Resoldering a brass lens hood

[Jim C.]

My poor Darlot is getting the spit and polish treatment, it's gone from poo brown
to a nice gleaming brass, but the lens hood came to me separated from the flange,
interesting to note that it's soldered as opposed to being rolled on, which was
how I thought they were done. It's a tight fit on the flange but since I'm going to use a
front mounted shutter, I don't want the hood portion to pop off unexpectedly.

There are two methods I'm thinking of trying to resolder the hood back on -

1) Place the flange with the hood attached onto a hot plate and
heat till the solder that's already there flows again

2) Use a small butane torch and try to heat evenly till the solder flows.

Has anyone ever done a resoldering of a lens hood ?
I'd be interested in your thoughts.

[lenser]

Jim,

If you don't get the answers you need here, jump to a musical instrument repair person.

While I never had the challenge you describe, I did have a repair guy that was a friend do considerable restoration work on several brass lenses and camera body parts for some of my favorite antiques. While in his shop, I watched him do a couple of soldering jobs on a trumpet and a sax. I don't remember the method (I wasn't watching that closely) but I do remember his skill and that the results looked flawless.

Tim

[Steven Tribe]

Get bright brass/old solder everywhere where you want the flux/solder to stick.
Do 2 stage soldering. First a thickness on one surface - then heat up the other item (lens hood) and apply and push steadily home.
Ordinary soft solder is quite good enough - this is no model steam engine!
Excess solder is very easy to remove (mechanical).

[Leigh]

1) Place the flange with the hood attached onto a hot plate and heat till the solder that's already there flows again

A hot plate is not nearly not enough. Solder melts at around 700°C. You'll need the butane torch.

Be careful what type of solder you buy. There are two kinds: "acid core" and "resin core".

Acid core cannot be used for your application. It will destroy the brass over time.
Acid core solder is commonly used for plumbing work with iron or copper pipe. Water washes the flux away.

Resin core solder is used to build and repair electronic equipment of all types.
It is specifically designed so it does not damage copper alloys like brass.

- Leigh

[GSX4]

I did mine by just replacing the hood ring back on in the same place (friction fit) and used my gas stove to heat a few key areas around the hood. It re-melted the solder, I just heat up 3 points around the circumference first one after the other. Take the hood and fitting away from the heat if you see brass changing color. I did this a few times. It has held so far. i did not even need to add anymore solder.

[Jim C.]

Thanks for all the responses so far, there seems to be quite a bit of solder still on the hood and the flange,
so essentially it's pre tinned, but I might just add a teeny bit more to get it well attached.
I may go with my hot plate idea since I was able to keep a pot of pewter 650º F for a project, my goal is even heat
all over to reflow the existing solder.
Leigh, I'm no stranger to soldering, but you have me a bit confused, I don't see much difference with either rosin or acid flux,
rosin is less aggressive than acid flux and supposedly inert especially for electrical work, and both can be washed away.

[Steven Tribe]

The hot plate idea is a no-goer! You will only transfer real heat through the edge and the whole brass assembly will heat-up during the period that the critical temperature is eventually reached. Propane/butane flame is far quicker and area restricted.

[Leigh]

Leigh, I'm no stranger to soldering, but you have me a bit confused, I don't see much difference with either rosin or acid flux,
rosin is less aggressive than acid flux and supposedly inert especially for electrical work, and both can be washed away.

There's a huge difference in how the two fluxes react with copper and copper alloys.

Acid-core works on copper plumbing pipe because the water washes the flux away.

That does not happen with a lens.

This is certainly not my idea. Research the subject on the web.

- Leigh

[Jim Jones]

A hot plate is not nearly not enough. Solder melts at around 700°C. You'll need the butane torch. . . .
- Leigh

The solder traditionally used for electronics (60%tin/40% lead) melts at 370 degrees F (188 degrees C). The slightly preferable eutectic solder (63%/37%) melts a few degrees lower. Lead-free solders, mandated in some countries for at least some purposes, have a higher melting point. A butane or propane torch may be the most convenient source of heat. Perhaps a gas stove will suffice. A large soldering iron would do a messier job.

[E. von Hoegh]

You don't know what alloy the solder already on the lens is, therefore you won't know the melting point.
I'd use one of the solders Jim mentions above, and I'd clean off all the old solder. Put some rosin (or soldering paste if you don't have rosin) in the joint, heat gently and evenly untill the solder melts and wicks into the joint when applied. If you use soldering paste, clean well with boiling water, several times.

The most important thing with soldering is to get it bright and shiny clean. Good luck!