ASME Y14.5-2009 4.3g usage stirs the pot
ASME Y14.5-2009 4.3g usage stirs the pot
(OP)
I expect to back off an approach to tolerancing that I am taking which is understandably unpopular with a valued supplier. But here's what keeps going thru my head: When it comes to rather small, uniform injection molded or die-cast parts, tolerances are more based on inch/inch or mm/mm than individually toleranced features of size. So all of the features in each mold cavity will be well controlled with respect to each other. Then there will be a 'pattern shift', so to speak, with those features in the other mold cavities (or cores). I came up with a sample part to consider. (Please ignore wall thickness issues and other good practices, which I have ignored, for the most part.) Does anyone see improper usage of the 2009 Standard? What do people like/dislike about this approach?





RE: ASME Y14.5-2009 4.3g usage stirs the pot
I can see what you are doing, and it makes sense to me. What is your vendor's objection?
RE: ASME Y14.5-2009 4.3g usage stirs the pot
RE: ASME Y14.5-2009 4.3g usage stirs the pot
I think it's one of those things where it is legal per the standard, but from a real-world manufacturing viewpoint I too might be left scratching my head.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: ASME Y14.5-2009 4.3g usage stirs the pot
RE: ASME Y14.5-2009 4.3g usage stirs the pot
Thanks for reminding me about ASME Y14.8, pmarc. Bob has a copy. I'll go get it.
RE: ASME Y14.5-2009 4.3g usage stirs the pot
I figure that using your complex feature as a datum is perfectly legal, and feasible if you specify that it applies at MMB. This makes your datum_A profile tolerances sloppier. Is that acceptable?
The whole point of datum targets is that everyone who handles your part has the same repeatable datums, even though the part is a fairly inaccurate casting. Datum targets are marginally useful for accurate, rigid parts. They are a good idea for castings.
RE: ASME Y14.5-2009 4.3g usage stirs the pot
It is very reasonable to think about this topic in terms of how to inspect something. But also consider the opportunity for some folks to take robust design and process qualification to the point of zero or near-zero inspection... That's kind of funny, now that I think of it. I know of a place (I'm sure you do, too) where they have zero or near-zero inspection down to a science, but forgot the robust design and process qualification parts. Oops.
RE: ASME Y14.5-2009 4.3g usage stirs the pot
I don't see anything illegal on your drawing, but there are some issues that I would point out.
Datum feature A is a "mathematically defined surface", described in Section 4.13 and Figure 4-28 of Y14.5-2009. So your drawing is legal per the standard, I think, but you're applying one of the brand new tools and you may suffer the pain of being an early adopter. JP is right that it will be very difficult to simulate (I hate that term) datum feature A. Not impossible, but there are some significant practical difficulties. Datum feature A needs to be referenced at some particular "boundary condition". The example in the standard uses the BSC modifier for the mathematically defined datum feature - that is, the datum feature simulator has the basic geometry of the datum feature. Other options are MMB (Maximum Material Boundary and LMB (Least Material Boundary). The actual geometry (or the cloud of points scanned from it) then needs be fitted to the simulator, so that there is contact on the high points. This is not straightforward, even for CMM's with high-density scanning capability. Different softwares will fit the point cloud in different ways, with different datum reference frames as a result. The amount of difference will depend on the form error of datum feature A.
Another issue is simultaneous requirements. There are three profile FCF's that all reference datum feature A only, so all of the features controlled by these FCF's are treated as a composite pattern. It doesn't sound like this was the intent.
There's also another standard that you may want to look into, if you haven't already. It's Y14.8-2009 (Castings, Forgings, and Molded Parts). This standard deals with mold-related issues such as parting lines etc. Here's a link to an article written by Don Day, the chairman of the Y14.8 subcommittee:
http://me
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: ASME Y14.5-2009 4.3g usage stirs the pot
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: ASME Y14.5-2009 4.3g usage stirs the pot
Your feature RFS is legal as per ASME Y14.5, but not totally feasible.
If your datum is a feature of size at MMB, you can make a fixture that simulates that MMB condition. Parts that are not close to MMB can be wiggled around on your fixture, thereby simulating the bonus allowance.
I am comfortable using features of size without MMB, as long as the feature is very much more accurate than the tolerance being tested. Holes for dowel pins are a good example of this. Try sketching out the expanding fixture needed to capture your feature RFS. I think it will be a challenge.
RE: ASME Y14.5-2009 4.3g usage stirs the pot
Peter Truitt
RE: ASME Y14.5-2009 4.3g usage stirs the pot
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: ASME Y14.5-2009 4.3g usage stirs the pot
Peter Truitt
RE: ASME Y14.5-2009 4.3g usage stirs the pot
Peter Truitt
RE: ASME Y14.5-2009 4.3g usage stirs the pot
I liked your drawing, in fact I liked your first drawing more :)
Unfortunately you did not use Mismatch on your drawing and the limits of using "mismatch" is exactly what I am looking for.
Something like "if it could be described using "MIN" and "MAX" (mostly MAX), then it's mismatch, but if it requires more detailed measurement, use profile"
RE: ASME Y14.5-2009 4.3g usage stirs the pot
RE: ASME Y14.5-2009 4.3g usage stirs the pot
Datum targets B1 and B2 are located on the parting line, this will cause the gage and measurement unrepeatable. Datum targets should be located on features not subject to processing variables, such as parting lines, flash extensions, etc. Datum target B1 and B2 need to be moved or relocated at a suitable place, please ref to 4.3.1 Datum Target Location ASME Y14.8M-1996 for more detailed information
SeasonLee