Step on surface allowance?

[GSKMP]

I have a stamped part with a suface height requirement of .380/.365". In order to acheive this on the non-flat part after stamping, the supplier milled the face leaving a .005" step part way across the suface. Dimensionally the part meets the requirment, but I consider the step unacceptable for function of mating part. I cannot find anything in Y14.5m/GD&T to support my case with supplier. Do we really need to call out something as simple as "no Steps permitted" or specifiy a flatness tolerance on all our drawings?

 

[powerhound]

The short answer to your final question is "yes". If your tolerance allows steps and you don't want them, you need to say it. There is a way to eliminate this according to the new standard. See the following tip:

http://www.tec-ease.com/tips/may-09.htm

It is a common misconception that the supplier "should know better" and all kinds of other nonsense like that but the bottom line is that one should apply tolerances (including "form" tolerances) based on a little forethought up front in order to get what you want.

There is a new symbol in the new standard that is for a Spotface. They had to do this in order to make a spotface mean something different than a counterbore because of a lawsuit that had to do with a supplier creating a spotface on a casting that wound up breaking through an o-ring groove and thus ruining the parts. The supplier wound up winning the lawsuit even though they probably should have known better than to break into the o-ring groove.

If you have no flatness callout less than .005 on your print, then you are probably going to have to buy those parts unless your supplier is willing to rework or remake them.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[ctopher]

You may also note a surface finish or roughness, or both.

Chris
SolidWorks 09, CATIA V5
ctopher's home (updated Aug 5, 2008)
SolidWorks Legion

 

[powerhound]

GSKMP,

Perhaps you could post a drawing of your part and allow us to offer some advice on how to correctly apply GD&T. It's possible there are other issues with the print that may rear their ugly heads the next time you have these parts made.

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[powerhound]

See p.162 at the end of para. 6.4.2.1.1 for an example of how to apply flatness on a unit basis per the 1994 standard. This will prevent your problem from happening again.

In case you were interested; by default, your flatness error could have been up to .015 and the part would still have been good and/or it could have been out of parallel by .015 and still been good UNLESS you had a parallel callout and a datum that it was tied to. Did you have any datum structure and GD&T applied to the part at all?

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[GSKMP]

I was just looking for an opportunity to hold the supplier accountable. Appears I am out of luck. I'll update this forty year old drawing to correct this and look at other potential issues. Thanks for your advice.

 

[fcsuper]

ASME Y14.5 and its predecessors were written to clear up issues like these. The standard was born out of a multitude of mid-20th century lawsuits.

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