Switch to Metric? Yes or No

[Steve Peterson]

There's two kinds of countries. Those that put a man on the moon, and those that use the metric system....

That is a great quote.

My biggest issue with conversion is the sheer bulk of imperial rulers in my shop. The rules on my tablesaw fence, hand wheels on the metal lathe, more than a dozen tape measures, squares, calipers etc. The complete list would go on for several pages. It would be awkward to be partially switched to metric, so all of them would need to be switched.

I do use metric in a few applications. Some default to cm, others use mm, others use microns or meters. I still have to be aware of which metric scale to use. It seems like I am often scaling between cm and mm. Sure, the conversion is easy, but it is also easy to forget and end up with a size that is 10X larger or smaller than expected. This error rarely occurs with imperial measurements. Construction is always in feet and everything else is always in inches.

[brent stanley]

The control panels for the L.E.M. at least read out in Imperial measure.

Yup, it was converted for the operators.

[Martin Wasner]

For most people, calculating how much would be 12 times 2 9/16 will take longer than calculating 12 times 65mm (if you work within 1/16 or about 1mm accuracy these two distances are about the same).

My hat is off to you if you can do that in your head in either scenario. But switch it around and rearrange the math. 12x2.5625, or 12 x .065. In this odd case, I can start wrapping my head around swapping the meter into a fraction, 1/16 in this case, and actually get pretty close in my head if I'm just looking for a ballpark. 12/16, or basically .75m. I have to grab a calculator to get the actual which is .78. So I'd be off by 30mm with my ballparking. For me to do 12x2.5625 I have to compartmentalize it, (12x2=24)+(12x.5625) well thats kinda 12x.5=6, so I'm up to 30+(12x.0625). 12/16 is 3/4, so 30-3/4" I did that in my head and double checked it with the calculator.

Real world application though. You've got a 24-3/8 opening that is getting a pair of doors with a 1/2" overlay and a 1/8" margin between the doors. 24-3/8+7/8=25-1/4 then divide by 2 for the pair and you get 12-5/8. That's easy mental math that doesn't require a calculator at all.

Call that opening .62m with a pair of doors with a .013m overlay, and a .003m margin between the doors. .62-.023=.597 Then divide by two to get the door size which is .2985m I still got there without a calculator, but it took me a second longer.




For doing math mentally, being able to break the things before and after the decimal into two parts makes it easier for me. When I can break meters into fractions that makes me happy because I know that .375m(3/8)+.5625m(9/16)=.9375(15/16)m. A base 2/4/8/16 system is really easy to wrap your head around. Erratic and base ten fractions are the devil though and I can't wrap my head around the math very easily because I'm not familiar with the numbers like I am on the regular carpenter fractions.



The thousands of years comment is because the units come from things that are used day to day. That's the history of the units and where they came from. I don't know anyone that uses the circumference of the earth in a day to day at all. But from post agriculture to the pre-industrial revolution it gave people units to get close enough on most things. (That is unless of course your into building massive megalithic structures precisely laid out with sacred geometry, that's a different/fun topic all on it's own)


Both have their place, I use both, so in my view there's no advantage to either. I work in the trades, so I'll likely get puzzled looks for explaining things on prints to contractors in meters though. But in a shop full of metric machines and using european hardware, I have to think in both.

I was explaining to a guy I was interviewing recently about doing math in your head quickly was kinda like knowing your phone number. You don't figure out your phone number, you just know it. When you've added certain numbers together for so many years they become like your phone number, you just know that 1/4+3/8=5/8.

[Martin Wasner]

I still have to be aware of which metric scale to use. It seems like I am often scaling between cm and mm.

Just do it all in meters. That's the only unit anyways, why mess with a decimal point and a word.

Mille - 1000th
Centi - 10th
kilo-1000

I worked in a cabinet shop for a while that used feet and inches. Traditionally cabinet shops run purely in inches, anything else confuses our poor simple minds, but the dude doing producing all of the shop drawings was an architect and wanted us in his system. It caused some problems for me when glancing at a print and seeing 2' 3-11/16" as 23-11/16". Which are not the same at all....

[Glen Gunderson]

For cabinetmaking I find sticking with mm much easier. Using the numbers in Martin's post above, combining a 620mm opening + two 13mm overlays - 3mm gap and then ÷ 2 to arrive at 321.5mm for each door is easier for me than using .62m, .026m, and .003m. The decimal and having to think about how many places are after it just makes it slightly more awkward. And of course if you're doing cabinets you don't need to go through all the steps each time, you can just remember to add 26mm to the opening for single door cabinets and 23mm for two door ones when using that overlay and gap.

