It is not solely about tolerances, though they can be critical in certain
operations. For example, a steel beam, pre-drilled with say 6 holes each
end, and designed to bolt on to a column at each end also pre-drilled, may
be 10 000 [10 m] or even 15 000 [15 m] long, yet the tolerance may be no
more than 2 or 3 mm each end if the holes are to line up.
But it is primarily about convenience and avoidance of errors where sticking
to mm makes most sense. As you can see in the beam above, mixing cm and mm
for that beam will just add confusion. Start mixing cm and mm everywhere
else and errors will be made. The principle of using mm only has been well
established, and is now too well entrenched (even in the US) to even
consider changing.
You say that you were never educated in the metric system, and that is
unfortunate, for it looks like you are doing what I imagine most of us did
when first dealing with the metric system - looking at it in the overly
complicated context or framework of how we work in imperial/USC. When you
ditch that - which does require a change in thinking, albeit a very
straightforward change - then suddenly metric becomes simpler, and,
critically, easy to visualize, even when working with mm on large buildings!
John F-L
----- Original Message -----
From: <a-bruie...@lycos.com>
To: "U.S. Metric Association" <usma@colostate.edu>
Sent: Saturday, December 11, 2010 1:16 AM
Subject: [USMA:49150] Re: Construction SI
Of course the components would be mm, they are all small items and should
be mm. I am talking the layout of these drilled holes (not hole size),
studs, columns, or walls for buildings, or slopes, pitches, room sizes,
levelness, and areas sizes -- mm precision does not make sense. Cabinetry,
is not building construction, needs more precision than a building. What
is the tolerances in construction that requires +- 1 mm exactness, that cm
or tolerances of +-.25 cm can not be used? A drill is a drill is a drill,
it is not hole distance, or board length or layout. Just for reference
1/16" is 1.6 mm rounded. 1/8" is 3.2 mm 1/4" is 6.4 mm, since I am
American and was never taught Metric in school.
Anyways I did not think 1.1 cm, 2.2 cm, 3.3 cm .... 9.9 cm would be a
problem. I guess it does not matter.
Id put my money on the sun and solar energy. What a source of power! I
hope we dont have to wait til oil and coal run out before we tackle that.
I wish I had a few more years left. -- Thomas Edison♽☯♑
----- Original Message -----
From: "John M. Steele" <jmsteele9...@sbcglobal.net>
To: "U.S. Metric Association" <usma@colostate.edu>
Sent: Friday, December 10, 2010 7:40:04 AM GMT -05:00 US/Canada Eastern
Subject: [USMA:49117] Re: Construction SI
Centimeters might suffice for some measurements. But many fasteners, panel
thicknesses, cabinetry thicknesses, drill holes etc would require
millimeters. One or the other would have to be labelled on the drawing
with units EVERYWHERE. Drawings that have a standard unit unless otherwise
noted are MUCH easier to read. By convention, including ANSI SI10 and
other standards, that dimension is millimeters, in virtually all
industries. (IC chip design would be more likely to use micrometers)
Calculators which offer engineering notation (powers of ten which are also
powers of 1000) allow convenient substitution of prefixes for the
engineering notation, whereas centimeters require you to stop and think
every time. Structural calculations would be a nightmare. In construction,
the first order of business is that the project shouldn't collapse.
If you want "rounder" numbers, just insist most dimensions be a multiple
of 10 mm. Problem solved. Anyway, a prefix doesn't create a new unit. It
is still the base unit with a prefix substituted for a power of ten in
scientific notation. (I think Pat will contest this.)
From: "a-bruie...@lycos.com" <a-bruie...@lycos.com>
To: U.S. Metric Association <usma@colostate.edu>
Sent: Fri, December 10, 2010 6:54:25 AM
Subject: [USMA:49114] Construction SI
First, is there an archive of this forum?
Second, I still do not get why the building industry choose to favor
millimeters vs. using centimeters. As a toolmaker, of course, millimeter
and micrometer is mostly used in the blueprints but millimeters in
construction? When a quarter inch is refereed to most often, as in a slope
of 1/4" to 12", in metric would simply be 2 cm to 1 m or 2%. Or using 8.25
cm vs. 82.5 mm for 3 1/4". When building homes and skyscrapers, mm, do not
make sense, to me.
I do not get their reasoning.
Id put my money on the sun and solar energy. What a source of power! I
hope we dont have to wait til oil and coal run out before we tackle that.
I wish I had a few more years left. -- Thomas Edison♽☯♑
