linear or ordinate dimensions
 

linear or ordinate dimensions
all,
what's preferred in today’s industry? linear or ordinate dimensions. i prefer linear and guessing machinist would like to have that way as well. am i correct in this assumption?
i know there's no right or wrong answer, i'm just trying to get a feel what machinist would prefer.
thanks,
macduff
colin fitzpatrick
sr. mechanical designer
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most machinists i have talked to prefer ordinate, especially boxed, a list of x and y dimensions with a description, far easier to work to rather than matching up linear dimensions.
ordinate is fine in some situations... but don't forget that sometimes your drawing will have a standard tolerance for dimensions over a certain length and you can really screw up your part by dimensioning that way if you're not careful.
i think ordinate dimensioning is fine if you have a simple part that doens't require a high degree of accuracy applied to it's tolerances. or if you have a drawing that either doesn't have any general tolerances or says something like, "all linear dimensions are ±0.5, uos."
the biggest problem with ordinate is that you get tolerance stack up. our toolmakers like ordinate so that is what we give them but when we have to keep feature to feature relations tight we will use a linear dimension. so you end up with a drawing mostly in ordinate with some linear dims.
why do ordinate dimensions stack up if you come from a common datum, surely it is linear dimensions that stack up, if you do not come from a common datum?
you measure from an edge to a hole. one tolerance. you do the same for another hole. another tolerance. these holes may have an important relationship to each other, so if you dimensioned directly between the holes, you eliminate one of those toleances.
the exception to the above is if you used basic dimensions.
ewh that is true if you have only two holes but if you have say four, dimensioning from one to the next stacks up to a greater tolerance does it not?
if they matter surely putting a positional tolerance or mmc solves that.
i would use basic dimensions and a positional tolerance, but if not, i would dimension from one hole to the others. you are right that a tolerance stackup would occur with more than two holes in my example.
i prefer toolmakers that can add and subtract as needed and read prints across the full scope of acceptable print standards.
i make things easier to read for machinists when i can, but design comes first.