Hello all,
I've spent most of the last two weeks designing some microwave receivers for a new project, and am pleasantly surprised at how easy it has been do work almost 100% in SI units.
For example, I ordered some superconducting wire. The catalog of the U.S. based supplier listed wire diameter EXCLUSIVELY in micrometers. I called the company and asked for a quote for 1000 m of a particular wire. Right as I said the word "meters" I remembered that I'm not in a metricated country, so I asked the representative if I they sold wire by the foot or by the meter. The gentleman said either way was fine, but he gave me the prices all in the cost PER METER. My kilometer of 140 �m diameter wire is sitting in the lab.
I was also shopping for connectors and other electronics components. The first connectors I looked at were specified ONLY in millimeters. There are also drawings showing how to machine the part to accept the connector. These drawings are EXCLUSIVELY metric. I looked at several catalog pages for various other connectors and surface mount components from various American companies, and found that catalogs are pretty evenly divided between quoting millimeters (inches) and (inches) millimeters.
I will also point out that other parameters, including operating temperature, voltage, resistance, etc. are 100% metric everywhere. While the naysayer would point out that most lengths are soft-converted to metric, there's no denying that I found two catalogs in metric only but NO catalogs in inches only!
I've been designing a dozen or so new mechanical components around these parts, and I do all my drawings and solid models in millimeters. This has worked perfectly, since all the component data sheets I can find already give dimensions and tolerances in millimeters. I'm also interfacing to some surplus components from a different spacecraft, and all designs and drawings for these American-made parts are 100% hard metric.
Over all, I find that it is very smooth and simple to design parts all-metric. There's no denying that at least for the things I'm working on it's easier to work in millimeters. For example, an M3 screw is 3 millimeters in diameter, comes in lengths of even millimeters, and takes a clearance hole 3.4 mm diameter. That's pretty easy to remember! Compare this to an equivalent common inches part, e.g., a 3/16" #4 screws, at 0.112" diameter by 0.1875" long, with a 0.133" clearance hole.
Also, the drawings come out noticeably simpler, since most dimensions are in round numbers. Even the soft conversions usually only have 1 or 2 digits to the right of the decimal. Standard metric parts like screws and pins are easier to work with than inches parts because dimensions are in round numbers. The metric drawings are noticeably easier to read than a similar drawing for a part designed in inches.
Finally, given the strong support I see in the catalogs for metric dimensioning and the ready availability of metric parts and fasteners, I get the strong feeling that I'm not the only one out there to make the switch!
J.
