Cowl Ventilator – V

.876-11In part III I mentioned that I would explain why including the I.D. of the trunk was important. We will use that to make a small stud to align the ventilator with Evergreen tubing.

First we need to thicken the end of the trunk. We want the ‘stud’ to fit down inside the Evergreen tubing so everything aligns. The evergreen tubing that matches the trunk .438 in. dia is Evergreen #234. This has an I.D. of .381 in. Let’s keep to the .020 in. wall thickness so our stud will have to be .381 – .040 = .341 in. dia. Round that to .340 and the radius is .170 in.

We will be drawing a new circle on the bottom of the trunk. Since it is an open tube let’s make it easier and fill in the bottom with a face. Draw a line across the open end of the trunk and it will fill in immediately.

.876-12Delete the line we drew so we are looking at a ring and a filled circle.

Now select the circle too. Hover over the outer circle a moment to let the tool infer the center of the circle. Move to the center and draw a circle .340 in. dia (.170 radius). This will form our stud. Now draw another circle with a .150 in. radius. This will create a .020 wall for the stud.

Let’s pause a moment to see what we are doing here. We now have three circles as shown ..

  • .438″ – this is the O.D. of our trunk the same as Evergreen #234 tubing.
  • .398″ – this is that .438″ O.D. minus .020″ walls.
  • .340″ – this is the I.D. of the evergreen tubing. This will be the O.D. of the stud that will fit the I.D. of the Evergreen tubing.
  • .300″ – this creates a .020 in. wall for the stud.
.876-13First .. select the center .300 dia. face and hit delete. Now let’s pull down our stud.
Select the inner ring – the one that is .340 in. dia. then select the Push Pull Tool. Press and release the Cntrl key to create a new facep and pull down .250 in.
.876-14Next select the next ring out. Select the Push/Pull Tool – Press and release the Cntrl Key to create a new face and pull down .125 in. Select the outside ring. Select the Push/Pull and pull .125 in. (you did not create a new face by pressing the Cntrl key this time as we are but extending the ring we pulled down earlier).

Finally select the circle between the two rings we just pulled. It will turn blue. Hit delete.

.876-15Turn the ventilator so you can look down the cowl into the trunk. Select the circle between the two rings you see and hit delete. Then select the purple ring, right click and Reverse Faces.

.. and .. we are finished.

FinishedHere’s the finished Cowl Ventilator ready to insert into a length of #234 Evergreen tubing and installing on a model.
crossectionFinally .. a cross-sectional view so you can see what all of the work did internally. This is the mesh that gets uploaded to be printed.
CVGroup_1I created a mesh with 4ea of the Boiler Hatch ventilators, 8ea of the Engine Room ventilators and 12ea of a N scale ventilator and uploaded to Shapeways and dropped an order. They passed the initial checks .. so far so good. I was a little leary of whether the N scale ventilators would pass simply because of the small size – Shapeways has .. sensibly .. a minimum physical size as people have to be able to handle them. With small parts sometimes you have to gang them on a sprue. Will see if this prints without doing that.

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