This article will show you what is inside side winders on roller blinds and give you some hints on how to install or fix them.
Basically they work as cogs, activated by the links on the side-winder chain. When the chain is pulled, the chain’s links – which slot into cog grooves inside the side-winder – force the winder to turn. Depending on the configuration of the window, the blind can be rolled so the roller is exposed (as in photo right) or reverse rolled so the blind covers the roller. It can be set on brackets inside the window frame or above the frame.
The blind fabric is rolled around a central metal tube. The top edge of the blind is attached to the rod by double sided tape (shown to the left, in pink). The two parts of the winder are pushed into the rod at each end and then attached to the window frame on brackets. Generally, the winding unit is made of four parts. The parts are joined together by a screw in the inner end (see hole in the end of the right-hand piece, photo below left). The next section is the casing for the bearing which allows the blind to revolve. The two left-hand parts form the bearing and the cog mechanism (see also, photo below right, which shows the cog raised for attaching the chain). 
The side-winder chain is joined into a loop which should hang down about three-quarters of the height of the blind (see window photo, extreme right). Thus the chain should be cut to a length of three-quarters the length of the blind drop multiplied by 2.
Once the chain is wound around the cog it will be joined together by a clip (below right), BUT FIRST, it is important to position the chain length correctly. If the winder is to be on the left side of the blind, attach the chain, as shown below left, with a short length on the right-hand side. If the winder is to go on the right side of the blind, attach the chain with the short side on the left (that is, the short end should be at the back of the winder once it is in position on the window). Connect the parts of the winder together again with the inner screw. With the blind rolled around the inner tube, press the winder sections into each end of the tube. Connect the chain together by placing the end knobs of the chain into the clip holes (see below right) and close the hinge firmly. Attach the brackets to the window frame. Slot the roller into the brackets. Test the system. Most kits include a small clip that can be attached to the chain to stop the roller at the correct position as it is rolled up.
