# Mixing measurement systems, bad idea, or really bad idea?



## MontanaLon (Aug 22, 2019)

Being tool poor I am always on the lookout for cheap tools. Today I found them. 2 dial indicators and a test indicator for $10 each. Brand name too. But then I looked close and they are that funny European measuring system that will never catch on. M m m m m metric. Now I need to drink something to get the taste out of my mouth.

So, avoiding the debate on which is the better system, (we all know it is the inch anyways) my machines have knobs and graduations in inch and I don't see a DRO in the future any time soon, how bad an idea is to mix inch and metric? I mean, other than the loss of money I will suffer when they finally admit defeat and convert back to the imperial system, what ill could I suffer by buying these m m m m metric tools and putting them in the bottom draw of the tool box? I mean who knows, someday I may actually need to measure something to .02  of the cube root of the volume of a gram of water. But what are the chances of that? I suspect they are the cause of spontaneous shop combustion but have no proof. Seriously, they knock the imperial system as being difficult to convert and based on something as arbitrary as the measurement of body part of a man who rose to power through divine means. They based theirs on what they imagined would be a round fraction of something they had no way to accurately measure.

But seriously, will cats and dogs live peacefully together if I give these tools a home? Or will chaos consume my meager shop as I furiously multiply divide by 25.4 and wonder why my parts never measure up to spec?


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## pstemari (Aug 22, 2019)

98.5% of dial/test indicator use only involves the zero mark. It's seldom that you actually try to measure something with an indicator, unless you're doing something like aligning a drive shaft with a motor.

Sent from my Pixel XL using Tapatalk


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## Latinrascalrg1 (Aug 22, 2019)

So long as you dont forget which system you are using and keep things consistent I dont see how it would hurt!


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## higgite (Aug 22, 2019)

Beware! Metric dial indicators are gateway tools! Don't get hooked!

Tom


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## darkzero (Aug 22, 2019)

Haha. As said, when using indicators for measuring runout it doesn't really matter. As far as using both systems for measurement, do whatever is comfortable for you. Lots of people can & do work with both.

Me personally, I use imperial for measurements & cuts, not just with metal. If I need to machine something with metric measurements I convert to imperial even though I have DROs (and digital calipers & mics) where I can switch to metric. It's just what I'm used to & comfortable with. Although I use 25.4mm to convert all the time, I'm lost when it comes to picturing metric dimensions. Like a couple of thou or 100 thou of an inch I can picture the size. But when it comes to a tenth of a MM or whatever I have no clue, I'm just not used to it.

But with fastener heads I can tell if it's a 10, 12, 14, 17, 19mm etc cause I'm used to it, I used to work on import cars. Speaking of fasteners, although I'm an imperial guy, I prefer to always use metric fasteners, I hate using imperial fasteners. I'll only use imperial fasteners if whatever I'm working on already has imperial fasteners. I don't like to mix metric & imperial fasteners for something I'm working, it's a pet peeve of mine. But here in the US, specialty screws are more commonly available in imperial so sometimes I don't have a choice

But when single pointing threads & making something from scratch where it doesn't matter if the thread is imperial or metric, I prefer to single point with imperial threads. I know I'm weird. Although I agree that the metric system is a better system, I'll always be an imperial guy unless the US fully converts over one day which I doubt will happen in my lifetime.


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## benmychree (Aug 22, 2019)

_I have not had to use the metric system yet, and do not plan to change, at age 74+. Likely the metric system will not be adopted in the USA for a long time yet, if at all._


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## NortonDommi (Aug 22, 2019)

As *pstemari *said  DTI's are used to indicate runout so it doesn't really matter.  If they are cheap I'd grab them.


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## Winegrower (Aug 23, 2019)

I have DROs on the mill and lathe.   It is pretty much immaterial which system is used, and it's very easy to mix.   For example, adding the DRO to a mill, it's likely that the mill measurements are imperial yet the mounting holes on the reader are defined via metric measurements.   

So there is no doubt about it, you need both.   Dial indicators, as has been said, are for the most part "indicators", not "dial measurers".


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## silence dogood (Aug 23, 2019)

If you are going to send a probe to Mars, don't forget to convert English to metric.  This is what NASA did a few years back, it only cost a little over a hundred million bucks.


