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Best Plastics, Composites, Rubber for structural antenna parts

90186 Views 212 Replies 43 Participants Last post by  300ohm
Just a warning note about using ABS for structural parts that I've mentioned many times before - hopefully what you're planning to use is the thick walled stuff that has little or no flex. If you go to Rona or Lowe's or Home Depot and shake a 10 foot ABS pipe like a sword it flexes a lot. ;) It seems to be rigid, but its not. If you shake a length of PVC like that it will seem like a wet noodle, so avoid using PVC for structural use either, except when recommended in build plans.

From experience I'm clarifying that ABS should never be used as a pole or mast, and it should be carefully considered if you're thinking of using it as a horizontal boom of any length more than a meter or a few feet.
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rigid PVC 1/4" tubes, to support the gap between reflectors in a GH10 or DBGH
I bought some rigid plastic tubing at a model building store. They weren't too sure of the material, but it was fairly rigid and good for non structural parts and came in a huge variery of diameters, I think they had from about 1/16" up to 2", with about 40 sizes in between, no exaggeration. The place I went to specialized in tiny materials for building doll houses, train models, etc...

I used 3/8" tube with a 1/4" ID to set the gaps between my reflectors, which were made from 1/4" copper tube. The ID was actually a bit smaller than the1/4" tube, so I used a 1/4" masonary bit to drill out the tube a tiny bit creating a step at the exact depth I needed so I could just shove the reflectors in and they would be at the correct gap. I can take the reflectors out to move the antenna and reset them without having to measure again.
grey UV resistant plastic gutter ferrules
For some reason these are EXTREMELY hard to find in Canada (impossible for me north of Toronto, anyway). I looked in 5 stores and the only kind anyone had were the aluminum folded sheetmetal ones. I don't know if it's because they don't stand up to the cold winters, or maybe it's just not a common practice in this area, but they don't seem to exist around here.

I do agree they are a great construction material if available locally. I spent a lot of time going through every isle of Home Depot and Lowes trying to find some other similar plastic tubing and could not come up with any good alternatives.
Just wondering, was anyone able to get these in Canada?
My new solution for hard to find items in Canada:

Drive to USA, drop wife off at the mall, drive to Home Depot or Lowes, buy parts, drive back to mall, pick wife up, drive home.

This solution works especially well now that our dollar is on the rise! I used this technique last weekend to pick up some #8 solid copper ground wire.
The electrical supply houses are much cheaper
I know, but I was there on the weekend and didn't have the time to go searching for stores that would probably be closed anyway. I did a search using the GPS I had with me and couldn't find any electrical supply places close to where I was anyway. At least I got the wire, which was my #1 mission.
what kind of plasic-based tubing (besides gutter ferrules) has been used successfully?
I found some unknown plastic (the salesperson said it was one of a couple possibilities, but I forget what she said now) at a model building store that I was able to get in a 1/4" ID and use with standard flexible copper tubing. To support the long flimsy 1/4" copper tubing I added supports that created a rectangular frame. The reflectors are attached to the tubing on the outside of the frame with 1/4" nylon cable clamps, and in the middle the OD of the tubing was just a hair under 3/8", so I used some 3/8" cable clamps for the small tube segments.

Here's a pic. It's a bit tough to see, but the tubing I bought are the short white tubes attached with the black clamps on the centre tube.

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Is that CPVC?
Yes, at the start of the build the only material I could find with all of the proper fittings was plambing CPVC. Half way through I found another store that carries electrical PVC and PVC fittings (T's, 90's, etc...) that probably would have saved me about $10-$15 on the build.

Would it also be possible to drill holes through the plastic frame and put both the reflector rods through it as well as the 1/4" ID supports?
It's possible, but the small white tubes in the middle are used to set the gap spacing, so it would be more difficult to do this through the tubes, and I wanted to minimize the amount of holes in the main tubes to keep the frame strong. I also wanted to be able to take the antenna apart easily while I was experimenting with it, by loosening the screws on the outer cable clamps I can disassemble the whole antenna quickly and put it back together in the exactly the same. Going through the frame tubes would also need some other way to secure the tubes side-to-side.

What gauge wire are you using for the zigzag
10ga, but last time I was in the states I picked up some 8ga for my next build. This antenna's been outside for about a month now and survived a few heavy storms with no issues.

What is holding the outer part of the reflectors, wire ties ?
I used 1/4" cable clamps, the ones that look are shaped like a "p" (or "b", or "d", depending how you look at it).

Did she say if it was UV resistant or not ? If not, I would spray paint it with a thin covering coat for outdoor use. I personally wouldnt spray paint the driven element though.
She didn't say, but I assumed it wasn't so I took off all the copper and gave everything a nice flat black finish.

Here's a closer picture showing how the reflectors are assembled. The white tube in the middle of the reflectors actually has 2 turns of electrical tape around it to give the 3/8" cable clamp a nice snug fit, without the tape it was a bit too easy to slide side-to-side.

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I noticed that when putting conduit into the fittings that it inserts 3/4"
All of my fittings also went in 3/4". I would think you would want to bottom everything out so you could dry fit it and possibly take it apart if you want to make slight changes as you progress through the build, and you want everything to go back the exact same way. Not sure about the 5/16", maybe other brands of fittings have different stop depths.

and possibly lubrication may be in order
Don't use lube, because if it's easy to go in, it's easy to come back out when you don't want it too. It may also interfere with the glue if you plan on gluing it all together when you are done. Just give a bit of a twist as you insert it and it should bottom out easily.
PVC stock shapes can be bought at most plastic supply shops. You can look in the yellow pages for plastic sheet/rod suppliers and you'll probably find one near you, or you can also buy online. If you have problems finding something let us know where you are located and somebody can probably suggest a local source.

No idea where you would find square fiberglass tubing. I don't think you'll find that in stock shapes easily.
If I run a length of abs pipe across my table saw, cutting it along it's length, then I may be able to heat it up with a heat gun and flatten it out.


Pieces could be assembled with ABS Glue for a non-conductive weather-proof frame.

I imagine you could even build an ABS "I-Beam" spine by gluing three strips together.
It may be an interesting experiment, but I think you are going to have a tough time flattening out the plastic. I think it will be difficult to get it to a uniform temperature where it will be pliable enough to flatten without melting the surface. Even if you do get it flat, when it heats up with the sun shining on it the stresses you have put into the plastic may cause it to warp. Let us know if you have any success.

There are stores that sell stock shapes of various types of plastics, so it would probably be a lot less work and not much more money to buy some flat stock to create your I-beam structure.
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