Simulation of a single daum plane
Simulation of a single daum plane
(OP)
I'm looking at 4.5.7.1 of ASME Y14.5M-1994. Are all the methods in my attatched tiff in compliance with the standard?
The paragraph doesn't say you have to have two datums and reference them A-B but that's all it seems to show in examples.
The paragraph doesn't say you have to have two datums and reference them A-B but that's all it seems to show in examples.
KENAT, probably the least qualified checker you'll ever meet...





RE: Simulation of a single daum plane
Chris
SolidWorks 08 0.0/PDMWorks 08
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog
RE: Simulation of a single daum plane
RE: Simulation of a single daum plane
It would seem technically more appropriate to use datum targets (3) for that example. There would seem to be a conflict in merging the 2 surfaces to obtain a single datum plane. If 3 points determine a plane, then that should be all that is required.
Am I thinking wrongly?
RE: Simulation of a single daum plane
Powerhound, GDTP T-0419
Production Supervisor
Inventor 2008
Mastercam X2
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: Simulation of a single daum plane
To me 3 is just a clarification of 2, though not in the standard as such.
4 was one concern I had, I've had drawings from a fairly experienced guy that if I recall correctly only had the 2 surfaces and no phantom/leader line. I didn't think it was really in compliance with the standard and in some cases could be ambiguous because of it (not the example I give though probably).
powerhound, I've done similar with the coplaner callout, I may do it in this case but at present no coplaner tol is called out and it's working but I'm going to look at the function a little closer.
KENAT, probably the least qualified checker you'll ever meet...
RE: Simulation of a single daum plane
If you are using 2 planar surfaces as a single datum feature, and a plane is still determined by 3 points, how does one know which surface is selected for 2 points and which for 1 point?
Would not 3 target points or areas be more appropriate?
RE: Simulation of a single daum plane
Either way, the standard says it's OK (my question was on how to properly indicate it not if it was valid).
You could make the same argument for any datum base on my understanding of your logic.
KENAT, probably the least qualified checker you'll ever meet...
RE: Simulation of a single daum plane
Is there a reason why you would not use this method only, since it is unambiguous and per the example?
Additionally, I would almost always recommend control of any datum, in this case thru the use of profile of surface with a phantom line and the number of surfaces spelled out under the FCF. To control the co-planarity desired of the two separate surfaces, as described in para. 6.5.6.
Also, I caution those of you who have a copy of the "proposed" 200x standard to leave it alone and not cite it until it is released even if it is an improvement. It only confuses those who are already confused. After it has been approved and released, have at it.
RE: Simulation of a single daum plane
How is 2 a misinterpretation? Are you saying my example isn't 'appropriate'? If so could you explain why.
Somewhat scarily I'm about the most knowledgable GD&T person around here so I try to use the 'simplist' or most easily understood representation of the GD&T so that others will understand. To me having the extension line, especially if clarified with "2 SURFACES" is probably clearest. However I wanted opinions on if I'd interpreted the standard correctly, especially since the '2 SURFACES' isn't mentioned for datums in the standard.
KENAT, probably the least qualified checker you'll ever meet...
RE: Simulation of a single daum plane
Chris
SolidWorks/PDMWorks 08 1.1
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog
RE: Simulation of a single daum plane
For whatever the reason, this is why I ask again, is there a reason you do not want to use example #1?
Additionally, the use of "2 SURFACES" text is also very clear in para. 6.5.6 when a single form control is desired on these datum surfaces.
It is my contention and opinion that the most unambiguous method should be used and that is example #1. If you choose to use example #2, so be it, I will always use and recommend #1
This is the preferred method and technique appropriate for use of multiple planer surfaces to simulate a single datum as intended by the Y14.5 committee, as it was sold to me over ten years ago by the Godfather of GD&T himself - Lowell W. Foster, and thats my opinion.
V. W. Mahoney
ASME Certified - GDTP S-0418
RE: Simulation of a single daum plane
RE: Simulation of a single daum plane
Q: is there a reason you do not want to use example #1?
A: I don't have great confidence that most other people here or at our machine shops will have a clue what A-B in the FCF means. Also I have 2 interupted datums so the drawing my start to get a little busy but that's not much of an argument.
KENAT, probably the least qualified checker you'll ever meet...
RE: Simulation of a single daum plane
However, to keep it simple I would use "(2 SURFACES)" and show an extension line between them. The part will start with that datum as one continual surface, then will have material removed. Logically (to me, anyway) the resultant two surfaces still represent the initial datum. It is allowable per the standard and may be easier to understand for those somewhat unfamiliar with the standard.
RE: Simulation of a single daum plane
My primary datum is pretty much per my sketch.
My secondary datum is actually 3 surfaces.
So using option #1 I'd end up with FCF like:
|A-B|C-D-E|F|
As well as a bunch of datum symbols.
For this reason I think I either go for variant of # 2 or do the surface profile version Powerhound brought up.
Based on the function of this part there is no real need for the surface profile on my secondary datum. I don't think it's needed on the primary either but I'll have to look closer.
(This isn't my drawing, it's an existing part with problems that I'm redlining)
KENAT, probably the least qualified checker you'll ever meet...
RE: Simulation of a single daum plane
RE: Simulation of a single daum plane
However, I'm also aware that it's not the standard yet perhaps some users won't make that distinction and perhaps that's what Xplicator is concerned about. Then again, we have little to no control over how others take/use information we post so ...
KENAT, probably the least qualified checker you'll ever meet...
RE: Simulation of a single daum plane
Any chance of getting a sketch of your 3 surfaces as a seconday datum that you mentioned above.
I now live in AL but came from MO, the "how me' state.
It would appear slightly unorthodox on the surface.
No pun intended.
RE: Simulation of a single daum plane
KENAT, probably the least qualified checker you'll ever meet...
RE: Simulation of a single daum plane
Remember...![[idea] idea](https://www.tipmaster.com/images/idea.gif)
"If you don't use your head,
your going to have to use your feet."
RE: Simulation of a single daum plane
Right on!
Chris
SolidWorks/PDMWorks 08 1.1
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog