I usually use 25x50mm rough cut timber for my oerminant layouts but I'm building a 4x2'ish portable layout and would like to use planed smooth so my fingers don't look like a cactus after moving the board around. I've found out that the planeing procces removes 5mm from the width and depth making the wool only 20x45mm so this may compromise the rigidity of the board. Can anyone make any suggestions of a different size in planed smooth that would be more appropriate? Many thanks.

My 4 x 2 Sundeala topped test board uses 18x38mm planed and is very strong and rigid. I would say you should be OK with 20x45mm.

Brilliant. Thanks for that information.

Hi IkBrunel,
If you mean 4 foot x 2 foot layout, I would suggest the 20 x 45 would be OK, especially if you use a couple of lengths as cross-members equi-spaced along the 4 foot length of the board. You could probably even go for 19mm x 38mm planed using the same method. 
Cheers Dennis.

Depending on what sort of point motors, or other 'under board gubbins' you are going to use, I'd suggest thinner but deeper, so maybe 18 x 70 PSE, or even 12 x 100 plywood. It also depends how/where it's going to be stored.

I've always used nominal 2" x 1" timber to frame my layouts but, as you say, once the rough stuff has been planed it's more like the 20mm x 45mm.
Never been a problem for me

My layout is in 3 pieces - 1 x 8' x 33" + 2 x 4' x 2', bolted together,  and all the framework is planed 2" x 1" and no problems.

Whatever timber you settle on I suggest not buying it from a DIY shed but maybe a local timber merchant, unless you really want 'bananas'

Without wanting to turn this into an engineering lesson, less can be more, so to speak.

Smaller timber, more of it, spaced regularly in multiple directions. Stronger than the same amount of wood if used in large sizes but only round the edges. Also worth remembering that the strongest shape (or polygon) is a triangle. Cross brace your square sections to form some triangles and it will be much stronger.

For reference, my last OO layout was on an 8x4 foot mdf board which was 9mm thick. Underneath it was braced using 45x12mm softwood which made 8 squares, each 2x2 feet. Each of these squares then had one diagonal fitted to make 16 triangles. No twisting, no sagging and didn't need a crane to lift it.

Quote from: newportnobby on December 30, 2017, 05:09:26 PM
Whatever timber you settle on I suggest not buying it from a DIY shed but maybe a local timber merchant, unless you really want 'bananas'

Oh contraire my friend. Most mainline timber merchants, Jewson, Travis Perkins, Nicholls timber is crap. If you buy kiln dried PAR (planed all round) from B & Q or Homebase it's much more stable and less liable to twist/warp.

Sad, but true.

Quote from: emjaybee on December 30, 2017, 07:56:09 PM

Sad, but true.

That's your experience. Mine has been completely the opposite. Guess we'll just have to agree to differ. The last time I bought timber from B & Q even the chap who was going to cut it to length couldn't find a straight piece.

It doesn't matter where you buy it from, split a few packs and pick out the straight ones. There are always a couple of bent ones in the 6 or 8 packs.

Matt

Quote from: mattycoops43 on December 30, 2017, 09:35:46 PM
It doesn't matter where you buy it from, split a few packs and pick out the straight ones. There are always a couple of bent ones in the 6 or 8 packs.

Matt

Agreed. I usually stick to single lengths that have had time to settle themselves outside of a split pack.

Yep, just because it's straight when you buy it, doesn't mean it will be a couple of weeks later...

When buying softwood today I don't think there is much difference in the quality of timber bought from the DIY superstores or most timber merchants.
Increasingly the softwood timber can be home grown Spruce, fast growing straight trees that are felled when the girth is not that great. Soft sappy timber, but hey, it fits in with the Forest stewardship aims of sustainable timber supplies. Traders seem to enjoy displaying this eco-friendly symbol, it's good P.R.  How many of us have opened a polythene wrapped pack of timber, cut the plastic restraining ties only to find half of the lengths
resemble a boomerang?

Ironically some of the best timber I have come across recently, during many years involved with woodwork, is the humble and inexpensive C.L.S. (Canadian lumber standard) studwork timber. Now this has a low moisture content (providing it has been kept dry) due to it's intended primary use for interior carcassing/plasterboarded walls. Even this has to be picked over to ensure lengths are not in twist or bent. The 38mmx63mm is a bit big for baseboards, but there is a smaller square section CLS if you can find it. Finding good softwood is not so easy, so I like the comment about opening packs at superstores to pick out some respectable lengths. It's a pain in the a** having to take back maybe half of the pack as it is not fit for purpose!