Shouldn't be a problem the rack on my lathe is made up of 6 or so 100mm sections, (don't know why) the ends have been perfectly cut and then they have also been dowel in place as well as the screws.

Alternatively you could leave a small gap between the racks (gear teeth will push against the sides not the trough) and use a short piece placed on top (upside down) to set the correct distance (add a bit of epoxy or tread lock if you are worried.)