Unkown symbol on drawing
Unkown symbol on drawing
(OP)
I have a drawing that has a circle with a horizontal line across it when specifying a range of dimensions (see attached picture). This is done for a diameter as well as linear dimensions. Does anyone know what this means? It is from a GE drawing.
I'm sure if I stay within the limits, it will not matter. But I wonder if it is acceptable to go over by a small amount, such as 0.5531 in the example?
Robert
I'm sure if I stay within the limits, it will not matter. But I wonder if it is acceptable to go over by a small amount, such as 0.5531 in the example?
Robert





RE: Unkown symbol on drawing
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: Unkown symbol on drawing
According to ASME Y14.5 all numerical values are absolute, so if 0.553 is specified on the drawing, it means 0.5530....00. If the measurement is 0.5531, then the part is out-of-spec.
RE: Unkown symbol on drawing
Assuming it conforms generaly to ASME Y14.5m-94 or similar (does it say on the print?) then .5531 would not be acceptable, the upper limit is .55300000000000000000000000000000000000000000000000000000... regardless of that symbol.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Unkown symbol on drawing
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Unkown symbol on drawing
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Unkown symbol on drawing
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Unkown symbol on drawing
When uncommon symbols are used, they should be defined in the drawing's notes. This is true even if they are a "company standard", since others are not likely to know what it means outside of the context of that company. At my company, we use an eyeball to ID inspection points. On each drawing where an eyeball appears, there is a general note that explains what it means. (yes, it is creepy when I put two eyeball symbols next to each other...thankfully there's no reason to ever do that on a real drawing.)
I guess a company could refer to their own standard within the drawing, but that would still have to be stated on the drawing, and copies of that standard would have to be made available to vendors and customers alike.
Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion
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RE: Unkown symbol on drawing
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Unkown symbol on drawing
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Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion
&
RE: Unkown symbol on drawing
Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion
&
RE: Unkown symbol on drawing
I am working at GE/Energy on NX and using some Inventor and I haven't seen that symbol in the year I have been here.
"Wildfires are dangerous, hard to control, and economically catastrophic."
Ben Loosli
RE: Unkown symbol on drawing
Yes, ANSI Y14.5M applies (it doesn't say which version, I assume the newest).
It is fine to say that .553 is an absolute limit for interpreting the drawing, but is it really the limit for a finished part? If so, I guess I am actually restricted to some amount less depending on the accuracy of my measuring equipment.
For example, if a linear dimension is 0.552-0.553 and I try to measure this with calipers with an accuracy of +/-.001, there is no way I can be sure the part is good. If I measure with micrometers with an accuracy of +/-.0001, then I can only say the part is good if it reads between .5521 and .5529. Is this right?
Robert
RE: Unkown symbol on drawing
RE: Unkown symbol on drawing
Your statement that you are "restricted to some amount less depending on the accuracy of my measuring equipment" is correct. But you are not quite correct by saying that there is no way to be sure the part is good when measured with caliper with an accuracy of +/-0.001. You can always have reading 0.552 or 0.553 and then the part would be OK.
If you measure with micrometer with accuracy of +/-0.0001, then the reading can be somewhere between 0.5520 and 0.5530, not 0.5521-0.5529.
RE: Unkown symbol on drawing
This points out how important it is to include the date of the standard when specifying what standard to use for interpretation.
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Unkown symbol on drawing
You can't assume it's '82 compliant just because it's made after '82; there's still folks out there working to the '60s version. If it has the "M" modifier on Y14.5, then by deduction it would be the '94 version; that's the only one that has the "M" modifier. Though I'm not sure that would stand up in court.
As for whether or not you can live with 0.0001, which likely would be eaten up by your measurement system accuracy ... it's up to the user's risk aversion. If the part could fail because it is 0.0001 or thereabouts out of spec, you likely will be risk averse and not accept it. On the otherhand, if it's a clearance hole and you can live with more, then it's a fairly safe move to accept it.
Now, as for the issue of how to measure it, per Rule #1; full form check at MMC and two-point check at LMC (Taylor's Principle). Don't know if it's a hole or a pin, but a caliper measurement would only be valid (i.e. in compliance with Y14.5 ... any version that I'm aware of) for the LMC size.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Unkown symbol on drawing
I don't understand what you mean when you say that calipers would only be acceptable for measuring LMC. Do you mean that they could only be used to verify that the part is not too small? I should also point out that for measuring the width, the part is small enough that the entire part fits between the jaws of the clipers so they would be reading the highs of the part.
RE: Unkown symbol on drawing
RE: Unkown symbol on drawing
RE: Unkown symbol on drawing
Rule #1 of ASME GD&T indicates that the feature must have perfect form at its MMC size (largest size for a pin / smallest size for a hole), but does not require perfect form at its LMC size (smallest pin / largest hole).
A convenient way to remember MMC & LMC is that MMC is Maximum Material (MASS) Condition of the workpiece, whereas LMC is Least Material (MASS) Condition of the workpiece. Notice that it's "of the workpiece", not of the feature; what's the mass of a hole? The smallest hole will result in the greatest mass of the workpiece; the largest hole will result in the least mass of the workpiece.
So, if it's a pin, you can check the lower limits of size using directly opposed points on the caliper. You cannot check the upper limits of pin size using a caliper because it doesn't consider form, which is required by Rule #1.
Jim Sykes, P.Eng, GDTP-S
Profile Services www.profileservices.ca
TecEase, Inc. www.tec-ease.com
RE: Unkown symbol on drawing
RE: Unkown symbol on drawing
Thanks for the clarification.
flash3700,
Thanks for the information. The .001 tolerance range on the dimensions pretty much gave their criticality away.
Robert
RE: Unkown symbol on drawing
It could be that the given range need not be met every time. This is because the eyeball might be specifying a statistical requirement, not one for every darn part. (I'm just thinking about Y14.5 paragraph 2.17 and Figure 2-24.)
But I can't say for sure. Any company that uses any sort of ST -- or eyeball, or KPC, or critical dim, or whatever -- should have internal standards or documentation that spells out the specific parameters such as Cpk threshold, sample size, etc.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Unkown symbol on drawing
My concern is still that does this then imply other dimensions are not critical? If so, do I need to bother hitting the specified tolerance on them...
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Unkown symbol on drawing
Basically, when there is a critical dimension then it must be addressed by your FMEA and control plan. It does not mean that the other dimensions can be out of print, just that being out of tolerance won't kill any one.
RE: Unkown symbol on drawing
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: Unkown symbol on drawing
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Unkown symbol on drawing
I'm still not convinced that details of what dimensions to inspect or how frequently etc. really belong on the drawing.
Surely it could change based on changing vendors, product maturity, changing processes...
At a previous employer, as I've mentioned before, there was a quality plan for each major product which addressed things like what dimensions to inspect and how frequently...
However, this is a bit off topic from the OP, sorry.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Unkown symbol on drawing
Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion
&
RE: Unkown symbol on drawing
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: Unkown symbol on drawing