Has anyone used JB weld to attach the horn to the wire? I know the proper way is to braze it with real silver solder. but that isn't the answer I'm looking for. I just want to save myself some work experimenting if someone has done this with success.
I made up two elevator horns for my Jr. Nobler. The upper horn was soldered with Staybrite silver solder (supposedly 7 times stronger than ordinary solder). In spite of a "perfect" solder joint it failed in the twist test. I thought it might have been ok for a .15 size model but clearly it would be an accident waiting to happen.
Hi Dennis;
Do you still have the failed horn or a better photo? I have to ask, how you considered it "perfect?" How much experience do you have at soldering and brazing? From what I can see in the photo you posted , I see a cold solder joint. No matter what material you used to connect the two pieces, it should resemble the photo of a finished joint in Brent's post, except for maybe color, depending on material. I make this assessment by the amount of build up I see around the joint. When making a solder joint, braze joint, or brazeweld joint (yes, there is s difference) what you see is important. On a solder joint or brazed joint, any type of build up does not enhance the strength of the joint, and only wastes material and may overheat and oxidize the joint. And as Brett mentioned, did you use a torch or a soldering iron? For a small model like a Junior Nobler, Stay Brite should have given you acceptable results for material that sized. Were there any gaps in the horn to wire joint? Fit up of the parts is critical. I don't mean to be argumentative, but I have used Stay Brite with good results for a long time. I am a trained welder by trade and have spent 45 years at it, including several years teaching it. No matter how you are trying to stick two pieces of metal together, using the proper materials, tools and technique is important and takes practice to get proficient. I'm going to assume that since you asked about doing this assembly with JB Weld ( which is essentially epoxy) you don't have much metal working experience or you might not have asked that question. If you had done a correct job with even standard solder, it should have taken some effort to get the joint to fail, not just one twist. And using Stay Brite, if done correctly, I doubt that you could have broken the joint, and the wire would have failed in a destructive test. Even using the more expensive higher content silver material, if not done correctly, that is no guarantee of success and won't make up for any short comings done in the fit up of the parts. With all of that being said, would I use it on a bigger piped or .60 powered model with 1/8" wire and thicker horns? Probably not. Everything has it's limits, But I have used Stay Brite on smaller parts where it's more appropriate. There is another thread where soldering tanks is discussed and that is another area where I would NOT use StayBrite due to the nasty flux it requires. Soldering and brazing is like any other skill that takes practice to get proficient.
Addressing the heating of the brazed drill rod joints in the oven, this is an annealing process to take the hardness out of the joint and rod after the brazing process. Every metal has a point where the grain structure changes state with heat and is called the eutectic point. Air hardened tool steel comes in many different alloys and degrees of hardness. You choose how hard the part you want to make needs to be and choose the correct material. After machining the part (carefully so as to not over heat it) you simply fire the part to a specific temperature, and how long you let it soak at that heat can determine results. Lots of cutting and punching dies are made with this material, along with forming dies. If you have had a 75 through '76 (I think) full sized GM automobile that was made at the old Chevrolet plant here in St. Louis, the frames are thinner than the previous years that shared the same frame. I spent a long, hot month the summer of '74 welding up the male die sections for the forming dies that A.O Smith made frame with for GM at their plant across the river. These die sections were made from D-2 air hardened tool steel, and needed to be modified to use on thinner metal, due to government mandates for better gas mileage on cars made in the US. This was right after the Arab oil embargo of the early 70's. To meet the mandates, the first thing they did was try and make cars lighter. That means thinner metal for the frames, and with no time or budget to make new dies, it was decided to modify existing dies to accommodate metal that was .030" thinner. I know that doesn't sound like much, but the weight savings over the whole frame was substantial, I just can't remember the number. I had to heat the sections up (which were about 12" to 18" long 4" thick or so and DAMN heavy!) to about 1200 degrees and maintain that temp while I ran stringer beads over the length of the die to cover the curvature of the business end with a special welding rod. I had a BBQ like grill made from 3/4" pipe that had natural gas and air fed into it and the section sat on that, and I helped it heat up with a LPG/Oxygen rose bud torch. Weld a few inches, then pound it flat with a ball peen hammer and repeat. The peening helped relieve the stress from the weld beads cooling, even though the parent metal was 1200 degrees. When I had enough metal built up, I had to anneal the section or sometimes they call it normalize it, to relieve all hardness and stresses. This meant heating it back up to 1200 to 1400 degrees, and holding it there for a short while, then burying the section quickly in a big wash tub of lime. The lime is a good insulator, and even after 24 hours in the tub, the sections were still too hot to handle with bare hands, but could be removed and the process repeated on the next section. Then the machinists hand ground the dies to a new shape, using hand cut metal templates to guide them. When they were finished, I heated the sections up to about 900 degrees slowly and soaked it there for a while, then set it aside to cool, and the section was like glass again.I think I came very close to heat stroke several times and didn't know it. That job lasted 7 day a week for about a month during their annual change over shut down. If I tried something like that now, it would kill me! That whole story is just to explain air hardened tool steel, and describe the temps needed to make it do it's stuff. Heating a flap horn to 500 degrees might be pretty close to the annealing point, because it's such a small part, and sometimes it's not so much the temperature, but the amount of heat and how long. Where ever the rod is purchased from should be able to provide the spec, or be in an engineering metallurgy book. If not done, the wire horns could snap like a twig. My education in heat treating drill rod goes back to my sailplane days, which was at that same time period. !/4" music wire was not available then, and I wanted something that size for a wing joiner for a sailplane. I cut myself a piece of 1/4" drill rod and consulted the machinists about how to heat treat it, and made the attempt. I didn't want it too soft, nor too hard either. I put it in the wing, and on the first launch, the rod snapped like the twig I mentioned before! It's a tricky dance but in retrospect, drill rod isn't the best material for that kind of part.
Get yourself some scrap material and the proper tools and start practicing, and just watch carefully as you do it to look for and see the changes that happen.
Type at you later,
Dan McEntee