Which is most prefereble Dimensions method? 1

[RathodAsit]

Dear All!,

As we are making GI Sheet metal and Busbars Drawings for Electro Mechanical Products, Please let me know which is the best method to call the dimensions,1.) Ordintate Dimensions(Pick two faces and give X and Y dimensions) 2. EDGE to Hole and then Hole to Hole, Tolerance used in parts are ISO2768-M.

Thanks in advance

Best Regards
Asit Rathod

 

[CheckerHater]

The best way to position the holes is to use BASIC dimensions either ordinate or hole-to-hole and apply feature control frames.

Leave ISO 2768 for non-locating dimensions.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[drawoh]

RathodAsit,

Both of your proposed methods are approved by the standards. Which of them will be clearest to the end users of your drawings?

--
JHG

 

[TheTick]

What is most preferable is parts that work. Whichever method yields functional parts for lowest cost would be my preference.

 

[randomdrafter]

We use Ordinate dimensioninig.Manufacturing is automated by feeding IGES file generated by a custom program from flat pattern.

 

[KENAT]

If relying on iso 2768 for locating hole patterns (which as CH says think twice about so doing) then think about the impact of how the location tolerances stack and what impact that has on fit etc.

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[RathodAsit]

Dear All!

Thanks for the sharing the knowledge.

CH, our LOCAL MFGs are not able to understand feature control Frames,

Drawoh,Randomdrafter & TICK, current situations we give ordinate dimensions and give flat pattern to the LOCAL MFGs so they can get RAW Size from the flat pattern.

KENAT, We already give Tolernace in Dim of the hole.(e.g. M5 screw we give 6.0 mm hole)

Regards
Asit

 

[KENAT]

RathodAsit, the size of the hole should be based in part on the tolerances from the hole location dimensions. Depending on if you dimension from hole to hole or from hole to edge/ordinate the tolerances accumulation will vary - and hence the clearance hole size may change.

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[RathodAsit]

KENAT, I believe you means to say tolerance stack up needs to calculate for all the holes in parts, depending up on that hole sizes will vary.

Do you have any standards to be followed? or what best practise you are following.

Thanks in advance.

Regards
Asit

 

[KENAT]

I work to ASME Y14.5M-1994 - sample calculations/formulas are given in appendix B but that assumes using position tolerancing.

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[randomdrafter]

Asit,how does part manufactured? In our case flat sheet is cut first [Nest method used to cut different size parts together] and then all holes/slots machined..later it will be formed to specific angles.The tolerance is fixed for this holes/slots.

Only threads/chamfers will be done after forming.We will not include these dimensions in flat pattern drawing.

If we need tighter tolerances those holes are done after forming.

There are various checks run on the flat pattern view to see all holes are as per standard/any break in profile etc....

 

[RathodAsit]

randomdrafter,
Yes same our mfg did it for Sheet metal parts, first nesting (Diff sizes, set in raw material sheet), and then punching and then cutting at last bending, and then Assembly HW fitting like rivets, Pop nuts

Regards
Asit

 

[KENAT]

Sure that's the typical process and trying to allow for that work flow should keep cost down etc. but...

Engineering drawing typically documents the finished item without specifying process unless process directly impacts end functionality. So dimension scheme & tolerancing needs to capture function first.

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[randomdrafter]

KENAT, Dimensioning scheme is as per standard any way. Only when there is tighter tolerance required we can change the scheme and go with GD&T.


Atleast in some area of sheet metal work hammer will take care any variation at end

 

[greenimi]

Quote:
" Only when there is tighter tolerance required we can change the scheme and go with GD&T"

This is the real world perception! (or at least some of the manufacturing companies act according to the quote above)

 

[KENAT]

"Only when there is tighter tolerance required we can change the scheme and go with GD&T."

This is not what any drawing standard I'm aware of says or implies.

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[randomdrafter]

KENAT , its not as simple as I wrote. We make 100,000 sheet metal parts [various sizes/shapes] per year for our products in-house. Majority of the parts are Class C parts [doesn't affect overall function of product much]. We use customized programs to generate parts, very little inspection needed for most of these parts anyway. We follow all the functional requirements by providing sufficient clearance holes/slots etc. so no question of fitment issues in assembly.

So whenever some critical requirements arises instead of our regular process [Ordinate dimensioning with default tolerances], we change to +/- tolerance or FCF wherever required. in some cases we even do machining in assembly. As far as I know there is very few issues arised over the years.

 

[TheTick]

There's always competing and conflicting influence on part dimensions. The makers want things easy to make. The inspectors want things easy to inspect. Some people just want that *one*special*dimension* that tells them what they want to know without doing any math (which they haven't done since high school).

The part still needs to function. Nothing is more important.

 

[powerhound]

The old myth...GD&T is only for tight tolerances. I guess it will never go away.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech
SSG, U.S. Army
Taji, Iraq OIF II

 

[randomdrafter]

Looks like i used wrong words. We use tighter tolerance when function requires,remaining time we just go with default tolerances.So far things working fine.