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P. Waller

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What is your rule for rounding up when converting the metric to mm?
I do not round in either direction, it is normally obvious what the designers intention is by the tolerance call out for each dimension.
If a bore dimension is .625" +.001 -.000 the intention is a diameter that under no circumstances be less then .625".

If you are concerned about the 4th decimal place you can already make parts in tenths and need not be asking questions here, a grinding forum would be a better place for such questions.
 

randyjaco

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I just don't understand why this country refuses to go metric. The imperial system is archaic. We are just being Luddites on this issue. It is time we bite the bullet and made the change. The vast majority of our manufacturing companies could do it over night, if it weren't for there current inventories.
Randy
 

Brento

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P.Waller i just ask bc some measurements like 4mm converted is .1574803. The book of drawings in metric does not have any tolerances. Since my work is all mainly imperial im new to converting everything over and not sure what type of tolerance i should use when converting. Should i round the conversion to the nearest tenth? I guess im asking for your opinion.
 

P. Waller

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P.Waller i just ask bc some measurements like 4mm converted is .1574803. The book of drawings in metric does not have any tolerances. Since my work is all mainly imperial im new to converting everything over and not sure what type of tolerance i should use when converting. Should i round the conversion to the nearest tenth? I guess im asking for your opinion.
Do you use machines that have graduated dials that resolve to 7 decimal places?
If the answer is yes you are in the wrong forum, if no they are like most hobby machines that are graduated in .001" divisions, ask yourself this question, "Self, how do I remove a 7th decimal inch (1 millionth) amount of material with a 3 decimal reading machine". The short answer is that you can not do so. It is likely that you could not measure it if you did manage to do so.

If the tolerance call out is +-.002" then you have .002" on either side, if the tolerance is 3 decimal places this means that in this example .0029" is acceptable as it is not .003"

Very simple, in your example above I would call that .157"

If the drawings that you are working from have no tolerance on the dimensions then someone dropped the ball, do not try it.
 

Brento

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Ok thank you. Exactly what i wanted to hear. I still have my machines in storage but ik the SB lathe is dials and my mill does have read out.
 

P. Waller

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Ok thank you. Exactly what i wanted to hear. I still have my machines in storage but ik the SB lathe is dials and my mill does have read out.
Much like "digital calipers" many DROs use 4 decimal displays, do not expect this sort of accuracy in use.
 

Winegrower

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One of the best uses for even the cheapest DROs on a mill or lathe is to set mm or inches. I feel sorry for anyone with his calculator trying to hit 0.4863 by reading the dials.
 

RJSakowski

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What is your rule for rounding up when converting the metric to inches.
The precision to which you carry out conversions depends very much on what the requirement represented by the dimensions are.

A metric dimension may be listed as 22 mm but unless otherwise stated, I assume 22.00 mm which would be .8661". If that 22 mm is the i.d of a bearing to be a light press on a shaft, you better be working to four decimal places. On the other hand, if that 22 mm is the diameter of a crank handle, I would probably round it off to 7/8".

I carry all my calculations out to four decimal places. I know that bothers some people but I am used to dealing with it. Most of my work is done to thousandths so the extra decimal place helps to prevent stack up errors. An example would be 10 holes .5002" apart. If I round to .500" and start machining holes, by the tenth hole, I would be .002" out

Bear in mind that virtually all of my design work is for my own use. I am aware of what the functional requirements are and what kind of machining accuracy is required to meet the functional needs. If I were designing in collaboration with others and cimmunicating with those responsible for executing the design, as I did in my professional life, it is a totally different ball game.
 
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cvairwerks

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I just don't understand why this country refuses to go metric. The imperial system is archaic. We are just being Luddites on this issue. It is time we bite the bullet and made the change. The vast majority of our manufacturing companies could do it over night, if it weren't for there current inventories.
Randy
DoD is pretty much the reason. They are the 600 pound gorilla in procurement. Going metric would necessitate a clean break in procurement and stocking. The public would freak out finding out that they would be spending billions on setting up, qualifying and then stocking metric hardware for the various programs. Then think of the logistics of having to handle both systems, in the same maintenance units, until all the imperial equipment was transitioned out. For some things, the equipment is in use for 40+ years...
 

philip-of_Oregon

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I'm a Visual sort of guy, It helps me if I ~SEE~ rather than read or hear.

