Profile -Chained Dimensions- Stack up 5

[ImnotfromMars]

If I have several chained dimensions, each defined with a basic dimension and a profile tolerance. Is the last dimension cumulative (sum of the basic dimensions + the worst case profiles) or can I just add all the basic dimensions in the chain and apply the profile once to the last edge?
Robert

 

[Belanger]

It depends on the datums used. I suspect that it's not cumulative (it only would be if the datums referenced are different). Can you post a picture?

John-Paul Belanger
Certified Sr. GD&T Professional

http://www.gdtseminars.com

 

[KENAT]

Generally non cumulative as Belanger says, unless I suppose you have some datum shift or something going on.

Fundamentally, basic dimensions are non cumulative, since the tolerance isn't on the dimension but on the feature itself.

Posting guidelines faq731-376

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

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[drawoh]

ImnotfromMars,

Your profile tolerances are with respect to the datums, not the previous dimensions. Unless you are doing something very weird with your datums, the tolerances are not cumulative.

JHG

 

[ImnotfromMars]

The part is similar to an electrical box, with several slots. Each slot was dimensioned with a basic dimension from the previous slot. Each surface was toleranced only with a profile tolerance. When the part was finished the last slot was considerably off. The person making the part measured each new slot from the previous in lieu of summing the basic dimensions.

 

[KENAT]

So they measured it wrong then by the sounds of it.

When measured correctly did it pass inspection?

Posting guidelines faq731-376

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

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[dingy2]

Chain dimensions are theoretical and tolerances are non-accumulative.

Dave D.

http://www.qmsi.ca

 

[ewh]

If the last slot was located from the previous slot only, then it is not suprising that it is off. The basic dimensions define each position as non-cumulative and they all should be located from the datum(s), not the adjacent feature (barring some datum changes as mentioned before).

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

 

[ImnotfromMars]

Thank you for your input. Yes the feature should have located from a common datum and not the previous feature.
Thank you for your assistance with this.