I would also add that in today's modern world, with many different items made on machine tools (plastic items are made first in metal and then a die is made to cast the plastic versions which will be sold), it allows far greater creativity to use metric whereas there are too many limitations in machine tool work if you use inches. 1 inch is too big for many things in today's modern world, even thousandths of an inch are too big. For some things even microns are too big, but then you would just use nanometres instead (1000 nm = 1 micron/micrometre).
And if 1 nanometre is too big, then use picometres, although I don't know how big atoms are in relation to that size, so I don't know if it would be possible to go that small, but at least in theory we can with the metric system, something that was impossible in inches as it would involve using very cumbersome fractions or many noughts after the decimal point.
David King
Euric wrote:
metre
Millimetre v inches September 7 2004, 5:42 AM
Some time ago, I came across an imperial site where an engineer waxed lyrical about thous (1/1000 of an inch) used in lathe work. As expected, he sang the praises of these obsolete units. They are much more handy in machine work than mere millimetres and microns, he states. Allowing the operator to work easily to exact tolerances, something appearantly not so easy in metric. Being a musician, I have no first hand experience in this field, so I took it with a grain of salt. Not long ago, I came across this piece burying yet another imperial myth. CNC stands for Computer Numerically Controlled machines.
These are excerpts:
CNC Resources
CNC Tip:
Disclaimer: CNC Concepts, Inc. accepts no responsibility for the use or misuse of techniques shown in this web page. We simply publish information we feel will be of interest to CNC users. In all cases, the reader is totally responsible for considering the implications, good and bad, of implementing one or more of the techniques we show.
Which mode is better, inch or metric?
Most companies work exclusively in one mode or the other. If the bulk of their prints are dimensioned in inch (as with most companies in the United States), they program and run the machine in the inch mode. If they happen across a print dimensioned in the metric mode, they convert all dimensions to inch (by dividing all millimeter values by 25.4) and still work in the inch mode.
If you are one of the many companies that still work exclusively in the inch mode, you probably don't know about the accuracy advantage of the metric mode. This advantage has to do with the least input increment of the input mode. The least input increment in the inch mode for the vast majority of CNC machines is 0.0001 in. In the metric mode, the least input increment for these machines is 0.001 mm. 0.001 mm is less than half of 0.0001 in (0.001 mm is equivalent to 0.000039 in), meaning your CNC machine will have a much finer resolution when the metric mode is selected.
To get an understanding of this implication, consider a common indexer. A five degree indexer has 72 positions (360 divided by 5). A one degree indexer has 360 positions. Though the one degree indexer is no more accurate than the five degree indexer, you can program it with a finer resolution. You can, of course, index 34 degrees with a one degree indexer and cannot with a five degree indexer. One way to compare this to the inch/metric mode selection is to say that working exclusively in the inch mode when the metric mode is available is like having a one degree indexer but only programming it in five degree increments!
Said another way, a ten inch long linear axis has 100,000 programmable positions in the inch mode. In the metric mode, the same ten inch long axis has over 254,000 programmable positions!
While people who have never worked in metric mode will find the transition a little cumbersome, if you do tight tolerance work, these accuracy benefits are well worth the effort. In many cases, you'll be able to hold size (or make less scrap) on work pieces that have been previously impossible to machine on CNC machine tools!
