Imperial or Metric?

[Robb White]

I have decided to get into woodworking and have acquired a number of tools and about to start buying woodpecker measuring devices 1281 square, 32" t-square and perhaps a story stick. The question is should I get imperial or metric? I have some green koolaid with plans for some more. The plan is to turn our formal living room into a library with built-ins, built-in master closet, amour, wood panel ceiling with recessed lighting and multi tiered out door decking. Haven't played with fraction much since school and wondering if going metric would be easier. Any thoughts? Thanks.

-Rob

[Judson Green]

Someone here, I forgot who, said one of the great things about imperial is its easy to divide in half.

[John TenEyck]

You'll make far fewer mistakes in metric. For whatever combination of reasons, however, I still work in imperial units - and I'm sure I make more mistakes because of it. A sort of compromise approach would be to use decimal inches.

John

[Kent A Bathurst]

You'll make far fewer mistakes in metric. For whatever combination of reasons, however, I still work in imperial units - and I'm sure I make more mistakes because of it. A sort of compromise approach would be to use decimal inches.

John

I am the exact opposite.

All my machinery is setup to read imperial - I would go nuts [I know - that horse left the barn a long time ago] in metric.

Plus - my soap box here - I have starrett analog dial calipers. Each "tick" on that dial face corresponds prciesly to a "tick" on my TS, my Biese CMS tables, the PC routers, etc.

[glenn bradley]

After a career of 30-odd years in octal, decimal and hex I escape to the warm embrace of imperial measurements in the shop to decompress. Fractions must use different pathways in the brain because my shop time is like deep meditation for me ;-)
That being said, I use both when I need to and being from the generation that experienced the move to and then away from metric I am comfortable with either.

[Wade Lippman]

Metric is so so so much easier to use. Try subtracting 2 15/16 from 9 3/32, or dividing 8 7/16 into thirds.
It would be wonderful if the US could go metric. Imagine one set of wrenches, and nuts always fitting bolts...

Sadly, I still use Imperial 80% of the time. Maybe I should bit the bullet and buy new measures.

[John Coloccia]

I would stick to imperial because that's what's easily, locally available for bits and things like that. That's what you'll find for markings on most US machinery. That said, there's no reason to use fractions just because you're measuring in inches, and there's no reason to use decimals just because you're measuring in meters. Imperial has an advantage in this regard as measuring devices in both decimal and fraction are commonly available, and you're free to use whatever is most appropriate for the situation. My favorite combination is 16R (aircraft ruled) gradautions...1/32, 1/64, 1/50 and 1/100 on the same rule. 50ths don't seem useful if you think of them like that, but if you think of it as .02", .04", .06", .08", then it's suddenly very useful and much easier to read than 1/100 if you don't need that precision.

Judson, I believe I've made the point many times that dividing by powers of 2 in fractional measure is trivial, and it's something we do all the time. Dividing something in half, is probably my most common math operation in the shop. Midpoints, router bushings, setting up a fence for a router, etc, all have that operation, and it's much easier to do it using fractions.

But most of the time, I'm working with decimal measure because that's most convenient for me. Stuck to my bandsaw are a couple of charts for freely converting between fractional inches, decimal inches, all the various letter and number drills, and all the metric equivalents. It's pretty trivial for me to work in whatever measurements are most convenient. Since I use a lot of hardware that's a mix of imperial and metric measurements, I don't really have a choice.

I also happen to think that the inch is a more convenient unit for basic woodworking. Centimeters and millimeters are too small, meters are too big, and no one actually uses decameters. :) Ditto for recipes in the kitchen. Ever try remembering a metric recipe. 180ml of that, 30g of this, 80ml of something else, etc etc. It's much easier to deal with 2 cups of this, 1 tblspn of that, etc. Just my opinion, but when I'm working in metric, I end up with lots of big numbers floating around, and converting to meters does no good because I still have to carry around the same number of digits of precision. Feet and inches just seem to work better for me to keep numbers small and manageable. Again, that's just my opinion.

Personally, I think metric measurements would be far more convenient for woodworking if fractional metric rules and tapes were more commonly available, and if things didn't jump from tiny little centimeters to gigantic meters.

Just to reiterate the point: Imperial does NOT imply fractions. You may use fraction OR decimal measure as you wish, and practically every common measuring device you might use is available as both.

[Chris Padilla]

I would say to get used to working in both. One little tidbit I picked up was that 1/32" and 1 mm are about the same so if you get used to working in one thirty-seconds of an inch, moving over or thinking in millimeters isn't that much of a change. The difference is less than 1 mil or 0.001 inch (1 mm is larger than 1/32" by 0.00081"). And unless you work in MDF all the time, you're sheet good thickness is going to be some integer of 1/32". I am slowly buying metric equivalents of just about everything in my shop these days. I picked up a '6 inch' metal metric ruler. I have a nice set of metric brad-point bits to complement my imperial set--both from Lee Valley. I recently picked up a set of metric center punches, too.

Finally, I think it is good for the brain to exercise your ability to add and subtract and divide and multiply mixed fractions.

And to John above, how about decimeters? :D 1 dm is about 4". :D :D

[David L Morse]

.. One little tidbit I picked up was that 1/32" and 1 mm are about the same so if you get used to working in one thirty-seconds of an inch, moving over or thinking in millimeters isn't that much of a change. The difference is less than 1 mil or 0.001 inch (1 mm is larger than 1/32" by 0.00081)...

Well, not exactly. The difference is actually ten times that. 1mm = 1/25.4" = .03937", 1/32" = .03125", .03937"-.03125" = .00812". That's 8mil not 1ml. Perhaps you're thinking of the fact that 4mm is within a little over 1mil of 5/32"?

I too am comfortable working in both systems. For example, anything that ends up in the barn is imperial and anything involving drawer slides is metric. (Not sure what I'll do if I have to build something for the barn with drawers.:D) As far as the kitchen is concerned it's easy to remember that 1tsp = 5ml and 1qt is nearly 1l. When it comes to pasta though it can only be 100g flour to 1 egg.

[Roy Harding]

As a Canadian of a certain age, I was a teenager when the metric system came in. Consequently, I use a mix of units for everyday figuring. When thinking of people's weight, I still think in pounds. When thinking of distance I use kilometres (25 years in the Army cemented that one home), when thinking of liquid measure, I use gallons (imperial gallons, which are bigger than your U.S. gallons).

In the workshop, I work in fractional inches, decimal inches, and metric. My tape measure is both inches and metric. Some of my tool scales are fractional inches, some are metric, and still others are decimal inches. You get used to it. What you want to avoid, if possible, is switching between the systems on the same job. If I start in metric, that's what I use for that entire project, if I start in fractional inches, that's what I use throughout the whole process, etcetera.

Conversion between the systems in the middle of a project is just asking for trouble.

[Kent A Bathurst]

After a career of 30-odd years in octal, decimal and hex I escape to the warm embrace of imperial measurements in the shop to decompress. Fractions must use different pathways in the brain because my shop time is like deep meditation for me ;-)

Base eight...........

You musta had a shop accident - which two fingers did you lose?

