Is the profile tolerance on my cone fully defined?

[rfkflf]

Hi All,

Having this debate at work. We use ISO GPS (BS 8888) but happy to hear how it applies to ASME Y14.5, I am sure it's not that different.

Problem:

How to fully define the profile/surface tolerance of a cone? As you can see from the image attached (apologies for using paint), I am trying to define a cone relative to datums A and B (a third datum would be pointless here as it is a revolved feature).

The shaft it sits at the tip of needs to be a linear dimension since it is defined as a shaft fit tol.

Are the two basic dimensions enough to define the cone? I feel like to locate the idealised cone from which to generate the surf. tol. you would require a basic dimension on the shaft as well. Otherwise the angle and offset from datum A can still be respected but the diameter of the cone be miles out. But i already defined the shaft diameter, just not with a basic/TED dim.

Do i need to dimension the shaft twice in my drawing, one TED and one linear? Fig. 8-18 on ASME Y14.5 seems to imply that you do not but its not super clear.

Thank you in advance.

 

[greenimi]

I think is IF you add a basic distance on the angular surface /conical feature and then add its coresponding its basic diameter THEN you would have a robust cone definition.
So, at basic distance is this/indicated basic diameter (again somewhere on the conical feature)

 

[SDETERS]

I would suggest not measuring to an edge of the taper. If that taper is ground, that edge is not very robust to measure to. I would suggest using Gage dimensions to control the diameter and size of taper

 

[Burunduk]

For the purposes of TED/Basic definition of the conical surface (to provide the basis for the profile of a surface tol. zone), you can either dimension a basic diameter on the cone on some basic "gage line" distance from datum A, or just give a basic distance from datum A to the cone's apex point. In either case do not dimension to the intersection edge with the +/- shaft diameter.

 

[rfkflf]

Thank you for the replies.

Burunduk: so are you saying to dimension the cone base twice? one TED and one linear? I ended up dimensioning to the apex of the cone.

But the question still stands if "legally" i can dimension twice in these kinds of situations. Although i dont have another example in mind it does happen when mixing GD&T with linear dims.

Regarding no dimensioning to the intersection edge. It is functional in my case and we are able to inspect it, so that has to stay.

SDETERS: I am not sure i understand the meaning of "gauge" dimensions.

 

[Burunduk]

rfkflf,
When I said you can "dimension a basic diameter on the cone on some basic "gage line" distance from datum A" I meant some intermediate diameter on the conical surface, somewhere between the apex and the cylindrical shaft. The location of the section of that size would be set by a basic dimension from datum A. Don't re-dimension a directly toleranced diameter by a basic diameter.

A basic dimension from datum A to the apex of the cone (as you say you did) achieves the same, so it's a matter of convenience how you give the basic dimensions to fully define the nominal cone.

 

[rfkflf]

Burunduk,

Ok thank you! I'll use the gauge line idea just because it feels wrong to dimension twice. Although technically I still feel it is correct to have a TED and a linear dimension because they are being used for separate requirements and in the end both requirements need to pass for the part to be good.

 

[Burunduk]

You say that it feels wrong to you to dimension twice, AND you feel it is correct at the same time. I understand about the different purposes, yet for me it feels more wrong than right.