Cast Part with a Flat Base Tolerancing help

M

Mezzaluna

#1
Hi everyone!
I have a question regarding tolerancing - don't know if this is the right place for it, but here goes:
I have a drawing of a cast part with a flat base. this base has a flatness of 0.5mm applied, and is a datum face: A
In the middle of the part is a boss with a shoulder. This shoulder has a parallelism tolerance on it: "0.2mm //" to datum A.
Question: is this a contradiction? if A is allowed to be 0.5mm out of flat, can we still specifiy the "0.2mm // A" for the shoulder? I can't make my mind up.
Can someone help?
 
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Stijloor

Staff member
Super Moderator
#2
Re: Tloeranceing help required

Hi everyone!
I have a question regarding tolerancing - don't know if this is the right place for it, but here goes:
I have a drawing of a cast part with a flat base. this base has a flatness of 0.5mm applied, and is a datum face: A
In the middle of the part is a boss with a shoulder. This shoulder has a parallelism tolerance on it: "0.2mm //" to datum A.
Question: is this a contradiction? if A is allowed to be 0.5mm out of flat, can we still specifiy the "0.2mm // A" for the shoulder? I can't make my mind up.
Can someone help?
Hello Mezzaluna,

The paralellism of the shoulder can still be specified at 0.2 mm.

The relationship with datum feature "A" is to the "true geometric counterpart" of datum feature "A". That is the imaginary plane between the datum feature and a simulator such as a surface plate or probe movements on a CMM.

So the datum feature can still be "wavy" within 0.5 mm and still be utilized as a datum feature.

Also see this interesting thread; "GD&T Parallelism Interpretation."

Hope this helps a little.

Stijloor.
 
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D

David DeLong

#3
Re: Tloeranceing help required

I agree with Stijloor.

Datum A qualified with a flatness tolerance of 0.5 mm. Once it meets that requirement, one must assume that the surface is perfect. You now have datum A.

A parallelism tolerance of 0.2 to datum A is OK and quite legal.
 
M

Mezzaluna

#4
Re: Tolerancing help required

:thanx:
Thanks guys - I thought as much but I had has this questioned. Here's another one if you would be so kind...the drawing has specified the 0.2mm as below:
[//][ 0.2 (S in a circle in the style of maximum metal)][A]

I've never seen an "S in a circle" symbol before - can you offer any explanation?

Cheers again,

Mezz.
 

Stijloor

Staff member
Super Moderator
#5
Re: Tolerancing help required

:thanx:
Thanks guys - I thought as much but I had has this questioned. Here's another one if you would be so kind...the drawing has specified the 0.2mm as below:
[//][ 0.2 (S in a circle in the style of maximum metal)][A]

I've never seen an "S in a circle" symbol before - can you offer any explanation?

Cheers again,

Mezz.
"S" in a circle means RFS (Regardless of Feature Size). It is an older symbol that is not used in the ASME Y14.5M-1994 Standard anymore. It means that the stated tolerance requirement must be complied with regardless the size of the controlled feature. No bonus tolerance permitted.

Stijloor.
 
M

Mezzaluna

#6
Re: Tolerancing help required

"S" in a circle means RFS (Regardless of Feature Size). It is an older symbol that is not used in the ASME Y14.5M-1994 Standard anymore. It means that the stated tolerance requirement must be complied with regardless the size of the controlled feature. No bonus tolerance permitted.

Stijloor.
Thanks Stijloor.
If is symbol is not used in the ASME Y14.5M-1994 Standard, what would be the current controls?

Cheers,

Mezz.
 

Jim Wynne

Staff member
Admin
#7
Re: Tolerancing help required

Thanks Stijloor.
If is symbol is not used in the ASME Y14.5M-1994 Standard, what would be the current controls?

Cheers,

Mezz.
In the absence of a modifier, RFS is assumed.

Added in Edit: Rather than using "assumed," I should have said that in the absence of a modifier, RFS is the default requirement.
 
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