Wood expansion/contraction

[Dan Griffin]

Morning. 
 

i have a lift up section on my layout. All was aligned fine but now we have had some warmer weather the wood has shrunk slightly and the track is now out of alignment. 
 

what do people do to stop this? 
 

i’ve seen people use dowels but with the wood shrinking would that help? 
 

the flap is made of ply top and bottom (to hide wiring) and softwood frames. The same as the rest of the boards. 

[meil]

16 minutes ago, Dan Griffin said:

Morning. 
 

 

what do people do to stop this? 
 

 

Paint it

[doilum]

Assuming it isn't a critical scenic section, consider relaying the track with over length copper clad sleepers at the joint. Solder a length of brass tube outside of each rail and cut in situ for perfect alignment. A lubricated nail or brass rod through each pair maintains alignment.

[Nick C]

41 minutes ago, meil said:

Paint it

Agreed - you want to seal the surfaces as much as possible to prevent the wood from gaining and losing moisture (which is what causes it to shrink and expand). Pay particular attention to the end-grain of the cut softwood.

[melmerby]

I have 4 lift up sections

3 use 22mm floorboards and one uses 10mm ply with a vertical central rib to maintain flatness.

None are painted

 

The only one that gives any trouble is a floorboard one with a 3' radius curved double track crossing it, where I have some side to side and vertical movement.

This is mainly due to the hinges I am using:

https://www.toolstation.com/hafele-concealed-cabinet-hinge/p65141

 

These have side to side and up/down play which doesn't cause a problem on kitchen cabinets but does on a model railway.

I intend replacing them with home made hinges as on one of the other lifting sections.

 

[Titanius Anglesmith]

Paint may help to restrict movement, but I wouldn’t count on it. 

 

On what axis is the movement occurring, ie up-down, front-back etc? If there are only one or two tracks crossing the boundary in, say, the middle of the board, then it would perhaps be best to mount the hinges close to that point. That way any contraction or expansion is pushed to the edges rather than the middle of the board moving. 

[Clive Mortimore]

Hi Dan

 

Wood is a natural product it will expand and contract, bow and warp, and twist in all directions. This is due to the surrounding atmosphere's humidity and temperature. Varnishing and painting all surfaces before assembly is about the best you can do, to minimising the effect. After assembly there will be surfaces where moisture can get in.  The more components in a structure that can grow and shrink can multiply the problem as the all start to do their own thing.

 

I note you say you have plywood both top and bottom of the lifting section. The expansion and contraction could be different top and bottom. Also is it wise to not being able to access your wiring? What if you need to modify it at some point or repair it?

[Andymsa]

Although personally not my favourite medium why not try MDF for the lift up section as it’s a very stable product as it’s not as susceptible to environmental conditions. 

[smokebox]

50 minutes ago, Andymsa said:

Although personally not my favourite medium why not try MDF for the lift up section as it’s a very stable product as it’s not as susceptible to environmental conditions. 

 

It may be the rest of the layout that is expanding/contracting more than the lift up section.  

[Dan Griffin]

One thing i will add is that the hinged end never has an issue, its the other end thats causes the problems. 

[Titanius Anglesmith]

4 hours ago, Clive Mortimore said:

Hi Dan

 

Wood is a natural product it will expand and contract, bow and warp, and twist in all directions. This is due to the surrounding atmosphere's humidity and temperature. Varnishing and painting all surfaces before assembly is about the best you can do, to minimising the effect. After assembly there will be surfaces where moisture can get in.  The more components in a structure that can grow and shrink can multiply the problem as the all start to do their own thing.

 

Being pedantic, that's not entirely true.  Wood mainly exchanges moisture via the end grain, as mentioned by Nick C.  As moisture is gained or lost, wood generally only moves across the grain.  There should be negligible change end-to-end.

 

2 hours ago, Dan Griffin said:

One thing i will add is that the hinged end never has an issue, its the other end thats causes the problems. 

 

Perhaps a photo or diagram may help us to visualise where the problem lies?

 

Another thought, how new is the flap construction?  Softwood is actually quite stable but only once it's reached equilibrium with its surroundings.  As bought from the timber yard it's often still a bit wet so still has some unexpressed movement in it.  Is this the first season of warm weather since you built it?  If so, you might find it will settle down now, especially if it's an indoor layout (is it?)

[Free At Last]

I have a similar situation... The board I am building my terminus station on is 12mm baltic birch 8ft long, sealed all round. The platforms are ratio kits (plastic) with the concourse fixed at one end and three platforms running off it. The platforms are not yet fixed and each are in two sections of approx 3.5ft each. What I am noticing is when the platforms are placed in position with all sections butt up then a day or so later when I go in to the shed there are gaps in between the sections. They can add up to between 4-6mm per platform length.

I don't know if it is the baseboard, the platform or both moving/creeping. 

My worry is what will happen when the platform is permanently fixed by the ballast.

[ISW]

11 minutes ago, Free At Last said:

I don't know if it is the baseboard, the platform or both moving/creeping. 

My worry is what will happen when the platform is permanently fixed by the ballast.

A 'trick' I saw somewhere on RMWeb is to wrap the platform edge in cling-film before ballasting. That way the cling-film can be removed once the ballast has set and the platform becomes removable.

 

Ian

[Free At Last]

1 minute ago, ISW said:

A 'trick' I saw somewhere on RMWeb is to wrap the platform edge in cling-film before ballasting. That way the cling-film can be removed once the ballast has set and the platform becomes removable.

 

Ian

I don't want it removable, I want to eventually fix it down but worried about where the 4-6mm of movement will go.

[Gibbo675]

6 hours ago, Titanius Anglesmith said:

 

Being pedantic, that's not entirely true.  Wood mainly exchanges moisture via the end grain, as mentioned by Nick C.  As moisture is gained or lost, wood generally only moves across the grain.  There should be negligible change end-to-end.

 

Hi There,

 

Not entirely true as dimensional inconsistencies may include Bowing, Crooking, Cupping, Twisting, or all a combination of all three.

 

Granted the moisture will enter and exit via the end grain rather more readily than by any other means this does not mean that wood will simply expand and contract across the grain considerably more than over the length of the grain.

 

Gibbo.