Applying Cylindricity to threded Features

[Madhu454]

Hi All,

I saw a drawing where the cylindricity has been applied to the minor dia of an external thread. Is this is legal specification?

Does really cylindricity is required for the threaded feature in real applications? I have heard that cylindricity is a very stringent requirement and should be specified only if it is required.

My doubt is can we apply cylindricity to threded feature.

Can any one help me in this regard.

 

[drawoh]

Madhu454,

The thread specification controls cylindricity, or some equivalent to it. My assumption would be that for some reason, there is a requirement for cylindricity on the minor diameter that is tighter than what would be imposed by the screw thread specification.

If the cylindricity is looser than the thread specification, then the thread specification controls the feature, and cylindricity is redundant.

JHG

 

[powerhound]

I would tend to think that the person specifying this is trying to achieve something that is better specified a different way. Checking the true cylindricity of the minor diameter of external threads seems an impossible task without ultra-specialized equipment or a very time consuming process on standard equipment. Might the person actually be trying to control the straightness of the threaded feature?

Powerhound, GDTP T-0419
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[dingy2]

I agree with powerhound on this one. Cylindricity of a minor diameter just doesn't make sense and I would question the ability to measure it appropriately.

If it is straightness that is required, then straightness at MMC and place "MAJOR" below the feature control frame. Now it can be confirmed with a checking fixture quite simply.

Dave D.

http://www.qmsi.ca

 

[MechNorth]

male thread at minor diameter has no functional reason to control the cylindricity. It's a bad call. female thread, on the other hand, sort of makes sense if an RFS/RMB pin is going to be used to determine the AME.

Jim Sykes, P.Eng, GDTP-S
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