How to prevent building in warps in BB frames?!

[centenary]

Hmmmm, not a happy bunny. Got some smooth planed 3x1 from the local wood merchants (not B&Q place) about 5 weeks ago. They've been stored flat on the garage floor to 'season' a bit before building. They werent wet when delivered and not damp when I built with them.

Built the first baseboard frame, it's basically a rectangle with a centre piece running down the middle length with cross members to be added. It's approx 3.7m long by 0.9m wide. It's laid flat on the garage floor. While measuring the legs from 2x2 today, I noticed one corner of the baseboard frame is about 2.5cm higher than the diagonally opposite corner!

The wood is good quality, I checked there were no warps in the pieces I used and built on the flat floor. I cut pieces square and to equal length on my chop saw which I checked before cutting, was square and true. I even used an engineer's square to check the ends of each piece was dead square after cutting before using a DeWalt 90 degree corner jig for alignment for gluing and screwing together.

Im gutted a warp has developed in the frame after all the precautions I tried to take to prevent this. The double garage is dry and doesnt have a big temperature variation as it has been draft proofed.

How can I prevent building in similar warps in my other baseboards?

[jed10]

I think the problem is that you only have the three long lengths (3660mm long) without any cross bracing to make the square. Over that length there's bound to be some movement. You might be able to pull it back into shape when you add the cross struts.

When making the next one, I'd be inclined to construct it differently. Create a U shape with one 900mm end plus the two long outside edges. Then add 860mm cross braces every 600mm until you get to the far end. Obviously you may need to adjust the exact position slightly depending on how this will fit in with your points on your track plan. (Don't forget to take this into account.)

Are you covering the frame or are you working open frame? If you are covering it with ply (9mm minimum) then once this is screwed to the frame it will help keep it all flat. Give the ply a coat of watered down emulsion on both sides after you have cut it to size but before you screw it down. This will seal it and minimise the chance of it warping. A dark colour (brownish) is ideal as it makes a good base colour to work on. I have read of some people painting the underside white to make it easier to see wiring when working underneath the board which I didn't do but makes sense.

[Bufferstop]

I gave up attaching cut and planed timber battens to ply worktops basically because cut timber always has a tendency to warp. Ply is much more stable, so I cut the 100mm deep long sides from the same sheet of ply as the surface, and the same for the ends. I use 6mm ply and make the sides and ends 100mm deep. The planed timber I use just for corner strengthening, if the board is wider than 300mm I use an 80mm deep strip that fits between the ends with several 40mm dia holes drilled through it for wiring. Large areas anything above 1000x400mm always require very careful construction, it's much better to make them from smaller modules doweled and bolted together.
For smaller layout and dioramas a block of rigid foam insulation edged with 4mm ply is quick and eay to construct. The only real downside is the need to bury attached point motors or hide them above ground.

[centenary]

Thanks for the tips, all.

Hopefully when the cross members are added with the ply top, it will be pulled into shape.

[RAF96]

I also used ply for my frames - heavy duty 18mm thick x 150mm deep. 9mm ply tops as I needed the flexibility to transition gradients, else the tops would have bern 12mm. Admittedly my baseboards are large (2 off 12’ x 3’ with 3’ linking boards) and very permanent.
Ply is another material where buying cheap can lead to disaster. B&Q and similar suppliers sheets can be warped on the shelf, never mind when you get it home.

[gppsoftware]

I also used ply for my frames - heavy duty 18mm thick x 150mm deep. 9mm ply tops as I needed the flexibility to transition gradients, else the tops would have bern 12mm. Admittedly my baseboards are large (2 off 12’ x 3’ with 3’ linking boards) and very permanent.
Ply is another material where buying cheap can lead to disaster. B&Q and similar suppliers sheets can be warped on the shelf, never mind when you get it home.

I've used 12mm 'structural ply' for my baseboards for years. Here in Australia, it is twice the price of non-structural ply but it does have the benfit of being largely flat the way we want it.
I use the same ply for all size and cross members. Never had a problem, even stored a layout in a Sydney garage for a year (temps 0c - 45c) with no problems.

I think the problem is that many people go for the non-structural stuff and ya gets what ya pays for.

[bootneckbob]

Looks like you are sorted now, but all my boards are 4ft x 2ft (basically) and have 20x25mm frames and cross struts; imagine an number 8 in old school LCD. All the boards are then fixed together. I've had no issues with warping and my layout (10m x 2.4m) is in a shed in the UK for the last 4 years.