hand laid switch problem (shorts)

Tim Holmes Aug 22, 2018

  1. Tim Holmes

    Tim Holmes TrainBoard Member

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    HI Folks

    I just completed a hand made turnout in N Scale, I followed the #4 size templates at HandLaidTrack.com, but did not purchase his jigs etc. The switch seems to work ok until the engine hits the frog (which is isolated and unpowered) and then something someplace shorts out. I have checked to make sure it is not thrown against the movement (the train is entering from the diverging route). Being new at hand laying switches, I am not sure where to look to begin to diagnose the problem. Can someone point me in the right direction?



    Thanks

    TIM

    San Luis and Rio Grande
     
  2. jdcolombo

    jdcolombo TrainBoard Member

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    You need some sort of continuity tester - if you have a multimeter, there is usually a continuity tester built in that emits a tone when there is electrical continuity between the two leads.

    With the tester, you check continuity between the two stock rails (e.g., attach red lead to one stock rail, black lead to the other), the "open" point rail and the "closed" (e.g., thrown) point rail, the open point rail and the closed stock rail, and each of the stock rails and the frog. There should be NO continuity between any of these points. If your continuity tester emits a beep (or light or whatever it does to show continuity), then you have a short. Once you have tracked down the short, then you can diagnose how to fix it. With a hand-laid turnout, the short is almost always the result of not cutting through the copper cladding of one of the PC board ties at the right spots. The FastTracks templates show where the copper must be cut in order to isolate the frog, stock rails and point rails from each other. I suspect that either you didn't make one of these cuts, or (more likely) you THOUGHT you did, but you didn't quite get through all the copper. Go back and look closely at all your cuts, and take your continuity tester and check continuity between both sides of the cut. If you get continuity, that's your problem.

    John C.
     
  3. acptulsa

    acptulsa TrainBoard Member

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    Generally when everything is fine until the locomotive passes over the switch, it means the locomotive is causing the short with a wheel or through the frame. The commercially built switches generally have quite a bit of plastic at the vee where the two inside rails meet each other. A wide metal wheel can bridge the two if the metal portions of those rails are too close together.

    Another potential for trouble is the contact which carries current from one side of the frog to the other (assuming you equipped the switch that way, instead of just wiring the track on each side of the switch). The commercial switches completely encase that strip in the plastic of the ties to prevent the locomotive weight from pressing the crossing rail down onto it.
     
    Last edited: Aug 22, 2018
  4. jdcolombo

    jdcolombo TrainBoard Member

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    Yes, good point. If the turnout does not cause a short EXCEPT when a loco is crossing it, then the likely problem is that a wheel is touching something it shouldn't, or something it SHOULD be touching is not the proper electrical polarity. My first suspect would be a wheel contacting either a wing rail that isn't properly electrically isolated, or contacting the wrong closure rail leading to the frog. It might help if you would post a close-up photo of the turnout.

    Another potential troubleshooting step is to do the following. Run your engine until it shorts the turnout, then note EXACTLY where the truck wheels are when that happens. That would help narrow the problem.

    John C.
     
  5. Tim Holmes

    Tim Holmes TrainBoard Member

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    Hi Guys:

    Heres pics of the switch that is the problem -- sorry for the delay in getting back to you all. Any input would be appreciated

    TIM IMG_0322.jpg IMG_0322.jpg IMG_0323.jpg IMG_0324.jpg IMG_0325.jpg IMG_0328.jpg IMG_0329.jpg IMG_0330.jpg
     
  6. SP-Wolf

    SP-Wolf TrainBoard Supporter

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    It looks like your short is to the right of the frog (In the photos). You should have gaps just past the second tie. And another PCB tie should be installed past those two - to hold that side together.

    Cut a gap here: - with another tie to the right of my circle.
    upload_2018-8-24_13-55-39.png

    Wolf
     
  7. acptulsa

    acptulsa TrainBoard Member

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    It looks like there's some solder just to the left of that circle he drew, where those two rails are closest together. That could be close enough to the other rail that the weight of the locomotive pushes them together.
     
  8. jdcolombo

    jdcolombo TrainBoard Member

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    also, you need guardrails. Without the guardrails, the wheels of a loco can slide over and contact a live rail that they shouldn't. Guard rails aren't optional; they are required for the switch to operate correctly.

    John C.
     
  9. r_i_straw

    r_i_straw Mostly N Scale Staff Member

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    Yeah, guard rails should be added.
    [​IMG]
     
    Tim Holmes likes this.
  10. Tim Holmes

    Tim Holmes TrainBoard Member

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    ok, that makes sense -- I didnt know the purpose of the guard rails -- I'll put them in on the one I'm getting ready to start here in a few minutes

    TIM
     
  11. Hardcoaler

    Hardcoaler TrainBoard Member

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    NS read of your work and wants to help. Your gift passed through Columbia, SC today en route to your home, but I think we have a slight problem with scale incompatibility. :)

    2019-01-30 Prefabricated Turnout.jpg
     
    chandlerusm and acptulsa like this.
  12. jlbos83

    jlbos83 TrainBoard Member

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    I do not agree with the need for that gap, however, you do need to make sure there is a break in the cladding of the far right tie between those rails, I don't think I see it in the pictures. I would have expected a short always without it, depending on your wiring. An Ohmeter would be very nice for testing that all of the cuts in the cladding are complete, I see at least one that looks suspicious. As you work on your next one, try more careful application of flux and less solder. Maybe less heat, or at least more concentrated where you want it (maybe a smaller tip). Look at the videos from that site (or perhaps they are on YouTube now) for how to solder that little track! Too much heat is the enemy of the PCB cladding, too much solder is the enemy of everything. File the cladding before you start to get a clean, shiny, surface. You can also allow a bit more clearance between the closure rails and the stock rails at the throwbar, check out r_i_straw's pic. Workmanship is very key with these beasties, each one will get better!

    Do you have a gauge to make sure your spacing is good? It is really important. Without a jig you need to really make sure you are checking every step of the way.
     
  13. acptulsa

    acptulsa TrainBoard Member

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    The first I saw of this was on the BNSF's old Frisco main. I thought, well. They finally caught up with us model railroaders.

    I love it when we show them how to do it!
     
    Hardcoaler likes this.

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