Straightness of a Hexogon C/S shaft

[Madhu454]

Hi All,

Just curious to know, what are all the ways to control the straightness of the center line of a hexgonal shaft. bacause there are 3 opposed faces. Does the staightness to be applied for the mid plane of all the 3 set of opposed faces?

 

[MikeHalloran]

There are zero ways to control, or to measure, the straightness of a center line, since center lines do not have a physical manifestation.




Mike Halloran
Pembroke Pines, FL, USA

 

[pmarc]

Madhu,
First of all Y14.5-2009 has introduced flatness of median plane of features of size containing two parallel planes and this is the concept you should go for. I would not use straightness of median line in this case and keep it rather for cylindrical features.

Since hexagonal feature is a set of 3 pairs of opposite planes, you could specify 3 times flatness FCF of median plane derived from each pair of planes.

And I would not say there are zero ways to control this. If the flatness FCF contains (M) modifier after tolerance value you can check with a hard gage that no portion of each pair of planes violates virtual condition boundary. Of course this would not give you the actual value of flatness devation, but would tell if the flatness is within the limit.

Things would get more complicated if flatness at RFS basis is specified.

 

[fsincox]

Mike,
While I may have to agree there is no direct way to measure it. It seems there are other measurements that have to be derived and can not be measured directly. How do I really find the center of a hole? I would hate to see this become the sole criteria.
One of the problems I have with runout is it is just an inspection method, is the part out of round or eccentric? As an engineer I would like to know.
Frank

 

[Belanger]

The old standby is always profile of a surface...

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