Saturday, December 6, 2008

Plant Your Crops

Lately a lot of people have been coming to me for help with views that have blown up, aren't showing right, or just plain gone missing. Nine times out of ten these views have had crops associated with them. Why are these views going wrong? Bad practices in creating the crop view in the first place. A cropped view is made of a closed sketch where once you select the crop view command everything outside the closed sketch is removed from the view. The closed sketch position is not locked to the view in any way unless you add relations and/or dimensions to lock the crop to your view. If the closed sketch is not locked and the view changes, the crop position can change also which may change you view in ways that are not acceptable.

How do we fix it? Fully dimension and relate your crop sketchs. Design intent must be followed through even to the detailing of your drawings. I know what you're thinking, "Haven't we been beaten with 'Design Intent' enough?" No! You can never stop thinking about design intent. If the details in your crop view can grow, shrink, or change in some way you must design your crop sketch to follow that intent. Usually I just find a closed spline encircling an area that is totaly unrelated to the parts in the view. Splines are fine, but harder to keep related to your parts. A 3/4 box with a single simple spline is better when you can. I understand that spline breaks are pleasing to the eye, but circles and elipses work well too. Relate centerpoints, midpoints, and endpoints directly to part geometry. You can also relate points to geometry outside the crop view.

Dimensions should be used on a crop view if you can't fully define the sketch otherwise. I have heard many arguments against them, 'The dimensions don't go away with the crop.', 'I don't like hiding dimensions because others don't know to look for them later.' and many others. There are several ways to hide dimensions. You or your group or company needs to decide on a standard and stick with it so everyone knows. The simplest is to use the hide function and show hidden dimensions function. It works very well. The other popular way is to create a "No-Plot" layer. Put all information that should not appear on the final plot on this layer. Dimensions from crops and other sketches, construction sketch lines, design notes, and calculation tables are just a few things that can go on this layer but the one thing that should always be on this layer is a large text "Do Not Plot Layer Is On" watermark over the title block. That way if you make a plot and forget to turn the layer off you will see it immediately. This layer can even be added to your templates.

Once your crops are fully defined (planted) you shouldn't have problems with your views related to crops.

Other view problems can include:
- 'Ctrl-Q' rebuild - Those are usually the first words out of my mouth, "Did you Control-Q?"

- Section lines that need to be rebuilt or that are in a position that would create a 'zero-thickness' condition (tangent to an arc edge). Edit the sketch line and fully restrain it as well.

- Section lines that somehow flipped their direction. - I don't see it often, but it does happen.

- Unhide parent views - Sometimes a hidden parent view keeps a child view from updating.

- Lightweight to Resolved - Make sure you have resolved any views that you are having trouble with.

- Overdefined and lost relations in a crop - Major changes to a view can lose relations or cause a relation to become over defined. This usually happens with changes that design intent did not anticipate.

Happy Detailing
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