Hi all:
I can't get over all the letters and even phone calls I've received from you all. What a bunch of great smart and kind people! I'm leaning to the idea of inserting a slightly smaller square tube inside the round tube, then welding it to the outer round tube at both ends. Several guys suggested this. It makes sense. They say to weld the inner square tube so that one of the corners of the square tube is at the top and not a flat side on top. This also makes sense. Everybody seems to agree on the following: 1. Tubes are less bendable than solid rods 2. Tubes are less expensive than rods 3. Filling the tube with cement won't help and might make things worse. 4. Wider diameter tubes are stronger than thinner tubes 5. Thick tube walls help prevent bending. (one person suggested that the tube wall thickness be .125 inch minimum) I've learned a lot from this discussion. Hope it helps some of you with your future projects too. Thanks everybody! John John L. Carmichael Sundial Sculptures 925 E. Foothills Dr. Tucson AZ 85718-4716 USA Tel: 520-6961709 Email: <mailto:[EMAIL PROTECTED]> [EMAIL PROTECTED] My Websites: (business) Sundial Sculptures: http://www.sundialsculptures.com <http://www.sundialsculptures.com/> (educational) Chinook Trail Sundial: http://advanceassociates.com/Sundials/COSprings/ (educational) Earth & Sky Equatorial Sundial: http://advanceassociates.com/Sundials/Earth-Sky_Dial/ (educational) My Painted Wall Sundial: http://www.advanceassociates.com/WallDial (educational) Painted Wall Sundials: http://advanceassociates.com/WallDial/PWS_Home.html (educational) Stained Glass Sundials: http://www.stainedglasssundials.com <http://www.stainedglasssundials.com/> (educational) Sundial Cupolas, Towers & Turrets: http://StainedGlassSundials.com/CupolaSundial/index.html From: Lloyd Tackitt [mailto:[EMAIL PROTECTED] Sent: Thursday, October 02, 2008 9:53 AM To: John Carmichael Subject: Re: Preventing Rod Gnomon Bending One other possibility worth mentioning - there is a type of structural steel that is a square tube - very rigid. ----- Original Message ---- From: John Carmichael <[EMAIL PROTECTED]> To: Lloyd Tackitt <[EMAIL PROTECTED]> Sent: Thursday, October 2, 2008 10:14:25 AM Subject: RE: Preventing Rod Gnomon Bending Hi Loyd: You agree with many of the other guys, so you all must be right! I'm so glad I asked you all. Thanks so much for writing. I REALLY appreciate it. Take care, John From: Lloyd Tackitt [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 01, 2008 12:22 PM To: John Carmichael Subject: Re: Preventing Rod Gnomon Bending If you can get thick walled pipe you will do better than getting a solid rod. The thick wall pipe is more rigid than a solid rod, possibly due to the increased weight of the rod, plus the somewhat truss like effect of the pipe wall. Pipe generally comes in 20 foot sections, to get one in 25' may be a special order, or it could be done with a threaded coupler, if the coupler isn't considered unsightly in your design. If you can go larger diameter you will gain rigidity, as long as you remain with thick wall pipe. 4" pipe will be more rigid than 2" pipe for instance. Drill stem (as used by oil drilling rigs) is a very thick wall pipe that would be ideal, but it may be hard to find where you are. Concrete won't help the rigidity issue for you in this case. Concrete in bollards (collision barriers) adds weight mostly, and keeps water and debris from accumulating inside. Have you considered a steel beam? An "H" (sometimes referred to as "I" beam) beam is very rigid. This assumes that the gnomon doesn't have to be round. They can be purchased in varying dimensions and lengths. Hope this helps and not confuses. ----- Original Message ---- From: John Carmichael <[EMAIL PROTECTED]> To: Sundial List <[EMAIL PROTECTED]> Sent: Wednesday, October 1, 2008 1:46:56 PM Subject: Preventing Rod Gnomon Bending Hi Guys: I'm designing a large 15 foot tall southwest declining nearly vertical dial that will have a very long polar axis oriented rod gnomon. But I've come across a potential problem that I've never had to deal with before and am seeking your expert advice or suggestions. Setup: The gnomon rod will be unusually long because one end will be attached near the sundial face and the other end will go down and be firmly attached to the ground. The reason that it will go all the way to the ground is because a second horizontal dial will be on the ground that will use the same gnomon. The original specs have the gnomon rod diameter as 2 inches, but it can be made wider if need be. The gnomon length will be about 25 feet. We have not decided if the gnomon will be a hollow tube (like a metal pipe) or a solid metal rod. We want to avoid using any gnomon support struts and we want to prevent bending. Problem: Since I'm not a metal structural engineer, I am concerned that the 2" diameter, 25 foot long gnomon might sag under its own weight or bend if kids hang on it. Keep in mind that it is attached at both ends, which should help prevent bending. Here are my questions: 1. Do hollow pipes bend easier than solid rods? (I'm guessing they do, but I'm not sure.) 2. Can a hollow pipe be made to bend less if it is filled with concrete? Or will the added weight just make bending worse? (This idea occurred to me because I've noticed that the metal pipe collision barriers around gas station pumps are filled with concrete. Is this to prevent them from bending if a car hits them?) 3. Would increasing the diameter of the gnomon give it added strength and prevent bending? Any help much appreciated! Thx John
--------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
