Tolerance for fabrication

[tvspgt01]

General tolerance for fabrication as per Indian standard.Fabrication means fabrication of supports using angles, channels, beams etc.Please inform Indian standard or International standard

 

[ctopher]

Try "Machinery's Handbook". I don't know any Indian standards.

Chris
SolidWorks 09, CATIA V5
ctopher's home
SolidWorks Legion

 

[KENAT]

ISO has some tolerance standards but I'm not sure if they have one for fabrication.

What kind of application are you talking about, are you talking construction or more like machine design or the like? For instance, I seem to recall an ex colleague that did some structural detailing say they worked to 1/16 or 1/8 of an inch or something like that.

I'll use machineries or similar for my initial estimates then information from vendors to refine it. For instance I used information from

http://www.precisionsheetmetal.com/home/materials.htm

to start a recent design then got feedback from the actual vendor.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[MintJulep]

There is no such thing as a "standard tolerance".

No standard's making organization can possibly have any idea what your design is.

It is the responsibility of YOU, the designer to assess your design and it's performance requirements and determine how much deviation from the nominal dimensions is permissible.

 

[KENAT]

Mint, maybe it's mucky terminology but I think maybe you're being a bit harsh. Certainly, at least in the US (and in my mind to any sane designer;-)) function should be the primary driver of tolerances, and this will vary by application.

However, you also have to ensure that your tolerances can be achieved at acceptable cost. This is where there are some rules of thumb and in some cases there are indeed tolerance standars such as (the in my opinion flawed) ISO 2768. While I have to say that I think this particular standard may tend to swing too far toward suiting manufacturing at the cost of function, it does exist.

There's a big difference between designing to stay within "standard tolerances" that can be achieved at reasonable cost by almost any competant supplier (obviously looser isn't usually a proplem for manufacturing, I'm talking about tighter) while ensuring function and not considering tolerance at all and just relying on some industry standard, block tolerance or other rule of thumb.

The former should be encouraged, the latter should be outlawed;-).

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[MechNorth]

The use of ISO 2768 comes up frequently in my coaching & training duties. I absolutely detest it. Here's what I tell my students; Consider that the standard was published in the early 1980's. Typically about 10-plus years of studies are conducted before a set of "standard values" is approved. OK, so that puts you back to the '60's or '70s when the study was done. Because it is based on "general" or "typical" capabilities of the day, you're not dealing with highly automated processes or equipment as we often deal with today. Add to that the reality that much of the equipment in use in "general" shops would easily have been 20-plus years old at the time. That puts you back around the 40's thru 50's when the "typical" equipment was manufactured. That means no glass-scale encoders, no automated feedback & compensation, no machine tool wear monitors, and heavy dependance on skilled machinists in a shaft-and-hole-basis fit system. While many of the machines built before the '60s were excellent machines, they do still show their age over time. Overall, it's not clear to me what they were actually using as a baseline. Add to that the fact that they only deal with SIZES and linear distances; no consideration of form or orientation, runout, etc. There's more to the consideration of applicable tolerances than just grabbing a number from a book. I've managed to convert a number of groups over.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[KENAT]

MechNorth, you don't have to convince me of the issues with 2768, however it does exist.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[MintJulep]

Kenat,

If you design something that requires tolerances that cannot be achieved within the cost constraints of the project then the design is failed.

A good engineer or design must have an understanding of manufacturing process capabilities and the relationship between requiring a narrow distribution of variation and increasing cost, be it more tightly controlled manufacturing processes, or by scrapping lots of parts on the tails of the distribution.

 

[KENAT]

I agree on everything you say in your second post Mint. I thought my "However, you also have to ensure that your tolerances can be achieved at acceptable cost." covered this.

The OP was poorly phrased and I thought that depending on what they actually meant there may be such a thing as a "standard tolerance" for specific applications. However, as I mention above for 2768 I'm not a fan that "tolerance standard".

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[MintJulep]

Well let's agree to agree then!

 

[MechNorth]

Ditto.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[MartinSr00]

There are AISC Standards for Structural Detailing. AISC is the American Institute for Steel Construction. Contact them.