Cowl Ventilator – IV

Inner Circles
.418circleSo. With the decision to make the walls .020 in. thick we can continue by creating the inner circles on our primitive.

When drawing circles in Sketchup you are given the radius of the circle in the text box. This is mostly for reference as far as I am concerned since I normally enter the dimension needed on the keyboard. The larger 0.876 in. dia circle has a radius of .438 in. That being after all the dia of the #234 Evergreen tubing we will be using for any trunk extension – (cowl is trunk dia x 2). Take .020 from .438 to get .418 .. this is the radius of the inner circle .

Draw a circle centered on the larger one .. let go of the mouse .. type in .418 and hit enter. It’s that easy. (the inner circle dia. will be 0.836 in.)

selectinnerfaceslinesIn a similar fashion the trunk has a .438 dia. The radius is .219 so subtracting .020 we get a .199 in. radius for the inner circle. Create that. (the inner circle dia. will be 0.398 in.)

Then select the center faces and lines of the model. The blue half-toning will show you selected the inner faces and the lines will turn blue when you select them as shown.

Hit Delete to remove them. You can delete the dimensions at this time also – there were there just for you dear reader.

Note: Examine the rings left – you will probably have remnants of the lines on the rings .. if so delete them (the lines not the rings!)

Lofting along Path
ringscreatedI will be using the Sketchup plugin Curviloft’s – “Loft along Path” – described as “joins contours along a given rail curve”. Ok. I’m not sure what that means exactly even though it is in English. No problem. It works.

We will be doing this twice .. once using the outer circle of the rings (creating the outer skin of the ventilator) and once again using the inner circle of the rings (creating the inner skin of the ventilator).

Outer Skin
.876-5I turned the model around so this will be seen better. I selected the outside circle and the arc (path). Now we can use the Curviloft tool. Click the too with the tooltip .. “Create Loft junctions following a given path”.
.876-6The skin (ok .. “Loft Junctions following the path”) will be created. You are provided with a view showing the hidden lines. You can spin this around. It will not be applied unless you left click on the screen somewhere (the green checkmark). ((the scroll wheel will rotate .. right clicking you have several choices including exiting without applying .. or .. you can simply hit the spacebar to exit with out generating geometry).
.876-7Click anywhere on the screen to generate the geometry. We are now looking at the outer ‘skin’ of the mesh. The white color is what the computer (and any 3D program) sees as the skin. The purple surface is the inside of that skin. This might be a difficult concept .. but this surface has no depth .. it is simply a face between points. The program is saying that it has generated the surface .. that this purple color is there to show you that you are looking at this surface from the ‘inside’. A good example would be a cube. From the outside you see six sides. In the ‘real world’ it is solid. Not in a 3D world. There .. you have six faces. The bit you see .. the outside are the outside faces and would be displayed on your screen as white. There is no inner bits .. just the underside of those outside faces .. and are shown in purple.

Notice that the face of the ring is also purple. Good catch! That will have to be flipped ‘right side out’ later.

Inner Skin
.876-8Now select the cowl inner circle, the trunk inner circle and the arc/path. By turning the model like this toward the camera I can easily select them all. When this is done you click the Curviloft tool as we did when we formed the outer skin.
.876-9.. again the fist thing that will come up is the black image with hidden lines. Click on the screen and create the geometry. Remember that ring face that is purple? We are looking at the ‘inside’ of that face and need to flip it. Select the ring face – it turns a purplish half-tone. Right click to get a context menu. Select “Reverse Faces” from the menu. When that is done select the arc/path and then hit delete. I had to also reverse the face of the bottom (trunk) ring.
.876-10In Part II I posted a photo of some orange colored Cowl Ventilators. The length of trunk from the cowl down to the first joint is different on them but the one venting the Engine Room looks to be approximately the width of the trunk in height. In this case, this is .438 – I will go with that. Subtract .125 from .438 to get .313 – we are making room for a ‘stud’ so we can align Evergreen tubing to extend the trunk as needed.

I used the Push/Pull and pulled the trunk ring down. I typed in .313 and hit enter.

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