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SI units tol
5

SI units tol

SI units tol

(OP)
How do you read these tolerances?
Not sure how to add this symbol here, but "<_" is "less than or equal to".

x<_10, +/-0.1
10<x<_100, +/-0.15
100<x<_500, +/-0.25
500<x, +/-0.5

If a dimension is 165 or 22.5, what tolerance is used?

I have never used this type before.
Thanks.

Chris
SolidWorks 10 SP5.0
ctopher's home
SolidWorks Legion

RE: SI units tol

This is a very typical tolerancing scheme used in ISO world.
Its based on assumption that for certain manufacturing methods accuracy of dimension becomes smaller (tolerance is wider) as the nominal size gets bigger.

If the dimension is 165 the limits are 164.75 - 165.25.
If the dimesnion is 22 the limits are 21.85 - 22.15.

RE: SI units tol

(OP)
So, the number falls within the range (x) it's that tolerance.
Seems odd to me, but I understand it.
Thank you!

Chris
SolidWorks 10 SP5.0
ctopher's home
SolidWorks Legion

RE: SI units tol

More like

If the number (x) falls within the range...

RE: SI units tol

I don't think it's just for ISO; I've seen it on prints that use ASME.  I've heard it referred to as a "graduated" tolerancing scale or method.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: SI units tol

(OP)
Thanks John.
Of all my years of drafting/eng/etc, this is the first I have seen this.

Chris
SolidWorks 10 SP5.0
ctopher's home
SolidWorks Legion

RE: SI units tol

Limits and Fits have been defined with a similar system for quite a while by ANSI B4.1-1967. Why other linear tolerances should be excluded would have been more the question im my mind.
There was an ANSI or ASME standard on metric tolerancing that proposed the ISO style, (DIN German) system it appears to have been withdrawn now.
Frank

RE: SI units tol

This looks like graphing restrictions or inequalities. I thought I had seen the last of these in Trig.

Powerhound, GDTP T-0419
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: SI units tol

The standard was ANSI/ASME B4.3-1978(R2004) General Tolerances for Metric Dimensioned Products; so it's more than 30 years old.

It was happily reassured in 2004 but later decision was made to transfer it from B4 committee to Y14 committee to become "drafting and tolerancing" standard.

As a result it was successfully "missing in action". Copies are still around. One may be surprised, how much it resembles ISO 2768.
 

RE: SI units tol

Thanks CH, I knew I had seen it before.
Frank

RE: SI units tol

It is very easy to assign general tolerances for the drawings which are dimensioned with Inches as dimesioning units. The preeceding zeros represents the toleance value.
Example; 14.0
         14.00
         14.000

General Tolerances
.X = +/- .01
.XX = +/- .001
.XXX = +/- .0001

Above shown is  just an exapmple. You might be familiar with this.

If you use milimeters (mm) in the drawings then the whole numbers should not be preceeded by zeros as per the satandard. You dont have provision to assign general tolerances as the example shown above. Since ISO standard uses mm as the dimensioning unit. it has to go for other methods for mensioning the genereal tolerances. The general tolerancing scheme you mentioned in your post is very coomon in ISO.

 

RE: SI units tol

Madhu454,
Do you work with the ISO system much, yourself?
Frank

RE: SI units tol

Sorry ctopher, Your initial question would not imply that to me. I am interested in a discussion with people who have used this system2 for a period of time and had to live with it.
Frank

RE: SI units tol

Frank,
What are your doubts/concerns about ISO system?

RE: SI units tol

Hi Frank,
Yes, I wrk on ISO system. We use Geometrical Product Specification (GPS) in our drawings. GPS is based on ISO standard constisting of more than 150 standards to completely define the part. It is very similar to GD&T,(but there are few differences compare to ASME standard). In our companey we dont use general tolerances in drawings. But I have seen many drawings created as Chris mentioned in his post.  

RE: SI units tol

pmarc,
Thanks, I think you know I have been interested in it for some time. I do not feel I know enough about it to have my own "doubts".

Madhu454,
Thanks, I sounds like you do not use the part we have been discussing here, I have been interested in issues like the stack up of these implied tolerances.

Frank

RE: SI units tol

Frank,
Yes, I noticed that you are really interested in the ISO GD&T language, or as Madhu454 said - GPS. And I also noticed that you sympathize with some (or most?) of the ISO's approaches to the tolerancing of parts.

I also remember that you already started some threads about the topic on the forum. The most recent one was about cummulation of tolerances for two round holes, right? Could you give any other example showing your concerns? I think it would be a best starting point for further discussion.  

RE: SI units tol

(OP)
Frank,
I don't understand your confusion.
My initial post is different than what Madhu454 had written, which I have used for 30 years.

Chris
SolidWorks 10 SP5.0
ctopher's home
SolidWorks Legion

RE: SI units tol

ctopher,
I am very sorry, I must be confused about the subject of your initial post:

"How do you read these tolerances?"

