Flatness control
Flatness control
(OP)
After reading several threads, flatness doesnt count on stacks unless leakage is of concern. Alex K. workbook does count it, see attached. The second stack shows a flatness 0.6 which makes me more confused. In my case, i am looking for the gap on top of the assembly far away from the flatness of the bottom washers. Do i care for flatness?
How about concentricity control? not most suitable but it appears in one of our drawing. I suppose it gets treated like position since is a location control.
thanks
How about concentricity control? not most suitable but it appears in one of our drawing. I suppose it gets treated like position since is a location control.
thanks





RE: Flatness control
In exercise 14-4, the value of 0.6 for distance A comes from the maximum flatness error allowed by the 10.6 - 10.0 size tolerance on the base plate.
In general, flatness errors in stacked components can allow them to overlap a bit. How you account for this depends on the tolerance schemes of the individual components.
As for concentricity, the answer again depends on the details of your application.
pylfrm
RE: Flatness control
And since the datum is formed from the highest points, the flatness error is only felt in the min direction.
If the thickness dim of 2.5 were not basic, but toleranced directly, then the flatness would not be considered in the stack.
In Exercise 14-4, the reason flatness is included is that the dim of 14.0-14.2 is not considered a feature of size, so Rule #1 doesn't apply. Any bumpiness on the table will indeed affect the unknown dim X. In the textbooks this is what they call an "offset" condition, where the stack is being done away from (offset from) the location where the parts actually touch. The flatness error shows up in both columns because the bumps could go down or up from the mating plane.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Flatness control
For stack 1, why is flatness applied at the min. wall thickness?
RE: Flatness control
J-P,
For fig. 14-4 then why 0.1 flatness is not included for the maximum X (14.8 maximum)?
I did not understand this fact. I am missing something, but I don't know what.
Thank you J-P.
RE: Flatness control
In my previous post I should have clarified that the "flatness" I was speaking of comes from the table (from its size tolerance). The actual flatness symbol on the flange and its 0.1 tolerance is ignored because of what I just mentioned -- only high point contact.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Flatness control
RE: Flatness control
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Flatness control
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future
RE: Flatness control
Apologies if you're referring to something else; I didn't see any mention of an envelope in the discussion so I'm not sure what you mean.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Flatness control
I saw you responding to allben's post about dimensions being "measured from the highest points (and not from the lowest ones)", so I wanted to remind that envelope requirement was not in play.
Sorry if it was confusing.
"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future