Exporting from Rhino for milling

I am working on a model that will be used to mill a pattern. The last tie I did work for this customer, I made sure that all my tolerances were dialed in sop that I had a completely closed surface in Rhino. The customer complained that he head to do extra work to rejoin surfaces that were offset. From my experience in working with people using NX or Inventor, the surface tend to migrate, causing the edges to overlap or otherwise not match up. My question is, what is the best format to export in so that I maintain the tight surfaces that I have worked really hard to create?