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Discussion Starter · #1 ·
Hi

Before I make a final decision, if I use 50mm XPS foam as my base board, what is the best way to attach all the wiring underneath?

I've seen people have a 3mm ply and glue the foam to that and others that have just glued to the foam to the supports.

If I go without the 3mm ply, I thought about using cable nail clips and push them straight into the foam, not sure how long that would last, maybe drop some glue on the nail before pushing them in.

Any thoughts.

Cheers
 

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Hi

Before I make a final decision, if I use 50mm XPS foam as my base board, what is the best way to attach all the wiring underneath?

I've seen people have a 3mm ply and glue the foam to that and others that have just glued to the foam to the supports.

If I go without the 3mm ply, I thought about using cable nail clips and push them straight into the foam, not sure how long that would last, maybe drop some glue on the nail before pushing them in.

Any thoughts.

Cheers
Building baseboards entirely of XPS foam (if I have read correctly) is an unusual thing to do - not many do it.
I would have thought that XPS foam would be insufficiently strong to prevent sagging and would therefore require support. It's moisture absorbing and warping properties are probably not well known in the hobby. I would also suggest that 3mm ply would also be insufficient.

My suggestion would be to used tried and tested methods such as ply construction and limit the use of foam to just track-beds on top of ply.

I built my boards using 12mm ply and these have lasted 25 years, including a year of storage in a Sydney garage with extremes of temperature from -5 to +40, with no impact whatsoever.

Using foam, you also need to consider how you are going to attach everything on top of it - some glues destroy polystyrene and it probably won't hold any kind of pinning.

With regards cabling, I would recommend just cutting slots like I did in the cork that I use: https://modelrailways.online/Pages/Vu/PowerFeedingwithDroppers
Run the cable through holes in the surface and do all your cable runs underneath.

Please don't bury cables in scenery: as sure as night follows day, you will need access to it. Better to access it from under the board than to have to destroy scenery to get access.

Something else to watch: some foams have chemical reactions with the shielding on cables, causing the latter to break down and short. I would suggest that XPS is a bit too much of an unknown for me to be comfortable with it.
 

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I would be tempted to consider self adhesive copper tape - Lidl are currently flogging a 10m long roll for £4.99
I wouldn't! With no disrespect, I wish people would stop recommending this rubbish!

It was a product promoted about 20 years ago by a (now defunct) UK DCC supplier IIRC and it was always underrated current-wise and people had all kinds of voltage drop issues which resulted in a plethora of 'wives tale fixes' to resolve which in turn, created further problems! Stay away from it - it's the wrong tool for the job.

Copper tape was invented for running power down walls for dolls house lighting. Use it for what it was designed for and nothing more.
 

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Building baseboards entirely of XPS foam (if I have read correctly) is an unusual thing to do - not many do it.
I would have thought that XPS foam would be insufficiently strong to prevent sagging and would therefore require support. It's moisture absorbing and warping properties are probably not well known in the hobby. I would also suggest that 3mm ply would also be insufficient.

My suggestion would be to used tried and tested methods such as ply construction and limit the use of foam to just track-beds on top of ply.

I built my boards using 12mm ply and these have lasted 25 years, including a year of storage in a Sydney garage with extremes of temperature from -5 to +40, with no impact whatsoever.

Using foam, you also need to consider how you are going to attach everything on top of it - some glues destroy polystyrene and it probably won't hold any kind of pinning.

With regards cabling, I would recommend just cutting slots like I did in the cork that I use: https://modelrailways.online/Pages/Vu/PowerFeedingwithDroppers
Run the cable through holes in the surface and do all your cable runs underneath.

Please don't bury cables in scenery: as sure as night follows day, you will need access to it. Better to access it from under the board than to have to destroy scenery to get access.

Something else to watch: some foams have chemical reactions with the shielding on cables, causing the latter to break down and short. I would suggest that XPS is a bit too much of an unknown for me to be comfortable with it.
you are correct in stating that there is an interaction between cable sheathing and polystyrene, as I had a sheet of 3" polystyrene stored under my attic based layout which was lying on top of a power cable going to a wall socket. A few years later I took out the sheet to make some scenery to find that the cable had sunk into the styrene. I don't know what the outcome would have been had I left it for a few more years, but a electrician friend of mine advised replacing that length of cable and re-route to the switch.
 

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Discussion Starter · #7 ·
Hi
Thanks for the replies, I have also looked into the problem of electrical cables interacting with XPS foam, which leads me to use a combination of the two, the baseboard support is going to look like this. So even if I used a combination of 3mply and XPS foam with the supports every 450mm it should be pretty sturdy

Rectangle Building Triangle Art Font
 

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May I respectfully suggest that asking for advice and then ignoring it isn't generally regarded as an ideal approach ?

There are issues with support of foam and I personally, don't think 3mm ply is sufficient in any circumstances. Then there are issues of chemical interactions between foam and wire sheathing.

Even if you put wires under the boards, they are still going to have to pass through the foam to get there.

Why are you persisting with foam ? Got a 'job lot on the cheap' or something ? It is going to create a very unstable base to which you are going to have all kinds of issues attaching things to it.

In the planning of my layouts, I adopt more conventional construction methods as I tend to want them to last and not suffer warping of sagging issues. I learned the hard way many years ago!
 

