For a hole, bonus tolerance can be calculated as:
Actual size - MMC size
Your net positional tolerance then becomes:
Tolerance at MMC + Bonus tolerance.
See the attached table for how it applies to your...
If you are at all concerned about the "accuracy" of your datum features, then its a good idea to apply appropriate geometric controls. I suspect the only reason you don't see them more often is that they are omitted for simplicity as a lot of the drawings are left incomplete by intent. For...
I agree with greenimi that from a functional standpoint, it sounds like it would be best to use the flat surface as a primary and the pattern of holes as the secondary datum feature. While you may not be able to easily establish a "center" for the feature pattern, that is not strictly necessary...
If you're specifying a profile tolerance, I don't think the method of definition is too critical, as long as the true profile is defined unambiguously.
Inspection with a CMM looking at the specific inflection points seems to be of limited utility. Admittedly, I don't have a background in...
If you're supplying 3D data with the drawing, then calling out the model as basic should work.
If there is some value in fully specifying the profile in 2D, making sure that radii callouts originate from their respective dimensioned center-points and using enlarged detail views might go some...
For what its worth, Y14.5-1994 states in para 1.8.6
"A curved outline composed of two or more arcs is dimensioned by giving the radii of all arcs and locating the necessary centers with coordinate dimensions. Other radii are located on the basis of their points of tangency. See Fig. l-30."...
Running a search for Gage R&R might be useful.
For example, here is a handy introduction to the subject (complete with a link to a spreadsheet)
http://www.dmaictools.com/dmaic-measure/grr
I don't really have a manufacturing/inspection background so I feel like I might be misunderstanding either your constraints or your setup, particularly when you say
I had assumed you were using surface B to edge find for your machining setup, using a method such as this...
Ronj100,
A couple of points of clarification as to your requirements:
1) My intent is to have the .250 dia dowel hole kept relative to datum -b- very close.
The upper segment of your composite FCF controls location of your .250 dowel hole (tolerance .030). The lower segment (which is not...
When a datum feature symbol is attached to the size dimension of a width feature of size, the center plane of the width feature (to be precise, the center plane of the true geometric counterpart) becomes the datum plane. See attached Fig 4-13.
If you instead attached the datum feature symbol...
I'm not hugely familiar with using datum targets, but I did have a question about this statement. If datum target C is calling out a line, then I agree with what you've said above. However, if it is instead calling out a point (impossible to tell from the available view) would you not need to...
I think in that case your best bet might be to use bidirectional positional tolerancing (Section 5.9 in Y14.5-1994). This should allow a tighter control on the 3.958 dimension while allowing a looser control on the angle/orientation relative to the DRF. See attached Fig 5-42 for an example. You...
Apologies in advance if this is not what you're asking for, but since the feature is located by basic dimensions, you should be able to calculate the basic X dimension using trig without affecting the actual tolerance value, as shown in the (hopefully) attached image.
If not, then I think I'm...
