How to convert from mm to Inches

[gphillips]

If I have something that was designed in mm and should be in inches, how do you convert it. What I mean is, I have a part that should be 26 inches long but it is 26mm long. Is there a way to convert all the measurements.

[msklein]

thanks JD i meant to say 25.40000048 rounded off to 10 places my mistake
I missed and stuck in part of the decimal equivelent to a mm

[mzobel]

1 in = 2.54cm exactly

national institute of standards and technology

http://ts.nist.gov/WeightsAndMeasures/Metric/upload/SP1038.pdf

3.2 Inch-Pound Units
Units based upon the inch, pound, and gallon were historically derived from the English system and subsequently were re-defined as multiples of SI Units in U.S. law beginning in 1893. For example, the inch is defined as the length corresponding to 2.54 centimeters (exactly); and the gallon is defined as the volume corresponding to 3.785412 liters; in other words, the inch-pound (customary) units are based on the SI units and multiplication or division is used to convert units from one system to another.

[Anonymous]

My calculator.... 🙂 (And my high school math instructor) (and
Autodesk Inventor which is based on cm, not inches)

1. In Inventor, draw and dimension a line 1 meter long.

2. Convert the units to inches. At five decimal places accuracy, the
dimension is 39.37008 inches.

3. Divide 1000 x 39.37008 = 25.399999999999

I find it absolutely amazing that people are willing to accept 25.4 mm
as a fact, when in fact it is not.

BTW, I was a math major, due to the inspiration of my high school
teachers. While 25.4 mm is a general value, quite often today we are
working to extremely high precision in aerospace. 25.4 mm is not
acceptable to me. We have all of this accuracy thanks to our computer
systems, and we stick to common knowledge, rather than scientific knowledge.

It's absolutely no wonder why Americans missed landing on Mars the first
time, due to their math.




--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
Instructor/Author/Sr. App Engr. Tel. (260) 399-6615
http://teknigroup.com

[Anonymous]

Actually, you were closer the first time... 🙂

1" = 25.3999999999999 mm
--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
Instructor/Author/Sr. App Engr. Tel. (260) 399-6615
http://teknigroup.com

[Anonymous]

On 12/23/2009 11:40 AM, Dennis Jeffrey wrote:
> My calculator.... 🙂 (And my high school math instructor) (and
> Autodesk Inventor which is based on cm, not inches)
>
> 1. In Inventor, draw and dimension a line 1 meter long.
>
> 2. Convert the units to inches. At five decimal places accuracy, the
> dimension is 39.37008 inches.
>
> 3. Divide 1000 x 39.37008 = 25.399999999999
>
> I find it absolutely amazing that people are willing to accept 25.4 mm
> as a fact, when in fact it is not.
>
> BTW, I was a math major, due to the inspiration of my high school
> teachers. While 25.4 mm is a general value, quite often today we are
> working to extremely high precision in aerospace. 25.4 mm is not
> acceptable to me. We have all of this accuracy thanks to our computer
> systems, and we stick to common knowledge, rather than scientific knowledge.
>
> It's absolutely no wonder why Americans missed landing on Mars the first
> time, due to their math.
>
>
>
>
The used the wrong units miles instead of nautical miles.

Machinery's hand book states 1"=25.4mm exactly.

Rich

[mzobel]

you have a rounding error in step 2
go the other way
draw a line 1.0E+020 in
look in Parameters and the Nominal Value is
2540000000000000000000.000000

it is a goverment standard

[Anonymous]

Wow! 🙂


--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
Instructor/Author/Sr. App Engr. Tel. (260) 399-6615
http://teknigroup.com

[mzobel]

By the way I am a old Toolmaker and I remember my shop teacher telling us that it was 25.4mm exactly and he also told us the year that the length of an inch changed. 🙂

[msklein]

Dennis,
when i went back and re-looked it up, a mm= 0.0393700787, which converts to the 25.40000040 when i did it to 10 places. So was my mm conversion number wrong ?
msk

[mzobel]

0.0393700787is a rounded of version
1"= 25.4 is exact

0.03937007874015748031496062992126 is still rounded off

[Anonymous]

Must be a difference between a Shop teacher and a Math Teacher. In any
event, we're all just splitting hairs.... 🙂

Have a Merry Christmas every one!
--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
Instructor/Author/Sr. App Engr. Tel. (260) 399-6615
http://teknigroup.com

[JDMather]

>Must be a difference between a Shop teacher.....

