Correlation of timber sizes

[Kody]

G'day fellas, I will very soon start to buy the timber for the crosspieces / spars that are fitted at the top of the sides to fasten the roof and ceiling. I only have two choices of timber to choose from at the store, (Bunnings). The sizes are 42 x 19 mm or 64 x 19 mm. When I convert these numbers to Imperial, they become - 1.65" x .75" and 2.52 x .75". This equates to roughly, 1 21/32" x 3/4" (or a big 1 5/8" x 3/4") and 2 1/2" x 3/4". I see where you fellas have said you use 2" x 1" timber to fit between the sides to then fasten the roof and ceiling onto. Does the timber measure 2" x 1" as finished machined (dressed all round) or is it reduced to the same size we have here, ie, 42 x 19 mm? Is this size suitable for spanning the walls spaced 60" apart? Or should I use a wider section like 2 1/2" ? I really don't want to buy 2 1/2" and then cut it down to a finished size of 2". I cant express how deep my hatred of the metric system is. Why don't "they" set up a decent standard of uniform increments for manufacturing the cut timber? I miss the Imperial system more and more each day. I built a beautiful 16 foot long canoe over forty years ago and the timber was all cut and finished to a standard size. The size I used was 1/2" x 3/4" and 1/2" x 1". It was a delight to use and the finished canoe was absolutely gorgeous.

Then not long after, in came the metric rubbish.

[pchast]

Lately a 1x2 actually measures 11/16 x 1 7/16 for the cheap stuff.

[mezmo]

Over here [USA] the standard wood [timber to you guys?] sizes are
now considered "nominal", in that they started out "the actual true
dimension" but over the Years have become smaller in actual sizes.

E.G, a 1x2 here is now actually 3/4in x 1&1/2in in actual cross-section size -
but then, don't believe that they really Are that size until you measure them
for yourself and verify it. The quality of the product has a Wide range
of variation here now and the trend for quality is ever downward, it seems.
You need to measure and verify each piece of stock you use.

Sheet goods are another area where quality is decreasing and dimensions
are becoming not actual/true as well. It is hard to find "True" dimensions at
times and you Must measure and Verify for yourself - just to know
what you have or are dealing with, or you will end up with a good case
of "the frustrations". Also, even after the 'due diligence' of measuring
for yourself, pieces can vary among themselves within the lot they are
in. And, verify what the actual thickness of the sheet good [wood, foam,
etc.] is, and that it corresponds to the dimension of what your framing
members will be for that application.

Those small dimension differences accumulate fast and will throw you off
your game. Since TD & TTT building is more akin to finish carpentry and
cabinet making [Using smaller dimensioned structural and finish pieces
and closer tolerances in general.] than rough carpentry, we just need to
keep ourselves aware of the specific dimensions we need for whatever
area/piece we are working on at the moment, and verify that the goods
we are using for such correspond.

It sounds like either size you mentioned would be OK if the longer/larger
cross-section dimension is placed perpendicular to the wall/floor/ceiling-roof
plane, and is oriented across the width as well. But, also keep in mind that gluing
everything together, resulting in a body unit/section, and then gluing those
together will have everything ending up reinforcing each other in a monocoque
of sorts. And not having to rip down the wood pieces, if you can use them as
they come from the supplier, will save much time and effort, only needing cutting
to length etc..

Cheers,
Norm/mezmo

P.S. The "2in x1in", that you mentioned from over here, is actually what we call a
"1x2" and is generally 3/4in x 1&1/2in in actual cross-section size as purchased, they
are not a true 1inch x 2inch in cross-section. So you wouldn't need to buy the larger
size you mentioned and then cut it down to 2inches, unless you wanted to do so for some
personal reason. Since the spars are 'mini-beams' in the roof, "the deeper the beam
- the stronger the beam" applies. One can use any depth [the longer cross-section
dimension] they want, the main consideration in a TD probably being how that would
affect headroom.

[GuitarPhotog]

American lumber sizes are unique and are based on some long-lost historical issues.

Here's a chart of "nominal size" i.e, "two by four" and actual dimensions in inches and millimeters.
http://mistupid.com/homeimpr/lumber.htm

<Chas>

[les45]

Our nominal 1X2 (3/4X1 1/2) is plenty adequate for a 60" width. That's what I used on mine with 1/8" luan inside and 1/4" plywood outside.

[aggie79]

Agreed 1x2 nominal - 3/4" x 1-1/2" actual - is plenty sufficient to span 60".