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True Position of holes, without Diameter symbol in Control Box??

SAM-IMC
let me lay this out for you guys and gals the best I can:

I have Datum A wich is a inside Circle recessed into the top of the part. We will call this "Datum A"

I have another recessed circle on the bottom of the part. We will call this "Hole"

"Hole" has a dimension callout that reads as follows: Dia. 7.06"
[T.P./.010/A] Notice there's no Dia. Symbol in the Cntrl Frame

I have never seen this callout before without the Dia. Symbol in the control frame when in reference to a datum that is a circle or cylinder, have you?

If I run this with both features as Circles, I get a measurment of 0 (ZERO)

If I run this with both features as Cylinders, I get some actual numbers, but I don't know if they are correct.

If I run this with Datum A as a Cylinder and Hole as a Circle, I get 0(ZERO)

I am confused as to which way i am supposed to do this. Is the callout on the drawing messed up, or am I giving Pcdemon incorrect features to calc this dimension?

Any help would be greatly appreciated.

Sam
  • let me lay this out for you guys and gals the best I can:

    I have Datum A wich is a inside Circle recessed into the top of the part. We will call this "Datum A"

    I have another recessed circle on the bottom of the part. We will call this "Hole"

    "Hole" has a dimension callout that reads as follows: Dia. 7.06"
    [T.P./.010/A] Notice there's no Dia. Symbol in the Cntrl Frame

    I have never seen this callout before without the Dia. Symbol in the control frame when in reference to a datum that is a circle or cylinder, have you?

    If I run this with both features as Circles, I get a measurment of 0 (ZERO)

    If I run this with both features as Cylinders, I get some actual numbers, but I don't know if they are correct.

    If I run this with Datum A as a Cylinder and Hole as a Circle, I get 0(ZERO)

    I am confused as to which way i am supposed to do this. Is the callout on the drawing messed up, or am I giving Pcdemon incorrect features to calc this dimension?

    Any help would be greatly appreciated.

    Sam

    If you could post part of the drawing it would help.

    From your description I can imagine a few possibilities.

    The Ø symbol should be there and is not due to oversight or other.

    Or I could be that the intent is to only control the location in a single axis, as a slot might be. The clue that this is the case would be in the basic dimensions. If there is only one basic dim locating the hole in one axis, I would go this way, but maybe report regular diametrical position too as a reference just in case.


    HTH
  • Is the Ø7.06 the same axis as Datum_A? If it is it's possible that there would be no deviation and therefore the measured would be zero. Probing it as a cylinder is giving you the bestfit of the cylinder which has at minimum 2 levels. The difference between the levels puts the position of the Ø7.06 feature in a different location than just using a simple auto circle and you would see different deviation. The drafter could have just missed it on the drawing but either way they are asking for the position of that feature. For me I would want to know the function of the feature to decide if I wanted to probe it as a circle or a cylinder. Either way works if it's in tolerance. I would think if the cylinder were important they would have asked for runout or cylindricity.
  • Is the Ø7.06 the same axis as Datum_A? If it is it's possible that there would be no deviation and therefore the measured would be zero. Probing it as a cylinder is giving you the bestfit of the cylinder which has at minimum 2 levels. The difference between the levels puts the position of the Ø7.06 feature in a different location than just using a simple auto circle and you would see different deviation. The drafter could have just missed it on the drawing but either way they are asking for the position of that feature. For me I would want to know the function of the feature to decide if I wanted to probe it as a circle or a cylinder. Either way works if it's in tolerance. I would think if the cylinder were important they would have asked for runout or cylindricity.


    Per ASME Y14.5 the location tolerance zone applies to the entire length of the feature unless specified otherwise. This means that it is never proper per the standard to use only a circle to report position, you should always use a cylinder. For this very reason Xactmeasure will not let you report the position of a circle. Please be careful about giving incorrect advice.
  • Per ASME Y14.5 the location tolerance zone applies to the entire length of the feature unless specified otherwise. This means that it is never proper per the standard to use only a circle to report position, you should always use a cylinder. For this very reason Xactmeasure will not let you report the position of a circle. Please be careful about giving incorrect advice.

    So your saying that if datum_A on my part is only .060" thick and there are 30 holes spaced out over that plane Xactmeasure won't let me position them? With material that thin creating a cylinder is pretty much a time sink, both in programming and in execution. I've never NOT been able to report them with Xactmeasure.

    I am aware of the standard but honestly with a touch probe the CMM is never truly measuring the entire length of a feature. Even with a scanning probe if that feature is not a thru hole you can't probe it right up to the surface it intersects. The point could be argued and in my opinion my information was not incorrect.
  • So your saying that if datum_A on my part is only .060" thick and there are 30 holes spaced out over that plane Xactmeasure won't let me position them? With material that thin creating a cylinder is pretty much a time sink, both in programming and in execution. I've never NOT been able to report them with Xactmeasure.

    I am aware of the standard but honestly with a touch probe the CMM is never truly measuring the entire length of a feature. Even with a scanning probe if that feature is not a thru hole you can't probe it right up to the surface it intersects. The point could be argued and in my opinion my information was not incorrect.

    Material that is only .060" thick is not typical of most situations. In that case your assessment is correct from a cost effectiveness perspective.

    I just checked v2011mr1 and you are correct it does allow circles. When I took the Pc-Dmis GD&T class in Oct. of 2010 circles were not allowed. I have pulled my course book and reviewed my notes from the instructor stating just as I did previous why there were no circles allowed for position.


