Machining and Carpentry

Decimals all the way. I.e. smaller than a millimeter is 0.9mm or really smaller are nanometers and picometers. But they are all just meters without so many extra 0s.

Now for fun try to explain how to notate inches & feet addition. I've had to, and learned a few things.

RickR

The people who install sheetrock, have their own convention. Since accuracy to 1/8 inch is plenty, they call out "48 plus 6" to tell the cutter to cut at 4 feet 3/4 inch. (4'-3/4"). It would be easier in metric--123 dot 8, to a better accuracy. :-)

"Brian" wrote in news:3odhf.2392$id.2159@trnddc04:

I'm an engineer in the US that uses metric exclusively. (Germany parented company). We do precision machining in high volume. The common names of metric units and some info, note that, for lack of a better term at hand, the 'base' unit changes depending on the length of the measurement: Meter: Typically used only where the measurement exceeds 1 Meter, and is the common used base unit for large measurements, not exceeding a kilometer. Centimeter: In my experience, rarely used, see next Millimeter: Generally regarded as the normal everyday base unit, above 1 mm and below 1 M, although it is common to see dimensions of much more than 1 M given in mm (i.e. 1500mm = 1.5M)

Below 1 mm, microns are generally taken as the base unit.

0.1 mm: Generally referred to as either 'tenths' or 'one hundred microns' 0.01 mm: Generally referred to as either 'hundreths' or '10 microns' 0.001 mm: Universally referred to as 'microns' 0.0001 mm: Typically referred to as 'tenths of a micron'

The metric system, once you are used to it, is MUCH easier than the US system. I wasn't really exposed to it heavily until I started my current job in my mid-20's. I had been through machinists school using US units. Now that I have come to use it daily, I can barely do US units anymore. Even in home carpentry, I use a tape graduated in metric units.

How is that tape measure divided out? Like on an english tape measure it is divided out to feet, then inches, then fractions of inches down usually to

1/32nds. So on one of these metric tape measures, how is it layed out? All in millimeters?

Another question - for example let's take a common unit of measurement in the english system a carpenter might use - 1/4 inch. That would be close to

6 millimeters. Let's say a machinist (or carpenter) was using a little smaller than that - 5 millimeters. Now, he wants to cut it in half. Does he call it 1/4 of a centimeter, or as it appears people are saying he would call it 2.5 millimeters? In the english system, if you want half of 1/4, you would use 1/8 inch. What if he wants to cut the 2.5 millimeters in half again - does he then use 1.25 mm? In half again - .625 millimeters? Do engineers using the metric system *never* use fractions like in the English system? They always use decimals like I mentioned above?

Brian

. So on one of these metric tape measures, how is it layed out? All

Yes

That's "Imperial," not "english." a carpenter might use - 1/4 inch. That would be close to

Uh, Bri, what do you do when you need a tenth of an inch?

I do high end finish carpentry. I have two years of engineering school under my belt. In situations (e.g., panelling) where I have to divide a distance by three or seven in the hexadecimal/binary system we use, that doing the math, while well within my abilities, is a *very* clumsy process. Quick, what's a third of 11' 4 5/8" to the nearest sixteenth? Now, what's a third of 347 cm to the nearest mm?

I got burned once when ordering a door. I needed a 3 foot wide door (36 inches). That is a common size, and is often notated as 3-0 (3 ft, 0 inches). But when it showed up, I got a 2-6 door (2 ft, 6 inches). The kid behind the counter had taken down 3-0, but the one in the back ordered 30 (inches). Had to re-order and wait.

There are many times I wish we could just force an overnight change-over to metric. Kind of like that one country that suddenly forced everyone to drive on the other side of the road. A few painful moments, but 'tis the sharp knife that cuts the quickest and hurts the least'.

daestrom

They decided to change over on a Sunday, to avoid traffic problems. It was the worst traffic jam in years -- everyone wanted to try it!

In school you could tell the Electrical Engineers from the Civil Engineers. The EE's used log decitrig slide rules and the Civil's used regular trig rules. It's so easy to convert with calculators, it now doesn't make much difference. During WW II, the Air Force used decimal navigation tables and the Navy stayed with d-m-s. It's hard to break with tradition.

Even after changing to metric, we'd still be stuck with things like machine threads and pipe sizes and 4X8 foot plywood. It would take awhile to completely change over.

"Brian" wrote in news:nithf.6818$Dx3.5460@trnddc07:

It is millimeters, every centimeter marked larger, every meter marked. Much like inch/feet/yard on a typical tape. The one I use is graduated in both inch and metric.

That would be 2.5 millimeters and 1.25 millimeters, and finally, 625 microns.

You never use fractions in the metric system. Always use whole numbers or decimals.

No centemeters on it? Sounds like a lot of little lines with no real way to read where you are. I'm assuming they must have centimeters to help you keep track of where you are. Imagine a tape measure with nothing but

1/16'ths of an inch and no inches or feet. Only yards and 1/16ths of an inch. That would be impossible to make measurements with.

I was just trying to find out exactly how they do machining and engineering. do they divide things into tenths or binary fractions. I guess what everyone is saying is they use tenths, and don't ever use fractions the way we do in the "imperial" system. BTW, I rarely use 1/10 of an inch. maybe 1/16 or

3/32. Just wondering how they divide things into smaller and smaller units with the metric system (SI).

--------- The metric system is based on powers of ten. nanometer (nm)=1/1,000,000 meter millimeter (mm)=1/1000 of a meter centimeter (cm)=1/100 meter kilometer =1000m megameter =1,000,000 meter

Common usage is in cm, mm or m and going up is km, etc SI units use powers of 1000 - eg nm mm, m, Km, etc However, a metric tape will have m, cm and mm marked just as an Imperial tape will have feet, inches and fractions of inches (1/16, 1/8,1/4,1/2) marked. Plans may have mm marked (say 3250) or meters (3.25) marked. Ditto layout for weights etc -factors of 10.

By the way, have you heard of "mils" as used im machining? 1 mil =1/1000 inch

That is my experience too. It is almost universal in the metric world that units are multiples of 1000. Thus micrometre, millimetre, metre will be used, but not centimetre or decimetre.

Note that about 40 years ago, the term 'micron' was officially replaced with 'micrometre'. This made it consistent with microwatt, microgram, microfarad etc. The term 'micron' is still widespread (even the metric system has legacy issues). But the term 'micrometre' is now becoming seen in documents on a regular basis. So staff need to know that these two terms mean the same thing.