flatness of a conical surface

[djhurayt]

A vendor has suggested that we use a flatness straightness (I don't know which one of these voices in my head was thinking flatness, I'll get on him about that if I every find out who it was ) call out as shown. I'm not sure I fully understand what this is really accomplishing but even more so:

How the heck do you measure/evaluate this characteristic?

This device is basically a check valve that only allows fluid past it from the right as a force pushing the ball to the conic surface is reduced.

 

[powerhound]

That's not flatness, it's straightness.

Each element along the conical surface has to be straight within the tolerance shown.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[djhurayt]

Thanks ph, I correct my OP.

This surface is created via a grinding wheel moving perpendicular into the surface while the part is turning about its axis. Under this process I would think that one swipe of a profilometer tip over the surface would qualify this characteristic. maybe / maybe not

Should this callout be specified at "X" places around the surface. ???
Or how is this normally handled?

FWIW: a thorough understanding (as in able to argue subject matter) of GD&T is not one of my strongest skills

 

[SwinnyGG]

If you wanted to actually gauge the whole surface, you'd need to measure every local line on the surface at 3 points- so three circles with your profilometer.

 

[tbuelna]

Since your objective is to achieve precise contact between the ball and seat surface at the prescribed location, you probably should be more specific defining characteristics like waviness, ovality, surface texture, etc. right at the local contact interface. And relax the tolerance requirements away from this location. For example, the .002 circularity profile tolerance specified at the gauge diameter would not seem to provide the sealing quality required for a fluid check valve.

 

[chez311]

you probably should be more specific defining characteristics like waviness, ovality, surface texture, etc. right at the local contact interface. And relax the tolerance requirements away from this location. For example, the .002 circularity profile tolerance specified at the gauge diameter would not seem to provide the sealing quality required for a fluid check valve.

If you wanted to control ovality, a circularity callout would be one method to do that... profile and runout being others.