# Metric Swap Over?



## Axis39 (Jul 3, 2019)

Hope this is the correct forum…. Anyway…

My son and I build cabinets and furniture for a living. We recently did some shop upgrades, including some Festool purchases. After watching a [ile of Youtube videos on using some of these Festool tools, the metric thing has been popping up.

It's been something I consider every few years… But, this is really the first time I've tried it. I actually bought a few tapes measures that show both. I mean this is REALLY the first time I've done anything about even looking at metric, other than it being an annoyance and something I have to convert… I realized when I got these tapes that a millimeter is smaller than 1/16"... Duh. Smaller always means more accurate. Been using nothing but .5mm pencils or knives for the majority of our work for a while now.

Yesterday, I was on the job site doing some installation.. There were a few complicated bits I was working on (the entertainment cabinet style pocket doors for the appliance garage being the main culprit) and decided to do as much s I could in metric.

Othe than my perception of sizes, and not being able to imagine what size each thing was… things like what would normally be 1/4" and something I can just see, I have to now measure. I know I'll get used to it, and I kinda want to keep trying this system out.

The math is SOOOOOO much easier. The mm being smaller and more accurate…. I dunno, the only downside is that living in the US, I will have to keep converting. But, I have to do some conversion the other way now (especially when buying cabinet hardware).

Anybody else made the move?


----------



## Foghorn (Jan 30, 2020)

I've been doing both for many years here in Canada. I prefer metric due to the simple math and less chance for mistakes but am comfortable with both and can visualize the size of something in either. I've been in industrial construction for many years and the majority but not all dimensions on prints and models are in metric. Most of my tapes are dual measurements along with most of my rulers.


----------



## northwoodsman (Feb 22, 2008)

In 3D printing and laser graving and cutting I use the metric system, it sure does make math MUCH easier. The hardest part for me is estimating still. Having used inches and feet for over 50 years those measurements pop right off. When it comes to the metric system I have to get out a tape or a ruler for anything over 1 mm. My brain just can't grasp it.


----------



## RyanGi (Jan 13, 2021)

I'd really like to swap over, but it would be a big change since all my stuff is imperial. I do enough stuff with it that I keep myself pretty fluent in both, and go out of my way to try to think of the conversions so I keep up on it. My retirement plan takes us overseas and it'll be a requirement there, so I'm trying to learn it. It's like learning a language, you gotta practice.


----------



## wapakfred (Jul 29, 2011)

While I haven't switched completely to metric, I use it often for the simplicity. It appears the US will never switch which is too bad, but resistance to change is pretty stuiff. I have the same issue as you, I can't visualize dimensions in metric….but making measurements and working the math with it is a piece of cake.


----------



## sunnybob (Oct 12, 2021)

I spent 60 years working with imperial, and then moved to a metric country! Been here 14 years now. I made a definite effort to convert, and stuff less than a foot (300mm) is now much easier with metric. Larger numbers take a lot more effort. The doctors here always ask my height, and saying 1.85 metres is way more difficult than saying 6ft.
I still cant convert 8ft x 4 ft boards accurately.


----------



## controlfreak (Jun 29, 2019)

As I have been going down this road the only real obstacle is things like mortice chisels. And me not thinking bought a set of metric chisels to start with. Because I mostly set the mortice off the chisel it never bothered me. So that said, other than terms like 4'x8' sheet or 2"x4" (which we all know isn't) I may need to try to see how going all metric feels.


----------



## redlee (Apr 11, 2016)

There are only 3 countries left that havent converted, Metric is easier but the old die hards cant seem to take the plunge.


----------



## MadMark (Jun 3, 2014)

English units excel at halving, quartering, etc. without the decimals becoming unrealistically long. This helps when figuring centers of circles converting from dia to radius, finding half measures, etc. To me a two place decimal, correctly implying the desired accuracy, mis-specifies the dimension. 1/8" is .125" *not* .12 or .13 +- .01". As a CAD operator I've rasslled with this for years.

Half of a fraction simply doubles the denominator. Easy and fast to do in your head. Half of 1/16 is 1/32, Half of .0625 is … QUICK! LOL And the five place decimal sets an unrealistic tolerance (and thereby, cost) specification.


----------



## ibewjon (Oct 2, 2010)

If I remember correctly, the USA was going metric soo, so in the late 60's, early 70's, there was a big push in school to learn it. Then,. NOTHING. Metric sure is easier, but if no one wants to learn and use it, it will not happen here. Sad…


----------



## Bearcontrare (Oct 6, 2020)

Sorry, not on THIS lifetime.
After I'm dead people can use centipedes and whatever they like.
For now, millimeters are gor FIREARMS, not for the woodshop….


----------



## MadMark (Jun 3, 2014)

Use'ta work for Florida DOT. Metrification has HUGE impacts. EVERY sign with a distance on it needs to be replaced and/or moved. The entire length of the interstate currently has mile markers on both sides every .1 mile. Going to makers every 200m is a CHORE. The exits all need to be renumbered since most are based on miles. Think of the impacts on all the local vendors with signs and adverts that say "just off exit 109" that have to be reprinted.

