Dimensioning an elliptical hole 2

[bbrown611]

Hello,
I'm detailing a drawing that has an elliptcal mounting hole on a bracket. I'm not sure what method of dimensioning would work best.

I thought of locating the center with basic dimensions, definining the feature of size by minor and major diameters with a position callout.

My other idea is to use profile of a surface.

Are any of these options acceptable or is something better I should consider.

Thanks in advance,
Bill

 

[ewh]

I would dimension it as a circle at an angle to the surface.

 

[bbrown611]

Thanks for the reply ewh.
That may work, but I would like to describe my situation a little better in case I'm painting the wrong picture.

This mounting hole is normal to surface, but has the profile of an ellipse. I believe the intent of the design was to create a 2-way locator, but I don't know why an elliptical shape was used instead of a traditional slot.

 

[ewh]

As long as the path of the cutout is clear, I would still dimension it as a diameter, simply because the definition of the elipse is based on the circle. Maybe if you used a section view to ensure that the intent is clear.

 

[TheTick]

If it is a true ellipse, then it has a center which can be used for position. Major and minor diameters (and angle if not squared with view) fully define size and shape. Perhaps add a note that says the profile is indeed elliptical.

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[bbrown611]

Thanks ewh and Tick for the replies! I going to dimension the major and minor diameters and throw in a section just to ensure the intent is clear.

Regards,
Bill

 

[KENAT]

Had one a while back. Just found the drawing and...

Dimensioned the Major & Minor 'radius' (basic)

Dimensioned to the center (basic)

Used Profile of a surface.

Had a callout to the Ellipse saying "Ellipse" which the FCF was attatched to.

Can't claim credit for it though, my checker had marked up the print.

To my mind just giving positional for location and the minor and major and not using a profile you're not really fully defining the feature but I may be wrong. Even adding the note 'ellipse' you're still not really fully defining the tolerance all around without some kind of profile.

 

[Kwan]

All you need to define an ellipse is the location, major radius (r1) and minor radius (r2). The formula for the ellipse is:

x^2/r1^2 + y^2/r2^2 = 1

So providing the major/minor diameters and the location is enough for the machinist. I'd also say ellipse in a note to decrease confusion.

 

[KENAT]

By not defining the feature I meant defining the tolerance on the feature, sorry should have been clearer.

The block tolerance (or tolerance on the dimension) may apply at the max & minor but what about the points in between?

To back this up, on older similar parts the ellipse just had a +- tol on the major and minor dimension. When we put a profile tol of roughly equivalent value on the feature the vendor complained they couldn't meet it. Basically from what we could gather before they were only inspecting the max and min dimensions, not checking the form all around the ellipse.