I already wrote that you can have some additional widgets for inventing and building the machine. Even if I had not mentioned it, that would be a reasonable thing to do, if I insist on splitting the crank turning work, you can pretty safely assume that I am also willing to split the inventing and building work in one way or another.
But even if you would not get anything for inventing the machine, it would not really matter significantly. As you both keep turning the crank, the relative amount of work you both did would approach one half and both of you would have half of all the widgets. Compare that to the other scenario where the guy does all the crank turning, there the relative amount of work you did approaches zero as the guy keeps turning the crank making his relative amount of work approach one.
But even if you would not get anything for inventing the machine, it would not really matter significantly. As you both keep turning the crank, the relative amount of work you both did would approach one half and both of you would have half of all the widgets. Compare that to the other scenario where the guy does all the crank turning, there the relative amount of work you did approaches zero as the guy keeps turning the crank making his relative amount of work approach one.