No - no - not those two fingers - I can see them from here. :D :D :D

[roger wiegand]

Starting today I would go metric all the way, without thinking twice about it. I'm about 60-70% of the way there now and it is awkward. Being a scientist in the US I pretty much think metric so having to convert to read an inch scale on a machine is a pain. Doing calculations in fractions just seems dumb and an invitation to error. I don't have any tools that read in decimal inches, except perhaps an electronic caliper that will do that trick. One day I will just have a garage sale of all the inch scale tools and be done with it. Half the stuff we get, like "3/4" plywood" is actually 18 or 19 mm anyway and not actually 3/4".

[Jim Becker]

I have the ability in my shop to use both systems having European produced machinery and rules that offer both measurements...and metric is very appealing for many reasons. I have to force myself to do a full project in metric at this point just to get started, but "in the moment" I too often forget to do that! LOL Aside from hole-drilling where I'm very limited with metric, doing the deed shouldn't be too painful. One of these days...

That said and back to the original question. If I were starting out today and knew what I know now, I do believe I'd embrace metric in my shop fully. But as a 57 year old guy who's been using the so-called "Imperial" system for all my life, switching means actually thinking about it...as I already mentioned.

[John Coloccia]

And to John above, how about decimeters? :D 1 dm is about 4". :D :D

Truthfully, I think the decimeter is a far more useful measure for most human sized endeavors. Somewhere along the way, it was declared that thou shalt only use mm, cm, m and km (microns, nano-meters, etc going down). I think decimeters would be excellent in the shop, if only it didn't turn into this useless, oddball unit. I think metric did an awful lot of good for us engineers and scientists. Doing any sort of engineering or scientific work with imperial measurements can sometimes be quite a pain in the butt.

But IMHO, they botched up the actual length of the unit. What they SHOULD have done, IMHO, is made the meter equal to 10 inches, and simply continue from there. This business of trying to define it relative to the size of the Earth was silly, and in the end they didn't even achieve that. Inches, feet, cups, tablespoons, etc are all human sized measurements. They evolved as convenient measurements in day to day life. The meter was defined rather artificially. Maybe they thought it would be used for navigation some day, but pilots and sailors all still use nautical miles, because they're so darn convenient.

Anyhow, as others have said, I just work in both systems, and also interchange fractions and decimals as convenient. It's not so bad, other than having to keep two sets of tools kicking around the shop.

[Keith Weber]

I have decided to get into woodworking and have acquired a number of tools and about to start buying woodpecker measuring devices 1281 square, 32" t-square and perhaps a story stick. The question is should I get imperial or metric?

Just a get a story stick without any units at all, and you won't have to deal with either! Just make everything "about that big", and all the matching parts the same size.

Seriously, though... While metric has its benefits, I find it to be easier just dealing with imperial in the US. Most people here wouldn't know a centimeter from a centipede, and most of the hardware and tooling that you'll find are in imperial measurements. It's easy to get a 1/2" router bit, a 1/8" drill bit, 3/8" bolt, or an imperial tape measure without going further than your local hardware store. But try to find a 10mm router bit, a 7mm drill bit, a 8mm bolt, or a metric tape measure, and finding things you need just got a lot harder -- especially if you need them right now.

In woodworking, I tend to work in fractions as long as it's easy (say, midpoint of 26-1/2" is 13-1/4".) When it does get more difficult, (say 17-5/16" divided by 3), I might just switch to decimals, just to make the math easier. Using decimals in imperial measurements is no different than doing it in metric, so long as you have a method of conveying those measurements to your workpiece. I have both imperial scale and digital readouts on my slider, so I can quite easily work in either. The thing is, though, that the number of times that you need to resort to digital imperial measurements in woodworking is almost never. I also find it humorous when some woodworkers start making measurements to the 1/1000th of an inch (for purposes of accuracy vs. ease of deriving a measurement), and claim that their tablesaw cuts are able to cut to that accuracy.

[Mike Henderson]

Metric is sooooo much easier to use, but most of the tools in my shop are imperial and I use that a lot.

Mike

[John M Wilson]

This business of trying to define it relative to the size of the Earth was silly, and in the end they didn't even achieve that.

Well, it was a bunch of guys in France during the revolution, and surveying was all the rage. They were shooting to have the distance from the pole to the equator equal to 10,000,000 meters, so the circumference of the Earth would have been 40,000,000 meters. The actual number is about 40,007,863 m, so they only missed by 1/5 of a millimeter. Pretty good for a bunch of guys doing the math (and surveying) by hand.

The reason that they picked this size of measurement however is far more fundamental than some obscure Earth measurement that very few people could verify. To have a true system of measure for use in laboratories across the world, they picked units that a Ben Franklin era lab could reproduce. What's a meter? It's almost exactly the length of a pendulum in a grandfather clock (2 second period: tick, tock takes a pendulum 0.993 meters long). A kilogram is the mass of water in a cube that's 1/10 of a meter on each side. And so on...

[Mel Fulks]

The way I heard it is different. The foot was based on the King's foot . The meter was based on the JESTER'S foot ("shoe on, toe unrolled ,round ball on end included".

[Phillip Gregory]

I use imperial units in the woodshop because that's what all of the lumber, tools, and fasteners I can get locally use. However pretty well everything metalworking or mechanical is metric rather than SAE (imperial) any more. The only things that are still SAE are some very particular items like hitch ball nuts and 3-point hitch stub pin nuts. So all of my woodworking tools are imperial while the vast majority of my metalworking stuff is metric.

Oh, and at work we use metric measurements pretty well exclusively, except for weight and height which we figure both ways.

[Keith Weber]

So all of my woodworking tools are imperial while the vast majority of my metalworking stuff is metric.

Oh, and at work we use metric measurements pretty well exclusively, except for weight and height which we figure both ways.

Phillip,

Without getting into too much detail, I was wondering where you are located, and what your line of work is.

The reason I ask, is that I am curious as to what machine shops are using for measurements these days. I recently fabricated a new, re-sized overarm blade guard support for my Altendorf F-45 because the saw was too wide for my narrow shop. When I went to buy 3 pieces of metric tubing for the job, I was shocked at the price quote of around $1100. I was told by two big metal suppliers that they don't make metric tubing in the US, and they had to get them from Europe. The closest imperial equivalent was only $130, so I went that way and machined the ends where I needed to mate to the existing metric pieces.

If machine shops were working almost entirely in metric, I would think that it would be a pain to machine every bit of imperial stock down to get metric sizes. It wouldn't be that big of deal if the piece was machined out of a larger block, but if the end product included a bunch of metric flat bar and plates, it would entail a significant amount of extra work (or extra expense to order the metric stock). I guess they would just pass these expenses on to the customer.

It's easy enough to get measuring tools in metric and anything digital can be switched at the push of a button, but choices in US-made cutting tools are limited in metric. Also, a lot of the metric hardware that you see in the hardware stores is in those metal "special hardware" bins that sell individually-packed at a significant markup to the bulk-bin prices on the SAE hardware. I guess that it wouldn't make much difference to a manufacturing company which would order hardware by the pallet, but for a passionate hobbyist like by myself, metric is an expensive pain in the butt.

