The ferrule on my son's violin bow snapped open. This is the little metal piece near the end of the frog... You can see the split along the edge. I'm holding the two pieces together in this picture.
This not being a particularly expensive bow, I decided to try my hand at repairing it. I am not a luthier -- any more than I am a watchmaker or clockmaker; that doesn't stop me -- and this is not a usual repair... That said, it's not particularly difficult either. I was inspired by the instructions on this page.
These are the parts that need to be removed to access the ferrule.
The idea is that ferrules are typically soldered together from two pieces: a flat piece and a round piece. This video explains the process, which reminds me of many jewelry soldering tasks.
But since this bow was not that expensive, I think the ferrule was assembled as one piece. From looking inside the break, it looked like the ferrule was brass plated with something shiny. It is slightly magnetic, so perhaps it's stainless steel?
In any case, I can solder brass with a little flux! So apply flux wherever you want solder... and don't put it where you don't!
The task is basically a soldering job and a jewelry job. For that, I like to use fairly soft, lead-free silver solder. It's easy enough to slice off a small chip to use with a chisel.
Bind the works up with soft iron wire. This holds the ferrule together as you solder, and gives you a handle that is far from the flame!
If you're careful, you can plant the solder chip in the blob of flux. Then, when you heat the joint, the flux melts, and then the solder follows the flux into the joint. Be very careful to apply heat slowly, so that the flux doesn't splatter and knock the solder away! Also, if you overheat the joint, the flux will burn away, leaving oxidization everywhere, and then the solder won't stick to the joint. Worse, it will probably stick somewhere else...
I didn't photograph the soldering process itself because I didn't have enough hands free. Once the soldering is done, there is some scaling, oxidization, and flux.
I like to dissolve most of the flux in isopropyl alcohol.
Then you can file away the excess scaling and solder (gently!)...
Try the fit of the ferrule on the frog.
File until it slides on with some friction, but not too much. It's difficult to describe what you're after, but it's very easy to feel what "too tight" feels like. I also interleave the job of polishing with the job of fitting, since polishing the inside of the ferrule adjusts the fit to the frog. Because the solder made a bit of a fillet, which I wanted to retain, I also filed the frog a little bit. You wouldn't want to do this to an expensive bow, but this bow had a plastic frog, and didn't seem to mind the offense.
To start the polishing, I start with sandpaper. Things were clean enough that I could start to sand with 600 grit
... and then move to 1500 grit
... and finally polish all surfaces.
I like to use premade polishing paste in a stick. Even though it's intended to be used on a powered buffing wheel, I just scrape the stick onto a piece of fabric and polish by hand. You have better control of the polishing of small parts that way.
Keep trying the fit of the ferrule on the frog as you polish, until it fits perfectly and is polished.
Slide the ferrule onto the bow hair. Make sure it's oriented in the right direction!
This bow has the hair anchored by a screw... Slide the cover on...
Slide the ferrule on..
And press the spreader in place. The spreader may be a bit tighter than before, since the solder joint takes up some space. Don't force it! I did force, and was rewarded with a split solder joint. I had to start back at the beginning! If it doesn't fit, carefully file the spreader so that it does....
And finish the job by reassembling the frog.
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