First the base is drafted to be shaped like a rectangular with holes for fixation

Then the reciprocal mechanism is based on a cam-gear and shaft, which can be modeled using the ellipse tool

Then the reciprocal shaft which is holding the brush at its end can be modelled using lines and mirroring tools

In order to hold the reciprocal shaft and the cam gear in constant contact, a spring loaded mechanism is added using basic circles and lines then the coping tool

The housing for the spring loaded mechanism is modelled using lines tool, then mirroring.

To download the dxf file

dxf