Stack up with cones difficulty 1

[ImnotfromMars]

I am stacking up a series of axial dimensions and have encountered a difficulty. Any help would be appreciated.

There are two cones (inside and outside cone) of the same basic angle which will be assembled together. Each cone has a basic angle, and a basic dimension from a vertical face to a gauge point which is at the same nominal diameter on both cones. The gauge points have a toleranced diameter and a profile of a surface geometric tolerance. On one cone the profile tolerance exceeds the diameter tolerance and on the other it is within the diameter tolerance.

On an axial stack up should I include the form tolerance and the offset from the diameter tolerance or should I just include the offset from the diameter?

Robert

 

[MechNorth]

Robert, please post a graphic so we can be sure what you're looking at.
Tks
Jim

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[MikeHalloran]

Huh? Should gauge circles be toleranced?



Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

If I've understood correctly I'd include both for a true worst case.

Ken

 

[ctopher]

ImnotfromMars,
Can you show a pic?

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)

 

[ImnotfromMars]

Hello,

Thank you for the replies.

I made an error in the original description. It should read the surface on which the gauge points are attached have a profile tolerance.

I have sketched an example and posted it to filcker.

http://www.flickr.com/photos/33544050@N00/266445040/?rotated=1&cb=1160523866265

Robert

 

[KENAT]

Imnot,

I'm having trouble with the dimensioning scheme, I think you've double dimensioned the cone shape but haven't dimensioned the 'end' of the cone.

The 1.8/2.2 & 1.9-2.1 would appear to be controlling the same thing as the profile but with different tolerance.

However, it's late in the day and my brain quit working a while ago so someone please point out the error of my ways and give Imnot what he needs.

Ken

 

[ctopher]

I'm having trouble with the dimensioning scheme also.
If I were the machinist, I would be a little confused on what the dims were for at the point on the conical surface.
I would make them two separate parts. Then maybe cut one side to meet the overall dim X.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-06)

 

[MechNorth]

The assembly looks a lot like a conical taperlock, commonly used in molds. Let me preface the following comments by saying that I am basing my poste on ASME Y14.5M-1994.

The use of a surface profile for the conical surface combined with a BASIC diameter at a median point (think of it as a construction pivot point for the line representing the conical surface, or anticipated contact point such as the pitch-diameter of a thread) is ok. When I've seen this combo, the BASIC diameter was used to generate a datum.

An overriding problem is that you can only use linear tolerances on a Feature of Size, which requires two opposing points. Unfortunately, a conical surface does not have opposing points. So, the toleranced diameters in the middle of the cone are incorrect and completely unverifiable by definition (some will argue that you can measure across a male taper, but only with vision systems, not with contact measurement). Similarly, the toleranced diameter at the opening of the female cone is not a Feature of Size, so you can't tolerance it that way. The toleranced diameter on the outside of the male part is, of course, fine.

Now, throwing away the above points, here are some other considerations;
- the toleranced diameter does not have a positional tolerance, so it could shift entirely to one side or the other without penalty...typically not what you're looking for.
- the surface profile locates the conical surface wrt Datums A and B.
- If you sketch the tolerance zones that you propose, you'll find that the toleranced diameter on the female part reduces the tolerance zone of the surface profile by .024" diametrally, assuming it is centered on Datum-B. On the other hand, the toleranced diameter on the male part results in a tolerance zone that exceeds that of the surface profile by .061" diametrally... therefore the surface profile overrides the diametral tolerance making the diameter tolerance irrelevant.


Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca

 

[ImnotfromMars]

Thank you for all the replies and the assistance with this.

If I understand correctly from MechNorth "On the other hand, the toleranced diameter on the male part results in a tolerance zone that exceeds that of the surface profile by .061" diametrally... therefore the surface profile overrides the diametral tolerance making the diameter tolerance irrelevant".

Then a measured diameter of 2.2" at the gauge point on the male part (assuming the gauge dia is to -A- and -B- )would result in a unacceptable (scrap) part.

Robert

 

[MechNorth]

That is correct, the 2.2"-dia would be outside of the tolerance zone defined by the surface profile, and therefore unacceptable.

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

http://www.profileservices.ca