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## Downunder Bob (Aug 23, 2019)

USA  will certainly change to metric in the near future. All other english speaking countries have changed. So much in USA is already metric . Your money, all scientific and medical measurement has been metric for some time. If you have a close look at all your imported lathes and mills etc, they are built as metric machines and just have an imperial leadscrew fitted and a couple of gears changed to make them work in imperial. 

All your imported vehicles are metric, so mechanics already have to deal with both. Your speedo's are in metric miles, they measure tenths of a mile not yards or feet. Even your micrometers are metric as in 1000th inch. 

Gradually you will have to change, but it will probably be more by default and stealth, than actually a planned changeover like we did here in Australia. NZ and UK also did similar.

Once you get used to it metric is much easier and quicker,  I learned in imperial until I was about 20 then I had to learn metric now I'm ambidextrous and apply work in both and easily jump from one to the other.


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## timmeh (Aug 23, 2019)

.004" = 0.1mm, .040" = 1.0mm near enough for rough stuff.
Metric to Imperial, ÷ 25•4.
Imperial to Metric, × 25•4.
Learned both, switch as needed, sometimes count apples an' oranges together, an' camouflage 'em so's ya canny tell wots  wot.


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## Martin W (Aug 23, 2019)

We use both everyday. Metric is way better in my opinion. Less mistakes and more accurate.
Cheers
Martin


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## NortonDommi (Aug 23, 2019)

Downunder Bob said:


> Once you get used to it metric is much easier and quicker,  I learned in imperial until I was about 20 then I had to learn metric now I'm ambidextrous and apply work in both and easily jump from one to the other.


  Likewise, learnt in Imperial then all school exams and apprenticeship was in both as the changeover happened.  Happy to work in either but still find Imperial easier and quicker for some things fractions for example.


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## matthewsx (Aug 23, 2019)

Um, not really an issue IMHO. The fact that this is your hobby means you have learned to measure things, buy a cheap digital caliper if you don't want to do the math.

John


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## Aaron_W (Aug 23, 2019)

Nothing wrong with using metric, just be careful using conversion, better to stick to one system or the other on a given project. Conversion provides one more place to introduce error.




Downunder Bob said:


> USA  will certainly change to metric in the near future. All other english speaking countries have changed.



Not true the UK still measures speed and distance using the mile, beer, cider and milk can still be sold by pints, acres are used for land measurement, and weight in pounds is still used for some applications. Canada still uses Imperial or US Customary Units for certain applications like construction. Canada has a particularly awkward case where it uses Imperial in some applications and US Customary in others (they are not the same thing).

Very few countries have truly gone 100% metric. Even the French who invented the silly thing continue to use the Birmingham gauge to measure hypodermic needles, because that is what the world wide medical community have adopted as a standard (the metric system gave awkward measurements in that use). 
Other common non-metric measurements used world wide include Fahrenheit for cooking, psi for tire pressure, pixels / dots per inch for video screens and printing, thread count threads per inch is widely used for textiles, BTUs are often used in metric countries as a measure for HVAC systems.  


Conversely it is a myth that the US is a non-metric country, it has recognized and approved the metric system as a legal system of weights and measures since 1866. US Customary Units (not the Imperial system which is British) have been defined by metric units since 1893. Since 1968 packaged goods must be labeled with both customary units and metric units. 

Where the US differs is that it has not imposed the use of the metric system, only encouraged its use and allows industries to adopt it naturally. It is highly used in science, and technology, the automotive and aerospace industries, little used in construction. Mixed in most other areas as the market demands.


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## Ken from ontario (Aug 23, 2019)

I prefer to work with one system but I'm still capable of working with both if the project leaves me no choice.
I have a conversion chart pinned on my task bar(on my computer), use it to verify what I can not visualize, it is extremely handy.





						mm to inch conversion - Search
					






					www.bing.com


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## RJSakowski (Aug 23, 2019)

I usually do all my designs in inch measure.  My tooling is almost all inch measure.  Imperial fasteners are more common and less expensive. Raw materials are most easily found in inch sizes.

However, if needed, I can and will use metric measure.  One project that I had was drilling 96 holes in an 8 x 12 array.  The holes were on 9mm centers.  Now, I could have converted all the coordinates to inches and dialed in each hole but it was far easier to switch the DRO to metric and just increment by 9.00mm.