And in comparison to fractions it's so much easier. 22 11/16" + 7/8" ÷ 2 for instance isn't something I can do very quickly in my head, though maybe that's because I don't do it that often. And even if it does only add a few seconds for each measurement, it's more error prone for me at least. I make mistakes far more often when doing that kind of thing with fractions than I do with mm or decimal inches.

[mreza Salav]

My hat is off to you if you can do that in your head in either scenario. But switch it around and rearrange the math. 12x2.5625, or 12 x .065. In this odd case, I can start wrapping my head around swapping the meter into a fraction, 1/16 in this case, and actually get pretty close in my head if I'm just looking for a ballpark. 12/16, or basically .75m. I have to grab a calculator to get the actual which is .78. So I'd be off by 30mm with my ballparking. For me to do 12x2.5625 I have to compartmentalize it, (12x2=24)+(12x.5625) well thats kinda 12x.5=6, so I'm up to 30+(12x.0625). 12/16 is 3/4, so 30-3/4" I did that in my head and double checked it with the calculator.

Real world application though. You've got a 24-3/8 opening that is getting a pair of doors with a 1/2" overlay and a 1/8" margin between the doors. 24-3/8+7/8=25-1/4 then divide by 2 for the pair and you get 12-5/8. That's easy mental math that doesn't require a calculator at all.

Call that opening .62m with a pair of doors with a .013m overlay, and a .003m margin between the doors. .62-.023=.597 Then divide by two to get the door size which is .2985m I still got there without a calculator, but it took me a second longer.




For doing math mentally, being able to break the things before and after the decimal into two parts makes it easier for me. When I can break meters into fractions that makes me happy because I know that .375m(3/8)+.5625m(9/16)=.9375(15/16)m. A base 2/4/8/16 system is really easy to wrap your head around. Erratic and base ten fractions are the devil though and I can't wrap my head around the math very easily because I'm not familiar with the numbers like I am on the regular carpenter fractions.



The thousands of years comment is because the units come from things that are used day to day. That's the history of the units and where they came from. I don't know anyone that uses the circumference of the earth in a day to day at all. But from post agriculture to the pre-industrial revolution it gave people units to get close enough on most things. (That is unless of course your into building massive megalithic structures precisely laid out with sacred geometry, that's a different/fun topic all on it's own)


Both have their place, I use both, so in my view there's no advantage to either. I work in the trades, so I'll likely get puzzled looks for explaining things on prints to contractors in meters though. But in a shop full of metric machines and using european hardware, I have to think in both.

I was explaining to a guy I was interviewing recently about doing math in your head quickly was kinda like knowing your phone number. You don't figure out your phone number, you just know it. When you've added certain numbers together for so many years they become like your phone number, you just know that 1/4+3/8=5/8.

First of all, I work with both systems and oddly enough,mostly imperial because my tooling is mostly imperial and so it becomes tricky to convert back and forth).
Secondly, Yes I do all the math in my head. I rarely (if ever) use calculator (honestly don't know where my calculator is and if it has battery!). I am fortunate enough (and not old enough yet!) to be able to do these faster than using a calculator.
As for your example and numbers you gave, they look odd because you are still fixing your head to work in the imperial system and numbers coming from there. If you are working with metric system and going with the example you mentioned for doors you can simply design it in the metric and everything will be a whole simple number in metric. European tools/hardware are all metric and I don't find them difficult to work with at all. True, powers of two (1, 2, 4, 8, 16, etc) is good if everything you do is going to be multiplied or divided by two. But as soon as you want to divide/multiply things by factors other than two or you want to even add two fractions with different denominator (8 11/16 + 23 5/8) it slows you down.

Anyway, each one to his own.

[Keith Outten]

No metrics for me...EVER.

Concerning NASA I was the QC Inspector on the Space Shuttle Engine test stand my company built in the early 1970's and all of the drawings used imperial measurements. I was the project inspection coordinator at NASA Langley for ten years inspecting all of the wind tunnels and high pressure piping systems. All of the drawings we were provided and those we created used imperial measurements.

I worked on several submarine and aircraft carrier hulls at Newport News Shipbuilding, everything was done using imperial measurement. I worked on construction projects for nuclear power plants, fossil fuel plants and a host of our large projects from Carolina to New York state, they all used imperial measurements.

