Dual Unit Dimensioning 3

[ewh]

Y14.5-2009 ¶ 1.5.4 states "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."
What would be the situation where ALL dimensions are dual dimensions (inch over metric)? It seems the standard adresses a mix of inch and metric dimensions, not a situation where both inch and metric values are included in each dimension. Shouls we still include the units in such a drawing?

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[randy64]

For the customer I support, the secondary dimension is in brackets. Depending on the client, the primary may be english or metric. So, if english is primary and metric is secondary the dimension looks like this:

.250 [6.35]

I know this doesn't really answer your question about how 14.5 handles this, but just thought I'd throw it out there. BTW, we follow 14.5-1994, but this dimensioning scheme is called out in our customer's drawing standards and in the drawing tolerance block which supercede 14.5.

 

[ctopher]

I have talked to numerous shops that don't know what the abbreviations are, and gets worse every couple years.
I do the same as randy64, but I add a note stating what the primary and secondary dimensions are.

Chris
SolidWorks 13
ctopher's home
SolidWorks Legion

 

[CheckerHater]

Essentially, everything you add to your drawing either compliments or superseeds the standard.

As long as you made it clear, you should have no problem.

The bigger question is why? Are there people out there who are not understanding metric? Is it so difficult to stick to one single unit of measurement? Either one?

 

[ewh]

Thanks!
It isn't that people are not understanding metric but that the company is international and working in only one unit of measurement has been determined not feasible. Not all drawings are affected, but we want to have a clear understanding of those that are.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[looslib]

The intent of the spec is where a primary dimension is not in the default units of the majority of the dimensions. We used to design all parts in metric, but a wheel and tire are universally done in inches. So the bead width and rim diameter where dimensioned with the added 'IN' to each dimension.

Dual dimensions do not need the additional unit nomenclature. You may do as Chris does and add a note stating what your dimension units are.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[dgallup]

When we do a dual dimensioning drawing (which I try to avoid like the plague), the the units callout in the title block is primary[secondary] just like the dimensions themselves:

mm[inch]
6.35[0.25]

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[CheckerHater]

Double the dimensions = Double the errors

Avoid like a plague, fight tooth and nail.

 

[looslib]

Have to disagree with the double the errors, at least if you are using CAD for your drawings. The ability of most CAD packages to insert dual dimensions means there is no conversion mistakes of the dimensions.

I also don't like them. We used a CAD package at a prior company that we wrote a program to gather all dimensions and build a conversion table so tey would be listed on the edge of the drawing showing the metric dimension and its inch conversion. We always considered this table to be reference data only. Our machine shop and NC programmers always wrote their programs in inch units. When we switched CAD programs, the new one could not produce the table as easily, so we eliminated it on all drawings.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[marshell]

I would check out SAE J390 (Dual Dimensioning) it explains how to do this, and could give some mutual agreement between you and the customer if you were to follow and reference it on a drawing.

 

[berkshire]

The real fun with dual dimensioning, is making sure the tolerance stack ups work, in both sets of dimensions.
B.E.

You are judged not by what you know, but by what you can do.

 

[looslib]

Not sure of others but Pro/Engineer claims that they make the secondary dimension smaller than the main diemsnion to compensate for rounding errors and to be sure the secondary dimensions will not cause the parts to fit if manufactured to them.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[berkshire]

and to be sure the secondary dimensions will not cause the parts to fit if manufactured to them.
That's exactly what I am talking about.
B.E.

You are judged not by what you know, but by what you can do.

 

[juergenwt]

No dual dimensioning! As for CAD dual dim's - 5/16 - 7.9375mm or converted prints with just 7.9375 on the drawing. Drives the shop nuts because they can not relate to mm sizes. Most do not have the slightest idea what .1mm looks like.
Change the system to metric and be done with.

 

[berkshire]

How much fuss and bother this is, depends on where in the world you are. In the USA there are still a lot of machines out there calibrated with inch dimensions.
DRO's with dual dimension switching have taken a lot of the pain out of dual dimensions. However I always add a note to a dual dimensioned drawing saying that the bracketed dimensions are there for reference, and that the, un bracketed dimensions, are the ones you work to.
This was a major PTA when Britain went metric in the late 1960's , now there seems to be some of this in the USA where companies will tell you loudly they have no problem with metric dimensions, but when you get on their shop floors you find out they do still have a problem with it, especially in smaller shops with older machines. And going the other way do you want 8mm or .3152" there are some dimensions that will round out to 2 decimals, there are others that are a pain. Give the primary units on your drawing, include the other units as a courtesy, then put a note on the drawing saying that.
B.E.

You are judged not by what you know, but by what you can do.

 

[fcsuper]

Dual dimensioning is not supported by ASME. Y14.5 used to support it back in the 70's, but that was dropped in the 80's. In fact, there are solid arguments against dual dimensioning under ASME standards. You can have drawings with both inch and metric units, but individual dimensions with both are not allowed. I covered this issue awhile ago here:

http://www.fcsuper.com/swblog/?p=72

Does ISO support dual dimensions? Yes. There is even a rule for rounding tolerances: the secondary unit tolerance range always fits inside the tolerance range of the primary unit.

In general, the practice is that the secondary unit is stated in brackets. I'm not sure if that is from any current standard.

Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion

 

[ewh]

Thanks, Matt!
I'll try the argument in your blog and see how well it is received here.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV