3DDave - In a perfect world Y14.5 would have incorporated the terminology we are discussing here that would make it consistent with its own intent in 2018. I will work towards ensuring this happens for the next release of Y14.5, and I hope all members, support group, visitors at meetings and...
Good Morning Burunduk,
Yes, there is a deliberate difference between Y14.5's median line and median plane material and the more complete and more specific information in Y14.45. The job for Y14 SC45 was to write a standard to provide guidelines for the data content associated with GD&T...
Burunduk,
If I am correctly understanding the point you are making, I think the issue is that we should have been more clear about the intent of the note applied to 3.23. The intent of the note is to point out that Y14.5 's definition of derived median plane does not acknowledge the LMC, so...
3DDave,
Size tolerances and all tolerances at RFS do not use the related AME. We have a "hole" in the standard wrt relatively short features.
It's a problem for hard gaging too, since position RFS, for instance applies to the axis that is defined by a thing (the UAME) that cannot be reliably...
Hi Burunduk,
I think any feature of size that is short enough relative to its size, cannot reliably orient a UAME. This includes any 2D feature of size too, of course. I think it would be OK to apply a position tolerance to either the width on the circular shaft and the groove with fully...
Hi Kedu,
The words just say "shall only be applied at regardless of feature size". Now that I've thought about this more, I wish that restriction specifically applied any time a tolerance is associated with a +DFT, -DFT or "Draft adds material" or "Draft reduces material". The resolved...
Hi Kedu,
I knew Don well. I wish he was still with us so I could discuss that figure with him. I think it is wrong, but Y14.8 almost sort of supports it by including tolerances at MMC and LMC in the figures. I say almost sort of because Y14.8 doesn't explain how to deal with tolerances that...
Hi Kedu,
Sorry for the lack of replies lately. Work is thankfully super busy for a few weeks.
I think only RFS can be applied with <FF> +DFT oir -DFT (or draft adds/reduces material). I tried to explain why in an earlier comment. The 2D diameter or width has to be on the feature, not in the...
Hi Kedu,
Yes, that is a figure that I have seen before. With a drafted feature that has a 2D size tolerance at one end only, I would not apply MMC or LMC. In fact, you bring up a good point. There should be a rule that prohibits modifying a tolerance at MMC or LMC if that tolerance is...
This may not be directly helpful for the topic, but I thing the world would be a better place if MMB and LMB were expanded to all features. I think we could then get rid of the terms virtual condition, resultant condition, inner boundary, outer boundary, and worst case boundary. Simpler is...
Hi Burunduk,
It could be done using profile of a surface if there was a method for specifying the MMB and LMB as separate values that comprise the profile tolerance zone (I also think the use of the terms MMB and LMB should be expanded beyond datum features, so we could then eliminate the terms...
Hi Burunduk,
Yes, you have summarized my likely to be wishful thinking correctly. Over 50 years of history with the current approach makes no more tolerances modified at MMC or LMC and a separate way of specifying a single boundary that applies to a surfce a tough sell.
Dean
www.validate-3d.com
Hi Burunduk,
I think those circular elements creating a feature of size are just as valid as the line elements at the ends of an elongated hole. I also would say that anything that can be measured with a CMM can be measured with hard gaging, but in some cases some special tooling may be needed...
Hi Kedu,
Uh oh, yet another very good question [glasses]. Thankfully, that public review draft of Y14.8 that you might have read includes a restriction that the Full Feature modifier may only be applied for tolerances specified at RFS.
The entire surface method vs. resolved geometry (axis...
tmillik,
I'd just like to say that your questions are good and valid. I think Burunduk's responses address your questions well.
The definition of feature of size should be both simplified and improved. It needs to a be a definition, rather than a list of examples. My personal opinion is...
drawoh,
Yes, that is exactly what I've state above. I'm also saying that this needs to be covered better in Y14.5. A circular element is included in the definition (list of examples rather than a definition, but in the definitions section anyway), but this question about the proper...
Hi drawoh,
Any relatively short (axial length) feature of size may not be able to constrain the orientation of an unrelated actual mating envelope (UAME) in a reliable/repeatable manner. A position tolerance on a cylindrical hole, for instance, is supposed to apply to the feature axis which is...
Hi Burunduk,
Yes, I completely agree with your assessment that the U part of UAME gets sketchy for features that are incapable of orienting the mating envelope due to insufficient length/depth. This is dealt with every time a sheet metal part is measured and really no different if the diameter...
Hi Burunduk,
How short can a cylindrical feature of size be? Can it have an axial length of 0.05mm? Maybe even shorter? Maybe it needs an axial length equal to its diameter?? What if a circle is printed in some zero thickness way onto a piece of mylar or onto a piece of glass? Is that 2D...
