Sunday, January 11, 2015

Point Jumpers and Track Feeders

Some time ago I wrote up how I did point jumpers on my Atlas O code 148 turnouts.  For N scale I'm using Atlas N code 55 turnouts.  My rule of thumb for track is simple - if it doesn't have a wire soldered to it, it's going to be unpowered sooner or later.  Turnout points are electrically connected by a contact under the hinge point, and by contact with the stock rail.  They are exposed to dirt, ballast glue, paint, scenery materials - in short they are almost begging to have electrical issues if you don't take measures to make sure they're powered.

My solution for N scale is the same as for O scale - solder a jumper wire between the point and it's closure rail.  Even though it's a bit trickier to solder a jumper wire to a code 55 point without melting ties, resistance soldering and solder paste make it doable without too much trouble.

Resistance soldering runs a high electrical current from one probe to the other, and anything in between gets hot.  Assuming you pinch the wire and rail with the probes, this tends to put the heat exactly where you want it - right where the wire meets the rail.  The rest of the rail gets heated from there, so if you wait long enough the entire section of rail will get hot.  Since that would melt the plastic ties, you need to get the job done before that happens.  In other words, timing is important.  And since how long it takes depends on how fast the joint and solder get hot, power is important too.  You can do it with regular solder, but it's easier with solder paste.  I'm using Iso-Tip silver bearing solder paste (http://www.iso-tip.com/products-page/smart-paste-series/).  Solder paste is basically a mixture of solder particles and flux.  For the resistance soldering station I'm using the American Beauty 250 watt unit that micro-mark sells.

Here's what I do.  First, scratch up the surface you want to solder a little (I use one of these things http://www.micromark.com/scratch-brush,8058.html).  The scrub it with a toothbrush and some 90% alcohol.  Clean fresh metal makes for an easier joint.  Then I strip a section of stranded #18 wire and cut off about 1/2" pieces of single strands.  Same treatment for the wire - scrap it up a little with some fine-ish sand paper, wipe with a paper towel damped with alcohol.  Put a dab of solder paste on a scrap, and use a toothpick to put a little bump of it in the web of the rail at the spot you want the solder joint to be.  I do it between two ties, one tie away from the point hinge (so there are three ties between the two soldered spots).  Using some tweezers you can now set one of the single strands of wire across the point, with each end mushed into the solder paste a bit.

For the soldering I use the tweezer handpiece, with the tips bent a little to make it easier to get contact where I want it.


Squeeze the jumper wire and rail web between the tweezer tips right at the solder paste blob.  After some experimenting I've found that setting the 250 watt unit to 90 and using the foot switch to hit the power for 1/2-3/4 of a second is about right - you get a nice solder joint and don't melt anything.  You'll need to experiment a bit to find the right power and timing for whatever soldering unit you have, so practice on some flex track you don't mind wrecking before you start mangling turnouts.  You may mangle a turnout too, but get the worst of it over on the flex track.


And a closeup of that - note that this attempt was before I went with the longer jumper to put the joint between ties, but it does give you the idea of what it looks like with the wire mushed into the paste.
A closeup of pinching the jumper into the solder paste jut before soldering



Finally, assuming everything went well, clean any residual flux from the paste off with the toothbrush and alcohol.  Here's what the end result looks like if you got everything right.

A nice point jumper

Closeup of a nice point jumper
Note that you will almost certainly not get it right the first time - the power and timing are critical for one thing.  It takes a little practice.  In the above photo you can see a little fuzzy in the background my practice turnout (kind of destroyed) and a piece of flextrack I used for practice as well.  Both for soldering point jumpers (you can practice on flextrack just soldering the strand into the web), and for track feeders.  You will destroy some flextrack and quite likely a turnout or two getting the process right.  Use a magnifier to inspect the joint - sometimes a joint can look OK to the naked eye but when you look closer it's not so nice.  Here's one example of what happens when you get the power and timing off (this one looks a little questionable to the naked eye, but with a magnifier it's pretty ugly).

Bad power and timing, jumper too short
Also notice in that photo that I was trying to solder right over the tie - not surprisingly that makes it more likely that you'll end up melting the tie, which is why I ended up going with a slightly longer jumper to put the solder joints between ties.  It is possible to re-flow and fix joints like that one if you get it right the second time, but if you keep re-flowing eventually you'll wreck the turnout.

You might expect that adding a jumper like that on each point would stiffen up the pivoting action of the points.  Surprisingly, it doesn't - the points still slide side to side with no noticeable additional resistance, and then stay where you leave them - there is no tendency to spring back.

I did consider other ways of powering the points.  Here's one I got as far as trying - soldering feeders to the bottom of the point hinge pins.

A rejected approach
There are two problems with that approach.  The first is that the hinge pin itself does get hot enough to melt the tie a little, and it's at possibly the most critical spot in the turnout to not melt.  The other problem is the wire needs some space to move, and I could quite see how I would keep it unrestrained after gluing ballast down.  I think the point jumpers are better all around.

Enough of point jumpers, on to track feeders.

