Reading Franks blog about the reliability of spirit levels and Dicks comment about taking measurements has caused me to think about the trials of being arithmetically challenged.
I suppose I have my English ancestors to blame for the Imperial measuring system, but at least they had the good sense to move away from it. I mean, what on earth is logical about 32nds and 64rths?
I’m being honest when I state that it was the Imperial measuring system that kept me away from woodworking for a long time. I just found the mathematics involved in fraction conversion just to complex (read prone to error).
Canada converted to the Metric System sometime in the late sixties or early seventies. But at that time in my life, I was too busy earning a living to think of metric other than when purchasing gasoline by the liter.
Then in the late eighties I moved to Australia that had adopted the Metric system with zeal, much more so than Canada where, because of the proximity of the USA and it’s influence on them, has sort of a hybrid setup. People in Canada still measure a person’s height in feet and inches and their weight in pounds. And they purchase a pound of butter, and use American letter-size paper.
So what has this got to do with woodworking? I ask you what could be simpler than measuring everything in Millimeters? A person six feet tall is 1800mm, and that’s normally how their height is expressed, although it doesn’t take a Einstein to convert this to 180cm, or 1.8 meters. But most measurements used by a cabinet maker are simply expressed in millimeters. For example the surface of a large desk would be 1525mm x 865mm (5’ x 4’10”). Any math required to subdivide a measurement is extremely simple. No fractional conversions are required. A measurement of 1525mm divided into three parts is 1525/3=508. Granted, we’ve lost one millimeter in this division, but 1/3 of a millimeter in each part is normally inconsequential in woodworking.
The thickness of lumber is measured the same way. A 3/4” piece is simply 19mm. [This would be called a soft conversion. A soft conversion is where an Imperial standard is converted to a metric measure.] But most woodworkers abandon soft conversion. There is no logic in using a piece of wood 19mm thick. Twenty millimeters would make more sense and subdivisions of that size would normally be done decimally, i.e. 15, 10, 5. I like to make my boxes with a 10mm thickness, but anything up to 15mm looks OK depending on the overall measurement of the box. A typical small box would be 215×145 x 90 (8,1/2” x 5,3/4” x 3,13/16”). The convention of measuring lumber thickness in quarters in unknown, and frankly, confusing to metric woodworkers. Lumber is measured in cubic volume not board feet.
I’m not trying to convince any of you to switch to metric. That would be impossible in the USA without massive changes – you can’t go it alone. Any of you that have an engineering background already know how superior metric is over Imperial. But it’s sort of ironical; you Yanks turned your back on the Monarchy and all its trappings when your nation was founded. You even introduced a metric monetary system. I guess your founding fathers wanted something to remind them of their roots so they kept the Imperial measuring system.
-- CanuckDon "I just love small wooden boxes!" http://www.dpb-photos.com/