All of my metalworking stuff is pretty much imperial (collets, end mills, drill bits, indicators, edge-finders, etc.) I do have a metric tap and die set and a full compliment of metric hand tools (wrenches, sockets, allen keys, etc.), though, and I like my temperatures in °C, so I'm not completely in the dark ages.

Keith

[Chris Parks]

Living in Oz we went metric in several steps, money was first then followed by weight, measurement and liquid measures. I was in my mid thirties and still measuring in imperial when an architect handed me the drawings to my new workshop all in metric measures and I have never measured in imperial since and chucked all my imperial stuff in the bin. It seems to me that the US being the only country not using metric is slowly changing by stealth because of having to deal with the rest of the world in manufacturing.

[John Coloccia]

It seems to me that the US being the only country not using metric is slowly changing by stealth because of having to deal with the rest of the world in manufacturing.

Nah. Like I said earlier, it's pretty trivial for us to work is both units so there is absolutely no reason in the world to change.

[Rich Engelhardt]

Haven't played with fraction much since school and wondering if going metric would be easier. Any thoughts?

Yeah - for anything longer than about 6" a story stick is the way to go & forget about those pesky little mm or fractions.
For stuff 6" and under, one of these:
Harbor Freight Digital Fractional Caliper SAE and Metric (http://www.harborfreight.com/6-in-digital-caliper-with-metric-and-sae-fractional-readings-68304.html)

is the way to go! You can use either/or, or both at the touch of a button. I use mine all the time to convert from one to the other - mostly when adding, subtracting or dividing fractions.

[Rod Sheridan]

Robb, now's your chance to go metric.

I went that way about a decade ago and haven't looked back.

Instead of 3/4" thick stuff I make 20mm stuff.

Instead of 2" thick legs I make 50mm legs.

That's the secret, don't convert imperial measurements to metric, instead use easy to use sizes in metric.

Since I design all my own furniture I design in metric sizes.

It doesn't matter that sheet goods come in imperial sizes (except for thickness), as you're cutting them to the sizes to want. Trees don't come in imperial or metric either, their products come in whatever we want.

Regards, Rod.

[John Coloccia]

The thing is that in the US, everything that's commonly available is imperial measurements. Router bits, drill bits, rulers, measuring tapes, markings on machinery, etc. It's not that it's impossible to do, but it's very inconvenient if you like the idea of walking down to the local Woodcraft and grabbing tool. For example, where are you going to get a rabbetting set in metric? Lee Valley doesn't even sell them, and Whiteside doesn't either. Metric bushings?

That's just one example. I briefly considered converting everything to metric in my shop, but after thinking about it for a couple of minutes I decided that it was just not very practical. It would be different if I were a cabinet shop, but I found that if your work requires lots of different bits, jigs, fixtures, maybe some special tools, etc, it turns into a big mess really quickly AND I'm still stuck with having to buy lots of basics by mail order.

What do you do up in Canada? Is everything commonly available in metric sizes?

[Rod Sheridan]

The thing is that in the US, everything that's commonly available is imperial measurements. Router bits, drill bits, rulers, measuring tapes, markings on machinery, etc. It's not that it's impossible to do, but it's very inconvenient if you like the idea of walking down to the local Woodcraft and grabbing tool. For example, where are you going to get a rabbetting set in metric? Lee Valley doesn't even sell them, and Whiteside doesn't either. Metric bushings?

That's just one example. I briefly considered converting everything to metric in my shop, but after thinking about it for a couple of minutes I decided that it was just not very practical. It would be different if I were a cabinet shop, but I found that if your work requires lots of different bits, jigs, fixtures, maybe some special tools, etc, it turns into a big mess really quickly AND I'm still stuck with having to buy lots of basics by mail order.

What do you do up in Canada? Is everything commonly available in metric sizes?

Hi John, I'm lost with the rebating issue, maybe I'm not awake yet this morning. When I cut a rebate the height of the rebate is controlled by the cutter height above the table, and the depth is controlled by the projection past the fence. These are infitely adjustable so I don't understand the imperial/metric issue?

That said my rebate cutter is metric, it's 125mm diameter and 50mm high.

I have both metric and imperial drill bits, and of course the 35mm cup hinge requires a 35mm drill bit, regardless of where you live.

Measuring equipment such as rules and tape measures are available in metric, imperial or combination.

The one item is screws, most of the screws I use are imperial, however I use some metric screws. Doesn't really matter as you buy a drill bit to fit the screws you have.

My machines have scales in mm/inches except for my planer which is digital metric only.

Regards, Rod.

[John Coloccia]

Hi John, I'm lost with the rebating issue, maybe I'm not awake yet this morning.

Lots of people use bearings. You run into the same issue with bushings. That, and router bits except for "plywood" bits, are mostly all imperial. If you mostly deal with sheet goods and things like that, it's not much of an issue. If you're constantly making new patterns and jigs, or maybe even buying jigs, it starts turning into a real pain in the butt because everything here is imperial.

[Duane Meadows]

If you mostly deal with sheet goods and things like that, it's not much of an issue.

Maybe because the thickness is all over the map! Nothing to find thickness varying even within the same sheet! Doesn't matter what bit you use, it's unlikely to match all the time!

Also try dividing a 20mm board into. oh say 7 equal pieces. Just as ugly of math can occur in metric as in imperial. No system of measurement is ideal in every situation. Just sayin...

[Halgeir Wold]

This is an interesting topic, and I've been pulling peoples legs around here several times, - can't promise I'll not do it again, but not this time..:rolleyes:
I personally find the historic development of measurements and units very interesting. but...
Using this or that is mostly about habit. I hold an equivalent of BSc in electronics, from the mid 70s, when digital systems operated in binary, octal, BCD and whatever have you. We learned rather quickly to convert powers of two by head, to decimal which was the expected output. Strangely enough, most imperial measurements are only fractional for less than one, - above it is actually metric.... length, weight, money..etc.

Less than hundred years ago, a number of trades over here still operated in "thumbs" ( actually related to the width of the male thumb by the first knuckle), - the inch is the british version of it, - hence "imperial". The problem was that here in Norway there were three different thumbs, - the old scandinavian norse now defined as 27.5mm, the official danish/norwegian, defined by law in 1615, of 26.17mm, and the then lesser used inch of 25.4............
This rather messy situation was also true for almost all other units of volume, weight etc.
The whole idea of metrification was about stndardisation of units, which they mostly achieved, even if they were a commitee......

[Chris Padilla]

Maybe because the thickness is all over the map! Nothing to find thickness varying even within the same sheet! Doesn't matter what bit you use, it's unlikely to match all the time!

Also try dividing a 20mm board into. oh say 7 equal pieces. Just as ugly of math can occur in metric as in imperial. No system of measurement is ideal in every situation. Just sayin...

And what is the plywood thickness of the week?! :) Ugh, drives me crazy. I have 'nice' cabinet grade A1 maple plywood and found a sheet or two that DID vary thickness within the sheet. When my Domino arrived, I threw out (not really, but it's gathering dust) my dado blade.

Actually, there is a cute trick I saw by Mr. This Old House Tom Silva on dividing up boards or just about anything and I now use it all the time. Take your tape measure and put it on one corner of your board and stretch it to the other side. You'll probably need to hold it with your finger as you then move the tape measure at an angle (creating the hypotenuse of a triangle) until you reach a NICE number to divide by and then tick off the mark on along the tape measure (the hypotenuse of the triangle).

