On Sunday, November 11, 2012 12:34:58 PM UTC-5, wrote:
On Sat, 10 Nov 2012 15:06:53 -0600, "Paul K. Dickman"

wrote:



The elections are over and it is time to get back to some on topic

discussions.



I am looking to put together a purpose built soldering machine and I want to

pick your brains.







I have a 6"x8" piece of 16g polished brass sheet and I need to soft solder

an 8" brass piano hinge to the polished side. The hinge needs to be

moderately well located along one edge, but the tolerances are loose. For

reasons of finish and subsequent machining, spot welding or riveting are not

feasible.







The polished side of the brass has a thin coat of lacquer and a sheet of

protective vinyl on it. I need to protect the polish and the lacquer in the

non soldered areas, so heat needs to be very localized and handling kept to

a minimum. It is for a production run of 100 pieces.







For prototyping I tinned the hinge with an iron. Then I would remove the

vinyl from the sheet in the soldering area. Using the rest of the vinyl as a

mask I would sand off the lacquer and flux the area and removed the rest of

the vinyl. The sheet was clamped between a couple heat shields and then

tinned. The two pieces got clipped together with spring clips, heat shielded

and sweated together with a torch.



This worked fine for onesey twosey, but would suck for a hundred pieces.







My plan is this:



I use a strip heater like this,



http://www.mcmaster.com/#die-strip-heaters/=k3s9ef



attached to a hunk of copper buss bar as an 8" long soldering iron.







The pieces will be tinned and clipped into a jig. I have a scrap of

architectural bronze extrusion that I think will work well for this. It has

enough thermal mass to warm up and not chill the work, but it has enough

flanges and surface area to release some of the heat and let the joint

solidify in a reasonable time.







The hot 8" iron will be clamped down on the hinge side with a couple of

toggle clamps, allowed to heat the pieces up till it sweats and released.

The pieces remain clipped in the jig til the solder hardens. (can be sped up

with water mist) The next set gets clipped in and the process repeated.







If I am lucky, I would love to eliminate tinning the sheet as well







I have about $400 parts and labor budgeted in for this machine. After that,

it's all piecework. My profit depends on being frugal and productive so I

don't want to spend a lot of time fiddling around.







If anyone has any ideas or insight or a better way, I would appreciate

hearing about it.











Paul K. Dickman



Greetings Paul,

I would try, like many have suggested, glue of some sort. But if that

doesn't work what about a resistance soldering unit? Instead of

heating the work whay not let the work do the heating? I have a little

100 watt resistance soldering unit that uses carbon electrodes on

either side of the work. The work usually brass, heats very fast, And

the heated area is quite localized. The unit I have is made by

Triton. I'm sure you could build one yourself.

Eric

We used to use a resistance soldering "machine" made of a large 6.3V filament transformer attached to a fixture with carbon blocks that clamped to the work. You could run the transformer primary through a variac to control the temperature.

Fair Radio has a pretty good selection of transformers. Alternatively, you could use a welder to power this. You ought to be able to jig something up to test the concept pretty easily.


I'd imagine you could skip the tinning of the sheet with a reasonably active flux.