If it ain't broke don't fix it

[Malcolm McLeod]

..True, powers of two (1, 2, 4, 8, 16, etc) is good if everything you do is going to be multiplied or divided by two. But as soon as you want to divide/multiply things by factors other than two or you want to even add two fractions with different denominator (8 11/16 + 23 5/8) it slows you down.

Anyway, each one to his own.

^Agree.

You can skew the decision in any direction you want if you cherry pick your example math:

Half of 19mm = 9.5mm (hard) or half of 1/2" = 1/4" (easy)

1/3 of 30mm = 10mm (easy) or 1/3 of 1/2" = 1/6" (easy too) - -until you grab a ruler...so lemme think ... that's about roughly ballpark approximately 5/32" = close enough.

[Ted Derryberry]

32-5/16"...........

[Cary Falk]

I work with metric at work(nanometers, angstroms,microns, g/L, Celsius, etc.) I prefer to work with inches and feet in the shop because I can visualize those measurements. Almost all of my shop is set up for inches. I like working with fractions. Metric won't get rid of fractions though.

[andrew whicker]

I don't have any numbers to back this up, but I'm guessing US switching to metric is more earth shaking than Australia. Contrary to popular belief, US manufacturing output increases every year (jobs within manufacturing may be a different story). And I'm willing to bet that most of those shops are full of Imperial cutters, drills, wrenches, hardware, etc etc. I think the politics behind a major switch would be difficult. Let's just let the free world figure it out on their own instead of doing a forcing rule.

As was pointed out earlier, it seems major industries (like auto) have already or are in process of switching over anyway.

Also... the NASA quote... NASA? What NASA? I kid, but seriously, did anyone watch the awesome SpaceX launch yesterday? I wonder if they use metric.

[brent stanley]

No metrics for me...EVER.

Concerning NASA I was the QC Inspector on the Space Shuttle Engine test stand my company built in the early 1970's and all of the drawings used imperial measurements. I was the project inspection coordinator at NASA Langley for ten years inspecting all of the wind tunnels and high pressure piping systems. All of the drawings we were provided and those we created used imperial measurements.

I worked on several submarine and aircraft carrier hulls at Newport News Shipbuilding, everything was done using imperial measurement. I worked on construction projects for nuclear power plants, fossil fuel plants and a host of our large projects from Carolina to New York state, they all used imperial measurements.

If it ain't broke don't fix it

I expect they were capable of converting to imperial for the outside contractors if needed, but these days, it's public law to use metric in gvt programs.

https://www.nasa.gov/offices/oce/fun...dards/isu.html

Metric in the moon missions makes sense considering it was a bunch of Canadian aerospace engineers and German rocket scientists.

Ducking and running....

[Martin Wasner]

Isn't NASA in the Bahamas?.... lol

[Wayne Lomman]

Our drawing conventions based on the Australian version of the metric system never refer to .375m for example. That is always just 375. If a drawing calls for 24.466m it is written as 24466. For any drawing for a residential building or smaller structure down to cabinet work, everything is in millimetres. There is no 'mm' after every measurement on the drawing, just the raw number. There will be a reference on the information panel as to what the units are.

Machining drawings will be in millimetres to 3 decimal places. Civil works drawings will show decimals to 3 places. Then the main units will be metres but roadworks can be kilometres as well when the job is large enough.

The common thread is that every unit step or part thereof is a multiple of 1000 from microns right through to kilometres. It works the same for weight and volume as well. Cheers

[Steve Demuth]

If it ain't broke don't fix it

Arguably, it is broke. As I said earlier, if you're just building something in your home shop from wood, you're mostly using length, and in makes only marginal difference whether you use metric decimal, Imperial - with binary fractions, or inches decimal. I sometimes use 2 or three in a single project.

But one key value of a system of measurement is agreement between parties on how big, how much, etc - and Imperial is the odd ball on that. As long as you're completely local in the United States, it doesn't matter, but as soon as we're interacting with the rest of the world, Imperial is broken, because it's the different one and forces us into conversion land.

The other sense in which it is broken is if you're needs go beyond simple length and volume measurements. The metric / SI system is vastly easier to navigate for anything involving energy, power, force or related concepts, and is already the standard even in the United States for electrical measurements. The inter-relatedness of those units with the basic units of length and mass is greatly simplifying.