Upon buying my New PEC 6 inch scale, I had the typical choices, so I bought their Imperial/Metric scale.

It does 1/64", and inches decimal (100 per inch) then side two has Metric ( @ 0.5mm for 2 (or 4) CM, then the rest in 1.0mmm Plus CM's. The Fourth scale is (IIRC) 1/32 . I use this 6" scale for most of my work, as it is nitrided a "Gold" color and is plain easy on the eyes.

Using the Metric Side, even when DOING Imperial Work helps me "keep" them relatively "together" in my mind.

Note: the Company Incra Rules is my "Go To Ruler" for All Wood Working, and has been since 1989. their thin Stainless Steel is perforated so a .5mm Pencil will fit perfectly, the ends have a removable "Tee Square" that can slide so either top scale or bottom scale is "On Edge" with the Tee.

They Provide 1/16, 1/8, 1/4, etc. line markings & holes then, With a Unique system in the center of their Scales, (a series of Diagonal Holes Marked +/- ) one can Accurately Draw LINES to 1/64 inch Plus whatever inch distance from the scale.

They even have a 3X4 inch X/Y Plotter "scale". As Well as a Special Order for a Metric Based Scale Sized to the equivalent nearest Inch length say 75X100 instead of 3X4.

I do not work for, NOR Receive $$$ for "endorsing" their Products, I simply pass the information On as an Avid User.

As my STANDARD Pencil in my shop is a Metric .9 Milimeter lead, I once took the time to increase the holes in one scale to .9mm, But that is a Lot of work, you gotta be just a bit OCD to "do That" ! ! ! ! !

philip, Oregon is dry this week, Next week Fall will start!
 

RJSakowski

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IMO, we don't go metric for the same reason that we clung to an antiquated television technology; legacy products. It took an act of congress to change to digital television, along with a government givaway of two converters to any household that requested them. We invented cell phone technology, along with CMDA protocols while the rest of the world has GSM protocols which make our CMDA phones useless when we travel abroad.

We developed an entire infrastructure over the period of 200 years base on Imperial measurement. While this isn't as important for consumables and short lifespan products, when it comes to long lifespan products like housing, Making repairs to or remodeling a 40 year old house would be a nightmare if the building supplies were all metric.. Probably the biggest legacy issue is the citizenry itself. We could very easily convert to Celsius for temperature. Most of the modern thermostats are already selectable. for C or F. If the TY stations and Weather Channel made the switch, it would relatively easy to train the populace to accept Celsius. And 110ºF does sound better as 43ºC

Most, if not all, of our durable goods manufacturing has gone metric already. The medical industry and the scientific community have been metric for as long as I can remember. I had been introduced to metric measurement over fifty years ago and have used both on a regular basis ever since. So what's left? For the most part, popular acceptance.

With learning a foreign language, it takes a fair amount of time to think in the language rather than translating from our native tongue. The same is true for Americans dealing with the metric system. When we look at 4", we don't see 10 cm; we have to mentally do the conversion. When we get to the point of thinking in mm, kg, and liters, we will have converted.
 

Bi11Hudson

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This one truely seems to be significant. It's like I said in an earlier post, "I stepped in it big time". So, I guess I should add this: We, as Americans, have had access to the metric system for a while. My studies indicate that the metric system was well supported by Thomas Jefferson. Just following the war of 1812... ... The concept was declined by the U.S.Congress because we (the States) were still mostly trading with England and wanted the maximum compatible system of measurement. With that in mind, standing with the imperial system as technology advanced has caused us to become seriously dependant on the "English" imperial system of measurement. If we had gone metric then, it would be a non-issue. Might also have helped during WW 1 and 2, using foreign made parts as "git by" repairs.

If I may bring your attention to the Ford Mustang II, from the late '70s if I recall correctly. The one that had a four cylinder engine... ... There were some 14 fasteners (bolts) holding the water pump to the timing cover. Six of those were 1/4-20, the others were M6X1. Caused no end of trouble for mechanics of the time, most of whom considered metric to be one step away from Martian. Especially as they were mixed. Drop one wrench and look around for that "odd one" size. Then grab the 7/16 again.

