Created vs shown dims

Really replying more to Rob, but...

Created dimensions are candidates for being overridden, hence are the only ones that can be easily faked.

It is also easy to create references to geometry that look almost right, but are subtley wrong, such as selecting the end of a line segment, not noticing a small round.

Created dimensions can also carry unwanted results. I believe if a line has an end-to-end dimension created, and a round added, the dimension, which should be to the intersection of the line and the next face, will instead not include the length of the round. The value change is automatic, but the meaning change is wrong.

The ugliest problem I've run into was a casting/machining where a contract engineer was given a hand-drawn drawing with about 150 (or so) dimensions, and missed where the origin was. So he built the model entire model dimensioned from one side and created the 150 dimensions on the drawing. Bad news was: the intent of the redraw was to change the design slightly. In some cases, to change a wall thickness which was one dimension on the original drawing required going through a stack of a dozen dimensions to get the desired result.

What should have taken one minute to do instead required a full re-check of the model and the drawing to make sure nothing else was changed incorrectly in determining which dimensions affected the wall thickness and what the new values needed to be.

Usual disclaimer - tools used poorly produce poor results. It's just that created dimensions are more easily poorly used.

x

The ages-old debate, created vs. shown dimensions...

My two cents: if you had asked me a year and a half ago, I would have been squarely in the shown dimensions camp. I used to tell everyone that at least 95% of the dimensions that appear on a drawing should come from the model.

Now... I'm split. What caused the change? Flexible Modeling Extension and 3D Annotations. Incorporating Direct Modeling into Parametric Modeling is powerful, but requires us to rethink modeling conventions. With Model Based Definition, there are differences between the way that feature-owned and non-feature-owned dimensions behave, and I haven't figured out all the nuances and repercussions yet. As a result, I'm no longer firmly on one side or the other of the issue.

David R. Martin II

Senior CAD Application Specialist

Amazon

The problem I have with shown dimensions is if I toggle them to ordinate in the drawing they convert to ordinate in the model. The ordinate dimensions then become difficult to work with in the model. Does anyone else have this issue?

I find it interesting this question rears its ugly head every so often. In the rush to get it all done at light speed, things tend to get overlooked.I will get the Old School CAD monkey stuff out of the way first. Drawings have been and still are an important and integralfacet to the product. In many cases the drawing is the contract between your company's supply chainand the supplier. In today's faster, faster, faster workplace, drawings seem to get dismissed and marginalized becasueof misused"CAD is Master" statements on drawings. Keep in mind, this process works best when every player in the product chain has access to the CAD and is capable of using it correctly. If one link in the production chain is incapable to read CAD or measure per the data, it is all for not.

Both created and shown dims have advantages and disadvantages. I use a combination of both becasue view orientationon drawings can work against you with placement of particular dims. Also, it is typical that as I model things I do not know exactly how I need to inspect a part so my "shown" dims do not present as I need them to. I may, if enough time permits, will redefine features to allow for shown dims. Other times, I do not have time to change the model. It's great to have the freedom to do both.

With that said, I emplore you all to sweat the details on your drawings no matter which "standards" your respective organizations use. What I mean by that is make sure your details are done well. Never assume the drawings "update" automatically. Whether you use created or shown dims has always been a matter of care and attention. In other words, good detailing skills are required regardless of the method used.