Speed limits need to be tweaked by the legislature since, say, 30MPH is 48KPH, but would have to be rounded up to 50KPH so the law would would have to be changed accordingly.
It's a HUGE investment in time and effort.

And for what? If we need to sell metric parts, we design metric parts. But changing over all the roads and highways makes little sense economically since it's all cost and little measurable benefit.


----------



## RichT (Oct 14, 2016)

I-19 from Tucson to Nogales is signed in metric. It's the only stretch of interstate in the country that is metric.

https://www.atlasobscura.com/places/i19-americas-only-metric-interstate


----------



## Barkley (Jun 28, 2019)

I've considering switching to Metric since Carter was president. Maybe I'll try it which will mean buying a few new measuring tapes and steel rules. Should I buy combo rules or just take the leap. If any of you smell smoke please call my wife.


----------



## redlee (Apr 11, 2016)

https://www.tiktok.com/@tomsilvatoh/video/6992334455985736966


----------



## BurlyBob (Mar 13, 2012)

Yeah, I'm building a Roubo workbench using Bench crafted hardware and plans. I'm also following a set of bench plans from Matt Estlea, a brit in the UK. His plans are in Metric.

It's been a bit of an adventure. I've printed off a 3 page conversion chart and constantly refer to it.

I have agree Metric in much more precise. I think that most measurement here in the use is for construction not fine woodworking. The delve into woodworking the more I appreciate my German woodworking heritage.


----------



## sunnybob (Oct 12, 2021)

The UK went metric many years ago, due to being so closely entertwined with europe. But the government kept miles, rather than kilometers (because of the cost of road signage), and they kept pints (because beer comes in pints, not 560ml's)

But there are many crossover measurements still in use. You can buy 25 metres of 1/2" hose pipe for example. Its also very common for people to still talk of things like "half a litre".


----------



## Sylvain (Jul 23, 2011)

> If I remember correctly, the USA was going metric soo, so in the late 60 s, early 70 s, [...]
> 
> - ibewjon





> There are only 3 countries left that havent converted, [...]
> 
> - Richard Lee


In fact USA is metric since 1866. See:
https://usma.org/laws-and-bills/metric-act-of-1866#history
The "US customary system" is a secondary system which has, since the 5th of April 1893, been legally defined by reference to the metric system. See:
https://usma.org/laws-and-bills/mendenhall-order#locale-notification
I guess the politicians then did not had the courage to make the metric system mandatory.

The US NIST has been a very important contributor to the refinement of the standards of what is now called the SI (International System of Units).

Major changes tend to necessitate 60 years to be fully implemented. In 4 years USA will reach the 120 years mark!


----------



## SMP (Aug 29, 2018)

> English units excel at halving, quartering, etc. without the decimals becoming unrealistically long. This helps when figuring centers of circles converting from dia to radius, finding half measures, etc. To me a two place decimal, correctly implying the desired accuracy, mis-specifies the dimension. 1/8" is .125" *not* .12 or .13 +- .01". As a CAD operator I ve rasslled with this for years.
> 
> Half of a fraction simply doubles the denominator. Easy and fast to do in your head. Half of 1/16 is 1/32, Half of .0625 is … QUICK! LOL And the five place decimal sets an unrealistic tolerance (and thereby, cost) specification.
> 
> - Madmark2


Pro tip: half of 6mm is 3mm (did that calculation in my head in a split second)


----------



## Tony1212 (Aug 26, 2013)

> English units excel at halving, quartering, etc. without the decimals becoming unrealistically long. This helps when figuring centers of circles converting from dia to radius, finding half measures, etc. To me a two place decimal, correctly implying the desired accuracy, mis-specifies the dimension. 1/8" is .125" *not* .12 or .13 +- .01". As a CAD operator I ve rasslled with this for years.
> 
> Half of a fraction simply doubles the denominator. Easy and fast to do in your head. Half of 1/16 is 1/32, Half of .0625 is … QUICK! LOL And the five place decimal sets an unrealistic tolerance (and thereby, cost) specification.
> 
> ...


Sure. And half of 9mm is 4.5mm, but you won't find a 4.5mm on your metric ruler. And bisecting 4.5? Pfft… Good luck.

I agree with the rest of the world that the metric system is superior to the imperial in many cases, but here is where it falls short.

I use metric for 3D printing and unless you specifically design something so the measurements are evenly divisible by two for as many divisions as you need, the decimal places get crazy. It's easy enough to do in CAD when you can just grab the center point between two points, but if you try to replicate that piece in the shop with rulers, you're always rounding.

For instance, a holder for a colored pencil set to fit in a certain width. Multiple tiers with all of the holes evenly spaced. If you're talking 6 or 7 holes per tier, it's a lot easier to lay out with fractions of an inch than mm.


