GD&T Callout for Twist of Hole Pattern in Extruded Tubing

[jpw76]

I need assistance clearly defining the allowable "twist" of a 3-lumen extruded tube. The extrusion has three holes that run the length of the part, and the twist of the part (e.g. hole pattern rotation from one end to the other) may not exceed +/-15deg over the length. It's almost like defining the allowable rotation of the "pattern" of holes from one end to the other.

It seems as though using the tube end face as datum A, hole #1 as datum B, and then assigning positional tolerance to hole #2 relative to datum A &B would get me closer to locking down the pattern, but I'm a little stumped on this one. Thanks!

 

[drawoh]

jpw76,

I do not believe there is a standard under ASME Y14.5 that allows you to specify twist.

I assume that what you want is for everything to be straight, and that you are anticipating that the error will be a twist.

If this were my problem, I would select a datum face, and specify its flatness, probably on a per-unit basis. I would specify everything else as parallel to this. Actually, I don't think you care what form the error is in.

JHG

 

[pmarc]

jpw76,
Are you able to post a rough sketch of the part you are talking about? I think I visualize the case but I am not 100% sure.

 

[jpw76]

Hi pmarc & drawoh--

Thanks for your responses. Please see attached for a rough hand-sketch of the part. I'm trying to come up with a more elegant solution for defining the allowable twist or rotation of the tube from one end to the other; specifically, the rotation of the pattern of holes. Is there a better way to specify this other than in the drawing notes (e.g. twist per tube length not to exceed +/-15deg)?

Thanks again for your thoughts. . .

--Josh

 

[pmarc]

jpw76,

The only method that comes to my mind which is clearly described by Y14.5 standard is to use concept shown in fig. 7-27 in 2009 edition or 5-40 in 1994 edition, so to define different positional tolerances at both sides of the tube.

 

[fsincox]

I think you may be in: "say it with a note" territory. The standards are there to commonize meanings and give basic definition to common symbols. There is nothing to say that all things are covered.
Frank