Editing parts in Catia, Parent-child relationship and Define in work object

Editing parts that you have made already, may involve redefining sizes for features like pad, pocket etc, reordering certain features, even deleting the features.

Redefining size - Redefining size is easy, and you need to double click on the feature on the solid, it may be pad, pocket, shaft etc. or on the specific feature in the specification tree for which you wish to change the size. In the dialogue box that opens up, you would be able to change its size as per need. This is essentially the same box that was presented to you using which you specified the size.

Shell made after rib (Reorder required in such situations)

Reordering features - It may sometimes be required to reorder certain features. For example, in the part, the designer forgot to create shell before the handle was made and the cup now has a handle that is hollow, so we need to reorder shell before the rib command.The specification tree clearly tells us the chronology in which various features were made i.e. we can see which feature was created first and which one created afterwards. Keep in mind that even if a feature is created after a certain feature, it may not be necessarily its parent, so you have to keep the parent-child concept in mind while reordering i.e. a child cannot be reordered before a parent. The parent-child relationship can be checked as previously explained. Depending on whether or not a particular feature is a parent of the other feature, or if is independent, you would be able to reorder those features. A child cannot be positioned before the parent, since existence of child is dependent on parent, so any illogical option would be shown in yellow by Catia in the specification tree.

'Reorder' command (invoked using right click), followed by specifying the order

To reorder, you would need to right click on any of the feature, and select Reorder. Subsequently, use "Before" or "After" option to reorder the feature. After reordering, ensure that the PartBody is defined in work object to display all features.

Deleting features - If required, you can delete a specific feature from specification tree, by using the key from keyboard. You can also right click on the feature and use the delete option available in contextual menu. Deleting features may have no consequences as such. However, if a feature is deleted, it would and will affect any children it may have. In a simple part, with very few features, it may not be as difficult to modify geometry, but in large parts it can be problematic. So, it's advisable to first check the relationship using parent/child option and then delete the features.

What do we understand by parent-child relationship?

In case of all parametric softwares, it's important to understand the parent-child relationship. Since a child cannot come into this world without parents, likewise a feature made using another base feature if the base feature ceases to exist.

Sketch (in red colour) made on face of a solid (gray)
(Planes shown in blue colour)

For example, if you see above, there a part (in gray) and on one of its face, we are making a new sketch for a protrusion (in red). Now, if we were to delete the main part, it would be impossible for the sketch and the protrusion to exist, since main body has been deleted. So, you would need to either re-specify another plane for the sketch or delete the feature made using the face. Perhaps, it would have been better to make a reference plane offset from a plane like XY and make a sketch on that instead and perform Pad operation uptil next. Similarly, if a fillet has been applied on the edge of a solid, if the solid is deleted, the fillet would not be able to exist and you would need to delete the fillet too or specify another edge on which it can be applied.

It's important to keep the concept in mind while you design and take into account any 3D projection, intersection or dimension that's been applied using an edge of 3D model as it will make modification somewhat difficult and you may need investigate before/after deletion so as to not disturb other features that may be depending on the part. Also, if planes are being used for feature construction, if it's possible, references should be taken from planes like XY,YZ and ZX as these cannot be deleted.

You can always find out the parent/children of a feature by using Right click>Parents/Children option. this would reveal the relationship it has with other features. You can double click on any of the feature to find it's children and parent. You can also zoom in and out as well as Pan in this window as you do in 3D space. 

Using parent/children command to investigate relationship

Bottle shell (done at the end)

What is the use of define in work object?

The part on your right could have only been built only if the Shell command was applied in the end (We will study shell ahead). So, the chronology of the features is important and while designing bottles, or other plastic parts which are of constant thickness, we need to keep this thing in mind. Also, in case you need to edit this part in future, you would need to edit it in a certain order. To edit such parts in order, we require define in work object option.

What will define in work object do?

The point till which a part is built and shown, is depicted with an underline on the feature. If this underline is on the Partbody or on the last feature you created (like pocket in this case), it means that the part is completely built and all features are shown and updated. However, you can use the option Define in work object, to see your part build only up till a certain point i.e. all features created after that would not be shown.

How to use define in work object?

Underlined Partbody, i.e. part completely built

The command can be invoked using right click. For example, if you wish to see build only till Pad.1, right click on the feature and select Define in work object. This will not show any of the features built after Pad.1 feature.

This is useful if you forgot to create features and it was desirable to have a certain chronology in them. So, the option can also be used to insert features in between other features. For example, if you desire to insert certain features between Pad and Pocket, you can Define in work object the Pad, and subsequently create the features you desire. This will insert the features in between Pad and Pocket. So, in case you need to edit a part like bottle, it would be first required to define in work object a feature like pad etc. so that it is not applied after shell.