bending/straightening copper tubing? Casting shape Working with metals? - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2021, 02:08:47 pm
content: I have some antenna fabrication questions..How does one straighten curved copper tubing so it looks pretty?also has anybody used a tubing bender? (for making pretty curved tubing, rings, etc. )Seems copper tubing is a great material for making durable antennas. And perhaps one of the most workable materials for a person without a lot of tools.Plus, if you can get it hot enough it takes solder really well. Then the conductance is as good as it gets.I'm just asking for your thoughts on working with copper tubing. I'd like to try making some different size loops, plus some other loop-like antennaslike a squalo. (a horizontally polarized omni antenna for VHF) and some small single frequency loops optimized for VHF, and also a nice biconical. This has been a goal for a long time. Notice how many of the commercial ones have this structure at the vertex of the points.What I am particularly wondering about is ho to make that fixture at the center of the biconical antenna where the two cones meet.-where the wires come together, and have it have structural strength. I'm including these photos to show how its done in some other antennas.Copper tubing is good for biconicals, Yagis and log periodic antennas, and broadcast TV and FM broadcast antennas. A nice biconical for VHF and UHF omni reception is high on my list,if I can figure out how to make the center piece at the feedpoint.Maybe 3d print it and then make a cast so I can make one out of molten metal for strength? I really don't know much about metalworking.I mean something like the octopod-like center piece of some of these antennas.@coppercone2 (I know you are also interested in this)

author: purpose
author_rank: Frequent Contributor
timestamp: April 20, 2021, 02:21:08 pm
content: Mr. cdev,How does one straighten curved copper tubing so it looks pretty?A wire straightener with the right girth of bearing might be your friend.

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2021, 02:27:59 pm
content: That's pretty, yes, it looks like a tool to have.Google finds info on them, thank you!

author: coppercone2
author_rank: Super Contributor
timestamp: April 20, 2021, 02:32:20 pm
content: Those big tubing benders you bolt to the table work niceYou can fill a tube with water and freeze to bake it bend tighterSand also worksConsider thin brass tube for weight and workability if you ca

author: purpose
author_rank: Frequent Contributor
timestamp: April 20, 2021, 02:43:21 pm
content: Quote from: cdev on April 20, 2021, 02:27:59 pmStrangely enough it's called a wire straightener. They're a bit pricey, so you could just grab some bearings with an outside form and nail them to a plank.I'll see if I can grab some links.peter

author: purpose
author_rank: Frequent Contributor
timestamp: April 20, 2021, 03:01:09 pm
content: Just look for U groove bearings and make sure the groove is big enough to handle the size of tube you have.No guarantee that it'll work, but worth a punt.

author: DrG
author_rank: Super Contributor
timestamp: April 20, 2021, 03:07:09 pm
content: Maybe this belongs inhttps://www.eevblog.com/forum/mechanical-engineering/?Quote from: cdev on April 20, 2021, 02:27:59 pmhttps://www.woodwardfab.com/product/tube-straightener-tt100/https://www.woodwardfab.com/blog/how-does-a-tube-straightener-work-tube-straightening-techniques/

author: themadhippy
author_rank: Super Contributor
timestamp: April 20, 2021, 03:29:10 pm
content: A bending spring is another common way of bending copper pipe,used along side a bit of timber with a hole to put the pipe in and you can get some very tight bends.Pipe benders are great for larger diameter or thicker walled material,but overkill for smaller stuff

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 20, 2021, 03:49:11 pm
content: Those wire straighteners will take the gentle bend out of your pipe or wire, but do little for kinks and dents.Dents are tough to correct, best is to put a rod of appropriate diameter inside and do a little judicious hammering (tapping) on the outside. The big bends and kinks can be removed in two steps. First use your hands to bend it roughly straight and then roll it under pressure between two flat surfaces.All of this is easier if the pipe is fully annealed. Which is problematic because you probably want antennas to be somewhat hard so they don't bend unintentionally. Copper is a work hardening material so the trick is to soften it and then work it enough to get the hardness you want.I heartily endorse bending springs for making bends. I have had far more luck with these than with any other bending method.