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## Ulma Doctor (Aug 23, 2019)

i jump between metric and imperial measurements as necessary, sometimes on the same project.
i find that to be a strength.
i have metric and imperial DTI's, drop indicators, calipers, 1-2-3 blocks, and mic's.
all of them get used


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## coherent (Aug 23, 2019)

I use both frequently. If I'm making a replacement part that  was originally metric or something that has metric measurements I do too. It really doesn't make any difference and long as the end result is the "size" you want... all of my digital calipers and tape measures have both anyway. I frequently use Autodesk Inventor as my go to cad especially for 3d parts. The great thing about it is I can mix and enter any dimension in mm, inch, feet, fraction, decimal ( 1.05 in or 23.6 mm, 1/32 in) etc., and it simply dimensions it correctly. Pretty nifty


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## pontiac428 (Aug 23, 2019)

I spent over 10 years living in Europe, where I learned what Celsius temperatures feel like, how far kilometers are to walk, and to resolve without conversion whether I need a pack of 40mm screws or 50mm screws. The process for figuring out how many 20kg sacks of concrete you need for 10qm at 100mm pour is the same as it is for 50lb bags per cubic yard. Liters per 100km in fuel gives better resolution than mpg stats. Ambidextrous, bilingual, whatever it is it's an added ability that I value.


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## Downunder Bob (Aug 23, 2019)

matthewsx said:


> Um, not really an issue IMHO. The fact that this is your hobby means you have learned to measure things, buy a cheap digital caliper if you don't want to do the math.
> 
> John




Yes a digital caliper will automatically measure in whatever system you set it to, then with the press of a button will display the same dimension in the other system. Problem solved.


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## Eddyde (Aug 24, 2019)

Martin W said:


> We use both everyday. Metric is way better in my opinion. Less mistakes and more accurate.
> Cheers
> Martin


Less mistakes, perhaps but it certainly isn't anymore accurate.


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## Eddyde (Aug 24, 2019)

Curiously, my former business partner, who was born, raised and learned his trade as a cabinetmaker in the south of France; told me, he actually preferred imperial measurements for cabinetmaking. He said he like the relative nature of fractional inch measurements.
Indeed, fractions can simplify doing layout in your head, Eg 4x ¾" = 3" as opposed to 4x 19mm = 76mm. When more precise measurements are required you can roll right into decimal inches.


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## Bi11Hudson (Aug 24, 2019)

Eddyde said:


> Less mistakes, perhaps but it certainly isn't anymore accurate.



Got to stick my nose in here. I have worked in the "fiber optics" business(splicing), where the "conductors", the fiber strands, were measured in microns. That's metric, the next step below millimeters. There's 1000 microns(micromillimeters) in a millimeter. Most machinists think in thousandths, or possibly tenths. 0.0001 inches. There's 39 thou, and change, to a millimeter. Just that mm isn't the smallest unit of measure there is.  

The bottom line, either can be as accurate as the other, it's a matter of what one is most used to. I do both, essentially interchangably. If what I'm working on is metric, I _try_ to stay metric. Doesn't always work out, but I try. On the other hand, my machines are calibrated in inches. If I was really good, I could work to a tenth of a thousandth. I'm *not* that good, but like to try. Further, my model trains are a mixed scale. HO, 3.5mm to the foot. Just how confusing can you get? 3.5mm ~ 0.1385inch. The metric is a little easier to work with here. A similar scale used in Europe is 4mm per foot. It's all a matter of what you're conversant with.

Most of the usage of a dial indicator is to determine out of round, eccentricity, things of that nature. The absolute measure doesn't really matter. As mentioned above, deviation from the "zero" is what matters, get that as small as possible. Whether it's 0.0004 in or 0.1 mm isn't important. Until you're comfortable juggling numbers in your head, a digital caliper does help.

.


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## Cooter Brown (Aug 24, 2019)

I worked at tool and die shop, prints would come in all time with the measurements in millimeters and we would convert everything to inches before starting any work....


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## Martin W (Aug 25, 2019)

Eddyde said:


> Less mistakes, perhaps but it certainly isn't anymore accurate.