----------



## RichT (Oct 14, 2016)

> Sure. And half of 9mm is 4.5mm, but you won t find a 4.5mm on your metric ruler. And bisecting 4.5? Pfft… Good luck.
> 
> - Tony1212


Funny, I can't find one of mine that doesn't have 0.5mm markings.


----------



## MadMark (Jun 3, 2014)

3mm ~1/8". I work in 32's, 1/32" ~.75mm, your .5mm rule doesn't measure .25mm. 1mm ~0.02"

Quick, in metric, If I need to dado a 4.5mm groove with a 3/32" blade, how far do I shift to make the 2nd cut?

Bonus points if you can do it in your head.


----------



## Sylvain (Jul 23, 2011)

> 3mm ~1/8". I work in 32 s, 1/32" ~.75mm, your .5mm rule doesn t measure .25mm. 1mm ~0.02"
> 
> Quick, in metric, If I need to dado a 4.5mm groove with a 3/32" blade, how far do I shift to make the 2nd cut?
> 
> ...


That is not fair, mixing US customary with metric makes things even more difficult; you have to know the width of the kerf in metric (or use metric blades).

now if 1/32=0.75, 3/32= 2.25mm (in my head) which happens to be just half of 4.5mm.

I don't have this kind of problem as I am hand tool only and work by reference most of the time.


----------



## MadMark (Jun 3, 2014)

Not fair is the reality of most shops. All router bits & cutters & drills, the incra, etc., have to be changed out. During transition you really need both.

I picked 4.5mm to see if any caught it was ~3/16. You win! but now set that .25 mm on your .5mm tool.


----------



## controlfreak (Jun 29, 2019)

I was ready to go all in on metric in high school. In chemistry and physics that was all we used. It wouldn't take long to get used to converting Celsius to "how warm is it" and car speed the same. Then at the last minute the US Senate killed the whole switch because if a sign said limit 70 KH was going into a curve and someone thought it was MPH they would go too fast and die. Yeah, how many people think a posted limit for a curve is 70 MPH anyway. It really pissed me off that for two or three years they ran PSA ads with songs and such to teach people the difference between a liter and a quart etc. and killed it over a stupid reason. I think I will buy some metric only rules to see what I can do. I just always find the metric marks on a side that is not touching the wood. I also like to have larger rough marks on one side and half marks or fine on the other.


----------



## Sylvain (Jul 23, 2011)

Dividing a board in equal parts without knowing the width of it.
Use the intercept theorem.
It works with any arbitrary unit.

It allows one to divide in 2, 4, 8, ... 
but also in 3, 5, 7, ... , 11, 13, ... which doesn't work with any rule without either a calculus or the intercept theorem.

Example of use:





In this example he uses an 8" length but he could have used a 16 cm or 20 cm line or a lath marked to 4 tooth-pick lengths.


----------



## wapakfred (Jul 29, 2011)

The only part of the anti-metric conversion argument I buy is about the cost of switching…on a national scale. It would be huge, which is why we should have started many, many years ago. Of course it would be relatively expensive to us on a personal level as well. But this can be a something where the switch is flipped; it would need to be phased in. Sadly, our government doesn't have the guts to do it, plus they are too busy fighting all kinds of partisan battles.


----------



## Sylvain (Jul 23, 2011)

> The exits all need to be renumbered since most are based on miles.
> 
> - Madmark2


Does that means exits don't have the same number in one way and the other?
Obviously when one start at one end, the distance is not the same as from the other end.
Then what is the meaning if one doesn't begin his/her journey from one of the ends but from an intermediate point?


----------



## JAAune (Jan 22, 2012)

Measure everything in inches and eliminate the use of feet. Buy a dial caliper and a decimal ruler (inches) and you'll get the benefit of metric with much less time and expense learning to switch over.


----------



## MadMark (Jun 3, 2014)

The signs are based on the interchange location. The intersection is where the roads physically cross, not where the exit ramp starts. Sometimes you'll have an access ramp wayyy early, but the signage is still the distance to the crossing. "Exit HERE for Exit 357 for US1 2mi" at mile marker 355.

Aside: Odd interstates run NS, evens EW. A grid was laid over the US and numbers start lower left corner. 10 at the bottom, 90 at the top, 5 on left and 95 on the right. Three digit "interstates" are beltway around cities. Not counting exiting for fuel & reentering, it is possible to drive to every corner of the country from any other corner nonstop, not a single traffic light! The bridges are designed to allow our heavy tanks to cross. Florida and Hawaii have "interstates" that don't cross state lines (I-4 in Fl runs Tampa to Daytona.) I-4 is also the national testbed for new roadway technology and has embedded traffic sensors, cameras, truck sensors, etc. for its full length.

State DOT's have mowing seaside for minority and female owned mowing business. Have the wife set up a lawn business. Buy *1* mower. Do enough jobs to just stay in business for three years (may vary) and put in for DOT mowing contract. Farm said contract out to contractors with more than *1* mower (& a crew) to do the actual work, and take 6% admin fee off the top for doing the paperwork without ever cutting another blade of grass.


