You shouldn't need to redraw.
In the SW drawing, have you set the scale through the sheet scale? or on individual views? If individual views, change to sheet scale and adjust sheet scale accordingly by right clicking on an empty part of the sheet and selecting properties.
When you save as dxf, in the save as dialog select options and enable 'scale output 1:1'
thanks, saves me some good time. looks like I had it set on individual views.