pic: Measure Thrice

[Richard Wallace]

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[Alan Anderson]

Originally Posted by Richard

Three challenges:

1) Provide an alternate description of the solid using two words.

2) Describe a procedure for fabricating the solid.

3) Describe a procedure for modelling the solid in Inventor.

1: chisel tip?

2: Cut a 1" length of 1" rod. Mark a vertical diameter on one end, and a horizontal diameter on the other. Grind off material such that the ground faces become half-ellipses, so that the curved "end" touches the tip of the horizontal diamter and the straight "end" is the vertical diameter.

(It might be easier and/or safer to do the grinding first, then the cutting. It is also possible to cut the diagonals rather than to grind them off.)

3: Extrude a 1" circle, a 1" square, and the 1"x1" triangle. Intersect them all at right angles (e.g. cylinder along the x axis, square prism along the y axis, and triangular prism along the z axis).

[Bill_Hancoc]

This is a very cool site that contains drawings a ton of polygons. It also has 3D color pictures that can be rotated of polyhedrons of varying complexity, I found one that looks like the Epcot center.
On to the goods

1.) Omni Cork Plug

2.) Put a screw in the bottom of a 1x1 cylinder and hold it verticly ^ (when its done) sorta like that drawn and mill out the triangle shape.

3.) Extrude a 1in. Dia. Cylinder, with a 60 deg. taper, 1in.

Looking at this site i described above i noticed that on the square face the piece removed by the triangle is a perfect parabola.

[Greg Ross]

Originally Posted by Bill_Hancoc

Looking at this site i described above i noticed that on the square face the piece removed by the triangle is a perfect parabola.

Actually, that would have to be a half ellipse, since the two extremes are parallel. The sides of a parabola never reach parallel.

[KenWittlief]

Chinese Screwdriver?!

[Richard Wallace]

Originally Posted by KenWittlief

Chinese Screwdriver?!

Good guess.

Originally Posted by Alan Anderson

1: chisel tip?

That's the one I was looking for.

Originally Posted by Bill Hancock

Cork Plug

This one is the probably the best. Note that the mathworld link says there is an infinite family of shapes that satisfy the challenge. The one with minimum volume has triangular cross sections.

I think the mimimum volume cork plug can be (approximately) modelled in Inventor as a loft from a thin rectangle one inch long by 1/1000th inch wide to a one inch diameter circle. The rectangle is sketched on a plane one inch from the circle and the long centerline of the rectangle projects onto the circle's diameter. I used a model made this way to generate an STP file from which we made a "minimum volume" cork plug on a Viper SLA machine at Emerson.

Of course, Alan's procedure is more practical. Just round the elliptical edges a bit and you end up pretty close to the minimum volume.

[Bill_Hancoc]

Originally Posted by GW (Greg) Ross

Actually, that would have to be a half ellipse, since the two extremes are parallel. The sides of a parabola never reach parallel.

If you were to extend the length on the main cylindrical feature the extremes would be parallel, but if you to expand the height and width so that the poece would always be a perfect square the sides of the parabola would just be intersecting with the corners of the square shape and would continue in a parabolic "line"

[Richard Wallace]

Originally Posted by Bill_Hancoc

If you were to extend the length on the main cylindrical feature the extremes would be parallel, but if you to expand the height and width so that the poece would always be a perfect square the sides of the parabola would just be intersecting with the corners of the square shape and would continue in a parabolic "line"

GW is right. The curved edge is elliptical, not parabolic. Referring again to the the mathworld site, an ellipse is a section through a cylinder (a circle is the special case in which the section plane is perpendicular to the cylinder's axis), while a parabola is a conic section (section through a cone).

[Greg Ross]

Originally Posted by Richard

GW is right. The curved edge is elliptical, not parabolic. Referring again to the the mathworld site, an ellipse is a section through a cylinder (a circle is the special case in which the section plane is perpendicular to the cylinder's axis), while a parabola is a conic section (section through a cone).

Correct. Specifically, a parabola is the special case where the section plane is parallel to one "edge" of the cone, so that the curve never closes on itself: http://mathworld.wolfram.com/ConicSection.html

[John Gutmann]

If you make this like the way everyone else is wouldn't there me more lines on the triangle? They wouldnt be hidden lines because they are outside of the projection of the triangle face.

[Madison]

Originally Posted by Bill_Hancoc

It also has 3D color pictures that can be rotated of polyhedrons of varying complexity, I found one that looks like the Epcot center.

Epcot's Spaceship Earth is the world's largest complete geodesic sphere. There are many other geodesic domes scattered around the world and a sphere or two, as well.