Soldering Advice Needed - Trying To Solder Rudder To Rudder Shaft

[scott t]

I have heard of using

I have heard of using resistance type soldering. Clamping the parts in the right area with both surfaces tinned with enough solder, then applying a electric charge. The amps through the mating surfaces heat up to melt the joint together.

They were soldering small brass tubes this way to make mast with yard arms.

I saw this while surfing the web but I don't know its location.
Maybe a search for resistance welding would turn up some information.
They used a modified battery charger to get there volt/current.

They do a lot of soldering here at work and they use wet rags to wrap the part they need to keep cool. Maybe some heat sink to draw off unwanted heat near plastic parts could help.

[crazy ivan]

Resistance soldering is an interesting

Resistance soldering is an interesting idea. Less likely to burn the flux and oxidize the parts that way. You would still need to take care that the parts, in this case, did not conduct too much heat back to the adjacent plastic hull. But it would be less risky than an open flame. I often use a high wattage (150 W) soldering pistol in these small applications myself.

The use of a heatsink certainly has merit. It may require that a little more heat be applied, however. In the electronics world, we sometimes use a hemostat clamped to the work to block the heat from being conducted back. With the bow plane assembly on the Dumas boats, the solder joint is so close to that low melting point styrene hull, you really need to get the technique right the first time; you won't get a second chance.

[scott t]

Here is one site from

Here is one site from a search for resistance soldering.
resistance solder web site

[Larry Kuntz]

I believe the problem is

I believe the problem is oxidation. Even with the flux, the flame tends to speed up the process of oxidation. I try not to use a flame if at all possible, but when necessary I use a soldering attachment on the torch. (no flame contact)

George ask me to look up some soldering info for him since I'm still in the electronics business at the University of Rochester (38 years at this job). The guys in the band (George's photo) keep me busy at times fixing their equipment when at all possible (I do their sound mixing, my other hobby).

I'll try to give George a little technical help with his up and coming article on soldering. I hope between the two of us we can help some of our fellow modelers.

Larry Kuntz
SC2385

[scott t]

A possible solution for the

A possible solution for the heat problem next to meltable plastic when making bow planes.

Have you seen the brass tubes for sale at the hobby shop that just fit inside each other?
Buy one tube the size of the rod supplied with the kit and the next size down. Solder the planes in the correct position on the larger tube. Now cut the plane + tube assembly in the middle of the tube between planes. Now you can assemble the two plane halfs in the boat and slide the smaller tube inside the larger tube. Solder the end of the smaller tube to the outboard ends of the larger tube.

This should put most of the heat far enough away from the meltable plastic and ease allignment of the planes.

You could also super glue the small tube to the larger tube and remove all the heat from the final assembly.

[crazy ivan]

That's an excellent sugestion, Scott.

That's an excellent sugestion, Scott. And it would facilitate any later removal of the bow plane assembly if so desired. Something I would hesitate to try if it were just soldered together per the original instructions.

[bradv]

I've just about finished building

I've just about finished building a Dumas Akula as well I followed the manual's advice and silver-soldered the tail fin on, as well as one of each of the dive-planes. This was easy as they could be done externally with the shafts removed from the hull. The remaining planes were a little trickier, as the shaft had to be inserted into the hull at this time.

First I tried silver-soldering again, but used a wet rag to "sink" the heat on the shaft inside the hull as well as some alfoil on the outside of the hull where the shaft penetrates to stop any radiant heat. These measures worked fine as my hull sufferred no heat damage at all. Unfortunately, I was sinking *too* much heat into the wet rag and couldn't get the silver solder hot enough to flow I didn't think just gluing the fins would work, so I compromised and soldered the remaining fins on using standard (electronics) solder. This requires substanially less heat than silver solder and gave me quite a nice joint which (so far) seems quite strong. Again, the hull was undamaged as I soldered fairly quickly - all I did was to spray the fin with water once each joint was complete, as per the manual.

Make sure your surfaces are clean - try either sandpaper or HCl. You'll be suprised what a differrence this can make! Also, remember to heat the work, not the solder.

[anonymous]

I've been following this discussion

I've been following this discussion with interest because fixing external controls has been a problem for me on a British R class submarine with very little space in the stern.

Last year I used epoxy to fix (push fit) brass tubes. This worked well and I have just removed these tubes by heating gently with a gas blowlamp. (The epoxy melts.)

I've just tried soft solder on them on as an experiment and this worked very well with a 50 watt soldering iron and Fluxite" flux (It's brown and sticky!) Tin the tubes first. I think I would prefer this method in future because it is quick to do and repair.

Generally I prefer silver (hard) soldering using a gas blowlamp because it is strong and foolproof. But with soft and hard solder you can build up a structure with the ability to remove the soft soldered bits.

I look forward to the article on soldering.