So for your 20 mm board (rather narrow!) into 7 equal parts, simply move your tape measure up the side of the board until it reads 21 mm and then tick off every 3 mm. :)

[Keith Weber]

Actually, there is a cute trick I saw by Mr. This Old House Tom Silva on dividing up boards or just about anything and I now use it all the time. Take your tape measure and put it on one corner of your board and stretch it to the other side. You'll probably need to hold it with your finger as you then move the tape measure at an angle (creating the hypotenuse of a triangle) until you reach a NICE number to divide by and then tick off the mark on along the tape measure (the hypotenuse of the triangle).

Now that's a neat trick. I hope I can remember that one!

[Phillip Gregory]

Phillip,

Without getting into too much detail, I was wondering where you are located, and what your line of work is.

The reason I ask, is that I am curious as to what machine shops are using for measurements these days. I recently fabricated a new, re-sized overarm blade guard support for my Altendorf F-45 because the saw was too wide for my narrow shop. When I went to buy 3 pieces of metric tubing for the job, I was shocked at the price quote of around $1100. I was told by two big metal suppliers that they don't make metric tubing in the US, and they had to get them from Europe. The closest imperial equivalent was only $130, so I went that way and machined the ends where I needed to mate to the existing metric pieces.

If machine shops were working almost entirely in metric, I would think that it would be a pain to machine every bit of imperial stock down to get metric sizes. It wouldn't be that big of deal if the piece was machined out of a larger block, but if the end product included a bunch of metric flat bar and plates, it would entail a significant amount of extra work (or extra expense to order the metric stock). I guess they would just pass these expenses on to the customer.

It's easy enough to get measuring tools in metric and anything digital can be switched at the push of a button, but choices in US-made cutting tools are limited in metric. Also, a lot of the metric hardware that you see in the hardware stores is in those metal "special hardware" bins that sell individually-packed at a significant markup to the bulk-bin prices on the SAE hardware. I guess that it wouldn't make much difference to a manufacturing company which would order hardware by the pallet, but for a passionate hobbyist like by myself, metric is an expensive pain in the butt.

All of my metalworking stuff is pretty much imperial (collets, end mills, drill bits, indicators, edge-finders, etc.) I do have a metric tap and die set and a full compliment of metric hand tools (wrenches, sockets, allen keys, etc.), though, and I like my temperatures in °C, so I'm not completely in the dark ages.

Keith

I work in healthcare in Missouri. Nope, not a machinist but we do a lot of work with various measurements and it's all metric, at least internally. The goofy part is that there isn't one metric set of units in healthcare. The most notorious example is that Europeans typically use molar concentration such as mmol/L where we use weight per volume such as mg/dL. Both are metric but the units are very difficult to convert between as you have to know the molar weight of the substance in question. Just like the imperial vs. metric conversation here there is a bit of debate over which one of those is "correct."

I mis-typed and really meant "mechanics' tools" rather than metal fabrication or milling tools. The only real significant fabrication and milling I do is with wood, which is why I am here instead of on the Practical Machinistforum. I do some shade tree mechanicing at home on various equipment and nearly all of it uses metric fasteners and metric measurements for parts (e.g. hub bolt circles). You can metric fasteners in most hardware stores and yes, it stinks to have to buy them individually or in packs of three where you can buy 100 similarly-sized SAE fasteners for about only twice as much. Bar, flat, angle, and sheet stock however is in imperial and I measure and cut in imperial units since that's what my measuring equipment (the same rules and tapes and squares I use for woodworking for the most part) are.

[Duane Meadows]

And what is the plywood thickness of the week?! :) Ugh, drives me crazy. I have 'nice' cabinet grade A1 maple plywood and found a sheet or two that DID vary thickness within the sheet. When my Domino arrived, I threw out (not really, but it's gathering dust) my dado blade.

Actually, there is a cute trick I saw by Mr. This Old House Tom Silva on dividing up boards or just about anything and I now use it all the time. Take your tape measure and put it on one corner of your board and stretch it to the other side. You'll probably need to hold it with your finger as you then move the tape measure at an angle (creating the hypotenuse of a triangle) until you reach a NICE number to divide by and then tick off the mark on along the tape measure (the hypotenuse of the triangle).

So for your 20 mm board (rather narrow!) into 7 equal parts, simply move your tape measure up the side of the board until it reads 21 mm and then tick off every 3 mm. :)


I agree, Chris. That is the easy way to do it. Doesn,t change the math issue though! A fraction is a fraction, whether it is a fraction of a meter(better?), or a fraction of a foot.

Yikes! 20 mm? Shows you my mind wasn't thinking metric! Who says you can't make error with metric?

[Terry Therneau]

I use metric as much as possible - I just find it easier. When ripping boards or planing I can make them what I want. For the router I bought an adjustable (dial) slot cutter, and smile every time I use it -- plywood variation was driving me bonkers. But mostly I'm practical, and switch from one to the other as needed.

Terry T

[Curt Harms]

Just a get a story stick without any units at all, and you won't have to deal with either! Just make everything "about that big", and all the matching parts the same size.

Seriously, though... While metric has its benefits, I find it to be easier just dealing with imperial in the US. Most people here wouldn't know a centimeter from a centipede, and most of the hardware and tooling that you'll find are in imperial measurements. It's easy to get a 1/2" router bit, a 1/8" drill bit, 3/8" bolt, or an imperial tape measure without going further than your local hardware store. But try to find a 10mm router bit, a 7mm drill bit, a 8mm bolt, or a metric tape measure, and finding things you need just got a lot harder -- especially if you need them right now.

In woodworking, I tend to work in fractions as long as it's easy (say, midpoint of 26-1/2" is 13-1/4".) When it does get more difficult, (say 17-5/16" divided by 3), I might just switch to decimals, just to make the math easier. Using decimals in imperial measurements is no different than doing it in metric, so long as you have a method of conveying those measurements to your workpiece. I have both imperial scale and digital readouts on my slider, so I can quite easily work in either. The thing is, though, that the number of times that you need to resort to digital imperial measurements in woodworking is almost never. I also find it humorous when some woodworkers start making measurements to the 1/1000th of an inch (for purposes of accuracy vs. ease of deriving a measurement), and claim that their tablesaw cuts are able to cut to that accuracy.

Well said. I think the two biggest problems with using metric in the U.S. right now is the relative scarcity of hardware and unfamiliarity. Most people can tell with a glance whether a piece of plywood is 3/8" or 3/4". Thickness in millimeters? Not so much - even though that sheet of plywood might actually be metric.

[Warren Wilson]

John -- I hesitate ever to offer an opinion in such august company, but the notion of basing a system of measurement on "human-sized" units would forego many of the benefits of the SI system. One of the aspects of the metric system I find most appealing is that it is NOT based on arbitrary "human" measurements such as the length of a dead king's foot or the twelfth part of that.

And once we begin measuring things other than length, it seems the metric system really shines. Relating length to volume to mass (i.e. 1 cubic cm of water weighs 1 gram) makes all calculations simpler than relating inches to gallons to pounds -- even after we decide whether we mean US gallons or Imperial gallons.

