GD&T Interpretation - Length of cylindrical feature & end surface form

[sombreroB]

Hi,

I have a question regarding interpretation of the drawing below. I understand that this is a basic question, but I have so far had little experience with GD&T...

My uncertainty concerns the way in which the form of the end surfaces and length are controlled.

My best interpretation is that length dimension is applied with rule #1 and so the end surfaces must sit within two pairs of planes separated by 76.00 and 75.90 mm. Additionally, these surfaces must be perpendicular w.r.t the A datum. I have drawn what I think this amounts to. Am I missing something? Or is the drawing ill defined?

Any help would be greatly appreciated.

sombreroB

 

[greenimi]

What standard are you using?

I assume ASME because of the 3rd angle projection, but that is not a vital factor.

Please advice.

IF ASME Y14.5, I think you are correct here: " so the end surfaces must sit within two pairs of planes separated by 76.00 "

but not here: " so the end surfaces must sit within two pairs of planes separated by 75.90 mm"

I haven't looked in details, I might be wrong.

 

[SeasonLee]

The difference of overall length 0.10 could be happened on either side, that means there will be a 0.10 perpendicularity error wrt datum feature A on either side, but the designer want a small tolerance zone, so perpendicularity of 0.05 is a refinement of 0.10 error.

The other two geometric callouts(position and runout callout) are all coaxial control wrt datum feature A.

Season

 

[sombreroB]

I believe the drawing is to ASME Y14.5-2009, but I must admit to being unable to distinguish between different versions.

Thanks for your comments thus far. I have another question if I may.

The depth of the hole on the left hand side is directly dimensioned. Is this correct? My understanding is that only features of size can be dimensioned in this way, but this is not a feature of size. Have I misunderstood?

 

[3DDave]

If the drawing is compliant with the standard the exact version will be on the drawing. If it isn't compliant then that makes things more difficult.

 

[greenimi]

The depth of the hole on the left hand side is directly dimensioned. Is this correct? My understanding is that only features of size can be dimensioned in this way, but this is not a feature of size

In theory you are correct, but in that case why you don't say anything about the countersunk holes (a cone is not a FOS either -feature of size--in ASME) or what about the chamfer on the right side (same as the cone: NOT a FOS)

So, depends how anal (read meticulous) you want to be.

 

[Belanger]

The depth of the hole on the left hand side is directly dimensioned. Is this correct? My understanding is that only features of size can be dimensioned in this way, but this is not a feature of size.

It is fine. There are many other things that can be dimensioned besides "features of size." Now, if you wanted to apply some sort of GD&T to that depth, then we'd get into the distinction of a feature of size.

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