Ordinate Dimensioning Vs Regular Dimensioning 6

[designmr]

I have a mounting plate that several components will be mounted. I have always liked to dimension hole to hole on my separate components, and have the same dimensioning on mounting plate for tolerance. If you do ordinate you really can't do that this.

Different Engineering manager's express their own preference for dimensioning, Ordinate vs regular dimensioning. Most say to avoid ordinate dimenions because of tolerance issues.

Anyone know is there really a difference between using Ordinate or regular???

Confused designer....

 

[ctopher]

Depending on the part's intended design.
Sometimes ordinate can be hard to inspect.
The tolerances would be different between ordinate and 'regular' dimensions.
If hole to hole works with how the mating part is dim, you can tolerance them the same. If the plate had ordinate and the mating part had hole to hole, the tolerances could be off.
Hard to say without seeing the assy.

Chris
SolidWorks 10 SP4.0
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SolidWorks Legion

 

[CorBlimeyLimey]

Depending on the machine shop, no matter which way the part is dimensioned, it will probably be made as if coordinates were used. It is unlikely they will reset the zero to the "seed" holes of various patterns.

 

[i2xtreme]

We use a bit of both, for example if a hole pattern needs to be held tighter then we would use regular dimensions between holes and only use ordinate dimension to one of the holes in the pattern. GD&T makes either method good as the dimensions become basic dimensions with no tolerance associated with them.

There is no need to just pick one method! Think of them as tools in your toolbox. Use what ever method or a combination that best describes the function of the part to ensure proper operation of the final assembly. We are heavy users of GD&T as it removes a significant amount of grey area.

 

[KirbyWan]

Our Machinist has asked when I dimension a drawing to use ordinate dimensions based on one corner unless there is a really good reason to do otherwise. Otherwise he has to rezero to each edge I call a dimension out from. Generally if you have a hole pattern, you want to drill one piece and then use that piece to match drill what it's attached to.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[designmr]

Thanks you all for your input, I appreciate it.

 

[beachcomber]

I usually try to dimension what I want, rather than what I think the manufacturer might prefer, because in my work you don't know who would be making it, or by what method.
So I would normally dimension the position of one hole (the 'seed' hole) and then the hole pattern relative to it.
You can then dimension the mating part holes in a similar way.

It all depends on what is required for assembly.



bc.
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[Updraft]

Ordinate dimensioning from a corner is very convenient for the machinist. However, ordinate dimensioning does not convey the design requirements. Think of the hole-to-hole/feature-to-feature dimensioning as "This is what is required" and the ordinate dimensioning as "Here is something to make the machinist's life easier".

We have many parts where the hole pattern is very important, but its location with respect to the edges is less critical so the tolerance to the edge is big. If the ordinate dimensioning and the manufacturing method that uses it can give you the requirements within your tolerances between features than that is not a bad way to go. However, you really cannot convert the tolerance from a feature-to-feature scheme to ordinate dimensioning so this is the dilemma you have to deal with.

GD&T is the most eloquent and unambiguous language for conveying the part's requirements. However, all parties involved must "speak it" well or it is just another foreign language. Someone once told me that GD&T is like French. French may be "the language of love", but if you are speaking French to someone that does not understand it, you are not going to get what you want.

- - -Updraft

 

[fcsuper]

Is this question the reason positional tolerances are perferred?

Matt Lorono
Lorono's SolidWorks Resources & SolidWorks Legion

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