefully check that the board projects above the Upper Octagonal Platform by at least 25 mm.
· If the above applies, then cut only THREE more boards, bearing all of the above in mind. The final FOUR boards will be cut to suit the dimensions of the gaps created in the process of fitting the first FOUR boards on alternate faces of the Upper and Lower Octagons, as described in Step 6.
Step 6: Fitting of Cover Boards to Tower Structure
· The Cover Boards are longer than the distance between the top surface of the Upper Octagonal Platform and the bottom surface of the Lower Octagonal Platform, as mentioned in Step 5.
· Now mark on one board the required positions for the two holes on the centre line of the board, such that the fixing screws will enter the octagonal platforms at approximately the mid-thickness point of the edge face of each octagon.
· Drill holes just large enough for the screw to pass through easily but with a minimum of clearance, and countersink both holes.
· Now drill and countersink holes in the other THREE boards, exactly matching the positions of the holes in the FIRST board.
· Fix one tapered cover board to the two octagonal platforms with screws ensuring that its width on the surface marked “INSIDE SURFACE” (on which the shape of the Cover Board was drawn in pencil) exactly matches the Octagonal Face Width of Upper and Lower Octagonal Platforms. As described in Step 5, this should result in the TOP end of the Cover Board being at least 25 mm above the TOP surface of the Upper Octagonal Platform.
· Now fix the remaining three Cover Boards in a similar way:
but leaving a space between each Cover Board (ie fix boards on alternate faces) and
ensuring that at both the top and bottom, the upper and lower edges of each board lie in the same horizontal plane
· The distances between boards for each of the four gaps should then be measured carefully. The width of the four remaining boards should be fractionally (say 1 or 2 mm) wider than the measured gaps, so that when these four boards are fitted, the risk of ‘poor joints’ is minimised.
· Each of the final four boards should be cut in accordance with the measured gaps (plus say 1 or 2 mm).
The final four boards can then be fitted using the same procedure as for the first four, but carefully side-ways positioning each board to give the optimum fit against the adjacent boards previously fitted.
Step 7: Bearing Housing Assembly
· The bearings (pre-fitted in bearing housings) supporting the rotating shaft, are located on the top surface of the Upper Octagonal Platform.
· However, rather than fixing the bearing housings directly onto the top surface of the octagonal shaped timber, it is preferable first of all to fix the two bearing housings on a short length of metallic plate, angle or channel which only needs to be stiff enough to avoid bending. A flat metal plate should be approximately 2 mm thick, but a length of angle or channel section of 1 mm thickness would be suitable.
· The distance between the outside faces of the two bearing housings should be no more than 85 mm, in order to fit in the space with a small clearance. Care should be taken to make sure that the two bearing housings are exactly in line and parallel to each other.
· The assembly of the two bearing housings on a metal plate, angle or channel can now be fixed with four woodscrews (see photo) on the upper surface of the Upper Octagonal Platform. The centre line of the bearings should correspond with a line running from the mid-point of one Tower Cover Board to the mid-point of the exactly opposite Tower Cover Board.
· A hole of 10 mm diameter should be drilled in one of the above two Cover Boards such that its centre is exactly in line with centre line of the 6 mm diameter threaded rod when fitted through the bearings. The position of the hole can be marked on the inside of the Cover Board by passing horizontally a short length of 6 mm threaded rod through the adjacent bearing and marking the position where it touches the Cover Board. After temporary removal of the Cover Board, drill the 10 mm diameter hole through Cover Board at a slight angle to the board so that when the Cover Board is re-fitted, the hole centre line is HORIZONTAL.
Step 8: Making and Fitting Rotating Shaft in Bearing Housings
· Cut a length of approximately 175 mm of M6 threaded rod and at one end temporarily fix two locknuts tightened against each other for later use.
· Replace the cover Board with the 10 mm diameter hole and then thread the M6 rod through the Cover Board hole and through the nearest bearing.
· Immediately the threaded rod projects through the first bearing housing, put an M6 locknut onto the threaded rod and wind it along the threaded rod for say 25 mm, by gripping the nut with a spanner and turning the threaded rod with a spanner on the outer of the two nuts previously placed on the opposite end of the threaded rod.
· Now place a second M6 locknut on the end of the projecting threaded rod between the two bearing housings.
· In stages, wind each nut further along the threaded rod until the end of the threaded rod passes through the other bearing with say 5 mm projecting beyond the bearing housing.
· Finally, adjust the positions of the two locknuts so that they finish up at opposite ends between the two bearing housings, abutting the bearing housings, with just a tiny amount (1 mm max) of clearance. The clearance allows the shaft to sit between the two housings and rotate freely, whilst being unable to move ‘to and fro’ by more than 1mm.
Step 9: Making Sail Attachment Bar
· Using a metal hacksaw make a Sail Attachment Bar in accordance with dimensions in the drawing BUT do NOT drill the central 6 mm diameter hole.