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2021, 07:20:54 pm
content: The tubing that I bought looks exactly like that, its in a coil. It would be easy to transform that into several loops of different sizes, but youre right, bending it is almost guaranteed to end up ugly. I can buy elbows in that size, and they are not very expensive, but then I have to solder/weld it well, each one.On youtube there is one guy who built a huge double loop for 80 meters. He uses copper transitions. It looks like he only used straight pieces. His loop is octagon shaped and performs really well he says. But he now wants to make a figure 8 shaped one. .QuoteI'll have to look them up. Thanks for the search term! This info is extremely helpful.What kind of material do you put indide the tube to bend it? The copper I bought is for HVAC and water piping and it came from a vietnamese company. Its pristine.. very nice and wasnt super expensive like I expected it would be. It seems to be soft copper. I'm sure the ohms per meter is very low as its thicker than the thick green-insulated wire I tried before.. Which was almost impossible to solder to.I want to make a loop thats two turns long if that can be used on a wide enough frequency range. A 80-20 meter range would be ideal.I think Jeri Ellsworth's loop is a good antenna that is as design-friendly as antennas get.

author: A.Z.
author_rank: Super Contributor
timestamp: April 20, 2021, 07:54:03 pm
content: you already got good suggestion for straightening copper pipes; now, to bend them and form a loop just find a bycicle rim (an old one will do as well), those come in different diameters (think child bikes), and are fine for the purposeas for the discone, the centerpiece may be realized by milling a block of teflon

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2021, 09:18:59 pm
content: Bike rimsmake good loop antennas themselves, it appears.Actually, the tubing I received is a big spiral of copper so its already curvedNot so far off of the big loop I want, if I unbend it gently.Still, its good to have this info.Quote from: A.Z. on April 20, 2021, 07:54:03 pm

author: coppercone2
author_rank: Super Contributor
timestamp: April 20, 2021, 09:41:32 pm
content: if you use pipe, be sure to know the hardware store sells a thin and thick one, so you don't think there is only one kind if you want to mimic someones hardware store project, they probobly bend differently.also get the big round deburring tool there to make your pipes not suck mechanically when you join themI much prefer brass tube, hobby shop tube that is used for steam things is great and is great to work with in comparison to copper. Copper kind of sucks for workability, if its big, try to go with brass. my professional loop antenna is made from brassI never bent it before, but if you need strait sections, I think brass is a better choice. cheaper and it will be lighter for the same strength. the last thing you want is heavy antenna. it also looks better as a scientific instrument IMO, when something is made of copper you just think hardware store kludge. you will get durability from brass like you expect when you purchase something, not a hoola hoop made of butter you are scared to tip over because you will be panel beating tube for the next day

author: David Hess
author_rank: Super Contributor
timestamp: April 21, 2021, 12:21:03 am
content: I always end up unbending copper tubing by hand. Bronze brazing rod works well for antenna elements. It is much stronger than copper.I hear their tubing unbenders are also next to their Bono safety googles.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 21, 2021, 12:21:13 am
content: Well, I just do it carefully, by hand. A sharp eyeball, lots of tweaks with the hands, and a flat surface helps too. And patience. Same for coils, you get nice clean helices when starting with straight tube with even hardness (if it's been bent and straightened too much, those spots will be work hardened more) and consistent winding.Coils can be adjusted after the fact, but you aren't going to fix short flats or bends once everything's wound up. To put it another way, there's a characteristic curvature that any turn-to-turn bending is going to favor, and you can't effectively correct features that are higher frequency (having more curvature error over a shorter length).Annealing can be a mixed bag. It relieves stress, it softens the metal, it's easier to bend. Especially, it's easier to bend out those short, tight curves. But it also collapses that much faster, it's extremely prone to kinking. Use a filler, if you can: Cerro alloys are low melting, good for this sort of thing and reusable of course; it may even suffice to fill with wax (over a long enough length that it doesn't squidge out?), or maybe ice, or sand (remember to pack the sand, and still there's a lot of free space between grains so it's not the greatest).As for a straightener, if you don't have a proper one, or bearings to make one, it's probably alright to do the same thing out of, like, wood blocks waxed up. It'll take a lot more pulling force of course. Use a clamp, maybe with shims, to set the gap spacing, and go slowly so you take out just a little bend at a time. Make a few passes at different rotations until it's smooth, then step down and so on.Or for straighter materials, as mentioned, brass tubing can be handy. As kind of mentioned but maybe not made clear: copper tubing comes in different thicknesses. The thin stuff is rigid, not meant for bending -- it will kink too easily. Thick stuff is usually sold in coils and is bendable. There's actually three or four grades of thickness but you'll most likely see just the two at the hardware store. Rigid is more properly copperpipe, and being pipe, its size is coded, only coincidental to its actual dimensions -- as it happens, copper pipe is about 1/8" larger than its code... and that's I.D., I believe? (Tubing is O.D..) Or 1/4" oversize in larger sizes I think. Or in metric countries, it's...whatever it is, you'll have to look it up. As always with pipe, if you need to know -- look it up!And aluminum pipe, often extruded, is cheap and plentiful, quite straight, and quite rigid and light for its size. You'll need to make good joints (RF connections), which can make the anodizing an issue, but it's usually not a big deal. Yagi, log periodic, dipoles, arrays, all good choices. Should be bendable too, at least over large radii, and given a jig -- would be great for a large loop where the bending radius is acceptable. (The anodizing might even survive the process?)Steel is fine too, anywhere you don't need large element currents -- not so much for loops, then, as dipoles and arrays. Galvanized steel weathers very well, and can be bolted, compression fit, flared, swaged, soldered, brazed and welded (but do take care to remove galvanizing before welding the area, and clean and protect the joint with appropriate coatings).Tim

