View Full Version : soldering slot car track rail

10-06-2008, 12:17 AM
I've been mulling over a problem we have in making better connections between track sections of our six lane slot car track. Soldering at each junction has proven to be problematic, so I'm planning to make each solder connection about an inch away from the end of each piece. I'll be tucking a tinned and resined strip of copper foil into the small gap between the rail itself and the groove in the plastic track section that holds the rail in place. There's about 5 thou or so of looseness there, so my 2 ounce copper foil will tuck in there fine, and not stick up above the track surface. Only thing left is to heat the rail for a short length to reflow the solder that's on the copper strip and bond it to the side of the rail.

I don't know if I'm making this clear, but suffice to say that the only place where heat can be applied is the top surface of the rail. Heat will have to flow down the side of the rail to be able to heat and remelt the solder which is already there on the tinned copper strip. There won't be any solder added during the heating process.

Normally you'd just get out the weller and force the tip against the rail to transfer the heat. Chances are pretty good that you'd melt some plastic and force the rail to change position, as well as probably adding some solder or oxides to the surface of the rail. To circumvent these potential problems, I'd like to use a focussed light source to direct heat to exactly the spot on the rail where I want it, and heat it this way. A halogen bulb is often made with a filament that is compact, but of some certain fairly short length. The shape is just right to focus into a rectangular bar of intense light, using nothing more than a magnifying glass.

I can make a base with a slot in it that defines the limits of where the light can reach, so I can keep it off the plastic track material. What I'm wondering is how well the chromed steel rail material will absorb this light, and I'm trying to determine how powerful of a bulb to use.

In all, there will be well over a thousand junctions to reflow solder on our track, if I did them all. We do have sections which are wired as power tracks, but connections from those following on to other track sections are getting worse all the time. To lift each area and make jumpers across all track rail sections is beyond doing at this point, so the method I've described seems about the best way to resolve the issue. In future, we'll make a routed track, or some facsimile of it, but for now we need to keep this one 'connected'. Any ideas?

10-06-2008, 01:01 AM
What about trying to improving the conductivity of the existing track, perhaps using contact cleaner and fine steel wool.


10-06-2008, 02:13 AM
I would suggest considering joining the track pieces using something like a battery tab spot welder. In general, a weld like this happens so fast that it does not heat an area near as much as soldering. This is why commercial nicad packs are spot welded and they used to tell you not to solder them.

10-06-2008, 02:23 AM
Ken, the existing track is staying for now. The problem isn't with the surface cleanliness and conductivity, it's with the connections between separate sections. As they plug together, the rails are spread a small amount when the pin from the next section is inserted. This is supposed to create a good connection and it often does, but with all the vibration and use, these connections become intermittent. I can't say we've tried every cleaner, conductivity enhancer, etc known to man, but I've been cleaning contacs and connections for decades and I can say that these aren't going to be fixed that easily. We've used conductive paint and worked it into the joins as best as possible, which helped a lot, but is not the permanent answer. Creating a direct soldered connection through a wire is as close as we'll get.

One thing that will get old fast is when we start rubbing through the chrome plating on the rails. I can see it starting to happen already. Tonite I believe we came up with the most viable solution yet to replace this track when time and money permits, but for now this track will have to do. It wasn't designed to have as much constant traffic as it's getting, but business-wise the high traffic is a good thing. Our painted surface is proving to be very durable- just have to make these joins between sections more permanent.

Spot welding, yes I'd love to be able to do that. I could reach maybe half of the connections, but the rest- I was trying to think of a way to do this from above but there's no way to pinch the rails unless one electrode can go underneath. At a minimum, 120 connections can't be done this way, it must all be done from above.

In hindsight, I would have wired every 6 lane section to a connector board on one edge of the track, and ran the dozen bussbars for the full loop. Would have been a lot of wire, but none of these problems. Oh well

10-06-2008, 02:33 AM
I think resistance soldering would be ideal here.

10-06-2008, 06:29 AM
Can you do "Dremel Roadworks" & sink a short slot next to each required joint to allow a wire braid next to the track?
You could use a polyeurethane sealer to give a neat paintable repair, I know it's a lot of work but it saves esoteric techniques and equipment and definitely gives a permanent job,

10-06-2008, 09:54 AM
I once made a type of resistance soldering tool out of a short piece of 1/2" copper pipe, a right angle compression fitting, and the carbon electrode from a standard D cell battery.

To make one, jam one end of the fitting into the copper pipe. Solder if necessary to hold it securely. Sharpen the battery electrode and use the compression fitting to hold it snugly. Solder a wire to the copper pipe and optionally wrap it with tape or something to make it more comfortable to hold. Of course you don't have to be this fancy, you can simply hold the electrode with the clamp from a battery charger...

Connect the handle to a low voltage source 6-12 volts should be more than adequate. Connect the other end of the power supply to the rail and touch the carbon to it. It should quickly heat up enough to melt the solder.

I did this a long time ago so I forget how well it worked but it is something you can try out quickly and it might just do the job.


10-06-2008, 10:02 AM
Its cold method one step further than paint. Its two part and its expensive but you only need a tiny blob. It not a paint since it has structural strength
Google conductive epoxy. Its available with pot life from 5 min to hours

10-06-2008, 10:37 AM
I was curious about what Rowbare had posted - resistance soldering

Did a quick google and voila - a resistance soldering tool being used on train track. (http://www.americanbeautytools.com/site/index.php?req=prod&cat=hobby&model=SC250)

Mr Rowbare is pointing you in the right direction.:) :)

10-06-2008, 03:28 PM
Darryl...Have you thought about an electrically conductive grease? I am sure that there are commercial products available if you check at the electronics supplier, but if not, you could even make your own by adding a little carbon dust to silicone grease, something that won't melt out easily.

