Giant Industrial Fans

All the best Sci-Fi films include large, slowly turning fans giving a sinister flickering light - Alien, Blade Runner, and that ventilator fan in Alien 3 that made mincemeat of the poor fellow cleaning out the tunnel. I wanted to create some similar fans for my Necromunda and 40k terrain, and this is how I did it.
The modelling of fans depends upon the mastering of one technique - making a close fit onto a curved surface - for example, to fit the tubular body of a fan onto the rounded side of a storage tank. Fortunately this is simple when you know how...
Imagine that you have a large storage tank which is to have a ventilation fan at the bottom (see the example in some of the pictures). The tubular body of the fan, which will house the fan blades, must fit onto the round surface of the tank. Provided the body of the fan is made from something fairly soft, for example plastic waste pipe or drain pipe, this is easily done.
Take a sheet of medium to fine grade sand paper and wrap it around the surface you want to fit to, in this case the body of the tank. Now rub the end of the tubing which is to become the fan body vertically up and down the sandpaper. The tubing is gradually sanded down to conform to the shape of the can. Take care to keep the tubing square in relation to the surface to be fitted. With care you will sand the tubing into a perfect fit on the curved surface. This makes the production of ventilator fans easy.

Materials

1. Tubing for fan body - eg plastic drain pipe, waste pipe
2. Plascard or card for the fan vanes
3. Small bore plastic or wooden rod for the shaft of the fan - the shaft should be at least as fat as the proposed width of your vanes otherwise you will have difficulty fitting the vanes.
4. Small size metal mesh for the fan grille eg the type used for rabbit hutches
5. Plascard, foam card, cardboard or similar for the base of the fan if it is to be a floor fan.

Method

1. Cut the tubing for the body of the fan to the required length and sand to fit the curved surface if fitting to a tank (see above). Decide how many vanes you want on the fan. Four is sufficient for small fans, six or eight looks better on larger (2 inch diameter upward) fans. Cut strips for the vanes which are about one and one half times as long as they need to be when finished. The large bore pipe in the photograph is an offcut from a piece of copper plumbing pipe that is sold as hand-bendable, hence the corrugated appearance. Look out for offcuts of interesting piping.
2. Cut a piece of rod for the fan shaft with length to spare in case of mistakes.
3. Fit the vanes one by one to the shaft, but do not glue them until they are all done. To fit the vanes to the shaft, wrap sandpaper around the shaft (one layer only). Hold the end of the vane against the sandpaper, twist it to get the angle on the blade that fans and propellers have, and then rub up and down the sandpaper-covered shaft to sand the profile of the shaft into the end of the vane. If you are using a small bore shaft you may have to use a thicker piece of rod as a hub for the fan, and attach this to your thinner shaft.
4. Glue the vanes to the shaft taking care to space them evenly. It is easier to get the spacing correct if they are glued on in pairs opposite each other.
5. Glue the shaft, complete with vanes, to the bottom of the fan and centred within the body. This will be the surface of the tank, if you are fitting to a tank, or the base of the fan if it is to be a horizontal floor fan. If the fan is on a vertical surface and the shaft keeps falling off then glue a block of cardboard or plascard to the end of the fan shaft first, let it fix, and then glue this larger surface to the vertical surface.
6. Cut the mesh for the fan grille but don't glue it on yet
7. Spray the fan and the grille, still unfixed, black.
8. Dry brush the inside of the fan with silver to pick out the vanes
9. Glue the grill in position
10. Dry brush the grille and the rest of the fan body

Once you have the idea you can improve the fans by adding detail such as control panels, rivet detail and fixing bolts.