value tolerance of flatness

[nnz]

Good afternoon,
I ask your attention to my doubt about the values to be attributed to geometric tolerances.
I understand the concept of defining dimensional tolerances according to the function that the coupling itself requires.
It is also clear to me that geometric tolerance is in fact a refinement of dimensional tolerance, which entrusts the designer with greater control over the features. It is not clear how to define the value numerically.

for simplicity we suppose to have a bracket to have to rest on a base. the support surface of the bracket on the base directs the bracket in the space and is therefore nominated to identify the primary datum a. being non-referentiable is no longer to be tolerated in form. I would apply to this datum a tolerance of flatness. How do I determine the value? Why 0.1 or 0.2? based on what considerations?

Thank you in advance.

 

[wert]

there are different conditions that determine the value of geometric tolerances. It is known that the designer would tend to consider each pair as precisely as possible but this meets the costs of the project. the norm en 22768-2 should guide you in identifying, because it takes into account the size of the particular while you have to know which degree of accuracy you can get with a given process (but this is easy enough to find). Then there are rules dedicated to fused artefacts, die-casts, etc. but I think this is not the case.

 

[nnz]

My speech is a general speech and clearly came out the norm uni en 22768-2 which as well known if recalled in the cartilage automatically defines the standard for the geometries represented. I wondered, however, how to specify a value different from the standard.
Thank you.

 

[wert]

My speech is a general speech and clearly came out the norm uni en 22768-2 which as well known if recalled in the cartilage automatically defines the standard for the geometries represented. I wondered, however, how to specify a value different from the standard.
Thank you.

depends on the machine you need to design. . If you need to realize the grinding wheel trolley, you will need to consider the maximum possible accuracy (but you cannot ignore the size of the detail), while if you are planning a base of an automatic carpentry machine, you will need to consider greater tolerances. everything depends on how much you can afford to spend; sometimes systems that compensate for physiological errors for the various types of process are adopted. to have an indication, you can empirically consider a value between 30 and 50% of what is indicated by general tolerances.

 

[biz]

is based on experience, then you do analysis helping, as well as of course with spreadsheets, even with software as This is. inventor and solidworks have computing tools that guide you into making conscious decisions. for bearing seats, for example, there are guidelines.

 

[nnz]

After performing an assembly analysis, the only analysis that comes to mind is stack-up in axieme context. therefore after a first attempt value (derived from uni en 22768-2 to 30/50%, as well as suggested by @wert ) I imagine changing it for dimensional needs. Although I have read somewhere that geometric tolerances are generally overlooked in stack-up phase. but I don't see any other way to define a numerical value.

 

[biz]

qui you make an overview of the tolerance calculation process