----------



## controlfreak (Jun 29, 2019)

> The exits all need to be renumbered since most are based on miles.
> 
> - Madmark2
> 
> ...


In the states mile marker 185 is the same point regardless of which direction you travel. Both directions will be at mile marker 185 and if an exit were near it would be exit 185 for both. The only difference is if entering a state from the south you start with a high number and if from the north a low number.

I don't see why they can't start with existing mile markers and add KM markers. As signs age and need replacement the old can be out with the old and in with the new.


----------



## MadMark (Jun 3, 2014)

The signs have to be moved to get units. No drivers want to see *100' / 30.48m* on the same sign. The signs need to be enlarged to have extra space. So you need to reposition the signs to even metric increments. Now a U-channel mounted sign isn't hard to move but an illuminated and possibly instrumented multi lane overhead isn't trivial to move - and the American public, that is already PO'd enough at traffic, isn't going to want more delays by tweaking signage.


----------



## ibewjon (Oct 2, 2010)

Mile markers start at zero south and zero west. St Louis is zero, Chicago is about 287. Zero at Iowa line on I 80, climbing as you travel east to indiana line. Some states just number in order, 1- 50. But no reference to mileage without a map. Many of those states have converted to mileage based exit numbers.


----------



## tvrgeek (Nov 19, 2013)

I know I should switch. Easier and all that. But I am "trained" in Imperial. I know what a "thou" is. 
We really missed the boat when we did not convert. A lot of industry is converted as we are in a global market. A few countries swapped driving sides, but a few resisted.

The other thing we messed up is base 10. Should have been base 12. Turns out it plays better in the universe. 
Baltic Birch is metric, so maybe that should be your guide.


----------



## MadMark (Jun 3, 2014)

If we had 12 fingers we'd use base 12 math.

Red reminds us of blood and is used as the color of help (red cross) or danger.

12 playing better is why hours, minutes, seconds, feet, degrees, months, the zodiac, dozens, days of Christmas, points & pica's, etc. exist in the sizes they do - all divisible by 12.

10 isn't divisible by anything except 2 and 5. 12 divides by 2, 3, 4, 6 and fractions nicely at 8 and 9. Much easier when you only do integer math (cubits, spans, fingers, thumbs, etc.)

Hence the "naturalness" of fractions - integer math.


----------



## controlfreak (Jun 29, 2019)

> Mile markers start at zero south and zero west. St Louis is zero, Chicago is about 287. Zero at Iowa line on I 80, climbing as you travel east to indiana line. Some states just number in order, 1- 50. But no reference to mileage without a map. Many of those states have converted to mileage based exit numbers.
> 
> - ibewjon


Right, I was using a nearby interstate as a reference that is north south in my local area but its terminus points make it east west


----------



## Sylvain (Jul 23, 2011)

If at least it were 12 based; but it is not. It is completely incoherent.






and length is only the easy part.


----------



## controlfreak (Jun 29, 2019)

> The signs have to be moved to get units. No drivers want to see *100 / 30.48m* on the same sign. The signs need to be enlarged to have extra space. So you need to reposition the signs to even metric increments. Now a U-channel mounted sign isn t hard to move but an illuminated and possibly instrumented multi lane overhead isn t trivial to move - and the American public, that is already PO d enough at traffic, isn t going to want more delays by tweaking signage.
> 
> - Madmark2


No, I am saying have the existing mile markers remain and new KM markers added where they are whole numbers. Then down the line remove the mile markers when the exits get renumbered with KM as the reference number. I am guessing that as the signs age they probably change whole sections at a time anyway. Hell, they didn't mind renumbering each exit on I-85 when they added a bypass loop around Spartanburg and it added a mile to the distance of the road. Just saying it is a way it could be done but not asking for it to be done. If they just ripped off the band aid 40 years ago like they were supposed to we wouldn't be having the conversation again and again.


----------



## Lazyman (Aug 8, 2014)

Sorry to be pedantic but smaller units does not mean it is more accurate. Metric is not any more accurate or precise then English units. It is just a different unit of measure. You may be just using the wrong terminology but an English measure of 1/16th inch is just as accurate as a 1.5875 mm. Try measuring that accurately with your your metric ruler. And doing math in decimals is not always easier. Can you triple 1.5875 mm in your head. I can. It is 3/16ths . Personally, I generally try not to use measurements less than 1/8th inch so having to measure small fractions of a CM with MM markings on a ruler would be a pain, especially after you hit 42 years old and you have to wear reading glasses to read any measurements that small.

If it is the decimals that make the math easier for you, there is no reason you cannot use decimals with English units. But if you are mixing fractions and decimals, trying to use both also becomes a pain. If I design and build using decimals and keep my smallest UOM as 0.1 inches to keep it simple, because you have to deal with materials manufactured based upon fractional standards, it means you may have to deal with 3 or 4 decimal places. Nope.

The problem with switching really comes when you try to mix and match the English and metric units. Until the materials and hardware are also manufactured to MM and CM measurements, mixing and matching will be annoying. Until they stop making 50.8×101.6 mm boards (that are actually 44.45×95.25 mm) and 19.1 mm plywood (that is actually 18.2562 mm) in 121.92×243.84 cm sheets, it just easier to stick with fractional inches, for woodworking anyway.


----------



## LeeRoyMan (Feb 23, 2019)

No changes for me. I use both as needed. I like using decimal equivalents for fractions and use the calculator to add or subtract them. I also just convert mm as needed. 
Too old to try one way over another. I guess I'll be bymathical until I'm done.


----------



## MadMark (Jun 3, 2014)

I invested in an 8" digital caliper that has mm/decimal in/fractional in. I'll gauge a part and if it comes out some oddball number I'll try one of the other scales and usually it'll land evenly on one of them. Pressing the button again gives me the accurate measure in whatever unit i'm working in.

Since I design what I make everything is Imperial, When I have to interface in mm I do, but for me, fractional is easier for woodworking. Even in TinkerCAD, making 3D parts, my first move is to change the units from mm to in.

This, for instance is mostly imperial but has decimal and metric spacings and drills.










Was arguing with someone about 3mm, they said I should stock 3 mm instead of #4 (3mm ~.120 vs #4 thru at .125) and I said it's not the screws, its the screws in four lengths, nyloc nuts, spacers, washers (steel & fiber), pilot drill, thru drill, tap, hex drivers, nut drivers, extra storage etc.

All my electronics shop work is in #4 or #6. I've got a little 4" sq 3d printed tray with both #4 and #6 pilot, tap, thru, taps, drivers and pinecone (AKA stepped drill) bits so that any #4 or #6 operation I have *ALL* the tools at hand.










Black is #6, red is #4. None is neither (pilot), alternate head, pinecone, etc.

With the 1/32" pinecone I can get most metric parts to fit.

My vision is getting worse & worse. The ophthalmologist says they can only do so much with diabetic retinopathy. I'm sorting and marking my tools in anticipation for needing more and more help. You can get a TAN or fry ants with a magnifier from the lighting on my electronics bench.

The DRO's are much larger and easier to see than hairlines for setting measures. I basically can no longer see hairlines in one eye. My depth perception is about shot too. (sigh) What a drag it is getting old … (If you recognize that lyric you're old too! LOL)


----------



## RichT (Oct 14, 2016)

> No changes for me. I use both as needed. I like using decimal equivalents for fractions and use the calculator to add or subtract them. I also just convert mm as needed.
> Too old to try one way over another. I guess I ll be bymathical until I m done.
> 
> - LeeRoyMan


Me too, LeeRoy. I guess we're "unit-fluid" whatever that means.


----------



## Sylvain (Jul 23, 2011)

The road problem is now a minor problem which would not affect many people.
The GPS knows what the speed limit is on the road I am on (and where the stationary radars are).
The GPS warns me if I am inadvertently 1km/h above limit.
Of course it knows where I am and which exit I will need to use.

If there is a temporary local limitation (e.g. work in progress) I can see my real speed in any unit as I can choose the unit showed by the GPS.


----------



## controlfreak (Jun 29, 2019)

I agree Sylvain, the only reason I ever look at a mile marker or exit number is to tell someone where I am or to report an accident. Other than that I use GPS if the path is unknown.


----------



## Dutchy (Jun 18, 2012)

> Measure everything in inches and eliminate the use of feet. Buy a dial caliper and a decimal ruler (inches) and you ll get the benefit of metric with much less time and expense learning to switch over.
> 
> - JAAune


Are there decimal inch rulers?


----------



## Dutchy (Jun 18, 2012)

Since a couple of years I use the imperial system sometimes..I grew up with metric. At first I found it difficult to work with the imperial system, but now I'm quite used to it. I speak here only for length measurements. In the beginning I converted the inch measurements into mm, something reasonable to do. But recently I tried to convert something from mm to inches and that is pretty difficult. My advice is not to convert as that will make it even more difficult than it already is. Think either in inches or think in mm. Yes and I understand that this is quite difficult at the beginning because the values mean nothing to you. Metric and imperial are two different things and should not be used interchangeably. It's just like with a foreign language you first translate but at a certain point you stop doing that.


----------



## Lazyman (Aug 8, 2014)

> No changes for me. I use both as needed. I like using decimal equivalents for fractions and use the calculator to add or subtract them. I also just convert mm as needed.
> Too old to try one way over another. I guess I ll be bymathical until I m done.
> 
> - LeeRoyMan
> ...


 It is easy enough to use decimal equivalents for the calculating part. I also have a calculator that handles fraction input and output which is handy with long lists or multiplication and division and you still need to use a fractional ruler afterwards. Metric definitely makes it easy to use a calculator without the mental decimal conversion and is also straight forward to understand, though not always intuitive if have not used it very much. The issue or annoyance for me is more about mixing units than being able to use either one. Except for very small things, I rarely need mm accuracy in a measurement. When your materials are mostly in 1/4" (6.35mm) increments, a metric ruler or measuring tape is just not that useful unless accuracy is not very important. For example, you would have to interpolate where 6.35mm is on a mm rule but on a fractional inch rule, you have an exact mark for it, making it the more accurate measurement, though since your pencil mark is probably wider than any inaccuracy, it may not matter anyway. We are talking about woodworking after all.

If you are going to truly switch over to metric, then you have to buy or mill/cut your materials in metric sizes to make that convenient. Then, you can use 5 mm increments for most of your dimensions and rarely have to use the mm marks on your measuring tools.


----------



## Axis39 (Jul 3, 2019)

Fantastic responses so far, guys! I appreciate everyone's input (even you curmudgeons, like me! LOL)

I am not sure I can totally convert, living here in the States.

I also agree with you guys who talks about using 100ths and 50ths of an inch, or using decimal. But, I work in the woodworking industry in the US. NOTHING is done in 100ths…. And, yeah, most of there stuff I measure in the shop I do to the 64th or 128th. I am, honestly, used to working to those dimensions. I adjust my tools by the thousandth all the time!

But, adding 13/16 to 5/64 can take a second… Adding 21 mm to 2mm. (Granted it's like a bit over 20 to a hair under 2, but that's if I start with Imperial. If I started with metric, it's just 21 +2.

Honestly, the most difficult part will be communicating with other Americans about it. If I start a project in Metric, like start the measuring in metric, than it won't matter, until I need to express to someone what a 600mm cabinet looks like.

I spent my day yesterday working metric again. It worked quite well, again… But, since the project had started in Imperial, it made a few things funky.


----------



## controlfreak (Jun 29, 2019)

> I converted the inch measurements into mm, something reasonable to do. But recently I tried to convert something from mm to inches and that is pretty difficult. My advice is not to convert as that will make it even more difficult than it already is.
> 
> - Dutchy


Makes me think back to the Mars probe that violently impacted the planet because someone failed to convert one to another. Converting back and forth is just inviting error. The same could be said for reducing fractions. I know its simple math but errors happen. I can deal with fractions but where metric really shines is all conversion is done via shifting the decimal. I just checked and a 1/2 mm (.5 but I am just messing with you) is roughly equal to 1/64". I don't usually work to that level but I can't see needing to divide a mm by any more than that. I haven't cought myself doing it lately but I used to in construction call out a measurement 24" and a fat 1/8th


----------



## Lazyman (Aug 8, 2014)

I am curious, John. What sorts of things do you make that require 64ths and 132nds? My CNC can probably handle that sort of fine detail but how can you measure, mark and cut to that level? A .5mm pencil lead is more than 1/64" wide.


----------



## JAAune (Jan 22, 2012)

> Measure everything in inches and eliminate the use of feet. Buy a dial caliper and a decimal ruler (inches) and you ll get the benefit of metric with much less time and expense learning to switch over.
> 
> - JAAune
> 
> ...


They're sold as 1/100ths or 1/50ths scale but I call them decimal rulers because I'm used to thinking of 1/100ths as .01" or /50th as .02". That's a habit from using dial calipers for most small measurements.


----------



## JAAune (Jan 22, 2012)

> I am curious, John. What sorts of things do you make that require 64ths and 132nds? My CNC can probably handle that sort of fine detail but how can you measure, mark and cut to that level? A .5mm pencil lead is more than 1/64" wide.
> 
> - Lazyman


1/64" is roughly .016" and marking at that level of accuracy is possible on small parts using a dial caliper (pointy tips can scribe) or using a steel rule and a sharp knife.

I can't speak for John but in our shop, we need to get within .005" on many cuts since multiple people and machines are working on the same project cutting different parts simultaneously. Working that way risks errors adding up until gaps and other discrepancies start showing in the finished project.


----------



## MadMark (Jun 3, 2014)

yep. tolerances accumulate. The incra holds +- 0.002" on any setting. Great for botch & remakes. Your tools need to be at least 4x, and preferably 10x, tighter than the tolerances on what you're making. I work to 1/32"+-0.002 on *every* cut.


----------



## LeeRoyMan (Feb 23, 2019)

I hope someday I can get a project that demands .005 tolerances.
I guess I should buy better machinery first.

So hypothetical question? 
Let's say you want to make a box with cubbies..

The overall length of the box has to be 2272mm long to fit the spot.
Your material is 17.462 thick, and you want 12 cubbies.

How do you figure out the size of each cubby?
2272 (Overall Length) - 226.98 (13×17.46 wood thickness) divided by 12 (cubbies) = 170.25 per hole.

Is this done in your head or with a calculator?
If it's done with the calculator, whats the difference what unit of measure you use?

