Positioning Irregular Shaped Feature
Positioning Irregular Shaped Feature
(OP)
I have an irregular shaped hole that is basically located and sized with tolerances (similar to the shape of this "0" if the left and right sides were flattened). I want to say it can be positioned with a dia. tolerance of .001 at MMC, but my book says I can only apply a positonal tolerance with cylinder, width or spherical features. A profile tolerance doesn't make sense because as the hole departs from MMC, it would break the tolerance zone.
I think I could use a positional tolerance attached to the height and one attached to the width, both with the note "BOUNDARY", but if they're the same tolerance it seems there's a better way.
Any help?
I think I could use a positional tolerance attached to the height and one attached to the width, both with the note "BOUNDARY", but if they're the same tolerance it seems there's a better way.
Any help?





RE: Positioning Irregular Shaped Feature
I think you are on the right lines, look at Fig 5-47 in ASME Y14.5M-1994 and paragraph 5.10.
5.10 explicitly says "The diameter symbol is omitted from the feature control frame."
5.10.1C says"...Where the same positional tolerance can be allowed for both {refering to length & width} only one FCF is necessary, directed to the feature by a leader and separate from the size dimensions.
If you need a sample diagram post again and I'll try and find time a lunch.
KENAT,
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RE: Positioning Irregular Shaped Feature
Link is to my understanding of what the standard means at 5.10.1C .
(Assume ASME Y14.5M-1994 1.1.4 regarding figures is invoked)
KENAT,
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RE: Positioning Irregular Shaped Feature
KENAT,
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RE: Positioning Irregular Shaped Feature
RE: Positioning Irregular Shaped Feature
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positioning Irregular Shaped Feature
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
RE: Positioning Irregular Shaped Feature
One of the most interesting things about GD&T per Y14.5 is that it often gives multiple ways to achieve essentially the same effect. Of course that's good and bad.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positioning Irregular Shaped Feature
Can size tolerances simply be converted to a profile tolerance (size +-.005 = profile tol. of .01)?
Is the size controlled in the upper frame or lower? My understanding is the lower frame does not control location...correct?
I also thought a composite profile of surface was only used with patterned features.
RE: Positioning Irregular Shaped Feature
Look at 6.5.9 in ASME Y14.5M-1994 page 172 & related figures.
Also +-.005 translates to an equalateral surface profile of .01, more or less.
Composite profile of surface is not only used with patterns, in fact the example in the standard is a single feature.
KENAT,
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RE: Positioning Irregular Shaped Feature
At first I couldn't recall using a profile control on a pattern of features, but on reflection I have used a note underneath the FCF to the effect of "3 LOCATIONS". The composite profile control only controls individual features though, and does not control the inter-feature relationship. The features are part of a group as established by the principle of simultaneous requirements and the note "3 locations".
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positioning Irregular Shaped Feature
RE: Positioning Irregular Shaped Feature
With Profile you are no longer locating the theoretical center of the feature, you are controlling the location of the actual faces.
Also I don't think you can really think of location dia in the same way.
Simplistically, you'd approximate what you want by a top line of FCF with .011 and bottom line .010.
In the case you describe initially I'd stick with your original way of doing it with position & boundary.
KENAT,
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RE: Positioning Irregular Shaped Feature
If one has an irregular shaped feature and wanted to control it location including orientation, positional tolerances at MMC with "Boundary" is the best way. It is easily confirmed on the shop floor with a checking fixture with a pin of its virtual condition shape, size and orientation.
Profile of a surface shouldt be confirmed with a CMM and is very costly. If one saw this on the drawing, it would be confirmed at least once in the life of the part while the positional tolerance at MMC with BOUNDARY could be confirmed on an hourly basis and included in the control plan.
The only time I have seen profile of a surface confirmed on a regular basis using a template was when the tolerance was 3 mm on the trim of a stamping. I really don't think that the profile tolerance was of any value in this situation anyway.
Maybe those drawings that had BOUNDARY were from my past trainees since we are both in the same neck of the woods.