· Drill the two 6 mm holes at each end, as per the dimensioned drawing, for attachment of the sails.
· The Sail Attachment Bar dimensions are not particularly critical. The bar should be approximately 30 mm wide and at least 1 mm thick, but no thicker than 2 mm. Two are required and they can conveniently be made from either flat rectangular bar or Flat Structural Restraint Straps available from builders’ merchants such as Travis Perkins.
· Both ends of the Sail Attachment Bar need to be twisted through approximately 15 degrees as illustrated in the photo. This can be done by gripping the bar at a point just beyond the mid-length point of the bar (towards where the sail is to be attached) and then grip the bar with a mole grip tool or an adjustable spanner at the point where the innermost edge of the sail will be on the bar (at least 20 mm from the mid-length point of the bar).
· A twisting action of appropriate magnitude on the mole grip tool or spanner (like with a screwdriver) will then cause the bar to undergo a permanent twist (ie the deformation caused during twisting, remains once the twisting force is slackened).
· Repeat this procedure to produce the same amount of permanent twist for the other end of the Sail Attachment Bar. The direction of twist is best considered as the twist effect caused by gripping a bar and twisting the ends in opposite directions. This can be achieved by turning the bar round through 180 degrees and applying a twisting action in the same direction as the first twist. In whatever way you choose to do it, the twists should be as shown in the photograph.
Finally, bend each end of the bar slightly in a direction which will reduce the angle between the two sails on the faces on the opposite side to the faces on which the Sail Attachment Bar is fixed. This will then help to provide a small clearance between the sails and the Tower Cover Boards. It will also probably give slightly improved performance.
Step 10: Making the Sails
· Mark out on the timber to be used for the Sails, the required dimensions for the four Sails and cut carefully with the wood saw.
· Once all four have been cut, then clamp them all together with as perfect a match as possible and then use a coarse file on all four edges to produce four sails which are as near identical in shape and size as is possible.
· Do NOT at this stage drill any holes in the Sails.
Step 11: Assembly of Sails on Sail Attachment Bars
· Now temporarily clamp one Sail onto the Sail Attachment Bar, no closer to the mid-length point of the Sail Attachment Bar than 20 mm. Then use the Sail Attachment Bar holes as a template for drilling matching holes in each sail, ensuring that the centre line of the Sail Attachment bar sail is in line with the centre line of the sail.
· Then permanently attach the Sail to the Sail Attachment Bar with short lengths of M6 threaded rod (or M6 machine screws) and nuts.
· Repeat the above procedures for the second Sail ensuring that there is the same amount of ‘overhang of the sail beyond the hole nearest to the mid-length position of the Sail Attachment Bar as for the Sail at the other end.
· Then find the perfect balance position for the assembly of Sail Attachment Bar and its two sails, by balancing the assembly on a knife edge or a cylindrical object (see photo), gradually adjusting the position until the balance line is found.
· Mark this position of the balance line and drill a 6 mm diameter hole in the Sail Attachment Bar at this ‘balance’ position. This procedure will ensure a perfectly balanced assembly leading to rotation of the sails with an absolute minimum of wind force.
· Carry out exactly the same procedures for the other Sail Attachment Bar and its two sails.
Step 12: Fitting Sail Assemblies on Shaft
· Remove one of the two M6 locknuts which were temporarily fitted on the end of the rotating threaded rod and wind the other one along the threaded rod until it is approximately 15 mm from the end.
· Place each Sail Bar (with its attached Sails angled away from the windmill Tower) onto the threaded rod, close-up to the M6 locknut. The Sail Attachment Bars should be on the ‘reverse’ side of the sails when looking towards the projecting 6 mm threaded rod projecting through the Tower Cover Board.
· Now screw a second M6 locknut along the threaded rod and tighten very securely against the two Sail Bars whilst ensuring that the two Sail Bars are at right angles to each other, thereby resulting in the four Sails being equally spaced from each other.
Step 13: Tower Roof
· Commence construction of the Tower Roof by cutting either three or four square blocks of wood, all the same size and each from a flat board of between 25 mm and say 35 mm thickness to achieve a total thickness of approximately 100 mm when they are screwed together.
· The side length of each square should be slightly larger (say 150 mm) than the ‘Across Opposite Faces’ dimension of the octagonal shape at the base of the roof (141 mm) such that the roof will provide a reasonable overhang beyond the Cover Boards at the top of the Tower.
· Screw each layer to the layer above it, ensuring that all the edges of the layers are in line with each other.
· On the top surface of the top layer, draw the diagonals. The intersection of the diagonals lines defines the centre point.
· On the top surface construct an octagon with its centre at this point with an ‘Across Opposite Faces’ dimension of 55 mm (using the procedure set out in Step 1) and also ensure that four sides of the octagon are exactly in line with four sides of the square block. Extend the lines of each side of the octagon, right out to the edges of the square block.
