Thread: Unit Conversion Charts/References - Lumber Sizes etc.

It's been done with a calculator and doesn't reflect the actual sizes available in oz
eg
inches mm fuinished sizes
2x1 = 50 x 25 = 42 x 19
3x1 = 75 x 25 = 70 x 19
4x1 = 100 x 25 = 90 x 19
5x1 = 125 x 24 = 120 x19
6x1 = 150 x 25 = 140 x 19
etc etc
1-1/4" is a non standard size =32mm
1-1/2" = 38mm roughsawn - when dressed is 35mm
etc etc

Good thing I haven't relied on it yet!

I just measured the 1 by 1, 2 by 1, 3 by 2 I was sold yesterday. This is Fingerjointed Primed DAR timber -

1 by 1 - 18 by 18
2 by 1 - 42 by 18
3 by 2 - 66 by 42

These measurements are again different...

There are a few issues here.

1. Straight out conversion from imperial to metric. 1 inch is 25.4 mm or 25mm for quick mental arithmetic. So 2 in is 50 mm, 3inch is 75 mm, 4 inch is 100mm etc.

2. If the timber was being prepped in imperial sizes, it would be cut to nominal inch multiples or submultiples, with some margin for error, So a nominal 1 in thickness might come off the saw at say 15/16th inch, depending on the saw, the blade, and the operator. Similar fudge factors apply in cutting material to metric sizes.

3. If the material is to be dressed for smooth faces and edges, machining will reduce the finished size of the material further. At a minimum, about 1.5 mm of material will be removed for each face or edge that needs to be surfaced. Depending on the condition of the raw stock and how it has been handled, surfacing may take more material off, e.g. if the material has bowed during drying or had deep saw tooth marks from milling.

Because all of these things combine, there is no quick mental arithmetic that will give you a machined finished size ( metric ) from stock initially milled in imperial sizes.

There is however a set of standard sizes which material is produced and sold in, and such material should be fairly accurately sized. You would be better to establish what standard sizes are available in your local area in the materials of interest and rework any imperial designs to use those sizes. The other alternative is to invest heavily in machinery that can mill and surface timber to the imperial sizes.

SoulSpirit,

Timber's still cut in imperial sizing pretty well (the machinery's still the same in some mills, so the standard's carried through.)

say 6" (152.4mm) rough sawn, shrinks a bit when dried, then milled down to finished dimension.

In hardwood, which shrinks less, this is supplied typically at 142mm width.
In pine, which shrinks more, this is typically supplied at 140mm finished width.

It's species dependent to some extent.

Here's a link I use when teaching.
http://www.chadwickstimber.com.au/cg...school_project

I'm sure that the sawmillers amongst us in the commercial mills will correct me if I'm wrong.

Cheers,

eddie

Thanks team.

I'm starting to understand the system a lot better now.

That link - http://www.chadwickstimber.com.au/cg...school_project

Is worth it's weight in gold.

thanks, need this table.

I have to ask why do you need to convert in the first place, Australia is metric has been for 48 years.

Originally Posted by China

I have to ask why do you need to convert in the first place, Australia is metric has been for 48 years.

He comes from Colombia, Sth America
Probably wants to convert US imperial to metric

You shouldnt need to convert timber sizes in Aus unless you are trying to work from US plans.

I find only need to convert when it comes to fasteners, screws and sometimes drill bits or router bits and then typically only fractions. I have had a smart speaker in my shed for the past few years now so I often just find myself asking it for help. For example if I wanted to convert 11/64th to mm I just ask the Google or Alexa "what is 25.4 divide by 64 and then ask it to multiply that by 11.

Thats my method then I need not have to focus on consulting a chart or tying up my hands with pencils or calculators.

He comes from Colombia, Sth America
Probably wants to convert US imperial to metric Then why does he list his Location as Coogee Sydney

Originally Posted by China

He comes from Colombia, Sth America
Probably wants to convert US imperial to metric Then why does he list his Location as Coogee Sydney

Have a look at Omega who made the recent post

I made a deliberate decision 30 years ago to only use metric measurements following a disastrous project.

An imperial drawing of a chair was partially converted to metric, and the chair was almost complete when I realised that the space between the arms was slightly less than the span of my backside. Oops! Demoralising, but I did manage to recover.

Subsequently, I have learned how to do CAD drawings and I now draw every project. "If I cannot draw it, then I cannot make it". The corollary probably also applies - "By the time I have drawn and refined something, I have probably worked out how to make it." Now, I never copy anyone's work, but if something is inspired by an imperial plan then I just convert it to metric in the CAD phase.

This works for me.

I was replying re the original post