Drawing which contains inch and metric dimensions 2

[geekman25]

This question pertains to drawings that have both inch and metric dimensions. This is a somewhat common practice in some industries, such as medical devices, even though not a good one. If the title block has a statement of "UNLESS OTHERWISE SPECIFIED, DIMENSIONS ARE IN INCHES", is it neccessary to place the end quote, double apostrophe " symbol after the inch dimensions, as well as the mm or cm for the metric dimensions? I am searching the standards, and found a lot of information regarding dual dimensioning and tolerances for them.

I would appreciate any feedback from the members of this forum (even humorous ones) to support my opinion on this subject.

Thanks.

 

[pmarc]

I understand the prints you are working with are inch-dimensioned with some dimensions in millimeters. If that is the case and you are following ASME Y14.5, look at paragraph 1.5.4 in '09 edition of this document. It clearly states that "where some millimeter dimensions are shown on inch-dimensioned drawing, the symbol mm shall follow the millimeter values." In this case you do not put " after dimensions expressed in inches.

Generally use of double apostrophe shall be avoided for inch dimensions. On millimeter-dimensioned prints, inch dimensions shall be marked by placing IN abbreviation after dimension value.

 

[KENAT]

If yo have note saying UOS dimensions are inches then no technically you don't need to put " or 'IN' - that's an English question not really standards;-).

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[CheckerHater]

From ASME Y14.5-2009:

1.5.3 Identification of linear units
On drawings where all dimensions are in millimeters or all dimensions are in inches, individual identification of linear units is not required. However, the drawing shall contain a note stating “UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN MILLIMETERS (or IN INCHES, as applicable).”

1.5.4 Combination SI (Metric) and U.S. Customary Linear Units
Where some inch dimensions are shown on a millimeter-dimensioned drawing, the abbreviation IN shall follow the inch values. Where some millimeter dimensions are shown on an inch-dimensioned drawing, the symbol mm shall follow the millimeter values.

Doesn’t look like standard somehow encourages use of dual-dimensioning at all.

As popular textbook stated: "Corporate America is going metric - inch by inch"

 

[dgallup]

Wow, I would NEVER put mixed units on a drawing. Dual dimensions if you put a gun to my head but mixed units never. Can you say Mars Lander crash?

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[ctopher]

You can mix if the secondary dim is indicated as reference. Other than that, I would never mix units in dimensions.

Chris
SolidWorks 11
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[CheckerHater]

dgallup,

Add Gimli Glider to the list :-(

 

[drawoh]

geekman25,

I agree with the others. Mixing units is a bad idea. Pick a set of units and use them systematically. Provide the alternate units when relevant, for reference only.

If your manager is determined to mix units, your note should say something like "WARNING, WARNING, WARNING: UNIT ARE MIXED ON THIS DRAWING. UNITS ARE SPECIFIED WITH EACH AND EVERY DIMENSION."

Hopefully, your length units are millimetres, not centimetres. There will be less chance of confusion with inches. I would strongly recommend that the drawings be prepared and plotted to 1:1[ ]scale.

If you are running SolidWorks, you can probably create dimension styles, each with the correct units, and the unit specified.

​

--
JHG

 

[CheckerHater]

I like mixed dimensions as much as the next guy; but I am genuinely curious:
I wonder if OP could elaborate on his statement: “This is a somewhat common practice in some industries, such as medical devices”

So geekman25, could you disclose us what industry you are in, and what particular application is forcing you to mix inch and metric randomly?

I often turn into “devil’s advocate” thinking that if someone does certain things certain way, they must have a good reason.
I understand identifying metric thread on inch drawing as metric, or vice versa, but, like dgallup said, wouldn’t go any further with gun to my head.

So, what gives?

 

[geekman25]

First of all, thanks to all who have posted and reinforced my feelings on this subject. I created our drawing templates (we are a startup company) a couple of years ago, based on 20 years of designing and drawing mechanical parts and assemblies. The templates were based on the ASME Y14.5 standard (mentioned by pmarc and CheckerHater above). I was recently told that someone (I'll let you guess the department they are in) is questioning why a particular drawing shows " mm " for a metric dimensions, but all the others do NOT say " IN " or the double apostrophe symbol for inches. Even though the title block has that statement.


Second, to answer CheckerHater, I am in the medical device industry, for 30 years now (the first 7 as a machinist)! Historically medical devices, such as catheters, have been called out with metric lengths (120 mm or 60cm) and diameters in inches (.039 for example). Many diameters are also identified by something called a "French Size" which is 1/3 of a mm or .013". Products may be called a 8Fr, 150cm with a .040" ID. Confusing? Yes, but a physician or other medical professional would know exactly if this is what they need. I can quickly imagine the size of the inside diameter, but have to think about the conversion for metric and French Sizes.

ctopher * "You can mix if the secondary dim is indicated as reference. Other than that, I would never mix units in dimensions."* ----I am not talking about "dual dimensioning" as I think you are. I fully agree that the seconday dimension MUST be a reference. I am talking about totally separate dimensions on the same drawing.

drawoh * "If your manager is determined to mix units, your note should say something like "WARNING, WARNING, WARNING: UNIT ARE MIXED ON THIS DRAWING. UNITS ARE SPECIFIED WITH EACH AND EVERY DIMENSION"* ----Actually, my manager is in agreement with us on this. He even asked me to gather info to support it. With all the responses above, I can defend my position, if I need to.

Thanks again to all who posted.

 

[CheckerHater]

Today I've learned something new.
Tnank you geekman25!

 

[Walterke]

Is it possible to put the mixed dimensions on drawings going to customers, but use single dimension drawings for actual production?

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[drawoh]

Walterke,

Think of my fabrication drawings as part of a contract. The PO says that you, Walterke, will fabricate parts for me as of my drawings, listed below. Each of my drawings states that dimensions and tolerances are as per ASME Y14.5M-1994. The drawings, effectively, are clauses of a contract.

You are agreeing to deliver the parts I have called up. The ASME or ISO standard explains exactly what the dimensions on the drawings actually mean. There is no ambiguity, unless I do something stupid like dimension my drawings in two sets of units.

The drawings that go to your customers generally are for reference. Alternate units are helpful, and there is no liability to them. I never call up a drawing standard on such drawings.

If my customer drawings do contain dimension data I am promising to achieve, then the ASME standard is called up, and my reference dimensions are contained within brackets, as per the standard. I will not call up alternate units on the real dimensions.

--
JHG

 

[ctopher]

Walterke,
They should be different drawings and P/N's.
It can be confusing having the same part on two different drawings, and different revisions.

Use one drawing with primary and secondary dimensions.

Chris
SolidWorks 11
ctopher's home
SolidWorks Legion