Converting from metric to inches in a plan

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Ok, I have a workbench plan in metric. I've gone thru all of the metric to inch conversions and wanted to ask those who have done this what happens here.
For instance, one my measurement is for 90 x 45 x 700 which converts to (roughly) 3.54 x 1.7 x 27.5 = I have a feeling that this is close enough to standard 2 x 4 = 3.5 x 1.5 - the 27.5, is really depended upon how long I need this piece and might be subject to other components.
However, I've got one at this: 70 x 70 x 810 which equals 2.75 x 2.75 x 31.8.
Should I make this 2.5 or 2 3/4 or 3 inches? Again, I recognize that it could change depending upon the other pieces, but for the purpose of buying lumber, do I just get something I can plane down to below 3 or AT 3 inches?
Experiences shared appreciated.
MJM
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On Jul 5, 5:54 pm, snipped-for-privacy@gmail.com wrote:

Is this a dressy bench or a work bench? If it's a dressy bench and you want to show off the wood, then you should buy thicker stock, joint it and plane it to thickness. If it's work bench you could built it up from dressed stock and make minor adjustments so you wouldn't have to do the milling operations 2 @ 5/4 stock + 1 @ 1x stock puts your right around the 2.75. Making it from built up stock also provides "instant" tenons and mortises by having the middle piece project to form a tenon or having a void to form a mortise.
R
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Ricodjour,

This sounds right. I'll wait until I get more "chime ins".
Thanks for the response.
MJM
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wrote:

Our fine friends at Lee Valley will sell you all the metric tapes and rules you need. I have all of those metric tools. Even a metric watch.
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Robatoy wrote:

Only 10 hours in the day?
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50. (I charge by the hour.)
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snipped-for-privacy@gmail.com wrote:

I would just use metric measuring tools and skip the conversions. <G>
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"B A R R Y" wrote

Exactly ... 3.5 tick marks = 3.5 tick marks ... a rose by any other name still gets the job done.
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On Sat, 05 Jul 2008 21:12:02 -0500, Swingman wrote:

But if you just do that and follow plans you'll end up with a bench 2.54 times smaller than you expected... ;-)
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A large part of the world has gone metric in the last 50yrs but it hasn't been a simple process. The international timber trade for instance remains Imperial and so even in Europe we are often working in metricised imperial. This means for instance that we buy sheet materials in a standard size of 1220 x 2440mm which turns out to be an 8' x 4' sheet. The thickness of the sheet however is metric, precisely sanded to 6, 12, 18, or 25mm - increments of six millimeters, except they aren't because they are metric equivalents of 1/4, 1/2, 3/4, ad 1". And that doesn't apply to certain thin materials which are sold as say 3.2mm thick but which are actually 1/8". Confused? You will be.
As for your plans, the dimensions are clearly metricised inches in that 70mm is 3" planed in a metric planing machine to a metric 2 3/4" (What we call a nominal 3"). 45mm again is 2" sawn timber planed both sides to finish at 45mm. So by all means convert to inches again but there are two pitfalls to avoid:
1. Check three times that things 'add up'. eg 12mm (1/2") plus 12mm(1/2") makes 24mm which is not as much as an inch or even 25mm which is a metric inch.
2. Never add or subtract a mixture of the two systems. A millimeter less than an inch is a dimension on no rule which cannot even be expressed as a decimal or fraction of either system.
If you go for a beer in a bar in France you always ask for a 'demi' which means a 'half' and the barman gives you 250cl, a quarter litre.Why? Because it is a metric half pint, despite the metric system being standard for 200yrs in France beer is still drunk in pints which aren't Imperial Pints but metric equivalents, and not for that matter anything to do with American pints which are something else again.
HTH
Tim W
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A good reason to stick with wine or spirits in France.
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And a pint's a pound the world around...
Another reason customary units (some Imperial, some SI, some American, some others) is that they were determined by custom to be convenient for particular applications. Stress analysis is simpler with force-based units as you don't have to divide or multiply by the acceleration due to gravity. Pascals are way too small to be practical, for most uses, it takes several hundred thousand of them just to blow up a party balloon. If you have to stick a 'k' 'M' or 'm' in front of the unit most of time you use it, it's the wrong size to begin with.
--
FF

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wrote:

pint is only a pound in the US and nowhere else.
Tim W
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wrote:

same as 1/2 kilo, 500 ram, not the 453 or so grams a pound weighs.
Moreover, an "ons" (pronounced almost the same as an ounce) always was 100 grams, not the 28 or so a "real" ounce is.
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Best regards
Han
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My car gets about 28 mpg in Michigan. As soon as I drive across the border at Port Huron, the mileage jumps to almost 35 mpg!!
Must be the oxygen-rich Kanuckistani air, eh?
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snipped-for-privacy@mtavirgin.net says...

Hmmm, here in NZ which has been metric for 50 years or so, sheets also come in 1200x2400, (very few in 1220x2440) and additionally to your imperian fractions in 7mm, 9mm, 15mm and 16mm and 20mm thick, depending on material.

An interesting thought. 250cl is a very large glass of beer. 2.5 litres. Gosh. Those French sure can put it away. Just a bit more than 4 pints, by the way.
A standard glass of Beer in Germany used to be "A Half" ( of a litre) being 500ml. For people with less capacity, or thirst, you could get "A Small" (1/4 litre). Except the beer industry wanted to raise prices, but didn't dare do that, so they shipped smaller glasses and the sizes became 400ml (or 40cl) and 200ml (or 20cl) respectively.
I expect the French demi will refer to 1/2 a standard beer, rather than half a pint, the latter would be closer to 300ml than 200ml.
F.W.I.W. -Peter
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I left some of them out. The range of thicknesses is further complicated here by the veneered sheets because the veneer is applied onto a standard board so it finishes always thicker.

You could also ask for a pound (lb) of something in the market when I was young, at least from the older traders although what you got was 500g.
Tim W
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Tim W wrote:

And often when you buy 1/2" plywood you'll actually get 15/23"' buy 3/4" and you might get 11/16", etc. etc. ---- Posted via Pronews.com - Premium Corporate Usenet News Provider ---- http://www.pronews.com offers corporate packages that have access to 100,000+ newsgroups
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.
Stuff that comes in 23rds is a bear to work with. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I know. my bad... just a typo..
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Spruce ply and other sheeting types plywood's and other rough construction sticks (2x4s etc) are imperial thicknesses, Fir ply and hardwood veneer ply is in metric thicknesses.
Only 3 countries left in the world still on the imperial system, Libya, Burma, USA. Come on! Get with the program. Why convert? Buy a metric tape and a couple of steel rules.

Stuff that comes in 23rds is a bear to work with. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I know. my bad... just a typo..
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