drawoh,
Coplanar is a more rigid control than parallelism. Not only do all the features must be parallel but they must also lay in the same plane. Think of coplanar is a flatness control of multiple features. Check out pages 171 & 172 of the ASME Y14.5M-1994. Notice the profile is not aligned to...
Flatness is a low level control which can only be applied to a single feature. Parallel is mid level orientation and form control which must be aligned to a datum. Profile is the top of food chain which can control form, orientation and location. For multiple features that are coplanar it's the...
I guess the simple answer is the LMC virtual condtion boundary isn't for fits. If I remember correctly it's just to ensure the wall thickness values don't exceed a worst case minimum. You should use only it for that purpose.
Profile is the highest level defining control that exists. It can control location, orientation and form. Figure 6-18 just illustrates one of the special derivations of profile which is used in this case to control only orientation and form and not location. It can be used to control just the...
Profile is only used in conjunction with basic dimensions. Locating surfaces using +/- tolerances are subject to Rule #1 in the USA. Rule #1 called the Taylor Principle states that size at the Maximum Material Condition also controls the form. That's okay for simple relationships as long as an...
You can do do it that way but does it best imply what the function of this part actually does? What is the function of this is part?
Using a pattern of holes seems like a smart thing to do however it has some luggage which might make it not as desirable as the alternative. By declaring all...
Suggest the mating gasket surface be the primary datum and the female thread of the aligning and mating nut be the secondary datum. Those two datums of one end's fittings would surfice to constrain 5 of the 6 degrees of freedom. The other fitting's similiar features would constrain the sixth...
"However, we need good control of the location of the ends."
Those ends are the datums. This is a rather unusual part but the logic still applies. Since this part is probably flexible then it's the usual practice to simulate how it's restrained in use and replicate that in the fixturing to check...
Position is used to locate features_of_size by their centerlines or centerplanes not to locate surfaces.
Runout is used to define parts that spin on an axis. Either in usage or when being manufactured.
If you would describe how the part functions I can suggest the best datums to define it. The...
Normally invoked as a slope refinement specified as a second callout. This is a common way to control the waviness within the total tolerance control which must have an equal or bigger envelope. Useful if the part can stand to be warped but not rippled.
Because the boundary callout pins the virtual condition boundary. The virtual condition boundary ensures the worst case fit of the mating part is line on line contact only unless you want an interference. Makes perfect sense that the shape of the tolerance zone of a slot type feature NEEDS to be...
You can't orient to something which does not already exist. That is simple rule to remember since this principle must be consistant for everyone involved in the process. The machinist would be unable to align to that coordinate system.
Slots which mate with a floating or fixed fastener are...
The ASME Y14.5M-1994 document is hard to extract the meaning from since it's written in legalese. However, the first few pages of chapter 4 explaining datum selection criteria are fairly comprehensible. The whole essence of the GD&T system is won or lost here by good or bad datum selection. Have...
The datums are selected because they are the features that are the most important ones for the part to function properly. Ones the mate or align are good. Ones that both mate and align are the best. There is a logical chain of datums and directly toleranced features from the first to the last...
The hole pattern is simply represented by the virtual condition boundarys which are normally just pins on the functional gauge. My way has simple datum target landings (each one must contact the part at least at one point) and pins which are expanding if the holes are at RFS and if at MMC then...
Well I can start making assumptions too just like you're not suppose to do. Guessing the three holes are mating and aligning features so they're probably the best choices of datums. Assuming this is a Free State Condition and some type of fasteners either fixed or floating go through these holes...
I don't know if you folks are aware of the Appendix E section of the ASME book. There is an extremely handy condensed tool there that's called the 'Decision Diagrams for Geometric Control'. It should help here somewhat. Suggest you peruse Fig E-7 for the essence of Datum Selections.
I've copied...
That person has used their imagination of how the GD&T works instead of being actually knowledgable and fluent. I see this silly stuff all the time. Found the best approach is ask them to point out the relevant sections of the ASME Y14.5-1994 book that justifies their technique of application...
That would be a fixed fastener situation. One would specify it with positional or orientation controls normally. Since a fixed fastener feature presumably aligns something like a dowel pin or a threaded fastener then relying on the virtual condition boundary of that feature does not ensure the...