· Similarly on the underneath surface of the lowest layer, construct an octagon with its centre at the intersection of the the diagonal lines of the square block and having an ‘Across Opposite Faces’ dimension of 141 mm (using the procedure set out in Step 1) and also ensure that four sides of the octagon are exactly in line with four sides of the square block. Extend the lines of each side of the octagon, right out to the edges of the square block.
· Before commencing the saw cuts, it is helpful to temporarily fix (with woodscrews) another square piece of timber underneath the lowest layer of the square block. This extra piece can be used for clamping in a vice or workbench, thereby making it much easier to make each of the eight saw-cuts required for the octagonally shaped roof.
· First choose an edge-line of the octagon on the top surface which is parallel to one of the four sides of the square block. This will be the starting point for the first angled saw-cut.
· Also, before making the saw-cut, mark on the two adjacent sides of the square block, the line along which the angled blade of the saw will travel during the sawing process - (see photo and diagram).
· Following the marked lines on the adjacent sides of the square block, make an angled cut along the plane joining the edge-line of the octagon on the top surface and the corresponding edge-line of the octagon on the underneath surface of the square block.
· Repeat the previous procedure on the remaining three sides of the square block, again each time marking out on the adjacent sides prior to making the cut, the line which the blade of the saw needs to follow.
· Then mark out the cutting lines on the top surface and on the adjacent sides, before making saw-cuts as before, but now for each of the four corner positions of the original square block.
· Careful completion of the above should produce a perfect 8-sided sloping 3D roof.
· All that remains is for the roof to be attached to the Tower Structure.
Step 14: Fitting of Roof
· Manufacture 2 Roof Attachment Blocks and 2 Angle Brackets as per Drawings.
· Use two wood screws (fixed vertically) to secure each Roof Attachment Block to the upper surface of the Upper Octagonal Platform, making sure that there is a small gap between the Roof Attachment Block and the Tower Cover Board, into which the Angle Bracket can fit. The positions of the Roof Attachment Blocks should be such that a line running between the two Roof Attachment Blocks is at right angles to the rotating shaft – ie the blocks are each 90 degrees away from the Tower Cover Board through which the rotating shaft projects.
· Using short wood screws (fixed vertically), secure the two small angle brackets to the underside of the roof in carefully measured positions which will enable the brackets to drop down into the narrow gap between a Tower Cover Board and the Roof Attachment Block (see photo).
· Measure carefully and mark on both Cover Boards the required position for a horizontal clearance hole to be drilled in the Cover Board for a wood screw to be inserted horizontally through the Cover Board and also through the hole in the Angle Bracket.
· After drilling the holes, at each side insert a screw (horizontally) and tighten it by screwing it through the Angle Bracket and into the Roof Attachment Block.
Step 15: Base Board (Optional)
· In order to prevent it being blown over in extremely windy conditions, the completed windmill should be secured to a fixed object, or alternatively, mounted by means of a vertical woodscrew on a base board.
· Mounting the windmill on a base board, with just one wood screw fitted into the underside of the Lower Octagonal Platform, will provide greatly increased stability. If the screw is just lightly tightened, this will enable the windmill to be easily manually rotated to ‘catch’ the wind in light wind conditions, without having to rotate the base board.
Step 16: Weatherproofing Using Yacht Varnish
· Gently rub all exposed timber surfaces with fine grade sandpaper.
· Remove all traces of dust.
· Apply three coats of yacht varnish, carefully adhering to the instructions.
Step 17: DIY Aid for Making Perpendicular Saw-cuts (Optional)
· I made this saw-cutting aid for the purpose of carrying out this project, as I don’t have a circular saw, and it enabled me to make excellent perpendicular cuts of the timber, for the Tower Central Core.
· The gap between the two sets of vertical boards was set as the same thickness as the saw to be used. The two pairs of vertical boards were set perpendicular to the horizontal base board, with the aid of a right-angled set square. They were then secured at right angles to the base board by the diagonal braces.
· The ‘front’ and ‘back’ gaps in the pairs of vertical boards were similarly lined up with each other, again by using the set square.
Step 18: Swivelling Windmill
Once you’ve made your model garden windmill, using the step-by-step instructions, you may wish to set yourself a challenge, as I did, of designing and making a windmill capable of rotating about a vertical axis. I used an 8 mm bore miniature thrust bearing (to support the weight of the tower unit and sails) together with 8mm bore radial bearings for a vertical M8 threaded shaft. You will see that this windmill has two sets of sails.
As may be seen in the video, it performs extremely well, swivelling as the wind direction changes. The combination of the double set of sails and the swivelling action, provides a constantly changing and interesting visual feature, even in very light wind conditions.
This is an entry in the