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Discussion Starter · #9 ·
Many years ago I was taught that you have two eyes two ears and one mouth, why to look listen and shut up until you know what your talking about.

I'm in the look and listen part of this project. I believe that everyone has something to contribute whether that advise is taken or not depends on a whole lot of factors and I would hope that disrespect was not one of them.

To put some context to my question, my existing layout baseboard started off a scalextric track made from 12mm chipboard over 15yrs ago and not only could I stand on it (85kg) it has not warped. However, it's construction makes it heavy and not very moveable. Converting it over to model rail gave me some experience in wiring up DCC, hornby/peco point motors, a control panel and soldering upside down but it didn't allow for landscaping. Especially since I want to model an iron layout.

The main reason I am considering using XPS foam is from a landscaping point of view, especially for cutting batters. First up I found out some the properties of XPS foam these include:
  • The closed-cell structure and lack of voids in XPS helps the foam to resist moisture penetration.
  • Uniform density distribution, and dimensional stability
  • The closed-cell structure of XPS imparts excellent long-term compressive strength and durability.
  • Because XPS foam is essentially a plastic material, it will not corrode or rot or support the growth of mold or mildew
  • Inert; resistant to low levels of acid, alkaline, and many chemical compositions. However, petroleum-based solvents will attack the foam.
  • Ecologically friendly (no CFCs or HCFCs are used in manufacture).
  • Also is pretty easy to shape especially with a blow torch to create some irregular landscape features
I have spoken to others who have used this material with success.

So compared to plywood, depending on the plywood I would have to seal both products, considering the amount of water based products that are used for landscaping and ballasting.

My new layout will have a number of inclines and I found that 12mm ply just didn't have the flex that I wanted to create transitions from one grade to the next. So I'm considering using 6mm for the inclines. I have worked out a way to cut the batters in the foam that would allow me to place the 6mm ply to create the grades I need, I just have to provide additional support underneath the ply as well, that's when it's cut. In fill I'm not so sure since the track is going on the side of a hill and on a curve.

I can do the same thing in ply going the cookie cut method, it's just getting the interface between the ply (underside of ballast) and the embankment (foam) that I haven't been able to work out.

After a bit of research on migration of plasticisers from PVC Cables into XPS polystyrene there seems to be a solution:
  • you can either use a cable with a migration resistant plasticiser
  • or prevent the cable from contacting the XPS polystyrene
Plasticiser migration from PVC cable in contact with EPS can also be effectively minimised. If the cable temperature can be kept relatively low (50–60°C for a 50% usage situation), the rate of migration will be slow and will not cause a problem over 50 years. Not sure how hot the cable gets for model rail layout and how often would you be running locos 24/7, also in 50 years I won't be around so is it a problem?

I have taken on board everything you have said. I have followed your link and I now have an alternative to putting droppers through the baseboard, rather than the globules of solder I had my old layout.

With the dropper wires only being 22 gauge wire (1.6mm dia) I could always over size the hole the droppers go through and insulate that so the droppers do not touch the XPS foam.

From a glue point of view there are plenty of options that are not harmful to XPS foam

If I glue the 3mm ply to the XPS foam that should provide better rigidity than either product separately, might even change it to 6mm ply depending on the price.

No cables under scenery - check

I would hope that you will still provide advice and if I do not take it and it all goes pear shaped feel free to say "I told you so" and there will be no hard feelings on my part, apart from me not listening.
 

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Sure, it's entirely your call.

One of the things I commonly see on layouts is people adopting methods which supposedly make scenery formation easier (ie various types of styrene/foam etc), but it is done at the expense of track-beds and usually results in uneven, variable track-beds which in turn, affect running performance for ever more.
Personally, I believe that the track bed is of the highest importance as it is the thing that will make or break a layout. I was simply trying to help you avoid problems.
One option to ensure a reliable track bed for your situation might be to place ply on top of the foam under the track.

Happy modelling!
 

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I have made sandwiches of 3ply, 40mm foam 3mm ply, which becomes incredibly strong, light and warp resistant. Standing my 150lb weight on a 3' 6" x 3' one, produces a deflection of just 1mm. It is also tolerant of shapes being cut out from above or below, to leave just a single layer of the ply - with a certain amount of common sense about how much and where...

Table Wood Electrical wiring Gas Flooring


Just to get the idea, these are just the droppers on a Shunting Puzzle, to which have been added, servos, polarity changing for the frogs, lighting etc. The small tunnel in the top right corner of the channel, is for wiring from the NCE control panel.

The 3' 6" x 3' board is to be used for an N Gauge run-around for some Berlin Military Train stuff and will have wiring, for Kato Unitrack run in grooves, Routed into the top ply. Those channels will have thin balsa strip laid in, or maybe Plastruct channelling to keep the wiring safe. Given the topic, the "handover of travel documents", hiding the channel under platforms, pavements etc, will require a minimum in the way of planning, marking and Routing.

That said, my, storable, larger layout, is made of 6mm ply, as per wartime a/c and Laser-cut by Tim Horne. The reason is simple - joining the boards together is perfectly possible with both formats, but far easier to manufacture in the ply boards, where the Patternmaker's Dowels and securing bolts also make for connections for 2 x Bus routes, one DCC and the other, DC.

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Hope this might be of assistance.

Julian
 
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