Then, a while back, the English opted for the metric system. Almost like a plot to leave us in the U.S. hanging on to an archaic system trying to catch up. It's like anything else, "Follow the money". Yeah, I'm waxing a little "salty" here. It's early and I'm not awake yet.

To digress; and it's not "off topic", although does come close. Someone had asked about a "conversion" chart on screw sizes, imperial to metric. For what it's worth, I am currently in the process of building such a chart of the smaller sizes. It is for my own gratification, so may contain some empty slots. And will contain some archaic machine screw sizes and threads that haven't been used for many, many years. Mostly as a curiosity, to satisfy my own desires rather than needs. I will post it when I have it far enough done to make sense.

Machine screws are a curiosity themselves. Starting with Size 0 at 0.060"X80TPI, about 1.5mmX0.5. Mighty close there. Then stepping by 0.013", damn near 1/3mm. Another curiosity, why not some other stepping. And, if you look at a Nr6-32 TPI, it's 3.5mmX0.8 (to 4 decimal places) an almost true metric thread. But that's why it is "in progress". Many of my models are (were) built in Japan. Which, for years, was half imperial and half metric. Go figure.. ... What caught my attention is the size Nr14. 1/4" is 0.250"X20, Nr14 is 0.242"X24 and M6X1 is 0.236"X25.4. Curious ... ...

Bill Hudson​
 
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jdedmon91

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I just don't understand why this country refuses to go metric. The imperial system is archaic. We are just being Luddites on this issue. It is time we bite the bullet and made the change. The vast majority of our manufacturing companies could do it over night, if it weren't for there current inventories.
Randy
Not that simple. The investment in measuring tools alone would cost a fortune. The company I retired from just made the outside the US use decimal system. We have returned product that came from the Mexican plant and photos of the measurements were in decimal.


Sent from my iPhone using Tapatalk
 

uncle harry

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That calculator is indeed sophisticated. I looked at the User Guide. Easy to set for entering Imperial or Metric, but converting is not so easy, it is part of the Conversion menu.The Staples calculator and others like it would be far simpler to convert between Imperial and Metric. I may have to get one for myself. I have an HP32 calculator which does all sorts of functions, but no Imperial to Metric, other than my entering 25.4/ or 25.4*.
I occasionally use a digital caliper having both metric & Imperial capability as a converter . Kind'a like using a slide rule, slip it to a position close to the
desired value on the engraved scale on it's length & then "tune" it to the metric or imperial digital value in question. Then hit the alternate system button for the conversion.
 

savarin

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If you blame the English for the imperial system you are stuck with why are your gallon and fluid ounces so different? (serious question)
 

RJSakowski

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If you blame the English for the imperial system you are stuck with why are your gallon and fluid ounces so different? (serious question)
We originally used the same system of weight and measures as the British. In 1824, the British Weights and Measures Act redefined the pint and therefore the gallon and the fluid ounce which was then the standard throughout the British Empire. We continued to use the old British system of weights and measures as we were no longer part of the British Empire.

A question back at you. We have a saying "the pint's a pound the world around" which is true for the American pint which contains 16 fluid ounces and weighs close to 16 ounces which is a pound. However the British pint contains 20 fluid ounces. How come?
 

Nogoingback

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Just buy a set of Mitutoyo calipers: they'll do the math for you by pushing the button.
 

RJSakowski

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Just think, before the internet and Google it would have been the subject of an all night discussion in an Irish pub. That is, after all, how the "Guinness Book of World Records" got started.
 

higgite

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If you can tell time with a clock that isn't metric, what's the problem with measurements that aren't metric? You metric guys are just lazy, that's all there is to it. ;)

Tom
 

Dave Paine

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We have a saying "the pint's a pound the world around" which is true for the American pint which contains 16 fluid ounces and weighs close to 16 ounces which is a pound.
I went to school in the UK, our saying was "A pint of pure water weighs a pound and a quarter, a gallon of water weighs ten pounds"

I did like Savarins link about how the US and UK fluid ounce changed.

It is interesting that the UK has generally gone metric, except for beer still being sold in pints and speed in mile/hr.
 

