Engineering Drawings and Tolerances

[jmas]

Does it required (as a rule) that every technical drawings (with dimension) should have specified condition for tolerancing? In other words can some dimension be left without tolerances?

 

[TheTick]

Unless you are outsourcing your work to aliens who can zap perfect parts into being, yes.

 

[jmas]

Dear Tick:
How many percentage of drawings you've been engaged with were completely tolerance-specified?

 

[PeterStock]

All dimenions must have a tolerance, either directly, in a GD&T, default to the title block or in notes. As far as all dimensions having a tolerance specificaly speced for that dimension, that can be rare some places. Thats when the default tolerance comes into play. If there is no default tolerance specified, the vendor is free to use his default tolerance, which may be different that you want.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[dingy2]

All dimensions must have a tolerance of some sort.

As per ASME Y14.5-2009 1.4 A "Each dimension shall have a tolerance, except for those dimensions specifically identified as reference, maximum, minimum, or stock (commercial stock size)."

Dave D.

http://www.qmsi.ca

 

[fsincox]

jmas,
It is quite common in my view in the buisness since 1980 to see drawings without proper tolerances specially fabrications and for small production runs. I am not saying this is ideal or the way it should be. We do not live in a perfect world.
Required by who is the operative question. ASME,ISO and I say they should.
Frank

 

[MikeHalloran]

A dimensioned image without tolerances is a 'sketch'.



Mike Halloran
Pembroke Pines, FL, USA

 

[fsincox]

Mike,
Not the first time stuff was made from sketches, I would bet. I would say the majority of the fabrication drawings I have seen imply unrealistic tolerances by the tolerance block impication. Just a fact.
Frank

 

[dgallup]

We were once given a "drawing" from an engineer at our companies headquarters in France. Every dimension was nominal even though there were weldments and mounting holes, etc. We asked him what the tolerances were. He said "In France we don't need any tolerances". Nearly died laughing.

 

[fsincox]

This is in no way a unique French problem, I feel the ISO has done more in this area to help than anyone, Seems to be mostly driven by the (DIN) Germans, though. My reaction is more sadness than laughing.
Frank

 

[ewh]

jmas,
There is no such thing as a perfect dimension. Some tolerance is involved in every one, because perfection is only a concept. Deciding what that tolerance should be is a requirement for any "proper" drawing and it can be extremely tight or extremely loose. There is no such thing as a "perfect" dimension, only a range of acceptable dimensions which provide for final design function.
Have you read ZEN AND THE ART OF MOTORCYCLE MAINTAINANCE? This book explains the concept fairly well.
A skilled fabricator can work to a drawing without tolerances on every dimension because they can make allowances for resulting dimensions, but don't expect a large product run with interchangable parts from such practice.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[drawoh]

jmas,

When you send out drawings, you write up a purchase order telling the vendor to fabricate parts as per your drawing. Your drawing is part of a contract. When the vendor delivers something, you pay him.

If you leave out tolerances or otherwise send out a poorly done drawing, the vendor does not really know what you want. Your ass is not covered when he delivers something that does not work. The vendor probably cannnot take you seriously when you tell him you are expecting high quality work.

JHG

 

[fsincox]

JHG,
I don't disagree with that, such is the state of quaility in our buisness. I just don't see quality improving in many things in my day to day life.

jmas,
I have stated my guess on the amount of drawings out there here: thread1103-265286, I would love to know what others see.
I have been in this buisness since 1980, I have 4 family members in the drafting/engineering field: My mother (many years befor me), wife and 2 brothers in-law.
The fields are hydraulic power units, specialty machine tools, water treatment machines, aerospace, motors and Oshkosh Truck (the one brother-in law I have the least experiance with as he is new to the buisness).
Frank

 

[drawoh]

JHG,
I don't disagree with that, such is the state of quaility in our buisness. I just don't see quality improving in many things in my day to day life.

...

Your response is drifting a little off topic. I have started a new thread.

thread1103-265799

JHG

 

[KENAT]

Back to the OP, if you work to ASME 14.5, then yes. I suspect most dimensioning standards would require it but can't be sure.

If you accept the fundamental fact parts will almost never be exact(statistically infinitessimly small chance), then yes.

I see a lot of spec sheets or drawings that are really spec sheets without tolerances.

I've seen a few sketches without tolerances but these were mostly one off 'hammer to fit, paint to match' type situations, often for some kind of test rig or something.

There are a number of ways to do the tolerance, +- on each dim, GD&T, title block tolerance or referencing some other tolerance standard such as ISO2768 or a workmanship standard or something or it can even be a min or max dimension where appropriate.

If you are relying on a separate tolerance standard make sure it is somehow explicitly referenced.

A reference dimension doesn't have tolerances.

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[TheTick]

How many percentage of drawings you've been engaged with were completely tolerance-specified?

Nothing gets my signature if not fully specified, wither with explicit tolerance or tolerance in title block. There's no such thing as "untoleranced", because there is no such thing as "perfect".

That's engineering: determining the window of allowable imperfection. Otherwise, it's just bad art.

 

[KENAT]

"How many percentage of drawings you've been engaged with were completely tolerance-specified? "

For actual formal drawings, I'd say close to 100%. Although, much of this was achieved by reliance on block tols.

If you ask ""How many percentage of drawings you've been engaged with were completely correctly tolerance-specified? "

Then it drops considerably.

Even for my own drawings mistakes happen, especially now we don't have any real checking process, but mine are probably better than anyone else here.

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[fcsuper]

I think the OP either was 100% answered by Tick, or didn't get the answer they hoped for, as they seem to have dropped away from this thread.

That said, 100% of all specifications need a tolerance zone of acceptability. This doesn't just apply to dimensions, but also performance specifications

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

http://groups.yahoo.com/group/solidworks & http://twitter.com/fcsuper