>Hi, I got a great 1930s surgical lightfixture recently, but it arrived with a broken 'arm.' I'd sure like to repair this with an adhesive, or otherwise avoid a visible weld. Picture is below, with a quarter included for scale. The broken ends are about dime-size and still fit back together lock-tight.
This arm is about 8" long, and holds an 8" diameter mirror in a chrome frame at the end of the arm, so the repair will be under some tension, but once mounted, it won't have any sort of active stresses.
I have no idea what the metal is, but the photo is accurate.
>From what I can see in the photo, it looks like pot metal, a zinc-based low-quality metal that's easy to cast and not very strong. If so, you couldn't weld it anyway.
My son (who is a welder and metalworker) swears by JB Weld, a filled epoxy formulated for metal. I've used it some, too, and it seems to work pretty well. You can find it in almost any hardware store and many auto parts stores.
It's a fairly stiff epoxy, because of the filler, and it's quick set (4 minutes, I think it says), so you want to get everything all together and ready to go. Mix it up in a small cup of some sort (the measuring cups that come in laundry detergent are sometimes good for this -- everyone with a shop should save these things -- or a small yogurt container, or something similar), using a small stiff stirring stick -- popsicle or Haagen-Dasz stick, small bolt, piece of dowel, etc. Wear plastic gloves (if you get disposable gloves, DON'T get the cheap ones, but step up one level - difference is about a dime, quality is considerably greater).
Mix up thoroughly, smear a thin coat on both surfaces, push together, hold while humming "Flight of the Bumblebees" or singing "That's Amore" or whatever your preference is, watching the clock for about five minutes. Then relax. If the repair works, you're home free; if it fails, you'll probably have to drill through the assembly and install a throughbolt.
>Regarding Bill's post, make sure you get the "quick" variety of JB Weld. There are two different kinds and one takes something like 12 hours to set.
I have also had luck with one of the epoxies that come in the twin tubes that look like hypos. Although most of the repairs I do that require such things get JB Weld, one case did better with the auto-mix epoxy.
>I'd question whether JB Weld is going to have the shear strength to hold the weight of the mirror in the long run. I would suggest drilling small matching holes into the broken ends first and using a cut section of a nail as reinforcement along with the JB weld. Make the holes a little oversize for the pin to allow exact alignment and fill the holes with JB as well.
Another alternative, though not invisible is to find a piece of thin wall tubing that will slide over the outside of one piece. Then use the JB with a little excess outside the joined ends, and then slide the sleeve over the joint.
>The primary advantage of "filled" epoxy is that it can be machined afterwards. If your objective is only to bond two pieces of metal, get an adhesive formulated just to bond metal with a high shear and peel resistance. The local hardware store only carries a small fraction of available products. Try an industrial supply like McMaster-Carr. They have an excellent on-line catalog with good descriptions, take credit cards, have no minimum order and are very fast. I keep an entire factory full of obsolete machinery running, often with their products.
>Looks like a die-cast part. Like Bill said no welding. I would follow Bill's advise using JB weld or a company called LPS makes user friendly metal filled epoxy sticks that have worked very well for me. The big thing here is to use a pin (i.e dowel) to add strength to the fix. Good luck!