"I have never used this type before."

I thought you were refering to ISO type tolerances.
Frank

RE: SI units tol

ISO 2768-1 gereral tolerancess to be more specific, I think I am so in a hurry to discuss them with someone that I read it in here where it was not intended.
Frank
 

RE: SI units tol

Frank,
What do you want to discuss about ISO 2786-1 in particular? It is still too general subject for a discussion. There is also 2786-2. Is it something you wanted to talk about too?

RE: SI units tol

pmarc,
I believe the determination was made, basically by concensis, that the general tolerances must be accumulative if you are looking at a worst case stack-up? Do we have any validation of that outside of our own conjecture?
There are also ISO standards covering casting and welding that are similar. These seem much more realistic to me than what we use and I am interested in the opinion of people who use these to they find if it works well for them?
Frank

RE: SI units tol

Kenat, I am not the one who seems to be more determinated to discuss about it.

Unfortunately for me, but fortunately for you, no further posts about ISO 2768 showed up in this or other thread on the forum. smile

RE: SI units tol

I've seen this type of tolerancing a number of times.  Not to re-open the 2768 debate here, but to me it does tie in.  As indicated previously, this system assumes that as a feature increases in size, its tolerance must be increased.  Going back to older machines & controls, I would have agreed.  With modern equipment's glass scales and encoders with ridiculously high precision and no length compensations, I don't think those numbers are realistic anymore.  I saw data from a 6-foot capacity lathe that held the same +/-0.001mm capability as a lathe producing parts of 11mm diameter.  It raised a red flag for me early on about 2768's scope of use and its dated assumptions / basis.

Jim Sykes, P.Eng, GDTP-S
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: SI units tol

Agree MechNorth, for molding/casting etc it makes a lot of sense but I'm not convinced it's universally applicable to machined parts any more (if ever).

In fact, whether features are done in the same set up is perhaps more of a factor these days.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: SI units tol

(OP)
I apologize for resurrecting this thread.
This subject keeps popping up here and there is still confusion.
If I have dims 10, 10.2, and 10.425, what are the tolerances per the tol block?

I get mixed answers. I'm not used to these type of tolerances as displayed per ISO.

Chris
SolidWorks 11
ctopher's home
SolidWorks Legion

RE: SI units tol

A dim of 10 gets ±0.1

A dim of 10.3 gets ± 0.15

A dim of 10.425 gets ±0.15  (or ±0.150)
 

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: SI units tol

10     +/-0.1
10.2   +/-0.15
10.425 +/-0.15

----------------------------------------

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.
 

RE: SI units tol

If it's greater than 100.  That means even one micron over 100 would get a tolerance of ±0.25 (at least per Y14.5 paragraph 2.4; I presume ISO also sees dimensional limits as absolute).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: SI units tol

The concept: "greater than or equal to" is not solely an ISO concept, it is just mathematics.
Frank

RE: SI units tol

Good point Frank.  I was just worried that some people will measure a number of 100.00001 and round it off to 100, thus giving it the ±0.15 (when it should really get the ±0.25 tol).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: SI units tol

Doh!  Cancel that last post. I forgot that we're talking about dimensions -- as in intended dimensions -- not actual, measured size.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: SI units tol

(OP)
I understand math, but I'm used to having each decimal place using a different tolerance.
Example:
.X = +/- .02
.XX = +/- .01
.XXX = +/- .005

This is not the same as the below if the decimal places in the tol block are different, only if they are as the ISO stated previously.
10.2   +/-0.15
10.425 +/-0.15

It's just as simple as I'm not used to using ISO.

Chris
SolidWorks 11
ctopher's home
SolidWorks Legion

RE: SI units tol

I was not easy for me either and for reasons I have given before I got to like it as, well, basically a less simplified general tolerancing method than the way we do it. I have yet to really have a dialog with people who use it seriously, kind of like GD&T  most only seem to pay lip service to it, IMHO.
Frank

RE: SI units tol

ISO 2768 by itself is NOT a valid identifier on the face of a drawing for the tolerancing standard. ISO 2768 must include the tolerance class, f(fine), m(medium), c(course), or v(very course).

From table 1 of ISO 2768-1, a dimensions of 25mm would have the following tolerances based on tolerance class.

f 24.9-25.1
m 24.8-25.2
c 24.5-25.5
v 24-26



 

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Ben Loosli

RE: SI units tol

2
Please let's not mix ISO 2768 with the ctopher's example being discussed. Nothing on the print says that this standard should be used for any tolerance interpretation. The general tolerances chart is only a convention. Someone picked a method that seems to be based on a 'manufacturing method accuracy vs. feture dimension value' concept - which is obviously more common in ISO world - but the numbers do not have to be corelated to ISO 2768 and the method itself is not reserved for tolerancing according to ISO.

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