I thinketh that you could possibly define an infinite number of datum points on a part. Then you could selectively use them as design requirements dictate. But to me it would mke no sense whatsoever to use the very same point, (or area) with a different identification.
I am beginning to believe that my theory of centerplanes not being a practical means of dimensioning is substantiated. Any one have an opinion in support or opposition?
Genman,
Perhaps the company has it own standard which will provide a clarification. Otherwise, in these days of computer generated drawings, my opinion is that symmetry symbol on a drawing should be avoided.
I have never seen the method you described. Over 50 years.
DesignBiz,
I also thought it to be an interesting question and was hoping for more responses. Perhaps there are not that many on this forum with CMM backgrounds.
It appears that a degree of tolerance relaxation would be appropriate for the .010+/-.005 and .015+/-.005 R. (Diff to verify and overly restrictive)
N is not required in the FCF for posn tol of .115 and .250 dias.
targets x and y are misapplied
Response to the OP.
2. No
3. No
4. No
A reiew of the drawing in question, indicates to me that excessive control have been established that will result in an excessive cost for a part. Sorry but my opinion.
Any similar opinions?
Problem: Rectangular part with a pattern of holes related to center planes of the part.
If a rectangular part were to have datum centerplanes in the vertical and horizontal planes, and these were specified in a FCF at RFS, and the part was to be verified by CMM, how would it be accomplished...
DesignBiz,
To illustrate my concerns over any attemts to label the centerline of a part as a datum feature, let's look at the Fig. 5-18 in the 94 standard. Imagine a datum identifier B attached to the vertical CL and C attached to the horizontal. I know of and dealt with a similar arrangement...
DesignBiz,
You have clarified your intent. I understand and agree. I had supposed you just MIGHT be making some reference to the use of rectangular pattern for PLTZ (composite tol)
DesignBiz
Cylindrical tolerance zones vs. rectangular tolerance zones for more accurate tolerance stacks.
The above statement from your last post caught my attention. Might you expand somewhat on the intent here?
Thanks
ProfDon,
My compliments to you for your example in your tips showing Separate Requirements. It makes perfectly good sense to me and is 'contradictory' to the one in the Standard.
The example is 2 keyways on a shaft.
JLang17,
Once the functional requirements have been determined, the proper datum features and relationships can be specified. Otherwise, you can spend a lot of time speculating on what might be an infinite number variations.
