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Author Topic: JB Weld brass to brass adhesion FAIL  (Read 18605 times)
oldskoolpunk
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« on: January 03, 2013, 07:52:03 am »

I just had a total failure with JB Weld. I was trying to attach a piece of square brass stock about 1/4" on a side to a brass plate. I sanded both pieces until they were shiny, then roughed them up with a file. I mixed the two halves of JB Weld epoxy on a paper plate, and stirred them until they were a uniform grey. I then applied that to the material with a plastic knife, and clamped both pieces together with 3 C-clamps for 4 hours.

When I took off the C-clamps, the square brass stock fell off under its own weight, with no other load on it. It hadn't adhered at all.

I thought JB Weld worked on brass.  Apparently not.

What's good for a brass-to-brass joint?
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Prof Marvel
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« Reply #1 on: January 03, 2013, 08:25:43 am »

My Good oldskoolpunk
I would recommend solder - hardware store "silver solder" is good for a very strong joint, but even hardware store soft or "plumbing solder" holds remarkably well.

Even if you do not have or cannot borrow a torch, one can cobble up an alcohol lamp and blowpipe to supply sufficient heat fro such a small joint.

yhs
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Argus Fairbrass
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« Reply #2 on: January 03, 2013, 02:42:33 pm »

I would say point number one you probably didn't leave it long enough for something of that weight. I've only used it on very light metals, such as a pair of broken sunglasses which are still fine. But heavy stuff I'd say you need to leave it for twelve hours minimum (you may want to go for twenty four if it's really heavy stuff).

Ensure it's spread evenly but thinly for the strongest bond, I even remember someone saying it'll set stronger if you gently heat it whilst curing. Soldering or brazing are certainly more recommended, but JB Weld is very good when it works properly, it's just a question of sussing it out a bit.
« Last Edit: January 03, 2013, 03:10:01 pm by Argus Fairbrass » Logged

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Oneiros
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« Reply #3 on: January 03, 2013, 06:28:19 pm »

I used it once many years ago. The process engineer (A chap called Richard) at the firm I work for came down from his ivory tower one day with his new packet of wonder material from across the pond... JB Weld.

I remember him proudly reading the packet to us, which stated that it could be used to repair many things among which was the engine block of a truck.

Unfortunatly, we then used it to hold a tiny piece of fiberglass to some MDF. Richard was confident that 6 hours curing time would be sufficiant as it was only a small piece of fiberglass, and not the engine block of a truck.

We then exposed it to 246 degrees centigrade of a solder reflow machine and watched his happy smile vanished. Oh happy days.  Grin
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« Reply #4 on: January 03, 2013, 07:35:19 pm »


Yeah JB weld needs a lot more cure time than 4 hours. 24 hours minimum, more in cold weather.

As well as sanding the surface it is important to clean it with alcohol or other degreaser to remove any grease or dust from the surface immediately before applying the adhesive. This step is absolutely vital on non-porous surfaces like metals.

Also JB weld is really a filler rather than an adhesive for the type of joint you describe a 2 part slow cure epoxy is ideal.
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oldskoolpunk
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« Reply #5 on: January 04, 2013, 07:35:11 pm »


Yeah JB weld needs a lot more cure time than 4 hours. 24 hours minimum, more in cold weather.

As well as sanding the surface it is important to clean it with alcohol or other degreaser to remove any grease or dust from the surface immediately before applying the adhesive. This step is absolutely vital on non-porous surfaces like metals.

Also JB weld is really a filler rather than an adhesive for the type of joint you describe a 2 part slow cure epoxy is ideal.

I got much better results with Devcon 5-minute epoxy. 
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« Reply #6 on: January 29, 2013, 07:43:50 am »

What's good for a brass-to-brass joint?

Solder, bronze brazing, or tig welding.  I've also used epoxy putties made by Kneadatite.  They have one that's a sort of coppery color.  They can cure in 4 hours IF nice and warm (a good halogen light will do), but overnight is better.  The guys's who make the original sculpts for "lead" gaming miniatures build armatures from brass wire and use these putties to do the actual sculpting, partly because (once hard) it holds up well against heat and chemicals used min mold making.
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