The reaper binder is a clever machine that cuts down the grain and then binds bundles of the grain stalks into sheaves. Let's take a lose look at how this works.
The machine is a ground drive machine. In other words the wheels traveling over the ground makes all the gears, belts and so on work. The first step is the cutter bar.
The cutter bar cuts the stalks of grain much like the way a hair clipper cuts hair. It's important that the grain all falls the same direction so that all the heads of grain are facing the same way. The wooden bars you see spinning on the reaper, called the pick up reel, have the job of laying the grain stalks in one direction on the canvas.
The grain stalks are then travel on the canvas bed towards the place where it is tied into a sheave. Once there is a big enough bundle of grain a mechanism trips and winds twine around the sheave then knots it.
Note... the twine is made from hemp. Not the hemp that gets you high, rather the fiber hemp. This is important as the twine will break down and can be eaten by livestock with no ill effect.
The sheaves travel down another canvas to a kind of basket and then off loaded for field hands to pile up in stooks.