And as to temperature, assigning 0 degrees to the freezing point of water then calibrating 100 of those degrees to the boiling point makes sense. I can't remember why Fahrenheit chose 32 degrees as the freezing point of water then sliced the difference to boiling into 180 degrees, but I do know the old system no longer makes sense to me.

And in spite of my respect for the SI system, like Roy I am "bi-metric," and think of body weight in pounds, distance in kilometers, temperature in celcius, and usually think of plywood as 3/4" and buy 8' lengths of 2x4s. Just don't ask me to quickly calculate half of 13' 7 7/8"!

[John Coloccia]

They defined the meter, rather arbitrarily, as 1/10,000,000 the distance from the equator to the north pole. It seems odd to me as there was already a common measurement in many different countries that, more or less, equaled an inch...even in France. They had the pouce. There was no compelling reason, other than it it was philosophically pleasing, to introduce an entirely new unit when they could have simply used the distance between the equator and the north pole to precisely define the unit they already had. It would have caused a heck of a lot less trouble to have a meter defined as 10 pouce, for example, and then continue on from there defining whatever other quantities they wished.

For example, when we wanted more experimental precision in defining our unit of length, we didn't introduce a new unit. We used the speed of light to more precisely define the unit we already had...the meter. I guess with the revolution and all going on, there was change in the air.

[Kent A Bathurst]

And what is the plywood thickness of the week?! :) Ugh, drives me crazy. I have 'nice' cabinet grade A1 maple plywood and found a sheet or two that DID vary thickness within the sheet. When my Domino arrived, I threw out (not really, but it's gathering dust) my dado blade.


Yeah - that pretty much sucks. No getting around it, AFAIK. In addition, any teensy out-of-dead-flat conditions can exaccerbate the problem when the carcass and shelves are run. All I can say is that my approach is this [assume nominal 3/4" ply]:

1. 3/8" x 3/8" stopped dado in ply carcass, using TS and dado stack.
2. With same dado set, double-rabbet the insert boards [shelves?] to leave 3/8" wide x 23/64" deep tongue. Sneak up on a scrap test piece for depth of cut [which means width of the tongue].
3. Carcass/tenon saw to remove leading edge of tongue to matched depth of stop.
4. Dry fit, with face float and / or wood block and 80g adhesive-backed sandpaper on block's 2 faces only [not on the edges]. A few quick swipes as/where required for tight fit.
5. the actual joint is hidden by the shoulders, so any imperfections there cannot be seen.

[Ernie Miller]

The thing is, though, that the number of times that you need to resort to digital imperial measurements in woodworking is almost never. I also find it humorous when some woodworkers start making measurements to the 1/1000th of an inch (for purposes of accuracy vs. ease of deriving a measurement), and claim that their tablesaw cuts are able to cut to that accuracy.

In my work as a harpsichord builder, I use digital Imperial exclusively for measurements under 6". In some assemblies, errors of a couple of thousandths of an inch can mean the difference between success and failure. It's not that I can cut wood to an accuracy of 1/1000 of an inch, but instead it's laying out what I need to cut accurately. Here's an example. Let's say the width of an octave on a piano is 6 1/2". There are seven white keys to an octave and they must be equal in width. So, divide 6 1/2" by seven and you get .9285". How do you draw a line .9285" away from another line onto a piece of wood? Using a ruler, we can take the closest available measurement which is 59/64" - if your eyesight is good enough to see those divisions. But 59/64" equals .9218" per key. Times that by 7 (for the seven white keys), and you get an octave that is only 6.4531" wide instead of 6.5". So what, you may ask. Well, if you multiply that error 7 more times (for the seven octaves in a piano keyboard) you end up with a width for the entire keyboard that is 45.1718". However, 6 1/2" (the desired width of a single octave) times 7 equals a keyboard width of 45 1/2". So using 59/64" as a measurement results in a keyboard that is more than 5/16" too narrow. That would be a disaster in a keyboard as the width of a key must coincide with many other assemblies in the instrument in order for it to function normally.

In order to avoid this cumulative error, I've abandoned the use of rulers altogether in certain areas - the keyboard being one of them. Instead, I use paper story sticks printed by a CAD program on my computer. I draw a series of lines 6 1/2" wide and use the story stick to divide those 6 1/2" divisions into 7 equal parts. This avoids the cumulative error problem - as long as I can accurately measure 6 1/2", I will at least know that I will end up with a keyboard of the proper width.

Unfortunately, this stuff keeps me awake at night.:(

Ernie

[John Coloccia]

In my work as a harpsichord builder, I use digital Imperial exclusively for measurements under 6". In some assemblies, errors of a couple of thousandths of an inch can mean the difference between success and failure. It's not that I can cut wood to an accuracy of 1/1000 of an inch, but instead it's laying out what I need to cut accurately. Here's an example. Let's say the width of an octave on a piano is 6 1/2". There are seven white keys to an octave and they must be equal in width. So, divide 6 1/2" by seven and you get .9285". How do you draw a line .9285" away from another line onto a piece of wood? Using a ruler, we can take the closest available measurement which is 59/64" - if your eyesight is good enough to see those divisions. But 59/64" equals .9218" per key. Times that by 7 (for the seven white keys), and you get an octave that is only 6.4531" wide instead of 6.5". So what, you may ask. Well, if you multiply that error 7 more times (for the seven octaves in a piano keyboard) you end up with a width for the entire keyboard that is 45.1718". However, 6 1/2" (the desired width of a single octave) times 7 equals a keyboard width of 45 1/2". So using 59/64" as a measurement results in a keyboard that is more than 5/16" too narrow. That would be a disaster in a keyboard as the width of a key must coincide with many other assemblies in the instrument in order for it to function normally.

In order to avoid this cumulative error, I've abandoned the use of rulers altogether in certain areas - the keyboard being one of them. Instead, I use paper story sticks printed by a CAD program on my computer. I draw a series of lines 6 1/2" wide and use the story stick to divide those 6 1/2" divisions into 7 equal parts. This avoids the cumulative error problem - as long as I can accurately measure 6 1/2", I will at least know that I will end up with a keyboard of the proper width.

Unfortunately, this stuff keeps me awake at night.:(

Ernie

When I print a pattern, I'm also sure to print a witness square, usually 4x4 (so I can accurately measure with my 6" rule). It's surprising how often it's off significantly. I thought using a printing house would be better. Nope. I haven't found a solution yet other than keep printing until it works.

[Fred Heenie]

I build in metric and sell in imperial. precise and no client math lessons required.
;^)

[Yonak Hawkins]

Try ... dividing 8 7/16 into thirds.
It would be wonderful if the US could go metric.

It probably would be good if the US went to metric but try dividing 1cm into thirds !

Really, we should go to base 12. More of our numbers would be shorter, and fractions easier.

[Ernie Miller]

When I print a pattern, I'm also sure to print a witness square, usually 4x4 (so I can accurately measure with my 6" rule). It's surprising how often it's off significantly. I thought using a printing house would be better. Nope. I haven't found a solution yet other than keep printing until it works.

