dimension scheme
dimension scheme
(OP)
i'm getting redlined on my dimensiioning scheme. i have always tried to dimension from a common edge (datum)and not use chain dimensions. the standard says that chain dimensions have the most tolerance stack while baseline/ordinate and direct dimensioning schemes have lesser tolerance stacks (AMSE Y14.5m-1994 2.7.1). any feedback on this to help convince this engineer that chain dims are not the way to go, other that giving him the spec to read for himself?
thanks for your time
thanks for your time
Sr. Pro/E Mechnaical Designer





RE: dimension scheme
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: dimension scheme
If they are rectangular using +/- on them yes this will add to the tolerance stack up.
RE: dimension scheme
RE: dimension scheme
Sr. Pro/E Mechnaical Designer
RE: dimension scheme
Frank
RE: dimension scheme
Sr. Pro/E Mechnaical Designer
RE: dimension scheme
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: dimension scheme
Please give us a simple sketch how you did this.
If you are following Y14.5 standard, the standard recommends basic dimensions usage together with position tolerance (eventually profile of surface callout). But this will also require some features of a part to be assigned as datum features.
Any +/- dimensioning scheme will create ambiguity here (even if you are dimensioning the centers of holes from common edge), because you never know from which feature measurements should be taken.
Only GD&T will help you to eliminate any misinterpretations of your drawing.
RE: dimension scheme
He is correct. For this particular case.
RE: dimension scheme
Sr. Pro/E Mechnaical Designer
RE: dimension scheme
Since you specified +/- tolerances, discussion of basic dimensioning would be irrelevant.
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: dimension scheme
I used to use datum dimensioning systematically, because I knew that was the way the machine shops wanted it. On a complex part, you wind up with a simpler drawing.
Today, machinists go straight to CNC on most parts. Your dimensioning scheme probably is not as critical for them. Dimensioning to show functionality is much more feasible now, consistent with readability.
If you are using GD&T positional tolerances, as you ought to be, you may have a requirement that your hole pattern must be internally accurate, but its location, less so. In this case, datum dimensioning is not meaningful.
I would say that on a machined part, your dimensioning scheme is not critical. The machinist will locate everything accurately from the datum, regardless of how you apply the dimensions.
If your part is sheet metal, you can punch the holes accurately on the flat sheet, but your bends are not accurate. I would avoid datum dimensions.
For weldments and castings, you are going to have to think through all your dimensions. Machining drawings are easier than all the rest.
RE: dimension scheme
Sr. Pro/E Mechnaical Designer
RE: dimension scheme
For such a simple pattern, I would default to the function as the guide for dimensions. In this case, I would agree with your engineer. The pattern's association to it constituants is more important than their relationship to the edge.
However, this line of reasoning should not be extended to include a long change of features where accumulation between features will cause the overall pattern violate design intent.
Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion
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RE: dimension scheme
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