Tom and all,
When I was wearing an engineer’s hat and working for a large company we moved to “the metric” system. This forced me to learn more then just conversion but to even think metric. You know, “that looks like it is 300mm” not “gee that is about 12” so if I divide or was that multiply by….” As an engineer we normal worked in decimal as in that looks like 12.000 +/- .006. Mixing the systems made interesting mismatches with rounding so we did a lot of learning. As a wood worker and a student you get a lot of fraction practice and a lot of people still can’t take ½ of ¼ and get the right answer. The more you do the better you get at it……
Without a calculator who wants to convert 11/16 to decimal then 7/16 to decimal to do the math, you just learn to do it. For us it is a way of life.
I remember hearing that we would be a metric nation back in 50’s, we even started to learn the system and when I had physics in high school we used both systems. Time marched on but as we all know we are a long way from being a metric nation even now 50 years later.
As a wood worker I guess I will stick to the “imperial”, after all the tools are still that way, and I don’t see this country changing in my life time. I do now as of this Christmas have two metric guide bushings so things are changing.
Having said all that, back to the subject at hand. I often use a table to find my way around the size issues. (Sorry all you metric people… it is in fractions.) That way I can just look at what bits and guides I have and pick which one to use. If you want to keep doing the math the way you have been fine but using the chart to check your math is always an option. (Tom knows his stuff so he does't need the table but as for the rest of you, it can't hurt.)
Since the size is more limited here as an attachment I will post the chart in the gallery. If you have trouble reading it let me know I’ll post new instructions. This is an expansion of a chart I did a while back. See:
http://www.routerforums.com/showthread.php?t=163
If someone want a metric chart I’m willing to do one but I will need common sizes of bushings and bits in metric…..
Ed