It's worse if you try to glue the pattern onto wood (or anything else). The paper will swell from the moisture in the glue and throw your pattern off. A long time ago, I thought it would be great to print out a pattern for an entire keyboard. The printing came out quite accurately, but gluing the pattern down was a disaster.

I have my full sized plans printed by a digital print shop that deals mainly with architects. I have to check every plan to make sure the dimensions have been printed correctly. In fairness to the print shop, they have very little experience in printing anything full size. Almost all drawing for architects are scaled down to a workable, readable size. It seems there is quite a learning curve involved in using these large scale printers. Nothing comes easy.

[Steve Milito]

It probably would be good if the US went to metric but try dividing 1cm into thirds !

Really, we should go to base 12. More of our numbers would be shorter, and fractions easier.
Then I'd need two more fingers!

[Chris Parks]

Nah. Like I said earlier, it's pretty trivial for us to work is both units so there is absolutely no reason in the world to change.

Your international industry has changed though, automotive being a prime example, is that correct? It might be trivial at your level but if a company is in an international metric world they have no choice.

[Pat Barry]

I live in America so I use metric only if needed. Ie: fixing my Chevy

[John Coloccia]

Your international industry has changed though, automotive being a prime example, is that correct? It might be trivial at your level but if a company is in an international metric world they have no choice.

For hardware? That has nothing to do with units for measurement. I'll tell you that I've worked on plenty of products, shipped internationally, that were made entirely with SAE hardware. I've been on site waiting for a shipment of bolts from the US because an SAE bolt was nowhere to be found in Germany.

But an enormous amount of engineering is still done with imperial units, irrespective of choice of hardware. The more "scientific" the project, the more likely to find the design in metric. For example, a lot of the robotics stuff I did was all designed in imperial units. A lot of the electro-optics I did later on where designed in metric. That makes sense as so many of the quantities we deal with are all traditionally defined in metric. Wavelength comes to mind. Some other stuff I did was a free flowing mixture of both, and it wouldn't be unusual to use metric and imperial quantities in the same sentence.

There's no compelling reason to us metric units just because you happen to use metric hardware, just like you wouldn't suddenly start using some oddball custom unit just because you use some custom hardware. Personally, I prefer metric hardware, but I don't use much of it. Why? Because when it's 6:00pm (1800 in metric) on a Friday evening, and I'm a couple of bolts short, I can shoot down to the local hardware store and get precisely what I need. For metric, I'm usually somewhat limited in my choices. This is changing since I'm putting together a good metric hardware kit that I'll keep stocked all the time, but it's a consideration.

[Art Mann]

After a career of 30-odd years in octal, decimal and hex I escape to the warm embrace of imperial measurements in the shop to decompress. Fractions must use different pathways in the brain because my shop time is like deep meditation for me ;-)
That being said, I use both when I need to and being from the generation that experienced the move to and then away from metric I am comfortable with either.

I can absolutely identify with that comment. I know exactly what you are talking about.

[Art Mann]

The origin of the inch may be obscure but the modern definition of a meter is even more obtuse. It is no longer related to any earthly distance. A meter is defined as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second. Of course, that has nothing to do with one's choice of measurement systems but I thought it was interesting.

[Ernie Miller]

The origin of the inch may be obscure but the modern definition of a meter is even more obtuse. It is no longer related to any earthly distance. A meter is defined as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second. Of course, that has nothing to do with one's choice of measurement systems but I thought it was interesting.

It's interesting that the dictionary definitions of Imperial units (inches, foot, etc.) always seem to reference metric units as a means of definition. Metric units, on the other hand, seem to have quite scientific definitions like the one Art gave for the length of a meter.

[John Coloccia]

It's interesting that the dictionary definitions of Imperial units (inches, foot, etc.) always seem to reference metric units as a means of definition. Metric units, on the other hand, seem to have quite scientific definitions like the one Art gave for the length of a meter.

By treaty, in the 50s, the US, Canada and UK agreed that an inch should be exactly 2.54cm. Before that, the US decided, in the 1800s, that a YARD should be some fraction of a meter. I forget the conversion because it's actually off a little bit, but interestingly enough it's STILL USED for surveying. So there's tons of survey data that exists, and that is still being generated, where THAT inch is different from every other inch on the planet. Figure that one out.

But before the definition of a meter by light was established, the situation for defining the meter was not particularly scientific in practice. The distance they tried to base it on was botched up (they missed by several kilometers), so the standard meter bar ended up being too short. So never mind that whole 1/10,000,000 pole to equator distance thing. 1 meter is exactly as long as this bar that Pierre just made. Uhm, oh...well OK! And thus copies were made and given to various countries, and that was the meter by definition. Well, at least now we all had actual bars of something that were all, more or less, the same length (not really, but close enough), so let's gather up all the countries that stubbornly refuse to use the meter, and let's all agree to use these funny looking meter bars to redefine the units that we actually use. :/

See, because this is what happens when you take a bunch of people that are used to drinking like fish, and you start badgering them about it. The temperance movement was getting into full swing, and people on both sides of the pond were getting nagged by teetotaling busybodies. There was, understandably, some general crankiness mucking about...

301733

And wouldn't you be cranky too?

They did eventually ban absinthe in France (and most everywhere else), but by and large the French told the temperance movement "Le scram" and then blew smoke in our face. Fine, well you can keep your stupid meter...or metre, or whatever, and we'll keep our inches and pints, not for any other reason other than a bit of widespread orneriness. If only I could remember why...

301733

And we can't put beer in our pint mugs anymore regardless, so what the heck difference does it make what we use? Oh, OK...I can use it to measure how much water to put in my crumpet dough. Wheeeeeeee.

[Art Mann]

Wildly off topic but that photo is just hilarious. How many modern men would like to touch lips with any of those women?

[Edward Schlesinger]

I have decided to get into woodworking and have acquired a number of tools and about to start buying woodpecker measuring devices 1281 square, 32" t-square and perhaps a story stick. The question is should I get imperial or metric? I have some green koolaid with plans for some more. The plan is to turn our formal living room into a library with built-ins, built-in master closet, amour, wood panel ceiling with recessed lighting and multi tiered out door decking. Haven't played with fraction much since school and wondering if going metric would be easier. Any thoughts? Thanks.

-Rob

Hi Rob,
Australia been on the SI metric system for years now. For engineering and crafts they use mm to avoid decimal markers. One can buy tape measures that have clear mm markings online at http://metricpioneer.com/shop.

Also lumber-wood is cut and sold in metric measure at place of origin,however labled in inches as 2X 4 as an example. As long as you draw plans starting in metric and take measurments you should be good to start.

[Dennis Aspö]

Not being american it's never really an issue for me, it's all metric.

But I have this uncontrollable urge to say how much I hate fractions and having to deal with them when I come across american made plans. Decimal inches would be such a massive improvement and very intuitive.

My tape measure has imperial on one side so I could read american plans plans, but inches are specified in fractions and it just frustrates me trying to find odd fractions on a tape meassure, so I just end up converting to metric.

[Warren Wilson]

Map of countries in the world that DO NOT use the metric system.
301883

[Pat Barry]

Map of countries in the world that DO NOT use the metric system.
301883
America USES the metric system also so it should be gray, not red.

[Jim Becker]

America USES the metric system also so it should be gray, not red.