RJSakowski

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If you can tell time with a clock that isn't metric, what's the problem with measurements that aren't metric? You metric guys are just lazy, that's all there is to it. ;)
We also measure angles in degrees, minutes, and seconds. This apparently goes back to antiquity, predating the ability to divide time into minutes and seconds by more than a thousand years.
Tom
I went to school in the UK, our saying was "A pint of pure water weighs a pound and a quarter, a gallon of water weighs ten pounds"

I did like Savarins link about how the US and UK fluid ounce changed.

It is interesting that the UK has generally gone metric, except for beer still being sold in pints and speed in mile/hr.
Also milk although on recent trips I seem to recall the canned beer and milk are now dispensed in ml. They probably won't be successful in changing a pub pint though as changing the size to 500 ml would serve 68 ml less beer.
 

hman

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One of the complications (difficulties?) I've frequently read about is the need to replace fasteners with the nearest equivalent size in "the other" system. Bill Hudson just posted a very nice screw size chart, showing Imperial (number) and metric fastener sizes, all sorted by major diameter.
https://www.hobby-machinist.com/threads/machine-screws-inc-archaic-sizes.71735/
Download the PDF. It should be pretty helpful when converting.
 

Bi11Hudson

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If I may: The chart referred to was for my own purposes, my own uses. There are a number of holes where metric and imperial thread "pitch" and TPI are not listed. The conversions there are for younger eyes than mine. Feel free to fill it in, long as you post the updated version!

I also would like you to take note of the many archaic imperial sizes that have not been used for many years Nr 14 VS 1/4-20 for example. We have stabilized(?) the industry to the point that many of those sizes are now obsolete. From 5/0-160 to 6-32 are still fairly common, especially in "optical" sizes or applications. Those larger are today figured by even numbers such as 6,8,10, &12. Anything larger is figured in fractions. While my tap sets have Nr 12, I haven't seen them recently. My interest in the odd sizes is pure purely academic. So far... ... But, I do like old machinery.

One other point I'd like to bring to your attention: Rounding... As stated above, by several folks, rounding is fine in some applications. And doesn't matter in others. Many of the conversions done with that chart came out to 7 or 8 places. At the 4th place, if it was 50 or less, it was rounded down. 51 was rounded up. Most measuring instruments stop at 3 places. Rarely at 4. That's my reference point. Your's may be tighter. Any metric conversion is liable.

Bill Hudson​
 

hman

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Thanks for clarifying, Bill. I was assuming that, by giving the link to your post instead of reproducing the chart, people would read what you said and use the information with due care. But we all know what value to give "assumptions."

Nevertheless, you've provided some useful information.
 

warrjon

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Being an Aussie I mostly work in metric but I have a couple of imperial mics incase I need to work in imperial, so I don't have to keep converting. I was almost in high school when Australia converted from imperial to metric so use both.
 

bollie7

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As another aussie I was in high school when we officially went metric. That was 1972. What is interesting is that 15 years ago TV's were sold by metric screen sizes ie 106cm, these days we have gone back to TVs in inch sizes. More than likely that is because most tvs come from China and the USA is China's biggest market. What is even more interesting is the kids here who will talk in feet and inches, even though they have never been taught that in school. If you ask them to show you approx how long an inch or a foot is, most of them haven't got a clue. Why is that? Well I reckon its because most the TV shows and movies they have been brought up on are of USA origin.
Then you have the weight of newborn babies, for some weird reason grannies can't understand the weight of a baby in grams. No it has to be in lbs and ounces. Yet they have no problem buying a couple of Kg's of meat at the butcher or 500 grams of butter. The funniest thing of all with this is most of these grannies these days were still in school when the country went metric. Go figure.
Now, when you go to buy self drilling screws at our big hardware store the size is mm for length and gauge for dia. huh?? Gauge hasnt been used here for 40 + years. I dont get why they just cant give the dia in mm as well. Talk about confusing. It just goes on and on.
Peter
 

Brian Hutchings

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Quote 'Talk about confusing'. Well yes it is and it would be a lot better to stick with inches and ounces.
I started work at a company making Imperial sized engines but then they got a license to make a French engine (stolen from the Germans) that was all metric.
The company set up a department to make these engines and equiped it with metric tools and drawings.
Much later, Ted Heath (Prime Minister) announced that England WOULD go metric, to which I and many others took exception. I always ask for Imperial measurements when buying loose goods but I know what the meric equivalent is and it's surprising (perhaps not) how many time a rip off is attempted.
Brian
 
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