Best Plastics, Composites, Rubber for structural antenna parts

90165 Views 212 Replies 43 Participants Last post by 300ohm, Oct 10, 2013

stampeder

Discussion Starter · Nov 26, 2008 (Edited)

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.

61 - 80 of 213 Posts

balm

· #61 · Jul 16, 2009

Thank you johnpost,

Yes, I sanded the each contact surfaces flat, but this is not easy to get perfectly flat.

So, I guess, HD must sell the PVC glue also...

johnpost

· #62 · Jul 16, 2009

balm said:
Yes, I sanded the each contact surfaces flat, but this is not easy to get perfectly flat.

try a flat file or sandpaper on a sanding block that might help in generating a flat spot, rather than the tendency to curve. also mounting the strap on a block and orienting the strap horizontal, then you have a view of the tool to the strap and might more easily keep it parallel to the base.

balm

· #63 · Jul 16, 2009

Thanks johnpost,

I will need to set up my old vice.

I bought some nylon (plastic?) bolts with nuts which are used to fasten a license plate to the car (Canadian Tire sells them). I assume they are UV.

I drilled a hole through the center of each strap and passed the bolt thru to fasten them tightly together, but I dont understand why when I tighten the nut against the strap it just keeps turning, never really tightening up. I checked and the bolt was not stripped, I even tried another one and same thing. I assume these are not meant to get really tight, especially without any kind of washer???

balm

· #64 · Jul 16, 2009

johnpost,

PVC gluing with PVC primer and PVC glue is solvent welding. The glue has solvent and PVC resins which dissolves some PVC and then it reforms new polymer chains fusing the pieces together.

the guy at the HD told me that the CPVC glue will not bond the electrical straps properly. This product was actullay in the plumbing section.

However, in with the electrical conduit section, there was another type of glue, which I believe mentionned solvent and PVC, I assume this would be the correct one.

Is CPVC and PVC the same thing? Thanks

balm

· #65 · Jul 16, 2009

Following 300ohm's suggestion,

I have sashed together the 2 straps using 3 tie-wraps, I think with a little glue this will be very sturdy for a stand-off...

I also placed the small strap passed underneath the larger one.

http://s638.photobucket.com/albums/uu110/stanicet/?action=view&current=IMG_0286.jpg

300ohm

· #66 · Jul 16, 2009

Is CPVC and PVC the same thing? Thanks

Nope. In plumbing CPVC pipe is used for hot water and PVC fro cold water.

have sashed together the 2 straps using 3 tie-wraps, I think with a little glue this will be very sturdy for a stand-off...

Good job, but like mentioned before, white nylon isnt UV resistant and can deterioate pretty quickly in sunlight. The black nylon sold at Walmart in the auto dept, $2.84/100 pieces, is UV resistant.

Grem

· #67 · Jul 16, 2009

Actually if I remember cpvc is more for supply lines and pvc is more for drain lines.... you can use pvc for supply but cpvc is better, kinda like you could strap a kite on your back and jump from a plane but a parachute is better.

johnpost

· #68 · Jul 16, 2009

there are universal plastic glues that have solvents and a combination of plastic materials. i don't think it works as good as specific glues which have solvents and that particular plastic; there are glues specific to PVC, CPVC and ABS (also there are variations for pressure ratings and setting time of concern to plumbers, likely only one of each type in general stores).

plastic hardware is strange stuff. some plastics have a property of being deformable, the types used for hardware are. after a nut has come tight it may stretch the bolt a whole lot, a number of turns. also these deformable plastics (if not stretched to the breaking point) can then relax and go back to closer to their original shape. also plastics are slick, often used as a sleeve bearing with metal because of this, can be though of as self lubricating. you can then turn a nut on an assembly tight and keep turning it (as the bolt stretches and with little resistance) and then if you stop before it breaks you can then watch then nut unscrew itself (as the bolt relaxes and shrinks and turns the nut with little resistance). makes you think you have a screw loose (that was punny).

plastic hardware works where it doesn't have to be real tight or you use some thread locking mechanism.

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johnpost

· #69 · Jul 16, 2009

i think CPVC is able to be used for water supply because chemicals don't leach out of it like PVC. depends on local codes on when an if it is allowed.

PVC and ABS are cheaper and used for waste.

Schmerm

· #70 · Jul 17, 2009

I went to both a Home Depot and a Rona this week and neither had sch40 fittings (1/2" elbows/tees/crosses). Instead, I ordered online from here: http://www.northernpvc.com

With tax and shipping, I got 17 tees, 3 crosses, and 2 elbows for $14CDN.

300ohm

· #71 · Jul 18, 2009

Interesting. They also carry 3 way, 4 way and 5 way fittings. Pricey though.

Feig

· #72 · Jul 18, 2009

CPVC vs PVC

PVC is PolyVinyl Chloride and CPVC is Chlorinated PolyVinyl Chloride. The difference is that the CPVC contains more chlorine atoms atached to the polymer backbone by 10% or more. This makes it more heat and chemical resistant and stiffer. Though it costs more it is my choice as the best material because of its stiffness and heat resistance since you want to paint it black for UV resistance which will heat it up in the sun. If it only came in black but doesn't because adding black pigment to the plastic reduces the stiffness and heat resistance acting like a plasticizer.

Feig

johnpost

· #73 · Jul 18, 2009

Feig

Painting CPVC or PVC can be tricky.

What materials ans process do you use? Why black? How has it worked for you and how long?

Feig

· #74 · Jul 18, 2009

Black blocks out all light from penetrating. Polyethylene will last about a year outside without additives, if you fill it with black pigment it will last in excess of 20 years. This is because UV light cannot penetrate into the plastic and only attacks the surface.

An exterior oil based flat black is what I use because the oil based solvents in the paint will slightly dissolve into CPVC giving it a good bite to help adhesion. Flat black hides scratches and glue much better than a gloss finish which highlights small flaws.

Spray paint is easy but it takes more than one coat and you'll probably use the whole can. I use a paint brush and can usually do it in one coat then go over it again to cover up the brush strokes.

I've only had my DBGH up for 6 months but it still looks good.

Feig

300ohm

· #75 · Jul 18, 2009

Spray paint is easy but it takes more than one coat and you'll probably use the whole can.

I find one thin coat with the cheap 96 cents a can Walmart stuff works well. Ive painted other garden pvc pieces Forest Green with it and theyve lasted well for over 5 years, with some fading. More, heavy coats tend to peal off in time. One thin covering coat is the key. I painted my DBGHs Flat/Satin Black with it and they are in great shape after 1 year. Figure using 2 cans per DBGH.

wildwillie

· #76 · Jul 18, 2009

Schmerm was there not a T.S.C. for farm supplies up near you they should have the parts, you were looking for i got everything i needed from there

Schmerm

· #77 · Jul 20, 2009

It's pretty far away, in Uxbridge. Nothing in the metro area.

I need some kind of tubing for holding the 1/4" colinear aluminum reflector rods to the center of the antenna. Without having to go online again and order 'unobtanium' fiberglass tubes, what kind of plasic-based tubing (besides gutter ferrules) has been used successfully?

DdDave

· #78 · Jul 22, 2009

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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Schmerm

· #79 · Jul 22, 2009

That looks nice and sturdy. Is that CPVC? 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?

edit: What gauge wire are you using for the zigzag?

300ohm

· #80 · Jul 22, 2009

Yeah, that is a nice simple sturdy build. What is holding the outer part of the reflectors, wire ties ?

I found some unknown plastic (the salesperson said it was one of a couple possibilities, but I forget what she said now)

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.

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