Technically true. I suspect the graphic is representing "general population"/"common man" tendency for use and here in the US, it's rare for folks not actively involved in certain industries and professions to use metric. And even those folks are somewhat forced to use "Imperial" just by how goods are labeled and sold in addition to things like road signage, etc.

I'm all for "all metric", but doubt I'll ever see it happen in my lifetime here in the US, even for my own personal use. It's hard to change...

[Keith Weber]

Do you need a metric hammer to pound your glue-ups into submission if you build something using metric measurements?

[Pat Barry]

Technically true. I suspect the graphic is representing "general population"/"common man" tendency for use and here in the US, it's rare for folks not actively involved in certain industries and professions to use metric. And even those folks are somewhat forced to use "Imperial" just by how goods are labeled and sold in addition to things like road signage, etc.

I'm all for "all metric", but doubt I'll ever see it happen in my lifetime here in the US, even for my own personal use. It's hard to change...
Its also expensive to change just for the sake of change. For someone just starting out I think the metric versions of tools such as router bits and drill bits are going to be harder to find, less options, and more expensive than their American counterparts. I looked up drill bits at home depot website and you get an equivalent set of metric and American but the metric set has only about half as many sizes and it costs a bit more so the cost per bit is about 2.2x the cost of the American bits. I took a quick look at Rockler and from what I see they don't even sell metric router bits.

[Dennis Aspö]

It's also expensive to keep using a different system from everyone else in an ever increasingly globalized world.

[Yonak Hawkins]

For someone just starting out I think the metric versions of tools such as router bits and drill bits are going to be harder to find, less options, and more expensive than their American counterparts. I looked up drill bits at home depot website and you get an equivalent set of metric and American but the metric set has only about half as many sizes and it costs a bit more so the cost per bit is about 2.2x the cost of the American bits. I took a quick look at Rockler and from what I see they don't even sell metric router bits.

I believe this is a matter of good business tactics to offer what the customer wants. However in a broader sense, an increasingly globalized world, as Dennis says, can't continue to use different methods of measurement, no matter what method is adopted. Business will eventually choose the most cost efficient path and the general population will slowly and begrudgingly adapt.

[David L Morse]

I find it interesting that metric sizes are used for the retail packaging of water, wine and spirits while beer is sold in imperial units.

[Halgeir Wold]

Do you need a metric hammer to pound your glue-ups into submission if you build something using metric measurements?

Yes you do - because a 4'' hammer is just too large to hit a 100mm something.. :-)

The light definition was based on comparing with the meter prototype, to the nearest fit, at an exact temperature and humidity.
Before todays definition there was another one also based on light, but a much more quirky one of light from krypton atoms at a certain energy excitation state,- 1 650 753.73 wavelengths of them, to be exact.....

[Jim Stearns]

Here's a good one I stumbled across recently. I bought a hardware assortment from Menard's. In it there were 1/4", 5/16" and 3/8" bolts, nuts, etc. Also some smaller #6, 8 etc. Chinese of course.
The thing is, the 1/4" bolts had 10mm heads instead of 7/16" like normal for imperial bolts. So 1/4" bolts with metric heads. I never saw that before.

Tonight I encountered it again. I just bought a Grizzly band saw. While assembling the stand I found the same thing; 1/4" bolts with 10mm heads.

[Charles Ratz]

For those that have switched to metric, how do you get used to "estimating" in metric? For example, I can picture a board that's three feet long, but not 1.5 meters. I have to convert in my head from a meter to about 40 inches x 1.5 = 60 inches or so. Liters aren't bad since it's about a quart but kilograms? Hard to do in your head.

Is it just a matter of practice and struggling until you have a feel for metric dimensions etc.?

[John Coloccia]

For those that have switched to metric, how do you get used to "estimating" in metric? For example, I can picture a board that's three feet long, but not 1.5 meters. I have to convert in my head from a meter to about 40 inches x 1.5 = 60 inches or so. Liters aren't bad since it's about a quart but kilograms? Hard to do in your head.

Is it just a matter of practice and struggling until you have a feel for metric dimensions etc.?

I use decameters, which is about 4" long. I never actually SAY decimeters, but I can reliably judge 4" (1dm..10cm), 6" (1.5 dm or 15cm) and 12" (30cm or 3dm). It's not exact, of course, but it's close enough to work with.

[Rod Sheridan]

For those that have switched to metric, how do you get used to "estimating" in metric? For example, I can picture a board that's three feet long, but not 1.5 meters. I have to convert in my head from a meter to about 40 inches x 1.5 = 60 inches or so. Liters aren't bad since it's about a quart but kilograms? Hard to do in your head.

Is it just a matter of practice and struggling until you have a feel for metric dimensions etc.?

Charles, you never had a built in ability to estimate things in Imperial, you learned by experience.

Same with the metric system, start using it and you'll become familiar............Rod.

[Chris Padilla]

Celsius or Fahrenheit? :D Or perhaps you might prefer kelvin? :D :D

[Chris Parks]

To be truthful and keep in mind I converted years ago some things for some people never quite "Gel". It is the generation that follows that never used any other method that truly gets it. I for instance have one big issue and that is the height of people. If someone asks me how tall I am I haven't a clue in metric. It is a bit like someone asking for your mobile phone number, most don't know it because they never have to quote it. If the police asked me for the height of someone I would have to quote it in imperial which given all the coppers have grown up with metric would be really funny. It seems all those who convert have isolated problems of this nature, my wife has never converted to measuring in metric but is fully conversant with weights etc through buying groceries.

[Rod Sheridan]

Celsius or Fahrenheit? :D Or perhaps you might prefer kelvin? :D :D

The numbers in Kelvin and Farhreneit are too large for my simple brain.................Rod.

[dennis davidson]

Why not use a set of dividers, almost no measuring required and absolutely equal divisions.

[Curt Harms]

For those that have switched to metric, how do you get used to "estimating" in metric? For example, I can picture a board that's three feet long, but not 1.5 meters. I have to convert in my head from a meter to about 40 inches x 1.5 = 60 inches or so. Liters aren't bad since it's about a quart but kilograms? Hard to do in your head.

Is it just a matter of practice and struggling until you have a feel for metric dimensions etc.?

A meter's a 'long' yard - about 3' 3"

A millimeter is about halfway between 1/16" and 1/32", actually 1/25.4"

6mm ~ 1/4"
8mm ~ 5/16
10mm ~ 3/8
13mm ~ 1/2"

A kilometer is a little over 1/2 mile, about 5/8.

Remember this is about 'estimating':)

[Shawn Pixley]

I want to use AU's in scientific notation just to be different.

[Mark Woodmark]

I agree metric seems easier to work with. As for working with fractions, I have memorized the decimal equivalents to the fractions through 32nds and some 64ths. This makes figuring with a calculator easy. For any odd fractions, I divide the top number by the bottom number to get the decimal equivalent. This is somewhat cumbersome and I round the decimal to 5 places in most cases. I find this to be accurate enough for most cases.

[Keith Weber]

I round the decimal to 5 places in most cases. I find this to be accurate enough for most cases.

