Why metric?I get questions from time to time if I have plans available in inches. Unfortunately, converting the plans to inches properly means actually changing the dimensions of the plans, so that the fractions work out to nice values. I went through this exercise of converting my combolock plans to imperial, and I found the exercise of working with an intricate mechanical design in fractional units to be very time consuming and frustrating, especially when calculations were needed.
Mechanical engineering simply isn't meant to be done with fractional units. In fact, most mechanical engineering work with imperial units is done with decimal inches. But where can you find a tape measure with decimal inches? I have never seen one. In the mean time decimal metric rulers and tape measures are readily available and used all over the world.
So the solution is quite simple: Design in Metric.
That said, inches are just the right size unit when working with buildings and construction lumber, but they just aren't very good units to use for engineering work where one deals with small distances and lots of calculations.
Generating imperial dimensioned versions of the drawingsIf you prefer to work in 64'th inches, or 1/1000 inches, instead of centimeters, you can You can generate imperial dimensions by loading the SketchUp model into SketchUp, and setting the units to imperial under "Model Info". However, the actual sizes of the machine are all worked out to be mostly even millimeters, so the units will not work out to nice even values in fractional inches or in thousandths inches.