I switch back and forth all the time, but I still visualize imperial. I'm working on visualizing metric distances so that they feel more intuitive. I still have to -think- that 100mm is roughly 4", 300mm is just less than 1', and 900mm is just enough less than 3' to be irritating. On the small side, 1mm is more than 1/32", 12mm is less than 1/2" but 13mm is more, and I always have to think about whether 16mm is less than or greater than 5/8". Exactly how wide is my Pfeil 16mm chisel again? That's just for examples.
My metric education started in Ecuador where I did some woodworking training. I went to a lot of work to do casework plans in metric, then got to Ecuador and found that the guys I was training were multi-lingual in imperial and metric, but had mostly imperial rules and tapes. I got my first metric tape in Ecuador - it has the Stanley name on it, but might be a knockoff, as the Stanley planes definitely were (my first clue was that the lateral adjustment lever was cast into the plane body). I still have the tape.
From a practical point of view, despite how you work, you have to talk imperial in the US. You can't go to a client and say that a cabinet will project 600mm from the wall, or that it will be 800mm tall. Most people won't be able to visualize it. So despite the fact that metric math is way more intuitive than imperial (i.e. binary-converted-to-decimal for distances less than an inch and a weird decimal/duodecimal hybrid for distances greater than an inch), imperial is still necessary in some places - not because people find the math easier, but because it's what they can visualize. And at the end of the day, I still have to break down a 4'x8' sheet into pieces parts, even if all of my project measurements are metric.
But while we're on the subject, I get 20mm holes in the MFT top, but what's with putting the holes 96mm on center? That makes the math easy - not! Is it related somehow to the 32mm standard for cabinet hardware (which doesn't really seem intuitive either)? I'm thinking that you can give people a perfectly good metric system and they can still make things harder than they need to be.
At any rate, the point is that the ease of math is not the point. It's the fact that imperial is so embedded in US society that, with the exception of people who have certain kinds of technical or scientific training or were raised elsewhere, people in the US intuitively visualize the distances of imperial measurements, but have to do mental arithmetic (dividing by 0.03937?) to visualize the distances for metric measurements.
So for others raised with imperial measurements, I'd ask the question of this topic a bit differently. Have you learned to visualize in metric? How did you have to change the way you think to do it?