My experience 8 years as a machinist on the shop floor tells me that 25.3999999999999 mm IS 25.4mm
Human hair is considerably larger than .0000000000001

But then I learned math on a sliderule - not a calculator.

[JDMather]

> We have all of this accuracy thanks to our computer systems, and we stick to common knowledge, rather than scientific knowledge.

I taught Machine Tool Operations for 5 years.

I've got all these kids coming into my CAD class thinking that they can make perfect parts because Inventor/AutoCAD/whatever goes out to how many decimal places.

Let's see them make something on the shop floor (or simply measure) to four decimal places (inch).

Drives me bannanas that AutoCAD defaults to 4 dec places on dimensions and so many leave it at that.

[Anonymous]

"But then I learned math on a sliderule - not a calculator."

So did I.... 🙂 Welcome to the Old Timers Club!
--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
Instructor/Author/Sr. App Engr. Tel. (260) 399-6615
http://teknigroup.com

[msklein]

freshman year of collage i went to my first class with the Ivory inlayed slide rule my father gave me and we were told to go buy a calculator ( my first question was what is a calculator). They made change over that summer. Enough time wasted. everyone have a happy Christmas and or Hanukah i may be late on that come to think of it.
msk

[mzobel]

Your math teacher must have learned his conversion prior to 1893. 🙂

and Until Inventor can fudge Constraints I am going to Model to exact values and show proper tolerance on the prints. Air bearing table - 0.000005" weld table - 0.5"

have a Great Christ Mass

[Anonymous]

Sounds like a good plan! 🙂

I'm glad that others also do not forget the reason for the season.
--
Dennis Jeffrey, Autodesk Inventor Certified Expert
Autodesk Manufacturing Implementation Certified Expert.
Instructor/Author/Sr. App Engr. Tel. (260) 399-6615
http://teknigroup.com

[Anonymous]

According to the ISO 1
foot (12inches)= 305mm



If you take 305/12 = 25.4166666666 recurring



Obviously this debate on the conversion factor is being muddied by the
various rounding and standards adopted world wide.



There has to be a specific reasons as to WHY the drawings that the OP
has received in DWG format are in IMPERIAL.



For may input, as some one who has worked on renovating 1800s
industrial machinery. Keep the original units as they are and use dual
measurements it's a bloody nightmare trying to work from one to the
other when the part is MEANT to be in imperial but the units shown are
metric and
vis versa.



SteveSmith5286 wrote:

I have a similiar problem.  Our company is to take control of 1500 to 2000 2004 Autocad dwgs.  They will be in metric.  I have been asked if they can be converted to inches.  How would you approach this?  I am using Inventor 2010 Pro.

Thanks

Steve

  

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[msklein]

I have a great idea we in the US break down and join the rest of the world and go Metric. Didn't Carter push a law about that back in the late 70's. Problem should then be solved. Only, then would we have to deal with legacy documents in Imperial for a time. But then we are in the season of miracles and i must be dreaming and at end of week get back to reality.
msk
happy new year to all

[Anonymous]

If I'm not mistaken, the law was passed.  Canada and the
US are officially metric.  Unfortunately the whiners are still
winning.

Richard

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<msklein> wrote in message
href="news:6309773@discussion.autodesk.com">news:6309773@discussion.autodesk.com...

I
have a great idea we in the US break down and join the rest of the world and
go Metric. Didn't Carter push a law about that back in the late 70's. Problem
should then be solved. Only, then would we have to deal with legacy documents
in Imperial for a time. But then we are in the season of miracles and i must
be dreaming and at end of week get back to reality.
msk
happy new year
to all