Rounding of Tolerances
Rounding of Tolerances
(OP)
This is a question about rounding tolerances. It is a product of dual dimensioning. I know the evils of dual dimensioning, but our customer does it, and so it is what it is.
I searched the archives but have not seen this particular question as it applies to tolerances.
Question: When converting the inch tolerance in the FCF of .014 it gets us 0.3556. Our rounding standards state that a tolerance of .014 will get rounded to 2 places for the metric. I am arguing that the metric number in the FCF should be 0.35, due to the principle of never adding tolerance (could allow a too-big part that won't fit/go together). However, we have another general standard that defines how to round numbers. It's the usual stuff about 0-4 rounding down, 6-9 rounding up and rounding 5 depending on even/odd.
Bottom line, I am meeting resistance by folks that are blindly following the rounding standard i.e. .199 rounded to .20, versus my belief that a tolerance should never be rounded up i.e. .199 rounded to .19.
Is there something in AMSE that addresses this that will back up my position (assuming I'm correct. If I'm not I'm sure you all will let me know)?
Thanks.
I searched the archives but have not seen this particular question as it applies to tolerances.
Question: When converting the inch tolerance in the FCF of .014 it gets us 0.3556. Our rounding standards state that a tolerance of .014 will get rounded to 2 places for the metric. I am arguing that the metric number in the FCF should be 0.35, due to the principle of never adding tolerance (could allow a too-big part that won't fit/go together). However, we have another general standard that defines how to round numbers. It's the usual stuff about 0-4 rounding down, 6-9 rounding up and rounding 5 depending on even/odd.
Bottom line, I am meeting resistance by folks that are blindly following the rounding standard i.e. .199 rounded to .20, versus my belief that a tolerance should never be rounded up i.e. .199 rounded to .19.
Is there something in AMSE that addresses this that will back up my position (assuming I'm correct. If I'm not I'm sure you all will let me know)?
Thanks.





RE: Rounding of Tolerances
thread1103-225708: Rules For Rounding Decimals
Chris, CSWA
SolidWorks 14
ctopher's home
SolidWorks Legion
RE: Rounding of Tolerances
RE: Rounding of Tolerances
http://www.dimcax.com/gdt_web/september-05.htm
Season
RE: Rounding of Tolerances
In the tip it says, "The ANSI/IEEE 268 standard, referred to in Y14.5..." I looked in Y14.5 (we use 1994) but could not find ANSI/IEEE 268 referred to, at least not in 1.2 REFERENCES. Anyone know where that might be? I'd like to have unrefutable documentation when discussing this.
RE: Rounding of Tolerances
RE: Rounding of Tolerances
http://mscweb.gsfc.nasa.gov/543web/files/GSFC-X-67...
Season
RE: Rounding of Tolerances
RE: Rounding of Tolerances
John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Rounding of Tolerances
To my understanding there is no way of applying exactly the same limits in both imperial and metric whilst using any known standards?
The best solution is to never dual dimension but failing that the limits must be tighter in the secondary system.
RE: Rounding of Tolerances
RE: Rounding of Tolerances
RE: Rounding of Tolerances
For reference I have just finished converting customer drawings with english being primary and default rounded to 2 places, some english dimensions were at one place and a few at three. The secondary was metric and every dimension was rounded to 3 places. The draftsman must have been taught as I have been.
RE: Rounding of Tolerances
RE: Rounding of Tolerances
DeSimulacra, you said, "I agree with MintJulep, if inches are the primary. I was taught that the secondary dimension be it metric or English is there for reference only and that the primary dimension is what tolerance is derived from."
On some of our drawings, where the metric is primary, we design to the inch and derive our tolerances from the inch and then convert to metric. I know, it's not proper and probably wrong, but when the 800 pound gorilla says to do it that way, you do it.
RE: Rounding of Tolerances
Fortunately unless you happen to work for any American companies this is not a problem for the rest of the world.
RE: Rounding of Tolerances
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Rounding of Tolerances
No wonder 800-pounds gorillas eventually went extinct.
RE: Rounding of Tolerances
“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV
RE: Rounding of Tolerances
You said"
On some of our drawings, where the metric is primary, we design to the inch and derive our tolerances from the inch and then convert to metric. I know, it's not proper and probably wrong, but when the 800 pound gorilla says to do it that way, you do it."
All that is fine, just remember, If you dimension in Inches and secondary in metric the default tolerance block will/should be in inches. The opposite will hold true if primary is metric. What you design in holds no relevance.
Another way to put it is why would you make your primary units inches and then tolerance in metric?
DeSim
RE: Rounding of Tolerances
We don't make primary units inches and then tolerance in metric.
What I meant to say is that on the drawing, metric is the primary unit, with inches in brackets (secondary). BUT, we design in inches and also base the metric on a conversion of the inches. It would seem to make more sense to always derive the secondary from the primary regardless of whether the primary was mm or inches, but that is not what the customer wants.
Re: Tolerance Block, the tolerance block on these drawings give both mm and inch tolerances based on number of decimal places and they are roughly equivalent.