General Drawing Tolerances 2

[brakemeister]

I am interested in finding out if the field is moving away from using a general, or boiler-plate tolerance block on a drawing format or if most organizations are continuing to use it. Any opinions would be appreciated.

 

[ctopher]

I can't speak for automotive, but for mechanical and aerospace...we still have it and will be using it for several more years.

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 06/08
ctopher's home (updated Jul 13, 2008)

 

[KENAT]

We have a boiler plate block on drawing format, in the US (ASME Y14.5M-1994 compliant(ish)) scientific instrumentation/metrology tools. Doesn't work as well for metric ;-).

People relying on MBD may be doing differently.

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

 

[GBor]

We definitely have a general tolerance block so that we don't have to specify a tolerance for every dimension...just those that need to be a bit tighter or looser...can't imagine eliminating it any time soon.

 

[ewh]

Same as above.

When the people fear their government, there is tyranny; when the government fears the people, there is liberty. - [small]Thomas Jefferson [/small]

 

[drawoh]

brakemeister,

Usually, tolerance blocks on drawings state that a certain number of decimal places indicate the tolerance. ASME Y14.5M-1994 states that you do not apply trailing decimals to your metric dimensions.

Most of my drawings are metric. I can use our tolerance block, or I can follow ASME Y14.5M-1994. I follow ASME Y14.5M-1994.

Going through each and every dimension on my drawings and adding or ensuring there is a tolerance easily adds around five minutes time to each and every drawing I generate. I think I have wound up with better drawings.

JHG

 

[KENAT]

In the UK we just had a single general tolerance, it didn't vary with decimals as most drawings were metric. This meant that as with drawoh we added direct tolerances to a lot of dimensions, we also usually showed limits rather than +-.

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

 

[MintJulep]

My view on "standard" tolerances may be found here:

thread1103-199111

You may find the thread in general of interest.

 

[KENAT]

Good memory Mint.

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

 

[ctopher]

Yes, good find. I forgot about that thread.

Chris
SolidWorks/PDMWorks 08 3.1
AutoCAD 06/08
ctopher's home (updated Jul 13, 2008)

 

[fcsuper]

The isn't a movement away from title block tols as far as I can tell either. However, there is just starting to be a move towards relying on the models themselves without drawings. However, even is such cases, tolerances are still required to be stated in the documentation of the model, and place .xxx tolerances is still a comment practice.

BTW, even if metric is employed, title block tols can still be used. There's no law saying you can't. Just make a note of this variation from the standard in your own company's drafting standards. It is acceptable within ASME Y14.100 paragraph 1.2 to not use particilar sections of the ASME standards as long as you are clear as to what differences you have when this happens.

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]

Yeah you can deviate so long as you explicitly state it but it seems to confuse many.

For instance in the rest of the world, for metric fasteners, if you just put M5 it means M5 thread standard coarse pitch. In the US you're supposed to put the pitch, this caused a lot of confusion with European employees, also our CAD didn't easily comply and Americans weren't generally as familiar with metrics and it caused issues there too. To get around this we have a note saying "Metric thread callouts without a pitch specifed are course pitch" however this still seems to confuse people.

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

 

[fcsuper]

Why didn't those crazy Europeans just use ANSI like everyone else? ;-)

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

 

[CheckerRon]

As friend and fellow poster to this forum "WHITMIREGT" likes to say, "In the US we are going metric---inch by inch."

 

[MotorVib]

in mining equpment the boiler plate block is the normial

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[CheckerRon]

From a checker and former pressure vessel designer's point of view, I say "Don't mess with the boilerplate, it might blow up on you."

 

[MechNorth]

As a GD&T trainer, I get to see what a lot of companies are doing. When I start a class, I often find that the represented companies are still using +/- linear & angular tolerances, both directly & in a general tolerance block. Through the material, though, they come to realize that GD&T is "the better way". You use basic dimensions to locate features wrt your datum structure, and to size features that are not being located by Position. Then, you apply specific geometric controls where needed, and put "UNLESS OTHERWISE SPECIFIED" and "NON-TOLERANCED DIMENSIONS ARE BASIC" and a Surface Profile FCF as your general tolerance to cover everything else. If you don't use the general surface profile, then you DO need to explicitly tolerance everything else and worry about the number of decimal places. By the end of a Fundamentals class, most companies are asking for a sample title block & general surface profile tolerance.

What I frequently find is that people forget that the general +/- tolerances apply to non-toleranced dimensions, so they end up with +/- tolerances locating the centers of holes, rads, etc., and / or conflicting with GD&T controls. Plus, you would end up with tolerance accumulation and wedge-shaped tolerance zones.

There is a growing use of the notation that I indicated above in conjunction with the general surface profile control. It's in use already in the Big-3 Automotive, in aircraft industries, space, consumer products, and the list goes on.

IF your company's goal is to stay with 2-D drafting or using paper drawings for manufacturing, designers won't necessarily notice the difference. If, however, you are moving toward Y14.41 (digital product definition standard) then the method I've outlined is how it will be done. In fact, Y14.41 prescribes a very limited number of uses for +/- tolerances.

I've heard that the automotive & some aerospace firms are mandating the use of Y14.41 for Tier-1 within a few years, which means Tier-2 and Tier-3 will likely follow shortly after if they are allowed to lag behind at all.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca