Joined: 26/11/2006(UTC)
Posts: 507
Location: Atlanta, Georgia
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Hi, I had an intermittent contact track problem and this is how I think I will fix it and retrofit existing contact tracks as needed. I'm happy for any replies of suggestions or improvements.  In the above picture the unmodified c-track isolated contact rail is intermittently touching the next track and making contact. I searched the internet for this problem and only found it mentioned on this YouTube video by Model Train Fun starting at 37:21 minutes (https://www.youtube.com/watch?v=2FMWxEPm__Y ). Model Train Fun suggested trying different track sections. I will do that moving forward, however for track already soldered to wires, I don't want to switch out different track sections. My c-track is not screwed down to the layout, but is sitting on top of a sound deadening carpet underlay (Ikea Stopp Filt), which allows a little bit of movement. I wonder if there would be intermittent contact if the track were firmly attached to the layout?  What ended up working was gluing a piece of paper between the track ends. In the picture above I'm about to slide a paper under the rail.  Here is after the glue dried and paper is trimmed back. As an improvements I want to 1) find material other than paper that will hold up to isopropyl alcohol used to clean the track and 2) trim a better track profile into the insulator. As an example of the variability in the gap between rails here is another unmodified joint with a generous gap.  I guess what caught me off guard was assuming that all c-track joints always have a gap between the rails, so I wasn't looking at the rail gap when trying to find source of problem. Take Care, Chris |
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 3 users liked this useful post by trainbuff
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 Joined: 23/07/2014(UTC) Posts: 8,475 Location: ENGLAND, Didcot
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Originally Posted by: trainbuff 
As an improvements I want to 1) find material other than paper that will hold up to isopropyl alcohol used to clean the track and 2) trim a better track profile into the insulator.
I would use some Kapton tape. This is a teflon type tape with very good wear resistance, and extremely good insulation capability/ Originally Posted by: trainbuff As an example of the variability in the gap between rails here is another unmodified joint with a generous gap. I guess what caught me off guard was assuming that all c-track joints always have a gap between the rails, so I wasn't looking at the rail gap when trying to find source of problem. I wonder if you are being caught out by temperature variations causing the metal rail to expand and contract. That would certainly explain the intermittent contact you see with a rail that is almost making contact as per your first picture. I don't know how much the rails can move relative to the electrical contacts under the track bed, but it wouldn't be impossible to get a gap like the last picture when things are really cold. I have been surprised at how much rails can move for seemly small temperature variations, leading to tracks going out of gauge when a layout is taken to an exhibition. a hall full of people is surprisingly warm, even if you don't think the temperature has changed that much. We also tend to think of metal as being a stable material, but the co-efficient of temperature expansion can be surprising. I don't know just what it is for the rails that marklin use, but it would be an interesting thing to find out.
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1 user liked this useful post by kiwiAlan
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 Joined: 06/05/2020(UTC) Posts: 54 Location: Göteborg
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Originally Posted by: trainbuff
As an improvements I want to 1) find material other than paper that will hold up to isopropyl alcohol used to clean the track and 2) trim a better track profile into the insulator.
I cut a small piece of electric tape and put between, I had to do this in several places on my layout. All my 15 degree R3 pieces have this problem, and also a couple of straight tracks.
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1 user liked this useful post by roberts
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Joined: 11/06/2007(UTC) Posts: 208 Location: Eslöv, Sweden
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I have used clear nail lacquer painted thin on the rail end.
Br, Peder
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2 users liked this useful post by pederbc
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 Joined: 26/07/2021(UTC) Posts: 635 Location: Sydney
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Originally Posted by: kiwiAlan ...but the co-efficient of temperature expansion can be surprising. I don't know just what it is for the rails that marklin use, but it would be an interesting thing to find out. For those who can't do it on the back of an envelope! https://goodcalculators....al-expansion-calculator/A few common metals with their coefficient. Z gauge is nickel but I don't know what HO uses. If it is stainless there are different coefficients for different alloys. It most likely will be a 400 series alloy. https://amesweb.info/Mat...-Coefficient-Metals.aspxDon't forget to calculate the track base. The plastic will have a higher coefficient than the rail. Also factor in your layout base material. Probably lower. It's most likely the track base plastic which has the greatest coefficient.
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2 users liked this useful post by Toosmall
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 Joined: 19/08/2008(UTC) Posts: 1,051
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Or you could just file the rail end down. That will increase the air gap. |
Modeling Immensee, mile/km 0 on the Gottard. SBB Era V.
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2 users liked this useful post by rbw993
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Joined: 26/11/2006(UTC)
Posts: 507
Location: Atlanta, Georgia
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Hi, Thanks for all the great ideas. I tried one more thing, cut from Marklin c-track insulators, that seems pretty stable but is a lot of work cutting and trimming. I think I will try the idea of painting the track ends with something like varnish or liquid electrical tape. I tried filing and a rotary tool first, but I was not able to make a smooth cut nor was I able to control the depth of cut very well.  I was able to get two of these L-shaped insulators from one c-track insulator.  |
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 Joined: 20/08/2020(UTC) Posts: 64
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In case the gap is different at each end of the track, you could just push the rail. It is not fixed to the plastic bed, so that applying pressure to the end of the rail will make it slide back and increase the gap.
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 Joined: 07/06/2022(UTC) Posts: 15 Location: Otago, Dunedin
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Had the same problem , just gently shaved the edge off the end of the rail with a Dremel cutting disc , problem solved , a file could also be used as stated in the thread earlier.
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 Joined: 04/02/2011(UTC) Posts: 3,563 Location: Paris, France
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Hi
This is a common problem with C track. When brand new, the rails are kept a fraction of mm away but after a few years and temperature cycles:
- the rails expand and contract differently from the ballast (plastic)
- the plastic contracts and become less elastic with the solvant evaporation
This makes the rail to come into contact and then trigger a false detection.
So filing with a Proxxon / Dremel or with a file can correct the issue permanently.
Cheers
Jean |
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4 users liked this useful post by JohnjeanB
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Joined: 15/10/2006(UTC) Posts: 2,319 Location: Washington, Pacific Northwest
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Feels like a good approach is to paint on an insulating lacquer on the ends where you have the contact tracks.
Then in the future, if and only when you find a false positive problem, then remember to look at the joints between track pieces and if needed cut the joint open again with a rotary and maybe insert a thin styrene piece which can then be painted and glue in place. |
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1 user liked this useful post by Minok
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