Extruding from inside

[rmatania]

Hi,   I'm a newbie with Fusion 360 but have viewed many videos and am now getting more familiar.

I haven't been able to find an answer to this question:

I made a simple rectangular open box by creating a solid, using the offset to define the walls and then extruding negative to hollow out the inside. The bottom of the box is on the X-Y plane.

I wanted to make a hole in the bottom but when I create a new sketch  or an offset plane on the inside bottom face and draw a circle on it, the circle appears on the outer surface.  I can draw circles on the other inner faces .
Thanks

[jhackney1972]

It really would not make a difference which side of the box bottom you created the sketch, it will extrude a a hole, just going a different direction.  I will make a guess, when you tried to create your second sketch for the hole, you selected the X-Y plane instead of the inside bottom of the box.  Another possibility is that when you hollowed out the box you extruded too deep and there was no solid bottom left.  Mode is attached to play with.  Next time attach your model for a definite answer to what happened.

[rmatania]

Thanks for the quick reply. The box has a 2mm bottom so I 'm sure I'm selecting the inside sureface for the sketch and it highlights it. For some reason selecting this surface for the sketch selects the x-plane not the inner surface.

[jhackney1972]

Go ahead and finish the sketch and then attach you model to a forum reply and the forum users and truly see what you did and is happening.  If you do not know how to attach your Fusion 360 follow these easy steps. Open the model in Fusion 360, select the File menu, then Export and save to your hard drive. Then use the Attachments section of a forum post to attach it.

[etfrench]

It doesn't matter if the sketch is on the inner or outer face.  It just needs to be on a parallel plane the the face you want to cut the hole in.  Experiment with the options in the Extrude dialog like Start and Direction.  Hint: You can use Start/Object to select the face to start from or you can use Direction/Two Sides or you can just make a normal extrude and select the direction.