Irregular closed feature
Irregular closed feature
(OP)
Received a drawing for a flexible plastic part stating GDT on irregular closed features.
I have no experience with this callout.
Could someone explain it to me. I have attached a picture of the callout.
I have no experience with this callout.
Could someone explain it to me. I have attached a picture of the callout.





RE: Irregular closed feature
If datums A, B and C are orthogonal, I have problems with the positional tolerance. It ought to have a diameter symbol in front of the 2. I am not sure about the word "BOUNDARY", either.
If I assume that the 2 is really Ø2, the irregular form should be located inside a 2mm circle centred on the nominal position. The irregular form outlines must be within of their correct position, allowing for positional error. The error can be increased at LMC of the irregular features.
You could print the maximum and minimum outlines of the irregular features on clear film. Sit the film on the face such that the feature outline is contained within the piece of film. You must be able to do this. Each feature on the film must be sitting within 1mm of its nominal position. Otherwise, you reject the part.
JHG
RE: Irregular closed feature
Figure 6-19 has a similar callout, no dia symbol for the position, however it is 2 separate FCF but attatched to the same leader, perhaps because the all around can't apply to the position.
Take a look at 6.5.5.1 & fig 6-19 that explain it.
KENAT,
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RE: Irregular closed feature
I think a composite profile would be more appropriate.
RE: Irregular closed feature
I do not see a problem with reference datums A,B, & C - primary, secondary and tertiary. Datum A is for perpendicularity to the mounting surface while datum B & C will give the location of the centre of the irregular shape hole.
The leader line with a circle around the elbow shown with the profile of a surface simply means "all around".
I don't see anything wrong with the call out.
Dave D.
www.qmsi.ca
RE: Irregular closed feature
paul
RE: Irregular closed feature
I cannot believe that you are agreeing with me???
There is just one exception I have though to your statement. The term "BOUNDARY" is used on noncylindrical features of size rather than any feature as you stated. A round feature of size at MMC really has the virtual condtion boundary superceding the centres as we have discussed here many times before.
See -
6.5.5.1 Boundary Control for Noncylindrical Feature - page 168
Dave D.
www.qmsi.ca
RE: Irregular closed feature
How is this center determined?
Can someone with a standard give a ruling on the "legality" of using position for an irregular shape? The references I have seem to indicate it is not proper. It just doesn't sit right with me.
RE: Irregular closed feature
Dave D.
www.qmsi.ca
RE: Irregular closed feature
The profile tolerance of the irregular feature is very much more accurate that the positional tolerance. The specification makes sense to me, although it is worth looking at the composite profile tolerance in Figure 6-25 in ASME Y14.5M-1994.
If I were inspecting, I would require each feature of the irregular hole to be located within the positional tolerance.
JHG
RE: Irregular closed feature
If one used a positional tolerance at MMC on an irregular shaped hole using BOUNDARY, it could be checked with a checking pin and fixture simulating the virtual condition boundary, location and orientation. It could be checked on a regular basis (in the Control Plan) and once the fixture is made, the cost on the shop floor would be minimal.
Dave D.
www.qmsi.ca
RE: Irregular closed feature
The only thing I see on the post that is slightly different from the example in the standard is the arrangement of the FCF, see link for what the standard has.
Very simplistically, the position is controlling the location of the irregular feature on the part, the profile is locating the size/shape of the irregular feature.
KENAT,
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RE: Irregular closed feature
In paragraph 5.3.2.1 Explanation of positional tolerances at MMC the arguements "In terms of..." are preceded by the statement "A positional tolerance at MMC may be explained in either of the following ways"... where in 5.10.1 the word "may" is missing... Go figure! Both paragraphs attempt to accomodate how one evaluates the control but they do not or cannot contradict paragraph 5.2.
Dave, You said, Maybe I missed the but paragraph 5.2(b) pertains to all positional tolerances with material condition modifiers. Therefore the surface "or boundary" with MMC or LMC tolerances always takes prescedance over centers no matter what type of feature it is.
HCIautoEng, As stated earlier by Kenat and reiterated by Dave... 6.5.5.1 & fig 6-19 explain your situation.
Kenat, I don't have a problem with one leader line, an ALL AROUND symbol, and a position control attached to a profile control. I don't think that it is improper since it doesn't modify the position control... only the profile control.
RE: Irregular closed feature
KENAT,
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RE: Irregular closed feature
RE: Irregular closed feature
http://www.tec-ease.com/tips/september-00.htm
http://www.tec-ease.com/tips/october-00.htm
http://www.tec-ease.com/tips/november-00.htm
To the comment above that position only controls center planes and center axes of features of size, the previously posted Y14.5 references establish that the position control at MMC, when applied to an irregular feature whose size is controled by a surface profile, provides the limitation of boundary location rather than center axis/center plane.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com