Dimension in Draft Rounds Down

Builder
Builder

This is the first time I've noticed this...  My driven dimension in a draft rounds down instead of up.  Is this the correct behavior?  Is there a way to fix it?  -Thanks.  

 

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6 REPLIES

Re: Dimension in Draft Rounds Down

Esteemed Contributor
Esteemed Contributor

Try this setting:

dimround.JPG

Bruce Shand
ST9 MP10 - Insight - Win10 - K4200

Re: Dimension in Draft Rounds Down

Valued Contributor
Valued Contributor

It is a checkbox in the dimension properties menu >Units Tab.  To set the value globally, you will have to set it as a style for your template.

Re: Dimension in Draft Rounds Down

Builder
Builder

Thanks.

Re: Dimension in Draft Rounds Down

Esteemed Contributor
Esteemed Contributor

There is a difference between what you were taught in grade school and what is required per ASME Y14.5M.

 

Always rounding the number up proceding a 5 creates a statistical growth bias that can cause enough strung dimensions to push a feature beyond it's intended position.

 

Increasing the preceding odd number and leaving the proceding even number has the best chance to create an even distribution of growth and shrinkage that should eliminate the statistical bias in either direction.

 

Example grade school rounding:  1.875 (1.88 grows 5 thousandths) + 1.625 (1.63 grows 5 thousandths) = 3.500 (3.51 using rounded values results in 1 hundredth over target value)

 

Example ASME rounding: 1.875 (1.88 grows 5 thousandths) + 1.625 (1.62 shrinks 5 thousandths) = 3.500 (3.50 using rounded values results in matching target value)

 

As you can see this is easily demonstrated with just two values.  Imaging having half a dozen in a strung dimension all rounded up and QA/QC guy measuring these by your rounded dimensions.  He's a couple hundredths off from the nominal and your part is flagged as out of tolerance!


Thanks,
Ken

Production: ST9 MP10
Testing: ST10 MP1

Re: Dimension in Draft Rounds Down

Esteemed Contributor
Esteemed Contributor

A good reason not to use chained dimensions too.

Bruce Shand
ST9 MP10 - Insight - Win10 - K4200

Re: Dimension in Draft Rounds Down

Siemens Phenom Siemens Phenom
Siemens Phenom

From the standard SI 10, American National Standard for Use of the International System of Units (SI): The Modern Metric System, in Apendix B.6, Rounding Values...

When rounding to fewer digits than the total number available, proceed as follows:

a) If the first digit discarded is less than 5, do not change the last digit retained. For example, 3.463 25, if rounded to four digits, would be 3.463; if rounded to three digits, 3.46.

b) If the first digit discarded is greater than 5, or if it is a 5 followed by at least one digit other than 0, increase the last digit retained by one unit. For example 8.376 52, if rounded to four digits, would be 8.377; if rounded to three digits, 8.38.

c) If the first digit discarded is exactly 5, followed only by zeros, round the last digit retained upward if it is an odd number, but make no adjustment if it is an even number. For example, 4.365, when rounded to three digits, becomes 4.36. The number 4.355 would also round to the same value, 4.36, if rounded to three digits.

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