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how to make a dome

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how to make a dome
I need to model a 250gal LP tank . The tank is a cylinder, which I am able to do, but it needs to have eliptical domes on each ends as lids. How do I make the lids and mate them to the cylinder.please help
Use the sphere
It will be a little complicated for the LP dome but not too hard. The sphere tool allows you to cut off one or both sides. Calculate the radius of the dome, cut one side to the depth required, then radius the edge. ie. Radius of dome is 20, depth of dome is 5. cut 35 from the sphere (r*2-depth). Keep in mind, radiussing the edge my reduce the cylinder diameter and you may need to play with it a bit.
How to model a tank
I hope you're still using VariCad (no, I'm not a shill!)
The way I model tanks, is to first make a model of the INSIDE of the tank, by making a cylinder to diameter and length of the "tubular" (inside) section of the tank. Then, (in 2D) draw an arc, the base of which is, the same diameter as your cylinder, the height the same as the "rise" (minus, of course, the thickness of the metal) above your cylinder that you desire the "dome" to rise. From this arc, you can determine the radius of the arc. In 3D, make a sphere of that radius. Then generate a cube, larger than the diameter of the sphere, position it, the "rise" dimension from a snap point on the sphere, however you can. Use the box as a cutting tool, subtract it from the sphere. There, you have your "dome".
Now, Change the insertion point of the "dome" to the center of the circle formed at the "bottom" of the dome, move the dome insertion point to the center of the "straight" cylinder, and there is the "top", copy and rotate the dome to the "bottom" of the cylinder center, boolean add the three object together.
Now you have built a "cutting tool" for the next step....

Now, using the "outside" dimensions of your tank,
Repeat the above.
Position the first "cutting" tool in the correct coordinates (position") to the second object. Use "boolean" subtract to "hollow" out the inside of your tank.
This is the only way I've found to model tanks correctly.
Hope this helps you in the future, I know it's too late for your problem, back in the stone ages.
Regards,
Bruce

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