    The standard was not written with the intention that Co-Ordinate Measure Machines would be the main tool used to evaluate whether or not parts were compliant with drawing requirements. Rather the standard expressly anticipates surface place, height gage, & dial test indicator inspection. (This is key to why Pc-Dmis does not evaluate Concentricity per the standard BTW.) It is up to us CMM programmers to find ways to use the CMM to meet the standard's requirements.
  • with a touch probe the CMM is never truly measuring the entire length of a feature. Even with a scanning probe if that feature is not a thru hole you can't probe it right up to the surface it intersects.

    Just wanted to point out that pcdmis evaluates the position of a cylinder over its defined length, regardless of where you take the probings. So as long as you've defined the cylinder to cover the entire length of the feature, it will be evaluated over the entire length. This can be good and bad (mostly good), but its important to know.
  • Just wanted to point out that pcdmis evaluates the position of a cylinder over its defined length, regardless of where you take the probings. So as long as you've defined the cylinder to cover the entire length of the feature, it will be evaluated over the entire length. This can be good and bad (mostly good), but its important to know.

    So if the cylinder is say 1.00" deep and is not a thru cylinder/Ø and you probe that cylinder at 3 levels 1.) .020" 2.) .500" 3.) .800" even though there is .200" of that cylinder that has had no probe hits it's TRULY being defined over the length. I agree that DMIS does attempt it but it is calculations based on the points taken.

    If I am measuring a cylinder that has been created by circle interpellation and the tool breaks down as it reaches that last .200" of the cylinder depending upon where I probe that cylinder will determine if that is detected. I understand and agree with the standard but DMIS can only calculate with data it is given and the data is coming from where the probe touches the part. This is why I suggested that I would want to know the function of the feature, so that I can inspect it at the appropriate level. It's the same on surface profiles. I can take a point every .100 on a grid but it can still miss excess material from the machine that just happend to jump one line of code while 3D'ing a surface leaving a .030" x .030" stripe across the part or a chip that causes a gouge on one pass of the tool. I have no claims to being an expert, it's just the way my mind see's it, and I truly mean no offense to anyone.
  • I cannot upload the drawing for certain reasons, but if you will imagine looking at the part from the top, you would see datum A as a circle and "Hole" would also be a circle inside of Datum A. Just like a concentricity symbol. There are other features that have this same TP Control Box that looking from the top of the part are other circular features that actually overlap Datum A by being slid in the Y axis, but not in the X axis.

    I picked the Hole in the bottom of the part because it was simplest to describe. but being a raw casting... I know that I would never get a TP with a measurment of 0(ZERO).

    Sam
  • I cannot upload the drawing for certain reasons, but if you will imagine looking at the part from the top, you would see datum A as a circle and "Hole" would also be a circle inside of Datum A. Just like a concentricity symbol. There are other features that have this same TP Control Box that looking from the top of the part are other circular features that actually overlap Datum A by being slid in the Y axis, but not in the X axis.

    I picked the Hole in the bottom of the part because it was simplest to describe. but being a raw casting... I know that I would never get a TP with a measurment of 0(ZERO).

    Sam

    So there are no basic dimensions locating the "hole" and the only datum in the FCF is A. I would say most likely there should be a Ø in the FCF and it was left out by mistake.

    Do the other circular features have the Ø symbol in their FCFs?

    Do they have any basic dimensions?

    Do they have any other datums in their FCFs or just A?
  • So if the cylinder is say 1.00" deep and is not a thru cylinder/Ø and you probe that cylinder at 3 levels 1.) .020" 2.) .500" 3.) .800" even though there is .200" of that cylinder that has had no probe hits it's TRULY being defined over the length. I agree that DMIS does attempt it but it is calculations based on the points taken.

    IMNSHFO, you need to learn more about ASME Y14.5 GD&T if you are going to be giving advice on it.

    Position does not control the surface of the cylinder, but rather it's axis. Even though you can not touch .2" of your theoretical cylinder, you have picked up .8" of it's axis and unless you have reason to suspect the the axis of that last .2" deviates greatly from the rest, you have enough to make a pretty good evaluation. As the CMM programmer part of your job is deciding whether or no that .8" is adequate and if not, finding another way, whether on the CMM or not. The CMM is not the only tool for inspection and in several cases is not the best tool.

    Please understand I am not trying to pick on you, or make myself look good by making you look foolish. I am trying to prevent misinformation being posted without contest.


    If I am measuring a cylinder that has been created by circle interpellation and the tool breaks down as it reaches that last .200" of the cylinder depending upon where I probe that cylinder will determine if that is detected. I understand and agree with the standard but DMIS can only calculate with data it is given and the data is coming from where the probe touches the part. This is why I suggested that I would want to know the function of the feature, so that I can inspect it at the appropriate level. It's the same on surface profiles. I can take a point every .100 on a grid but it can still miss excess material from the machine that just happend to jump one line of code while 3D'ing a surface leaving a .030" x .030" stripe across the part or a chip that causes a gouge on one pass of the tool. I have no claims to being an expert, it's just the way my mind see's it, and I truly mean no offense to anyone.

    As the CMM programer, and as an inspector, it is up to you to know, or learn, the methods of production used to create the parts you must inspect. That knowledge is a key part of knowing how much and which areas need the most attention to achieve the ultimate goal which is verifying and documenting the part meets the drawing requirements as interpreted be ASME Y14.5 or whichever standard is stated on the drawing or in the customer's specifications.

    A solid understanding of GD&T is as important as knowing how the features were machined and how they will function. Your comments demonstrate you do not have that knowledge of GD&T. No one is born with it. Just please be careful giving advice to others about GD&T until you can cite page and chapter from the standard to support your interpretation if need be.
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