author: coppercone2
author_rank: Super Contributor
timestamp: April 24, 2021, 05:10:54 am
content: if you want my advice don't even go near galvenized tubing if you are welding, if you can spend extra money to do construction with better materials, i recall you don't like bad smells and toxins.. its a serious low cost construction material that you need to be careful with. you need to strip alot if you braze it, I built a big welding table by brazing galvinzed steel and it stunk to shit of zinc even when I thought I had a more then liberal amount of material stripped. In retrospect when I think about all the work I put into it, and how much better it ended up looking with paint, it was not worth it. If paint is flaking off, it looks like garbage anyway, and if it rusts underneath, its almost no effort to clean that up before repainting the area. IMO its meant for neglected infrastructure with things that might go uninspected for ages, like a fence. I even see the train stations around here starting to go with stainless hardware because it just makes more sense.. even when they inspect it alot. If you really strip enough mateiral to weld without any galvanization overheating, it is so patch work that it does not make sense unless the object is massive, because it gives you half assed protection in the areas that normally wont rust. Maybe if you are doing a licensed huge lower frequency dipole antenna it starts to make sense. Welding it is like considered a bullshit sweatshop farm hand short on money first job kind of thing. If you are arc welding its so much more work to clean up galvanized stuff since the welder tends to blast through everything without a problem, but obviously you need to diligently clean up zinc.my other suggestion is that when you bend pipes you might want to consider hot bending, that is heat the area with a torch to make the thing softer. If you are good with managing hot objects it can make your life a whole lot easier, this goes for bending brackets as well.your gonna1) question how much money you are spending on abrasives to clean galvanized steel2) question why the fuck it still smells with all the safety3) question why you are saving pennies on pennies when you are connecting it to complex expensive equipment4) question why you are having to stand there and sand giant patches of clean metal to not make a smell5) question if the wear on your grinder or sander is worth it if you decide to go the easy way6) question why you are cleaning up tons of metal dust7) question the money spend on respirator cartridges that get fouled very quicklyjust say no to joining galvanized steel with anything but bolts and glue. i think i would rather dig a hole then do galvanized steel prep. it can be so easy and clean if you spend a couple of dollars more, working with it is like selling your soul.i know, lets go fuck around with a bucket full of acid while we are at it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 24, 2021, 05:44:29 am
content: Quote from: coppercone2 on April 24, 2021, 05:10:54 amTry using a lower melting filler. Don't use copper or nickel bronze; brass should be fine but be careful with temperature (and will give off some by itself anyway); silver solder best.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: April 24, 2021, 06:00:19 am
content: its still so much worse then anything else, its just not worth the money unless you are putting up a cheap roofeverything we have is quality, HP, etc. then when it comes to the antenna it turns into backwater bullshiteven a large welding table, with free 4 inch square tube, was not worth it. i should have bought non galvanized new tubing. it was just stupid to doAPC-7 connector goes WHERE?!its a ferrari with a body made of cut up school bus scrap as far as I am concerned. its serious war lord shiti don't know how to think about a RF radiator, maybe its like stealing a bus station glass plane to act as a window in your ferrari.