In O scale I did my feeders after the track was laid using the resistance soldering unit with the single tip probe to solder the flattened end of a #18 wire onto the back side of the rail base.  Very inconspicuous, and easy to not melt ties in O scale.  For my N scale layout though, I couldn't imagine doing that without melting a lot of ties, and also the pressure required on the probe would probably mush the track into the foam roadbed a bit (3/8" homabed in O is a lot less susceptible to mushing than the blue foam insulation I'm using for the N scale layout).  So I decided to solder the feeders to the bottom of the rail before laying the track.  I decided to use #22 wire for feeders - it's big enough to carry the necessary current for the relatively short distances from the bus (~12"), and it's small enough to fit between the ties without touching them.  Also I was able to find scotchlok connectors that are rated for #22 solid on the tap, and #14 solid for the bus.  I used the scotchlok connectors on my O scale layout and liked them, so in part selecting wire size depended on finding the right connector.

The process of soldering a feeder on is simple.  Cut out a bit of the pastic to expose the bottom side of the rail if there's not already a convenient exposed spot.  Scratch it up with a needle file.

Scratch up the rail for soldering
Strip a little bit (3/32 or so) off the end of the #22 feeder, and bend it over 90 degrees with some pliers, squeezing just hard enough to flatten the end a little bit (but not so much that it gets brittle).


A bit flattened on the end that will touch the rail
If you put the track on a little block (like you see in the photo with the file above) with the spot for the feeder just a bit off the end of the block, it makes it easy to use the soldering tweezers.  Put a dab of solder paste on the rail where you scratched it up, mush the wire into it, squeeze the tweezers down, and hit the power.  I find the same setting of 90 for 1/2-3/4 second works for me here too.  It's a little harder to not melt ties a little when soldering right up next to them like this - even if you're fast with the power, the residual heat from the wire, the joint, and the tweezers themselves can melt a little.  On the plus side, a little melting here is nowhere near as bad as it would be right at the point hinge.  On turnouts after I add feeders to the stock rails I also solder one onto the frog power eyelet using a regular old soldering iron and solder.  I'm still not sure if I'm going to power my frogs but it's a lot easier to solder the feeder at the bench than it would be with the turnout glued down to foam.  Finally, of course, clean up the joints with alcohol and a toothbrush.

Feeders soldered on
If you get a good solder joint it's pretty strong.  If you get a cold joint the wire may pull off as you shift the turnout around on the roadbed.  So inspect those joints carefully!  I'm willing to count on the internal connections in the turnout to power the rest of the rails (closure and the two little stubs off the frog), a decision I might regret later but for now it seems like a good trade off in retaining the strength and unmeltedness of the turnout vs. potential electrical trouble.

One final bit of soldering, this time rail joints.  On curves I've found it much easier to maintain a smooth continuous curve in the rail across joints if the rail joint is soldered.  Doing this requires a little test fitting and thinking, to make sure you get the soldered joint in the right place without having to cut out more ties after you curve the flex track.  I use the resistance solder unit again, but with the carbon jawed plier handpiece this time.  I tried mushing solder paste into the rail joiner, sliding the rails in, and soldering, but it turned out to be virtually impossible to get the rails to butt up end to end (not all the paste would squish out from between them).  In the end it turned out to be easier and better to use traditional solder.  As always, scratch up the rail surfaces that you want the solder to stick to and clean them off.  Slide the joiner on centered on the joint.  Keeping the joint straight is a little tricky but not hard - I lightly clamp the track half off the edge of my bench with the back edge pressed against a ruler to keep it straight.  Brush on a little good quality liquid flux (much better than paste flux).  If you use too much flux you'll eventually end up with a glaze of flux on the carbon plier jaws and they won't conduct electricity well enough to solder with - if that happens a little sandpaper will clean the glaze off.  Squeeze the pliers onto the top of the rail and the bottom of the rail joiner.  Be careful not to shift the rail position as you clamp down on it - I brace my hand on my leg (not the same leg I'm using for the foot switch).  Hit the juice.  The foot switch is critical here unless you have more hands than I do.  The power setting of 90 worked well for me here too.  Be ready with some nice thin solder at one end of the joiner, preferably on the outside of the rail.  As soon as the solder flows into the joint a little quickly move it to the other end of the joiner, and as soon as it flows there take your foot off the switch but don't move the pliers!  Wait for the joint to cool a little before you move the pliers.  If your eyeballs are into middle age or beyond, an optivisor definitely helps in all these soldering processes.

Soldering a rail joint
Unclamp everything and use the straight edge to make sure you didn't shift the rail a little with the pliers and introduce a kink while you were trying to do everything at once.  If you did end up with a kink, re-clamp, use the resistance pliers again to reflow the solder and let it straighten out.  You will probably get a little tie meltage, you can either ignore it or if it's to the point of looking bad cut off the offending ties.  If you melt too many of them from too many reflows, consider cutting the joint out, trimming both pieces back, and trying again.  Once you get the track pieces soldered together, you can solder the feeders on the bottom.

I was a little surprised that it actually turned out to be easier to get a good straight clean solder joint on N scale code 55 than it was with O scale code 148.  The bigger rail takes longer to get to the point where the solder melts, and it holds heat longer - that means you have to hold everything still for longer.  And since the rail is stiffer, you need to clamp against a longer straight edge.

That's about it for soldering and track.

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