Indicating allowable taper 1

[dgallup]

I have a part with a cylindrical portion that has to be closely controlled. Within the size tolerance I can allow a small amount on taper in one direction but it is detrimental if it tapers in the opposite direction. Cylindricity would cover it if I could allow taper in either direction. I don't see how I can use profile or any other gtol but perhaps I'm missing something. I plan to use a note but how to unambiguously express the allowable direction of taper has me puzzled.

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[MintJulep]

There is a "Conical Taper" control - although I've never seen it used.

 

[pmarc]

If this was plastic molded, casted, or forged part, there would be a solution. Paragraph 3.6.1 of Y14.8-2009 specifies some interesting methods.
For other type of parts (machinings for instance) I am searching in my GD&T Toolbox and see only an additional well-thought-out note.

 

[dgallup]

It is a machined part. What I have so far are two basic lengths to measure the diameter and a note saying that the diameter at the second point must not be less than the diameter at the first point. It's a fairly short cylinder so I think that is sufficient along with the diameter tolerance.

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[pmarc]

I would say this is insufficient condition, at least from geometrical point of view. If the actual smaller diameter is not concentric with the actual larger one, you may end up with a cylinder having different orientation of tapers on its both sides (if you are looking at the cylinder from the view where it is nominally a rectangle), yet satisfying your note. In my opinion something additional is needed if you want to be fully covered.

 

[CheckerHater]

Dgallup,

You may try to control straightness of the surface to make sure your cylinder isn’t barrel- or saddle-like.
What will it add to complexity and cost of quality control is another question, as you said the cylinder is really small.

Pmarc,

In my opinion, from geometry point of view, even with diameters being non- concentric, as long as rectangle looks like a trapezoid, you can say part has a taper

 

[pmarc]

CH,
But what if the rectangle does not look like trapezoid?

http://files.engineering.com/getfile.aspx?folder=56b4e405-6db5-4759-a449-deada68f470c&file=taper.png

 

[CheckerHater]

It still a trapezoid and it still has taper.

On the second thought, words "trapezoid" and "trapeze" have opposite meaning in US and UK.

Maybe your geometry is different from my geometry as well

 

[pmarc]

But I think you will agree that my picture is showing what dgallup wants to avoid. Regardless of how we call the figure, it meets his note, however does not satisfy functional requirement.

 

[CheckerHater]

I am not sure.
If it falls within dimensional envelope, and taper is pointing in right direction, maybe it’s a good part.
I’ve got the impression that dgallup is more concern with how the taper behaves between the diameters, than concentricity of the diameters themselves.
ASME allows to specify position of both ends of cylinder separately; if we hold one end tighter, this may help.

 

[pmarc]

CH, my point is exactly about surface behavior between diameters.

 

[dgallup]

I'm not concerned about concentricity of elements along the cylinder as it is all machined in one pass with one tool and one chucking. In the past we only had a diameter tolerance, which the parts met. However, we have found when the cylinder tapers in one direction it can lead to some assembly issues that don't happen if the taper is in the other direction. We are talking about less than a .001" of taper.

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[MikeHalloran]

If the part geometry allows rolling the coned surface on a surface plate, you could specify in which direction it should yaw while rolling. You could even specify a radius if you like.



Mike Halloran
Pembroke Pines, FL, USA

 

[dgallup]

Interesting idea.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[MintJulep]

I'm surprised that none of the GD&T experts have an "official" solution.

I think the simplest and clearest was would be a couple of sketches as a note on the drawing.

Nominal geometry in solid lines. Exaggerated taper as a dashed line.

Two sketches. One showing acceptable taper with "Taper in this direction is acceptable" The second showing not acceptable taper with "Taper in this direction rejected".

 

[CheckerHater]

Why not just say that taper is REQUIRED?
Specify BASIC taper of .001 and apply profile to the surface?