2000-10-25
I can't believe that wood products are cut so accurate that we have to
describe them in tenths of millimetres. Does anyone know enough about wood
working to know what the tolerance is on such cuts? And even if it were cut
perfect, how much is wood allowed to change from such factors as shrinkage
from dryness or swelling from absorbing moisture?
If the cutters can guarantee the accuracy to one millimetre, then 38 x 140
would be just as good. And if the tolerances are greater, then it is
possible some cuts could actually be 40 x 140. And even if they aren't,
what is wrong with calling them 40 x 140? Or if 40 x 140 is too many
syllables, then call it a 4 x 14, implying centimetres.
The same would apply to 50.8 x 152.4. There is no reason this can not be
called either a 51 x 152, or a 50 x 150, or even a 5 x 15. Who would really
notice the difference if they were made to rounded metric sizes? Where
would one or two millimetres make any difference? I just don't see it.
Even, Karl noticed that 0.75 inch plywood is really 18 mm and not the 19 mm
the conversion would tell us. We seem to be forgetting that inches are just
nominal names and even the so-called actual dimensions in inches might not
even be true. If we want people to accept metric, we have to call these
sizes by rational names, and dispense with these unnecessary soft
conversions.
John
One point that Marcus missed was that dimensional lumber may have
hard Imperial measures, i.e. 2x6x8 (2 inches x 6 inches x 8 feet),
but those are not the dimensions of the wood. Any carpenter will
tell you that a 2x6 is really 1-1/2 in x 5-1/2 in. One will only
find a 2x6 to be really 2 in x 6 in. if one were to use rough
lumber. Hard metric dimensional lumber could be made by simply
adjusting the planer to leave a mm more on each side. A 1-1/2 x
5-1/2 would become a 40 x 140 rather than a 38.1 x 139.7. The mill
could continue to cut 2x6 (50.8 x 152.4 mm) for as long as they wanted.
I too would be happy just to see soft conversion in the lumber
industry. I tire of seeing the so called 3/4 inch plywood labeled
as 3/4" when most of it is 19 mm. As a matter of fact the wrapped
plywood I see at Home Depot here in Saskatoon has the dimensions
2440 x 1220 x 19 printed on the wrapping, yet the store sign will
read 4' x 8' x 3/4".
I'd rather buy a '40 x 140 x 2440', a '4 x 14 x 244', a '0.4 x 1.4
x 24', or even a '0.04 x 0.14 x 2.44' than a 2x6x8 any day.
Greg
Calculating with feet and inches in the construction industry is only going
to get worse! Nominally 3/4" plywood now sold at Home Depot in Connecticut
is actually 18mm thick. If a person is going to keep working in fractional
inches, this is 23/32" (a little too fat), 45/64" (a little too thin), or
91/128". None of these fractions is easy to handle.
Karl G. Ruling
