Jieve
Mechanical
- Jul 16, 2011
- 131
Hello guys,
I have a number of GD&T and Dimensioning questions for you as I’ve been working on drawings to send to our shop. I am working to ISO.
1)If a hole is located at the center of a rectangular part, is it necessary to dimension the hole from the edges? I thought I read somewhere that where no dimensions are drawn, symmetry is assumed.
2)Modification of question 1: I have a rectangular part with two holes evenly spaced about the midplane. The hole are also equidistant from the edges of the part. Is it ok to simply dimension the distance between the holes, without dimensioning from the part edges? If so, is it necessary to include a centerline (or centerplane) to indicate that this symmetry assumption is correct under ISO?
3)I have a rectangular plate with a hole in the center. I would like to add a position tolerance to keep the hole within 0.1mm from the exact center. I am assuming that the best method be to make the midplanes of the part datums B & C (with the primary A being the surface the part sits on), and then specify that the position tolerance should be relative to A,B,C rather than making the edges of the part the secondary and tertiary datums? Am I correct?
4)I am somewhat confused about the use of basic dimensions. Assume I have a rectangular part with two holes spaced equidistant from the centerplane of the part. The actual distance between the holes is more important than the distance between any edge and any hole. In one scenario, I make the flat surface on which the part sits primary datum A, and each perpendicular midplane datums B & C. I specify a position tolerance of the first hole from datums A, B and C. Then I make the first hole datum D, and specify a position tolerance of the second hole relative to A, D, B. There is still assumed symmetry of the holes about the midplane. Is it required to specify basic dimensions to the edges B & C to the first hole, even though symmetry is assumed?
5)An extension to question 4, if I use a centerplane as a datum, is it necessary to add basic dimensions from the midplane to the hole?
6)I have seen another example where the part in question 4 had only datums A, B & C as described. One hole was dimensioned with basic dimensions from datums B & C, and the second hole was dimensioned from the first hole with a basic dimension as well. Both had a position tolerance with respect to A, B & C. I thought that this essentially means that both hole dimensions need to be inspected with respect to datums A, B & C, and not with regard to each other. When not using GD&T, when the position between two holes is important, the distance between holes should be dimensioned directly to eliminate tolerance stack-up. But what is the relevance of dimensioning between holes in this case when the datums (i.e. measurement locations) are specified as edges? Would it not have made sense for them to have dimensioned both holes with basic dimensions from the datums? This example was in an ASME book.
7)This may seem like a repeat question of one or two of the above, but assume I have a hole in a rectangular part. That hole has a position tolerance from datum B, which is the edge of the part. Can I use a basic dimension from the opposite edge of the part, or does it need to be from the datum edge?
8)I have 4 holes in a rectangular pattern on a rectangular part. Datum A is the flat surface the part rests on, and datums B & C are the other 2 perpendicular part edges. Each hole has position tolerances. One hole has a dimension callout 4x and the diameter. A position control frame is placed underneath this. All holes are the same size, but not all have the same position tolerance. Therefore, I use a position control separately on the other holes with deviating geometric controls. Is the 4x the diameter callout with the position control frame underneath OK even though the geometric tolerances are different on different holes?
9)Extension to question 8, except now datum D is one of the holes. I specify the position tolerance of another hole relative to frame A, D, B, where B is one of the sides. What distance would be measured upon inspection, the distance from datum D or from datum B? B is really only used to eliminate rotation in this case.
I know these are a lot of questions, but all questions I came across today while working on drawings. Your insight and help would really be appreciated, as always!
Thanks!!
I have a number of GD&T and Dimensioning questions for you as I’ve been working on drawings to send to our shop. I am working to ISO.
1)If a hole is located at the center of a rectangular part, is it necessary to dimension the hole from the edges? I thought I read somewhere that where no dimensions are drawn, symmetry is assumed.
2)Modification of question 1: I have a rectangular part with two holes evenly spaced about the midplane. The hole are also equidistant from the edges of the part. Is it ok to simply dimension the distance between the holes, without dimensioning from the part edges? If so, is it necessary to include a centerline (or centerplane) to indicate that this symmetry assumption is correct under ISO?
3)I have a rectangular plate with a hole in the center. I would like to add a position tolerance to keep the hole within 0.1mm from the exact center. I am assuming that the best method be to make the midplanes of the part datums B & C (with the primary A being the surface the part sits on), and then specify that the position tolerance should be relative to A,B,C rather than making the edges of the part the secondary and tertiary datums? Am I correct?
4)I am somewhat confused about the use of basic dimensions. Assume I have a rectangular part with two holes spaced equidistant from the centerplane of the part. The actual distance between the holes is more important than the distance between any edge and any hole. In one scenario, I make the flat surface on which the part sits primary datum A, and each perpendicular midplane datums B & C. I specify a position tolerance of the first hole from datums A, B and C. Then I make the first hole datum D, and specify a position tolerance of the second hole relative to A, D, B. There is still assumed symmetry of the holes about the midplane. Is it required to specify basic dimensions to the edges B & C to the first hole, even though symmetry is assumed?
5)An extension to question 4, if I use a centerplane as a datum, is it necessary to add basic dimensions from the midplane to the hole?
6)I have seen another example where the part in question 4 had only datums A, B & C as described. One hole was dimensioned with basic dimensions from datums B & C, and the second hole was dimensioned from the first hole with a basic dimension as well. Both had a position tolerance with respect to A, B & C. I thought that this essentially means that both hole dimensions need to be inspected with respect to datums A, B & C, and not with regard to each other. When not using GD&T, when the position between two holes is important, the distance between holes should be dimensioned directly to eliminate tolerance stack-up. But what is the relevance of dimensioning between holes in this case when the datums (i.e. measurement locations) are specified as edges? Would it not have made sense for them to have dimensioned both holes with basic dimensions from the datums? This example was in an ASME book.
7)This may seem like a repeat question of one or two of the above, but assume I have a hole in a rectangular part. That hole has a position tolerance from datum B, which is the edge of the part. Can I use a basic dimension from the opposite edge of the part, or does it need to be from the datum edge?
8)I have 4 holes in a rectangular pattern on a rectangular part. Datum A is the flat surface the part rests on, and datums B & C are the other 2 perpendicular part edges. Each hole has position tolerances. One hole has a dimension callout 4x and the diameter. A position control frame is placed underneath this. All holes are the same size, but not all have the same position tolerance. Therefore, I use a position control separately on the other holes with deviating geometric controls. Is the 4x the diameter callout with the position control frame underneath OK even though the geometric tolerances are different on different holes?
9)Extension to question 8, except now datum D is one of the holes. I specify the position tolerance of another hole relative to frame A, D, B, where B is one of the sides. What distance would be measured upon inspection, the distance from datum D or from datum B? B is really only used to eliminate rotation in this case.
I know these are a lot of questions, but all questions I came across today while working on drawings. Your insight and help would really be appreciated, as always!
Thanks!!
