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07-08-2016 11:54 AM

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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Re: Dimension in Draft Rounds Down

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07-08-2016 12:02 PM

Try this setting:

Bruce Shand

SE2019 MP5 - Insight - Win10 - K4200

SE2019 MP5 - Insight - Win10 - K4200

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07-08-2016 12:04 PM

Re: Dimension in Draft Rounds Down

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07-08-2016 01:41 PM

Thanks.

Re: Dimension in Draft Rounds Down

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07-08-2016 03:29 PM

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!

Ken

Production: SE 2019 MP5, Testing: SE 2020

http://Grundey.blogspot.com

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Re: Dimension in Draft Rounds Down

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07-08-2016 03:46 PM

A good reason not to use chained dimensions too.

Bruce Shand

SE2019 MP5 - Insight - Win10 - K4200

SE2019 MP5 - Insight - Win10 - K4200

Re: Dimension in Draft Rounds Down

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07-08-2016 05:14 PM - edited 07-08-2016 05:37 PM

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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