Delrin vs. Lexan vs. Plexiglass Rod

[mactec54]

amateur78t

Get a fiberglass rod, this will do the job for you, it will be-able to flex if it needs to, & do the isolation for you as well, the other materials would not be suitable

http://www.usplastic.com/catalog/ite...3193&catid=561

[Fastest1]

Why not just use electrical PVC conduit ( gray) and use it and the different fittings that are available? A large diameter should give you sufficient strength. A long piece installed vertically and braced via a T or 2 also attached to the tower, would be inexpensive, easy to build and readily available materials. You might even be able to foam fill and cap the end for more rigidity if needed. Just a thought.

[Dougal]

With the right design (i.e triangulated, not cantilevered) any of these plastics will work fine.

With the wrong design (i.e. cantilevered), none of those will work well.

[amateur78t]

Can you elaborate what you mean by triangulated, not cantilevered means and/or what it is exactly?

[Dougal]

Can you elaborate what you mean by triangulated, not cantilevered means and/or what it is exactly?

In the simplest terms, a cantilever sticks straight out and has the load attached to the end.
It results in high material stress and a lot of flex compared to other methods.
Cantilever - Wikipedia, the free encyclopedia

Triangulation is the use of smaller struts to form triangles so the load is taken as compression or tensions in each. The result is a lot better strength and stiffness to weight.

Like this:

[RomanLini]

But these plastics are stronger than wood and should last longer, should they not? I could break 1.5" wooden dowel over my legs/knees, but I could never do that to solid 1.5" delrin or lexan!

There's nothing wrong with wood, some decent hardwood struts, screws glue etc and then painted with some good UV safe enamel paint.

I'm surprised if as a radio amatuer you don't know a heap of people with wooden frame antenna setups and they can probably tell you the tricks of building them too.

[amateur78t]

I just don't think 1.5" o.d. wood is as strong as delrin or most super plastics. I need this to last a long time in high winds and climate conditions. Wood breaks much more easily, no?

I can't make a triangular set up, it has to be cantilever. The mounting configuration doesn't support it on the side of this tower.

Am I really asking to much for a 4' long standoff? Is it too long or is the load too heavy? What if the solid delrin rod was only 2' or 3' long and the antenna load was only 10lbs? I believe 1.5" solid delrin rod could hold 500lbs or more, correct?

[ahunter9624]

first i have to ask why did you post this question if you're going to doubt every answer you recieve? Second if it has to be strong and has to last for 5 yrs then why don't you look into carbon fiber tubing or rod? Its not as expensive as you would think and its stong as hell.

Braided Carbon Fiber Tube > Braided Carbon Fiber Square Tubes

Check out this company. I dont know if carbon will affect your signal or not but its more than strong enough. You will have to paint it since carbon fiber deteriorates in UV.

[Geof]

Just for interest's sake I clamped a piece of 1-1/2" Delrin on a bench with six feet cantilevered out. It sagged about 3 or 4 inches just from its own weight and I could push it down a further 6 inches just by resting my hand on it. And Delrin is one of the stiffest non-reinforced plastics available.

The suggestion made earlier to use a sailboard mast is the second cheapest, the cheapest would be a hardwood, which incidentally is stiffer than Delrin.

[RomanLini]

One of the problems with plastics is the resonance, they will act a lot like tuning forks wobbling in the wind. Hardwood will damp flexion quite well and is popular in antenna frames with a hundred years of common use. And many plastics have UV issues or get soft in the hot sun + attached to a hot metal mast etc.

Anyway just build it the way you want to...

[Dougal]

One of the problems with plastics is the resonance, they will act a lot like tuning forks wobbling in the wind. Hardwood will damp flexion quite well and is popular in antenna frames with a hundred years of common use. And many plastics have UV issues or get soft in the hot sun + attached to a hot metal mast etc.

Anyway just build it the way you want to...

Flexing in the wind has to do with building a stiff enough mount. You need to get the natural frequency of the structure above the frequency of wind gusts.

Seriously, I think the OP needs to pay someone to design this mount. The questions being asked and the reception of the responses suggests He's not getting it.

[amateur78t]

Dougal, I don't think you get it. I've already installed this with delrin rod.. AFter supporting the weight of my car with it, I wasn't worried about 15lbs of antenna weight with this stuff. I choose a 3' 1.5" solid rod for this standoff.

I also asked some local ham antenna experts that have done something very similar to this and it worked successfully and has lasted a long time (despite harsh environments).