KCC of Cylindricity Vs Straightness and Circularity

[Go_Bucks]

Hello,

The company's global team for a product family is calling out cylindricity as a KCC moving forward. Due to supplier relations/history on these products for our specific plant, we will be using straightness and circularity as KCCs. What are everyone's thoughts on this? Are we losing any control over the product by doing this?

Thanks.

 

[Belanger]

Converting cylindricity to a combination of straightness and circularity still leaves open the possibility of taper. Realize that cylindricity limits the taper (parallelism, so to speak), which is lost if you go with straightness and circularity.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[CheckerHater]

Total runout?

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

 

[drawoh]

Go_Bucks,

What is wrong with cylindricity?

--
JHG

 

[Go_Bucks]

@drawoh, for the record I would prefer cylindricity. The way it was described to me, our suppliers have been using straightness and circularity for so long it was "easier" to not change it and just add the KCCs to it to the current spec. I don't fully understand the reasoning, but I like to think there is logic behind it.

 

[drawoh]

Go_Bucks,

You need to specify what you want. You don't care how they do it. If they inspect for straightness and circularity and ship you good parts, everything is fine. If you inspect and find they are not cylindrical, you send the parts back, and they review their procedure.

I have never specified cylindricity. It implies to me that you need the part to be round and straight, but that you can tolerate a lot of diameter error.

--
JHG

 

[3DDave]

You can tell if it's important by looking at the sensitivity analysis for the function of the feature and any interactions with other parts. It's probably going to be in the stress analysis for the system, but there may be something in the performance analysis.