Title Block Tolerances

[Doogan]

What are some of the more common Title Block Tolerances used for inch units?

Is there any basis (standards) for these values?

My experience has been that a .XXX (3 place decimal) commonly corresponds to a +/-.005" tolerance, while a .XX (2 place decimal) commonly corresponds to a +/-.010" tolerance.

I ask the question because one of my company's plants is asking me to consider changing the Title Block tolerances to what they consider standard (for unknown reasons, unfortunately). These are:
.XXX ==> +/-.005" and
.XX ==> +/-.030" (to me the .030 seems larger than the usual).

Thanks for your thoughts in advance,
Doogan

 

[swertel]

.030 is WAY to big unless you are making a lot of soft goods, like fabrics, cloth, or leather wrappings.

I'd stick with you standard +/-.010, but it really depends on your product line.

--Scott

http://wertel.eng.pro

 

[GBor]

The loosest tolerances in our company (aeronautical industry) are:

.X = +/-0.1
.XX = +/-0.030
.XXX = +/-0.010

What industry are you in...that generally makes a difference. Also have to consider the application and the ramifications for a loose fit.

 

[fcsuper]

It depends on what principle technology that will be employed on the part being detailed.

Machined parts is frequently .005 and .010. Sheet Metal is a little more complex because they can maintain .005 in certain cases, but it jumps up to .030 (depending on the thickness of the material). Molded parts can be .005/per inch.

Tolerances should be set per the part and the design intent. General tolerances can be employed only if they are evaluated for each part.

For example, assuming your part is a sheet metal part that is over .080" thick, the general tolerance that is suggested is +/-.030 which could represent fold to fold dims. But you can also set hole to hole tolerances at +/-.008.

For precisioned machined components, such loose tolerances can be detrimental, in which case you may wish to use .005 and .010 and your ranges. Of course, the scale of your parts is also a factor. If you have parts that are 20' long, .030 may be a little tight.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[MintJulep]

Can your designs tolerate a +/- .030 variation from part-to-part and still function properly?

 

[MadMango]

I use to work at a sheet metal house, +/-.030 was common to reduce our rejection rate. This was 6-18ga steel, SST, and aluminum.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the be

 

[KENAT]

Not directly relevant but you may want to look at:

thread1103-222161
thread1103-199111

Our standard block (industrial/scientific metrology equipment) is:

.X = +/-0.030
.XX = +/-0.010
.XXX = +/-0.005

For some very precise parts this gets changed to

.X = +/-0.010
.XX = +/-0.005
.XXX = +/-0.002

The block also occasionally gets changed for things like cables or foam where even +-.030 is on the tight side. However, I'm not a big fan of changing the block too often, people get used to the default and changing frequently can lead to errors. I know these errors are the users fault for not reading the drawing but still, I'd tend to put tolerances against each dimension instead of changing the block most of the time.

As to the basis for these figures, I'm not aware of any directly relevant standard. I suspect it's based on perceived process capability and/or cost V tolerance data but don't know a reference. There was some debate on here recently that much of the perceived typical values may be based on out of date information. For instance ISO 2768 (please not I'm not recomending you use it as it has major problems in my opinion) is based on an Older DIN standard which in turn if you look at the revision history etc. suggests the tolerances are probably based on the capabilities of immediately post war (WWII) technology. I have a graph from Ohio State University that shows % cost increase V nominal tolerance, but again it's been suggested the information may be out of date and that the curve may have 'moved to the right'.


KENAT, probably the least qualified checker you'll ever meet...

 

[fcsuper]

Also, I would suggest not changing the title block wholesale. Older parts were detailed to the current tols. If those parts had their title block updated some day without proper evaluation (95% likely), it could create Form/Fit/Function issues.

One option is to consider using different title blocks for differnt types of parts or to allow the user to set the tol for their drawing (if you have a CAD program and template that is set up to allow the user to easily set those values).

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[KENAT]

fcsuper raises a good point. I sometimes get drawings that are moved from old formats to the new. Some old formats (our current company is a merger of several originals so various formats abound on older drawings) had different tol blocks but this often gets overlooked.

The points made above about tolerance being primarily driven by function cannot be stated strongly enough. however, in good design process capability does need to be taken into account.

KENAT, probably the least qualified checker you'll ever meet...

 

[Doogan]

Thanks everybody for your fast responses!

I will push back in favor of the .010 for my application.

Eric