Furnished by Frank Hermanek
(Originally Published: June 2008 Kingpin)
“A couple of months ago when I wrote about welding, brazing and soldering I suggested that you should try resistance soldering as it’s a great tool to make joints close to each other without remelting them. Well I took that advice and kitbashed a Bowser/Pennsy H9, a 2-8-0 Consolidation (Connie) and scratchbuilt a 1923 Mack Railtruck.
“Going back, years ago the price was right and I purchased the H9 kit. Never built it, as Belparire fireboxes are not to be found on my HO Gauge Imperial Valley Railroad. For years the kit sat on the shelf until along came an MRR’er article on modeling an ALCO N-5a in HO Scale. Simply great, as it gave construction guidelines and a list of commercial parts for converting the engine into a type N-5a. Finally, the H-9 could be transformed into a proper looking Connie; but not until all the cast-on details were removed and a new cab built. Removing the cab left gaping, see-through slots in the Zamak casting. These were filled in with Squadron Green Putty; and, following another MRR’er article, new components for the cab were laid out and cut from 0.010” brass.
“Assembling the detail parts into the cab was done using two “new” tools. These included silver-solder, a lead free soldering alloy, in powder and paste form, and a resistance-soldering unit. (The paste is both a vehicle, for easy dispensing of the powdered solder alloy, and a flux, which cleans the surfaces to be joined while preventing oxidation of the joint.) The soldering unit consists of a power supply with rheostat; an on/off footpedal for power input; a tweezer type handpiece; and, two electrodes – a ground (an alligator clamp) and a handpiece probe.
“The ground is attached near the area being soldered while the probe is “touched” to the spot being joined. This causes a low voltage, high amperage current to pass through the parts being joined. Resistance at the joint generates heat that melts the solder/paste making a clean, well-bonded joint. Heat is controlled and confined to the area being worked so it does not spread out to loosen neighboring details previously joined. Operation is simple: attach the clamp, touch the probe to, or near, the mate faces, and depress the foot switch allowing current to flow causing the solder to melt. When the solder flows the foot pedal is released BUT – the probe is held firmly in place until the joint has cooled and the solder has hardened. This takes only a few seconds and assures a tight joint.
“A rheostat on the power supply controls the amount of current delivered, so an assortment of parts and sizes, big or small, can be soldered. However, part size will dictate the amount of energy needed for joining. Therefore, it is best to experiment and determine what power level is right for the parts you’re working with. And, ALWAYS REMEMBER: touch, press and hold the probe in place until the joint has cooled.
“As noted earlier, the resistant soldering unit was used in joining the 2-8-0’s cab walls. To keep the cab’s corners tight and square components were fixtured using one-inch hardwood blocks purchased in Hobby Lobby. A thin bead of paste is spread along the inside of the joint to-be and the probe is then drawn along it causing it to melt and form a continuous, bright metallic fillet. This is repeated for the four walls and roof. The finished cab is shown in Photo 1.
“In assembling the 2-8-0’s cab I used the probe; whereas, the tweezer handpiece was mostly used to construct the 1923 Mack Railtruck shown in Photo 2. While the Railtruck’s cab was assembled using the probe, all the small flat details, as the sideboards and trucks were joined using the tweezers. As with the probe - release the foot pedal to stop current flow and maintain pressure, holding the tweezers shut, until the solder has solidified.
“Honestly, I could not have kitbashed the 2-8-0 or built the railtruck without the resistance-soldering unit. It enabled me to make joints, neighboring each other, that would have been impossible with a heated soldering pen or gun. Without the resistance-soldering unit neither the Mack Railtruck nor the 2-8-0 Connie would ever have been built.