GD&T for plate segment

[kingsboy55]

Hi, I'm interested to know how others would dimension a plate segment, a segment of 100° in this case, in which the only important features are three mounting holes. The three holes mount to a duct flange to retain a flexible seal between the plate segment and the duct flange. The entire outside profile is unimportant, it's only there to put some meat round the holes! It was presented to me with the outside radius of the plate segment as datum B and the end of the plate (one of the surfaces at 50°) as a datum C with the three holes controlled to datums A, B and C.
We frequently get segmented plate issues and differences about how segments, particularly of <180° should be dimensioned.

 

[drawoh]

kingsboy55,

That looks good to me. If the hole pattern is important, it should be your secondary datum, as you have shown. You may want your profile to slop entirely inside. Read up on unilateral profiles.

--
JHG

 

[kingsboy55]

Thanks drawoh! I'll do that.

 

[Belanger]

But then you'd probably want to add a circled M (called MMB) after the datum B reference in your profile tolerance. This is because it's a datum taken from a pattern of holes.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[mkcski]

kingsboy55

I have a few suggestions:

The 25mm and 50mm BSC dims define the radius of the arcs for the inside and outside surfaces and controls the coaxial location of the two arcs relative to datum axis B(established the the pattern of three holes). Although not necessary I would add the BSC radii (or diameters) of the inside and outside arcs. This would speed interpretation and prevent some from having to calculate the arc dim (bolt circle) that that passes though the three using the coordinate dims between holes

You all need to control the rotation of the two 50mm wide "ends" relative to the three holes - datum axis B. You should add a BSC dim from the center of one "end" holes to the "end" of the part.

Certified Sr. GD&T Professional

 

[kingsboy55]

mkcski,
Thanks for your comments, I did actually later add a reference for the arc radius through the 3 holes though I didn't add inner and outer arc radii, I figure someone should be able to ±25mm from the hole arc.
The ends of the plate are 100° apart, controlled by all round profile tolerance, implied symmetrical to datum B which I believe controls their 'rotation'.

 

[mkcski]

My preference is to not imply anything if an adding an extra dim (or symbol) avoids confusion and non-productive time wasted getting the confusion resolved.

Certified Sr. GD&T Professional