GD&T Flatness question

[Martin_K]

I want to put a flatness requirement on a circular plate, see attached picture. I want to have for example 0,5 as a general flatness for the complete surface but in tangential direction it must not be more than 0,2 per 200mm. I am fine with it being conical up to 0,5 though. I've been looking into the standard (ISO-1101) but it is not clear to me how to do this. There are ways of specifying a part of the surface but as far as I understand it does not take tangential versus radial in consideration.

Any suggestions? Thanks.

 

[3DDave]

Profile of Line would seem more appropriate - apply to "EACH CIRCULAR ELEMENT" and use the nominally flat face as primary and one of the diameters as secondary. Using the same references, apply Profile of Line to "EACH RADIAL ELEMENT" to control that direction. You could add a 0,2 per 200mm to the circular element control.

 

[Martin_K]

Thanks for the answer

Do you mean something like this? (see attachment). I would for the circular element have liked to write it as "0.5 / 0.2/200" but that looks a bit messy....?

 

[Martin_K]

Or like this, looks a bit more clean?

 

[3DDave]

Is that the symbol for Straightness? Should be an arc for Profile of Line.

 

[Martin_K]

Ops! Of course, sorry! It's Friday, apparently I have already checked out :-D

 

[greenimi]

Profile of a line is the camel hump symbol. What you have in your latest figure is straightness
And maybe the upper "straightness" should be changed with flatness within 0.5 (with no datums)
Keeping only the lower callout as profile of a line (with datums)

 

[Martin_K]

Yes, I accidently picked the wrong symbol

Ah, yes, ok. What do you think about this? A general flatness for the whole surface and then profile of line for each 200mm of each circular element.

 

[Martin_K]

Forgot the datums and could not edit the link

 

[3DDave]

I would use an unequal zone to push all the profile variation to the material side of the datum and/or indicate that the planar surface is for orientation only. I know there are ISO modifiers to do that, but haven't used it enough to recall the specific method.

 

[jonathan8388]

Couldn't circular runout also be adapted here instead of line profile?

 

[Martin_K]

Thanks everyone the answers

An axial Circular runout, yes, that could also work I think?

3DDave, I am not sure I follow, if you have the time to make a quick sketch I am interested.

 

[3DDave]

https://www.youtube.com/watch?v=B_jIvaEnMjw

The default is to split the variation allowed to both sides of the nominal surface, but the use of the surface as the datum feature places half the zone on the other side and is inaccessible. Making it unequal allows for all the acceptable variation to be on a single side of the datum feature.

 

[Martin_K]

Hmm....ok....yes I was aware of the offset tolerance thing but I have never used it. I think I need to digest it a little more before I dare use it on a drawing since I have to explain it later to the people that will manufacture the component :-D

Thanks

 

[3DDave]

Isn't that the amazing thing about a standard? It means having to still tell people what you want while pointing at symbols they don't understand, cutting out nothing from before there were standards.

 

[Martin_K]

Haha! :-D