Good luck,

10-06-2008, 03:58 PM
I feel like I've exhausted the conductive paint, grease, etc avenue, but maybe I just haven't used the right stuff yet. I've considered resistance soldering, and not ruled it out, but because the only place to get a conductive path through the rail is from the top, I think the rail would get displaced downwards from the pressure required to establish the current path through the electrodes, and it would press into the softened plastic. Maybe this wouldn't happen, I don't know. I could always to a test on a scrap piece of track. Resistance soldering is pretty cool and maybe I could make that work here. I'll consider it again.

10-06-2008, 04:48 PM
I know the conductive epoxy didn't sound that appealing but here's the conductive epoxy selector from masterbond. We used these guys while doing strange stuff that needed special glues when I worked in the test equipment industry.


A dallop of nickel filled epoxy with high peel strength might be just what you need. I'd wager that you could even use it on broken track sections if this is like the old tyco tracks I remenber from when I was a kid.

Hope this is helpful.


10-06-2008, 05:17 PM
go back to american beauty web site and look at the pliers that hold two carbons, one + and one -. i have the large ones that i run off their 2500 watt power supply for manufacturing battery cables. a simple plier could be home made to dothe same job in a much smaller proportion. i would love to have the chance to make something like that if i were you.

i have actually silver solidered with mine but its very powerful compared to what you probably need.

i modified mine so both halves of the plier are positive and i have made my vice the negative connection. makes it that much easier on carbons.

i did manufacture my own carbon holders based on american beauty's new design. fun project.

yours sound like a fun project also. and i impressed with the race track idea besides. if i thought it would catch on here in the frozen northland, i would be inclined to try it.

our area high school has a graduation class size of about 75 kids each year and we are the largest school district (by square miles) in wisconsin.

10-07-2008, 01:28 PM
I feel like I've exhausted the conductive paint, grease, etc avenue, but maybe I just haven't used the right stuff yet. .

Darryl...Devoe Paint makes an epoxy putty called Devcon. There are many different compounds such as steel epoxy, aluminum epoxy, and copper epoxy. The only hitch it that they are ungodly expensive. The plastic steel is $25 a pound so I can imagine what the brass or copper compounds are.

Have you tried plain old graphite grease? Is the problem a voltage drop or just not making contact?

10-07-2008, 10:51 PM
The problem is an intermittent 'not making contact', made worse by arcing at the points where contact is made, which then acts to eventually make even a fairly tight spring-fit junction go bad. Look at spade lugs, the almost universal connection method used for attaching wires to relays, pc boards, etc. They go bad, it's as simple as that. A complete non-contact is basically a full voltage drop, even under no current draw. A poor connection may not drop any voltage to measure, but will when a load is trying to draw current through it. A good connection won't drop any voltage when current is drawn.

It's all one and the same thing, just to different degrees. Two metals can touch without there being a conductive path through them if oxide has built up. This oxide is enough to make any conductive solution application a less than permanent solution to the problem, especially in a case like this where there's lots of vibration. It's also very difficult to get these pastes or whatever into the junction instead of simply laying on the top.

I think the real answer is to bridge the joins with a conductor, soldered in place. The only question I have is how to apply the heat without distorting the plastic track material or dirtying up the top surface of the rail. I'll be trying an experiment or two in the next few days, and we'll see what comes up.

10-08-2008, 12:25 PM
Darryl...good luck with it man. Any heat applied to the conductor is going to heat the surrounding plastic. Be sure the surfaces to be soldered are clean and bright. As was mentioned, spot welding would be a good solution, but not everyone has a dental spot welder (like they put braces together with). I wish you all the best.

10-08-2008, 12:51 PM
Thanks, Jim. and everyone for the ideas.

10-08-2008, 12:56 PM
I did not read every post here but I do not think I saw this idea. Try the cold heat gun. Many brands make them. Some work better than others. The deal with these is they do not heat surrounding areas only pin point. They advertise you can touch the tip and will not get burned. I have one. Made by Coleman. I have used it on small stuff and it works ok. It uses a battery as a power source.

May think about it.

Just my foolish input.:cool:

10-08-2008, 02:32 PM
i dont know if its doable, or if its been mentioned already, but what about making a small hole under the contact that you can solder a wire to? so you would be soldering to the underside of the track, and if it melts the plastic a little it would be ok as long as the track surface stays flat.

10-08-2008, 05:09 PM
The cold heat guns or pencils actually use the resistance soldering technique. The tips require that you bridge their gap through a conductor, which would be the pc trace, wire, etc, that you're trying to solder. The heat is generated in the tip more so than the conductor you are touching with it, so it differs in that respect. True resistance soldering as I see it is when the junction is heated by the current flowing and gets hot enough to melt the solder itself, with the tips being only the means by which the current is caused to flow in the junction.

Doesn't much matter in this case- I may try to rig up a special copper wire loop for my gun, one with a sort of flat and wide part that I can touch down on the rail. Maybe I can get enough heat transfer that way without having to use a liquid solder bridge from tip to junction, and without having to use too much pressure. The trick is going to be getting a good contact in a repeatable way, and making the solder flow in a short time period.

10-08-2008, 05:44 PM
If you really want to solder it, you might consider special ordering low temperature solder and a fairly active flux that isn't corrosive. Also make sure to use a big enough soldering iron, preferable one with tight closed loop temperature control.

Too small a soldering iron will cause a great deal of the part to have to be heated to a relatively high temperature before the joint area is heated enough to melt the solder. A big enough iron with good temp control will melt the solder and heat the part very quickly before too much plastic melts. I personally have a good Metcal PCB Rework Iron.