5 decimal places? 1/100,000th of an inch is accurate enough for MOST cases??? What exactly isn't falling into the "most cases" category in your shop? I'd love to see the equipment you're using that comes anywhere close to those tolerances or accuracy. I'm picturing 20-ton machines in a temperature-controlled lab where you can't touch the materials that you're working on with your hands.

[Mark Woodmark]

5 decimal places? 1/100,000th of an inch is accurate enough for MOST cases??? What exactly isn't falling into the "most cases" category in your shop? I'd love to see the equipment you're using that comes anywhere close to those tolerances or accuracy. I'm picturing 20-ton machines in a temperature-controlled lab where you can't touch the materials that you're working on with your hands.

I figured this would get a rise from someone. If not laying something out using datum measuring you could get a tolerance build up making some of your last measurements off. I would take a whole lot of dimensions, but theoretically it is possible. I agree with you completely, I read post on this forum that discuss accuracy of different things and for the most part feel that level of accuracy is unnecessary. The talk in this post of 1/1000,000 of an inch eludes to that. When I draw my designs up in AutoCAD, accuracy is a must. Not being accurate enough causes its own set of problems with the drawing.

We are working with wood, an unstable material in itself (I suppose that will be debated now too). I mostly produce wood art pieces of smaller size, what I have noticed over time is that it is more difficult to hide small dimensional errors on small pieces than it is on say a piece of furniture....Just my personal experience. I try to work in an environment of plus or minus 1/64". That doesn't mean my stuff is all 1/64" off someplace, it just means if necessary I will in most cases accept that

On a different note, I have been forced to start learning metric conversions for fractional inches, 50.8mm=2 inches, 25.4mm=1 inch, 12.7mm=1/2 inch, 6.35mm=1/4 inch, 3.175mm=1/8 inch, etc.....It seems like I saw the accuracy of 25.4 being challenged someplace here

[ian maybury]

It's a bit of a mess I think. Either system is perfectly usable, so practically speaking i think it mostly depends on what you are used to - but transitioning (at least as an adult) is not easy.

My early (mostly machine shop oriented) experience was imperial, but my formal engineering training was metric and inch together. I still have a slightly more intuitive understanding of stuff like e.g. engineering fits expressed in thou, but am generally happy to use either system for engineering calculations.

I as a result thought I was bilingual/ambidextrous and only slightly reluctantly bought quite a bit of equipment in the US with inch scales - the only option available at the time. (Incra positioners and the like)

I have to confess though that I ended up buying metric conversion scales and racks immediately when they became available to convert to metric - and couldn't believe how much working larger woodworking type inch dimensions and especially fractions had slowed me down and caused errors. Stuck with it for two years and gave up since it really wasn't getting any easier (probably my age), but haven't looking back since converting to mm….

[Andrew Pitonyak]

The simple answer is that it really does not matter... Some things you will likely be required to do conversions no matter what you do. Here in the states, you are not likely to purchase lumber by the meter, but rather by an imperial measurement (5/4 for thickness and dollars per foot). If you are using the green tools, then you will have some meter stuff going on.

It is probably more important that you are consistent in how you cut specific pieces. If your table saw is set inches, you probably should not measure in meters. I keep a calculator around in case I need to convert anything.

Oh, and I have mostly Feet / Inches for my measurements, but, I have bits in both 64ths and mm dimensions. Oh, I also have the lettered bits.

[Tom Clark FL]

I am a retired machinist, and in the shop we quit using fractions a hundred years ago. Oh, we might say a 1/4" screw, or a 1/2" bolt, but all measurements are done in thousands of an inch. When using decimals everything is in multiples of 10, just like the metric system, so the decimal system is every bit as easy as the metric system. If the piece you are working on is 12.568" long, and you want to divide it into 7 equal spaces - how simple can you get? 1.7954".

When I see woodworkers using fraction calipers I just laugh to myself because it is so ridiculous!

All machinist rulers read in decimals.

[ian maybury]

I'd have to say that it's the fractions that get me too Tom. That said while working for Polaroid Corp back in the 80s it wasn't unusual to see engineering drawings that mixed fractions (of the most obscure sort) and decimal inches….

[Mark Woodmark]

I'd have to say that it's the fractions that get me too Tom. That said while working for Polaroid Corp back in the 80s it wasn't unusual to see engineering drawings that mixed fractions (of the most obscure sort) and decimal inches….

That's just bizarre, what did the fractions look like?

[John Coloccia]

That's just bizarre, what did the fractions look like?

It was probably for historical purposes. For example, no one calls it a "Three hundred seventy five thou racket", and no one ever will. It will always be a "Thee eighths" drive. Sometimes you hold over numbers that look funny to the outsider, but make perfect sense to those who know and would be confusing if you "simplified" it.

[Mark Woodmark]

It was probably for historical purposes. For example, no one calls it a "Three hundred seventy five thou racket", and no one ever will. It will always be a "Thee eighths" drive. Sometimes you hold over numbers that look funny to the outsider, but make perfect sense to those who know and would be confusing if you "simplified" it.

They must be pretty old. I worked for a manufacturer for 33 years in various engineering department capacities and have seen drawings from as far back as the 1920's, but never saw anything like that. I guess I really have lived a sheltered life.

[John Whitmore]

They defined the meter, rather arbitrarily, as 1/10,000,000 the distance from the equator to the north pole. It seems odd to me as there was already a common measurement in many different countries that, more or less, equaled an inch...

Oh, the history is easy to understand: before the Revolution, rent collectors came out
once a year to collect X bushels per acre of wheat... and war debts from Louis XV were
so severe, that Louis XVI sent the collectors out with the largest bushels anyone had
ever seen. Hey, it was the royal bushel, you couldn't very well complain!
So, without changing any commercial contracts, the reaction after royalty 'left the
building' was to make a set of units for measurement that no temporal authority
could change. New contracts, with new principals, used the new units.

It was based on surveying because (again, before the revolution) the nobility
had resisted any attempts to accurately survey the country. After all, their traditional
view of their holdings amounted, in aggregate, to at least 150% of the national land
area (and no sale poirot of a surveyor was going to tell them otherwise!). When
the nobles were gone, the new landowners wanted accurate borders.

Roy Underhill once showed a lovely Danish inch ruler, which does not in any way
align with US inch markings; those traditional units were different in every jurisdiction
and decade, and the remaining ones are 'not approved for trade' for very good reasons.
In the US, the foot is exactly defined in centimeters, with a lone exception for
the purpose of surveying (thus, the "U. S. Survey" foot is now a different unit,
in order to keep old maps authoritative).
1 [international foot] = 0.3048 meter
1 [US Survey foot] = (1200/3937) meter.

[Halgeir Wold]

As the European wars progressed throughout medieval times, countries came and went, - or rather jurisdiction came and went. Thus Norway became part of Denmark, as war booty or compensation,, around 1600. The Danish-Norwegian cubit was established by Danish-Norwegian Law in 1615- and consists of 24 danish inches, or more correctly "thumbs" ( the length of the outermost part of the thumb) and is today equal to 26,17mm. There was also a Norwegian ( and I believe swedish) "thumb" which equals 27.5mm. The last one kept well into the 19th Century, at least in the boat building environment. Up here North it was also known as the "boat thumb", or Southern thumb ( from South of Norway ).