Can't sketch in assembly

[Anonymous]

Hello I've a problem with Sketching and extrude in the assembly mode.

When I'm making a sketch and I want to extrude it, I can only cut the sketch.. And if I chance the directin of the cut, there apears a error..

Help me please.

[JDMather]

If you go out to the shop floor and walk up to an assembly - how would you add a feature to an existing part?  You can only cut features.

If you want to add to a part you need to do it editing within the assembly at the active part level or at the part level.

Right click on the part you want to edit and select Edit Part.  Now you will be able to work with it within the assembly.

[jletcher]

You cannot add material  in assemblies only remove..

[Anonymous]

For one, any sketches placed in an assembly will only affect the look of the parts in the assembly, they will not actually change the parts themselves. Such edits must be done in the parts, which can be done in the assembly by doubl-clicking one of the parts. Any new parts must be made as a part and inserted into the assembly.

Extruding without cutting is not allowed in an assembly, only in parts. Assembly level edits are when you want to drill matching holes or features AFTER the parts are welded together or put in place for tolerance purposes. Alignment of bolt holes for example. They allow you to show this step for your drawing without actually affecting the parts themselves. Holes drilled in the parts that must be exact for alignment purposes would do little good if the parts were not made exactly or welded in place exactly. Doing this process after assembly assures the holes will be aligned.

Granted while modeling it makes no difference, your holes will always align. But in the shop while building it, such tolerances can not always be maintained, especially if different shops are building different components of the assembly. Doing this process after assembly ensures such errors do not occurr.

New parts can be created in place in an assembly by clicking "Create" on the assembly tab, selecting your template, and then selecting a plane or part feature. This is something one must just try to understand how the parts are placed. It all depends on your origin alignment in assemblies and parts. A process I rarely use.

[jtylerbc]

Everyone else has already stated that you can't add material in an assembly extrusion.  The second part of your question (why you can't flip the direction) is closely related.

When you flip the direction, you're pointing the extrusion in a direction where there is no existing material.  Since extrusions in an assembly are only allowed to cut, you've told Inventor to make a cut where there is no material to be cut.  That is what the error is from.