When you lay it out do you round up or down or mark the .25?
If you mark the .25 what's any different than marking any imperial decimal?

I'm not knocking the metric, I just don't see the difference, maybe because I'm set in my ways. IDK…


----------



## Axis39 (Jul 3, 2019)

> I am curious, John. What sorts of things do you make that require 64ths and 132nds? My CNC can probably handle that sort of fine detail but how can you measure, mark and cut to that level? A .5mm pencil lead is more than 1/64" wide.
> 
> - Lazyman


MadMark mentioned my solution for cutting accuracy. I have an Incra TS-LS Joinery System installed on my table saw. It is rock solid and more accurate than I am. You can dial, with the fine adjustment dial, 1/1000 at a time.

I don't have a CNC (and hope I don't go there… although, my son keeps talking about it).

I use calipers, dividers, a lot of metal rules (that are marked to 1/64 on some, and 1/100 on a few others. I use marking knives when the accuracy needs to be more than .5 mm. But, honestly, we do use self sharpening .5mm mechanical pencils for most of our marking (the lead rotates inside the barrel as you write with it, forever keeping your point smaller than .5 mm. Plus, I always mark arrow heads, not just a line. This helps me to know which part of the .5 mm to cut to.

I build high end custom cabinets and furniture. My joints HAVE to be tight as a frogs you-know-what. I HAVE to have everything square and my planes all have to match up. Many times my scribes must not ever see caulk… It's that kinda work.

LeeRoyMan, I like where you're going… Honestly, if I'm building something like that, I am probably not measuring like that… I'm gonna do what someone mentioned earlier in this thread (I think) about using some measurement longer, that is easily divide by what I need, then use center lines.

So, for your example, overall size is 2272 mm. I'd find the center of my material thickness, with dividers. Mark in that distance fomr each side. Then, lay a tape, on a diagonal so that 0 is on one of these centerlines, and 2280 (the next largest number divisible by 12). Then, I would move up the tape making a mark every 190 mm. This would be the centerline of each divider.

Before this week, I'da converted 2272 to inches…. Which is an incredibly awkward 89.4482 inches. If I round that to a typical 1/32 accuracy, I would have to consider if it was in between walls, or if it had an open end, or two. I'd have to cheat it one way or the other…. .4482 is a funny one, for sure…

If you were working to the 1/1000, you could end up in the vicinity of 560/1000… but, depending on how you round, it could end up all over the place… So, between walls, you cheat small, open end? All kinds of options, then.

But, most guys work to 1/16, maybe 1/32. So, a 32nd is .0312. Even to get there, you're talking a lot of rounding inaccuracies that would be introduced… Just as many, if not more than doing the math in metric.

That's why in your example, I wouldn't probably ever measure… Well, other than that first number (2272) and the stretched out diagonal (2280). But, after that, I'd use marking sticks, dividers, combo squares, etc.

And, all of those numbers I would throw into Excel, or do on a calculator. I have a fractional calculator, but it is just a construction calculator and won't go below 1/32 in it's calculations. So, if I can get away with marking sticks, or unmovable, fixed length, or notched, etc devices that don't rely on my eyesight, I will!!!


----------



## PCDub (Sep 24, 2017)

Well this is interesting-I ordered the Veritas Edge Rules that someone posted in the "Hot Buys" thread, and though they were advertised as having imperial measurements, they arrived with metric…

...hmmm… shall I return them? Or keep them to exercise the metric side of my brain… ???

(I'm old enough to have been taught metric in middle school-I remember when highway signs began to give distances in kms. I don't seen any reason to change the numbering of exits-most people don't even know they are mile approximations.)


----------



## SMP (Aug 29, 2018)

> 3mm ~1/8". I work in 32 s, 1/32" ~.75mm, your .5mm rule doesn t measure .25mm. 1mm ~0.02"
> 
> Quick, in metric, If I need to dado a 4.5mm groove with a 3/32" blade, how far do I shift to make the 2nd cut?
> 
> ...


Pro tip. Your alleged 3/32 blade is probably in metric and just "close enough" to 3/32 for woodworking. If you buy a decent blade they usually list both:

Here is a random Amana 40t blade i picked, check the plate and kerf:


----------



## MadMark (Jun 3, 2014)

I use Freud (Italian) LU83R10 TK blade. Spec sez:


> Kerf (in) 0.094


----------



## SMP (Aug 29, 2018)

> I use Freud (Italian) LU83R10 TK blade. Spec sez:Kerf (in) 0.094
> 
> - Madmark2


And 3/32" is .09375. Guess you are going to need a finer ruler to calculate the difference for that piece of wood that will move +/- 1/8" seasonally


----------



## MadMark (Jun 3, 2014)

Stupid comment. The assembled project moves as a unit. The point is that you were wrong, the blade width is NOT metric and that the blade tolerances don't stack. Initial fit is what matters.


