GD&T Circularity Problem

[FirdausAhmad]

Hi all,
i have 1 inquiries regarding circularity tolerance.
Let me provide an example
i have a ring part (PP Material) with diameter of 10+/-1mm
which mean the range of diameter is 9mm to 11mm.
this part undergoes additional process (involving heat),
and this part will be deform (not expand), and be sort of oval shape,
if i control the circularity after process by 0.5mm,
regardless after process diameter,
from my understanding, 0.5 in form tolerance representing the control range,
by right, if after process it will deform by 0.5mm (justify with circularity), regardless final diameter, it would be max 12mm diameter,

but i have another thought,the maximum diameter would be only 11.5, as the range 0.5 upper limit would be only 0.25
because for a ring shape, there should have a compression on other side, to allow for expansion on another side.
i assume 0.25max compression to allow for max expansion 0.25mm.

is there any rule in any standard explain about this case & situation?

Thank you in advance.

 

[drawoh]

FirdausAhmad,

I am familiar with ASME's (geometric) Dimensioning and Tolerancing standard, and I am looking at my copy of the ASME[ ]Y14.5[‑]2009.

The general concept of drafting to the ASME standards is that you call up what you want, and you inspect whatever somebody makes for you. If you are not doing the fabrication, you have no interest in the intermediate forms.

The circularity tolerance imposes a form control on top of the feature of size tolerance. A tolerance of [⌀]10[±]1mm imposes circularity of 1mm. Refer to paragraph 5.3.3, and Figures[ ]5[‑]10 and[ ]5[‑]11 in the standard. If a compliant part has a specified circularity error of 0.5mm, and a maximum diameter measurement of 11mm, the minimum diameter measurement must be 10mm.

In ASME[ ]Y14.5[‑]2018, see paragraph[ ]8.4.3, and Figures[ ]8[‑]10 and[ ]8[‑]11.

If you are fabricating this thing and you anticipate circularity errors, you should fabricate as closely as possible to the nominal diameter. That way, your process errors will not take you out of specification.


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JHG