Dave D.
www.qmsi.ca
RE: Positioning Irregular Shaped Feature
The use of hard gages is diminishing as more shops move from very large / continuous runs to smaller batches and essentially one-offs. The costs just can't be justified in many cases, unless the tolerances are grossly sloppy, in which case I'd use a surface profile anyway. I've dealt with automotive specialty suppliers that do still use hard-gaging, so I'm not saying it's dead, just diminishing from what I've seen. I've been in engine foundries and fabrication lines, worked with component suppliers (including large assemblies) that gave up hard-gaging over a decade ago. They CMM on a statistical basis typically, and with increasing frequency use SPC to minimize / eliminate final article inspection. This allows a plant to detect and correct a problem before it becomes an issue. I'm also seeing more widespread use of vision systems, which lend themselves nicely to profile controls, particularly for relatively thin pieces. As for cost of using a CMM to check a profile vs a fixture to check a BOUNDARY; consider the size/cost and handling issues associated with a half-ton workpiece engaging multiple features on a checking fixture simultaneously ... a CMM (gantry or arm-style) is more cost effective & easier in many cases. Of course, operators & programmers need to understand the CMM and its software ... that's another story...
While I was an early advocate of CMMs, I came to recognize the issues associated with them (establishing datums from points on a selected surface, sine error, averaging algorithms, sampling rate, etc.) and like to point them out to students who rely exclusively on them for their results. Each situation may warrant different methodologies & equipment, and inspectors need to think things over before jumping in with their usual practice.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positioning Irregular Shaped Feature
One offs or small runs, yes, go profiles although most only check profile (2 dimensional) of a line rather than a surface (3 dimensional).
I would recommend positional at MMC with BOUNDARY for high volume runs for an irregular shaped feature.
My background is in the quality area rather than design so I have been involved in statistical analysis for a while.
As far as CMMs and statistical analysis on GD&T, that becomes a completely different topic. Paul and I have discussed this many times in the past. Using a CMM on positional tolerances at MMC with BOUNDARY would blow anyone away. The results really wouldn't be fully confirmed but one would have data for stats.
The companies that years ago went fully CMM thinking that is was the best way are, in my opinion, wrong. There are applications for CMM and other times, a hard gauge will truly confirm the requirement. The above example of positional at MMC with BOUNDARY is an example.
Dave D.
www.qmsi.ca
RE: Positioning Irregular Shaped Feature
May be an example, again providing there are few features associated with it that must be gaged at the same time, and that the quantities justify the cost of the gage. We don't have enough info posted to be definitive.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positioning Irregular Shaped Feature
you said:
"Also +-.005 translates to an equalateral surface profile of .01, more or less."
In this case, wouldn't the surface profile zone be .005? If it was .01 then the feature could expand .005 on one side, then .005 on the opposite side resulting in a total increase of .01, which is greater than the +.005 tolerance.
Just thought of this and wanted to be sure I was thinking about it correctly.
RE: Positioning Irregular Shaped Feature
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positioning Irregular Shaped Feature
See attatched sketch. http://f
The light bulb just came on. You meant +-.005 was the tolerance on the length or width of your slot, I misunderstood. In that case, yes you'd want to use .005 SP see second image.
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KENAT,
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RE: Positioning Irregular Shaped Feature
KENAT,
Have you reminded yourself of FAQ731-376: Eng-Tips.com Forum Policies recently, or taken a look at posting policies: http://eng-tips.com/market.cfm?
RE: Positioning Irregular Shaped Feature
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Positioning Irregular Shaped Feature
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Positioning Irregular Shaped Feature
Let's say I want to use a profile control for the feature in my original post, and the size tolerances are +-.005. I want to confine the location to a diameter of .001, and allow size to adjust within a zone of .01. How do I show this?
"
It was meant to be corrcting my reply to the above but was still wrong.
The .001 positional doesn't make much sense but I think the OP would want FCF with .006 in the top and .005 in the bottom, but I've lost all faith in myself now.
KENAT,
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RE: Positioning Irregular Shaped Feature