----------



## SMP (Aug 29, 2018)

> Stupid comment. The assembled project moves as a unit. The point is that you were wrong, the blade width is NOT metric and that the blade tolerances don t stack. Initial fit is what matters.
> 
> - Madmark2


Every imperial random fraction has a corresponding metric fraction. Anyways don't worry about the kerf. Measure from your fence to the tip of the blade closest to the fence. No need to add in the kerf and subtract it.


----------



## redlee (Apr 11, 2016)

I think everyone should get themselves a Story Stick , then it doesnt matter.


----------



## redlee (Apr 11, 2016)

> Measure everything in inches and eliminate the use of feet. Buy a dial caliper and a decimal ruler (inches) and you ll get the benefit of metric with much less time and expense learning to switch over.
> 
> - JAAune
> 
> ...


I have the Mitutoyo ruler with 1/100 ths , cant see the fool thing.

https://www.itm.com/product/mitutoyo-182-202-fully-flexible-steel-rule?gclid=Cj0KCQjwsdiTBhD5ARIsAIpW8CIJJyERe9_WyjsckZNQzmmqY8EwGmw5lCO6ngxOdrdbEJXYsWUYnTwaAhQGEALw_wcB


----------



## Foghorn (Jan 30, 2020)

> Stupid comment. The assembled project moves as a unit. The point is that you were wrong, the blade width is NOT metric and that the blade tolerances don t stack. Initial fit is what matters.
> 
> - Madmark2
> 
> ...


The truth. In general and particularly in the construction industry, metric makes for less mistakes for the ones who don't share Matt Damon's abilities in Goodwill Hunting.


----------



## ibewjon (Oct 2, 2010)

I don't see the USA ever swapping to metric. Just not going to happen. It will always be a hybrid system. The NEC added metric numbers. For example, 1" conduit is 25 mm. Not 25.4 mm. But calling it metric doesn't make it so. If it was changed to true metric dimensions, it wouldn't thread into existing installations.


----------



## Foghorn (Jan 30, 2020)

> I don t see the USA ever swapping to metric. Just not going to happen. It will always be a hybrid system. The NEC added metric numbers. For example, 1" conduit is 25 mm. Not 25.4 mm. But calling it metric doesn t make it so. If it was changed to true metric dimensions, it wouldn t thread into existing installations.
> 
> - ibewjon


For sure. Pipe/conduit sizes in metric can be quite common here but are always outside diameter measurements and not nominal inside diameter measurements (NPS) as per the imperial system.


----------



## Sylvain (Jul 23, 2011)

Galvanized steel tubes remain as they were for backward compatibility copper tubes and more recent systems are metric here. 
There are adapters imperial on one side and metric on the other one.


----------



## david2011 (Apr 1, 2008)

> Every imperial random fraction has a corresponding metric fraction. Anyways don't worry about the kerf. Measure from your fence to the tip of the blade closest to the fence. No need to add in the kerf and subtract it.
> 
> - SMP


When designing in CAD the kerf cannot be ignored when making cut sheets. I'm not a commercial builder but even in my home shop kerf is a factor. The smaller the pieces, the more important kerf becomes. Metric fractional equivalents can have lots of places in the numbers. Cumbersome.

Everything I build is drawn in CAD first. I draw in inches and decimals because entering fractions in a CAD program is a pain. I still build in fractional inches because that's how the equipment was built. When it comes to plywood, does it matter what the measurement system is? Nominal 3/4" plywood can vary from 0.608" to 0.745" these days. One batch is 18.98mm; the next is 18.2 mm and nothing has been a true 3/4" or 1/2" for years. I've had to completely redraw designs because the material I bought did not match what I measured in the store two weeks prior. Yes, I take a dial caliper to the store when I start working on a design.

I could put a metric tape in my incremental fence but it would still lock in at 1/32" intervals and still fine adjust at 0.001" intervals. My metal lathe is built for inches and thousandths. That is designed deeply into the machine. Adding a digital readout to metal working machinery does not make it suddenly metric at the touch of a button. The gears and leadscrews are either Imperial or Metric from the beginning stages of the design work.

I don't object to using the metric system per se. It's just very difficult when most US retailers sell Imperial drill bits, router bits, taps and dies, fasteners and machinery. If they have any of those things in metric, it's not a good selection. It's nearly impossible to buy true metric machinery in the US.


----------



## LumberJockMan (Sep 8, 2021)

I don't think metric is easier for woodworking math.
You have a sheet of plywood 48 inches wide.
You can cut it into two 24 inch pieces or three 16 inch wide pieces or four 12 inch wide pieces.
4 feet in metric is 1220 mm.. you can't divide that by 3 and get a round number. It's not hard to divide by 2 or 4, but not as easy as 48 is.
Metric, it's easy to convert from cm to mm.. but how often do you really need to do that? Don't most people use mm the whole time? It's not like you are converting from km…
So I don't get the "math is easier" argument, at least in the case of woodworking.
By all means, use whatever you want .. I am not trying to talk you out of it.


----------

