Shell tool for exact internal dimensions?

[harry_hood]

Hi, 

Long time listening; first time caller here. 

I'm trying to build a camera lens hood (file attached) and I've got the general shape by doing the following: 

- extruding a cylinder of the total overall length. 

-working on 'adjacent' faces, sketching, then mirroring along the axis of the cylinder, a triangle, which I then extruded to create the end detail. 

-used the shell tool, choosing the ends of the cylinder, to create the final shape. 

The issue I see is that the shell tool allows you to specify material thickness, but I'm a bit stuck as to how I get the internal diameter I need in order to fit over the lens.  I see a kludgy workaround if I make the initial OD of the cylinder equal to the final ID + the shell thickness, but this seems intuitively wrong to me (and when I tried it, it didn't really work out). 

Any feedback or vague hints would be appreciated. 

Thanks! 

[TrippyLighting]

The ID is OD - 2 * Wall thickness ?

I am not sure where you see the problem.

[davebYYPCU]

Measure the original object, 

working from that diameter, plus clearance, = ID,

Od will be ID + wall thickness times 2 as Trippy says.

Wonky is these bits, needed or not they are not the same.  I am guessing they are not required, and you fix that with better sketch alignment.  When you get more experience, you would make 1/4 of the model and pattern the others for efficiency.

Blue lines (undefined) in your sketches have caused these sliver faces.

Might help....

[etfrench]

Adding ridges on the inside of the hood will greatly increase its ability to block light.   Each ring in this design will reflect any light hitting the inside of the hood (except for the very tips of the ridges).