Like a cube, only pentagons in 3d

Hello all;

I'm fairly new to autocad. I'm trying to construct an object (like a cube) made of pentagons. I originally thought it would be pretty straightforward, but all my attempts have ended in failure. I get lost in the UCS/WCS, if thats really the way to do it. I can get it laid out on a flat surface, but can't seem to get it to wrap together. I've seen a similar object but cannot figure how to make it work. Could anyone point me in the right direction?

TIA

Confused in Houston

Pete:?

I'm trying to construct an object made of pentagons.

Something like this?

Yes, only with 5 sided surfaces. How is that done?

Pete

Dodecahedron, perhaps.

Attached done with multiple SLICE operations.

Dodecahedron.dwg

GREAT! What shape did you start with, a sphere or a box or does it matter. Why didn't I think of slice?

Any solid sufficiently large will do.

Hello all;

I hope I'm doing this thread continuation correctly. I am still working on the 5 sided dodecahedron in CAD P&ID 2010 student version (free while in school). I have sort of figured out how to use "ROTATE3D", alinging to the object. Near as I can figure, I align with the shape and a common baseline. I get SOOOOOOO! close with this method, but still end up with the edge alignment being off by fractions of a degree (see attached file). Can anyone look to see what I'm doing wrong?

PS I'm rotating +63 deg. from the baselines.

TIA

Still but less confused in Houston

Pete

DoDec.dwg

Let me try that again. I hadn't saved it

DoDec.dwg

The angle is actually closer to 63.5 (See image).

I used a process similar to the one shown in post # 16 shown in this thread to derive the angle.

http://www.cadtutor.net/forum/showthread.php?t=29863

Ah ha! Narrowing it down now. THANKS. Give me some time to study "POST 16", I'll probably have more ???

You are really dedicated to be answering on Sunday. Me, I have no life.

Learning in Houston

Pete

I typically stop by at least once per day (because there is typically a dozen or so interesting posts since my last visit).

turbeauxpete,

After playing with the geometry a bit, I can tell you that the angle from baseline required to match the edges is close to 63.434949 degrees, but since I haven't done the work, I can't tell you that repeating that pattern will result in a closed polyhedron. Good luck.

:?YAHOOOOO!

Attention SEANT (thanks)

Hardheadedness pays off. I finally got it. I did cheat somewhat, but in the workaday world, time is money.

Step 1. (for those who care) Draw an inscribed, by center, pentagon of any radius.

Step 2. Draw five more pentagons by edge, attached to the original's edges.

Step 3. Using "ROTATE3D" not the "3DROTATE" gizmo. Select an adjacent pentogon and rotate up by 2 points (63.43494882 deg.). Pos. or neg. depends on how you select the 2 points of axis between the original and adjoining pentagon. (left to right is pos. right to left is neg.)

*Continue this for all five adjacent pentagons, after which all six pentagons should form a bowl.

Step 4. Mirror the "bowl" 180 deg. saving the original. Switch to Top view and rotate the mirror image 36 deg. (either direction).

Step 5. Finally. select top "bowl" and move it to join bottom "bowl" like the jaws of a bear trap.

I'm not sure as to how to derive the 63.43494882 degs, but it works.

As for 36 degs., that is half of 360 divided by 5 (72 deg.)

Sorry for the long post, but I retain things better if I force myself to write details down or be able to explain them to someone else. Besides someone else may be just as confused as I.

Thanks again to SEANT

Learned a lot in Houston

Pete

Sheesh! Forgot to attach file.

Finally.dwg

This is how I derived that angle (see attachment).

It was the same process used in that link I posted earlier, but, having looked at it again, that link wasn’t all that informative. This new attachment has some of the intermediate steps.

AngleCalc.dwg

Wow! but Darn;

OK - Again thanks to SEANT.

1. I duplicated the revolve and intersection operations just fine. The outer edge of the remaining intersection section is indeed 63.43494882 degrees. So far so good. (BTW: this method works for apparently any shape having an odd number of sides, I have tried 3 others.)

2. With that said, I can do a "ROTATE3D" command, selecting an outer pentagon and selecting 2point for a baseline of the common edge between the outer and original pentagon. as shown in the attached drawing. By specifying a rotation angle of 63.43494882 and enter, the rotated solid alings perfectly to the intersection object. I can continue this procedure around the original alinging perfectly.

3. Where I'm running afoul is when I try to use the reference choice of rotation angle aaaannnndddd ~~~~~~~~~~??? not being being able to accomplish much from there. I mean I can do many things, other than snap to that point. It would be so much more efficient to just select the top of the outer edge of the interection object and have the said pentagon just go there.

What am I doing wrong after all this learning? It's like showing up to class without a pen or pencil.

I hope I have been clear as to what my stumbling stone is. I hope it's not a ucs thing, I'm still lacking (but learning) in that area.

Oh well, thanks for reading my essay. I hope you can open my eyes

Very hot in Houston

Pete

OngoingDodecahedronThread.dwg

In a parametric program (like Autodesk Inventor, perhaps AutoCAD 2011) you shouldn't need to do any calculations, rotations.....

...all geometric relations. Let the software do the work.

The “Reference” option of the Rotate3d command has always been a bit spotty. I used the Section command to avoid the need to use 3dRotate, or realign the UCS to use the standard rotate with reference option.

Is the intention to do this type of operation for more shapes/-hedrons? It is a rather unusual task.

Interfere and Section, who would of thought. Great info Sean T. Ive got it down now. I'll end this thread with thanks to all, but don't worry, I'll be back.

! million gallons less in the gulf today, thank God.

Still hot in Houston

Pete

PSS

I'd still like someone to show me an example of ROTATE3D / Reference and ROTATE3D / Object

Pete in Houston