You are correct. It is not any more accurate than imperial. Like Bill said it is what ever you are confident with to add and subtract numbers in your head.
Our shop is a millwork shop and our machines have metric scales. It is easier for me to have a kid cut something say 750mm than just a hair over 29-1/2" or 29.527 or 29-17/32. This makes it more accurate for me.
Funny thing is I prefer imperial for myself. That's all I use in my hobby machine shop.
Cheers
Martin


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## WCraig (Aug 25, 2019)

To me, the main problem with "Imperial" is that you're forced to mix decimal and fractional measurements.  Eg the part is 0.800 wide and you want to put a 5/16" bolt just on one side of centre.  So I've got to convert 5/16 to decimal...where did I put that @#%@ chart again?!?  Oh, that's right, it is a four-decimal place number so I need to choose whether to round up or down.  Etc.

Who among us has't made a blunder when mixing fractions and decimals?

Placing a 6 mm bolt on a 20 mm part is a lot less drama.

Craig
Despite what I've said, the machines I've got and all the tooling are Imperial-based so that's what I work in.


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## WCraig (Aug 25, 2019)

BTW, how big are #6, #8 and #10 machine screws again?


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## Janderso (Aug 25, 2019)

benmychree said:


> _I have not had to use the metric system yet, and do not plan to change, at age 74+. Likely the metric system will not be adopted in the USA for a long time yet, if at all._


John, 
In the Ford manufacturing world, every nut and bolt used in their vehicles has been 100% metric for over ten years. Before that it was mixed.
Granted, most of the products are assembled in Mexico, Turkey, Canada or wherever.
The trucks are made here.
The new techs only need to buy metric.


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## Janderso (Aug 25, 2019)

WCraig said:


> BTW, how big are #6, #8 and #10 machine screws again?



I was curious,
#6.  0.13”.   9/64
#8.  0 .16”.   5/32
#10.  0 .19”.  3/16


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## JPMacG (Aug 25, 2019)

I work in imperial and try to avoid metric tools, but I will admit that imperial is an asinine antiquated system.  Dividing a foot into 12 smaller units is silly, and I don't understand why anyone ever thought that using binary fractions (1/2, 1/4....) rather than decimal numbers was a good idea.   I guess that is dates to the 18th century (or earlier) when a unit of length could be easily divided in half using a compass but there was no simple way to divide a unit of length by 10.


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## RJSakowski (Aug 25, 2019)

Machne screws increase in diameter by .013" for each number size starting with #0 @ .060".  To find the size of a given screw, multiply the screw swize by .013" and ad .060".  A  #6 will be 6 x .013"  = .060" = .138" and a #10 will be 10 x .013" + .060 = .190", for example.  Listed fractional sizes are approximations.


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## RJSakowski (Aug 25, 2019)

The size of machuine screws continues on the lower end with #00, #000, and #000 being .047", .034", and .021", respectively.


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## Bi11Hudson (Aug 25, 2019)

WCraig said:


> BTW, how big are #6, #8 and #10 machine screws again?



A while back, I posted a homemade chart showing decimal equivs for machine screws and small metric fasteners. Probably lost by now, though. Machine screws follow an archaic system that makes sense if you follow the system. It does not fit into our modern measurement system, and is often duplicated by fractional sizes. *Almost*, within a couple of thou anyway.

Machine screws have a base size of 0.060 in. Why? I don't know, but that's the system. For each size, add 0.013 in. A 1-64 machine screw is 0.060 plus (1x)0.013 = 0.073 in dia. A 2-56 = .068 + (2x.013) .026 = 0.086. Again, why .013? There are thread sizes at 8 TPI intervals, again, why? Who knows, the system is lost in antiquity. Maybe a very old copy of Machinist's Handbook could shed some light. But me, I don't care unless I run into one, a rarity these days.

And so on up the chart... A 6-32 screw is 0.060+(6x.013)=.138 Convienetly, a Nr 5 screw is 0.125 in, 1/8th. A Nr 8 is .060 +(8x.013) = 0.164 in. A Nr 10 is at 0.190, with a 3/16" at .1875. Most hardware stores use one and call it the other. Maybe that has some bearing on the [why] of 0.013. 1/4 in vs Nr 14 is just a few thou different.

The old school system goes far above 1/4 in, almost to 3/8 in. Modern sizing has taken over most sizes above 1/4 in, with Nr 12s being still in use but rare. There are(were) other sizes of fractional, as well. I recently acquired taps for 1/16-80. At  0.0625 vs 0.060, they will *almost* work interchangably. Almost ... ...

I personally work with tiny sizes, less than Nr 0. Nr 00 or 2/0 steps down the same way, at  -.013=0.047 in. There are several sizes smaller, optical screws and the like. 3/0 is the smallest size I work with, but there are several smaller. Then there's metric, re: modern eye glasses. If you pursue it much further, all I can do is wish you luck.
*
.*


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## Eddyde (Aug 25, 2019)

Interesting article on thread standards here: https://littlemachineshop.com/images/gallery/instructions/a_brief_history_of_screwthreads.pdf


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## WCraig (Aug 25, 2019)

I guess I needed to be more explicit about the #6, #8 and #10 machine screws.  My point was that working in "Imperial" with Imperial fasteners involves a hodgepodge of fractions, thousandths of an inch and arbitrary archaic anachronisms like the numbered screws.  Designing or laying out a part with tight clearances can be crazy-making.

Working in metric with metric fasteners is wonderfully boring by comparison.

Craig


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## Aaron_W (Aug 25, 2019)

WCraig said:


> I guess I needed to be more explicit about the #6, #8 and #10 machine screws.  My point was that working in "Imperial" with Imperial fasteners involves a hodgepodge of fractions, thousandths of an inch and arbitrary archaic anachronisms like the numbered screws.  Designing or laying out a part with tight clearances can be crazy-making.
> 
> Working in metric with metric fasteners is wonderfully boring by comparison.
> 
> Craig




Sure metric is easy, nice whole numbers 8mm, 9mm oh wait where did these 1.2mm, 1.6mm, and 2.5mm etc bolts come from. Are they DIN, JIS or ANSI spec bolts?  

The metric system is relatively simple when you ignore the human element. Human's love to make the simple complex.


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## Bob Korves (Aug 26, 2019)

I worked at procuring parts for large shops for 40+ years where we dealt with roughly equal amounts of metric and imperial fasteners, parts, and tooling.  That was because that was where manufacturing was during that time period.  We got used to it as it morphed.  It has now swayed more to metric in the U. S., and is continuing in the rest of the world.  One thing I can guarantee you.  You will not be able to decide which ways major manufacturers will go.  If you work in industries like heavy equipment repair, fleets of large and smaller trucks and automobiles, all kinds of ancillary equipment like tampers, pumps, mowers, road building equipment, and so forth, procuring parts needed to keep them all in service, you would understand that we cannot stem tides like that.  If they come up with a "new and improved" (and proprietary) system tomorrow to "replace them all", then we will have to learn a new system to add to the list we are already trying to keep track of.  And procure the tools to work on them.  We are in a position of reacting, and we will not change the future by resisting.  We will only be left behind.  Like our Whitworth tools.  With CNC machines, and the widespread use of making parts as needed, we may get to a point where nothing is interchangeable, and only the maker who sold the equipment will have access to the records kept while they changed part sizing and custom thread pitches and forms for each and every new piece of equipment, and would be happy to sell you some parts made on site to fit that specific serial number ONLY.  Ultimate proprietary equipment, keeping the competition out of your knickers.  Or maybe not, or maybe something scarier yet...  Do not underestimate the potential of greed mixed with new capabilities.


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## owl (Sep 2, 2019)

I use mixed measurements all the time (metric sockets on a 1/4” ratchet).  Also my tailstock ram is marked in either .2” or 5 mm depending on what I need (close enough to the same thing for most purposes).


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## lagweezle (Sep 5, 2019)

MontanaLon said:


> Being tool poor I am always on the lookout for cheap tools. Today I found them. 2 dial indicators and a test indicator for $10 each. Brand name too. But then I looked close and they are that funny European measuring system that will never catch on. M m m m m metric. Now I need to drink something to get the taste out of my mouth.
> 
> ...
> 
> But seriously, will cats and dogs live peacefully together if I give these tools a home? Or will chaos consume my meager shop as I furiously multiply divide by 25.4 and wonder why my parts never measure up to spec?



Clearly the only way to be safe is to keep those dreadful things out of your shop! Oh ... and uh ... PM me the URLs for them so I can buy them?


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