Slight warp on 5' x 14" baseboard - any fix?

[Lacathedrale]

I have a board made from 6mm marine ply and softwood braces in each corner. There are cross-braces of the same 6mm ply and softwood every 18" or so. Generally it seems stable, but I have noticed a shallow twist in the boards. Is there anything that can be done to save this, or am I stuffed? I was thinking a bottom panel and/or diagonals - but I've not tried to save a board like this, only rid myself of it!

 

Thank you!

[kitpw]

Is the board used (ie with stuff stuck on top) or unused?  If most of the top is covered with track bed, ballast and ground cover, you could try sealing the underside with dilute pva or paint to try and balance the two sides - it might stabilise it and, if weighted whilst wet to take out the twist, allow it to stay flat.  Twisting and curling are often due to the two sides being treated differently - veneered board always needs a balancing veneer on the back.

 

 

 

[ikcdab]

you dont say how deep the cross braces are, i usually go for around 100mm.

you also dont give the width, normally i laminate three secions of 6mm ply together to give 18mm cross braces.

generally if ply has warped, its difficult to get it back again, but i would definately try a diagonal cross brace, 18mm on edge. That can't bend, so you should be able to screw through from the top and flatten it out.

Ian

[Hibelroad]

It’s a bit difficult to say without some photos, however bear in mind that softwood as bought will not be straight and ply is often twisted. Are all the joints cut square? preferably with a mitre saw or great care if hand cut, even a few degrees off square can make quite a difference over 5 ft. Unless you have access to quite a bit of woodworking equipment it is difficult to make a good flat baseboard which is why laser cut kits are now so popular. 

[Happy Hippo]

You haven't given any dimensions for the board apart from a top thickness of 6 mm.

 

In my experience, a board built only of ply is usually very strong and stable.  As Ian has mentioned above, I also go for a minimum of a 100 mm depth to the side and end plates. Any soft wood is consigned to the inner corners where it's used as  fillets to thicken up the ply so wood screws have some depth to bit into.

 

I've also found that boards which are 'square' that is the four sides are of similar, but not necessarily equal, in length are more prone to not sitting flat.  Again boards with soft wood side and end members seem more prone to this.

 

These days soft wood, especially the alleged PSE, may leave the mill straight and square, but forced kiln drying, changes in humidity and poor storage before purchase will so render it anything other than straight and square.

 

Just seen your bb size in the title.

 

The above notes still apply

Edited October 29, 2022 by Happy Hippo
spelling

[Nearholmer]

The points above about different coatings (or not) are very true.

 

If you can, the best option will probably be to turn it into a guitar body, by skinning the bottom face and cutting access holes in that once it’s dried solid under heavy weight, on a dead-flat surface.

 

But, now-locked-in warp/twist forces can be amazingly strong, so even that might not cure it, I’m afraid.

 

Guitar body style construction (OK a few more braces inside) from the start is very stable. My accidental test-pieces were three 3’6” x 18” boards that I built for a never-got-beyond-some-track model of The Dyke in EM. They languished in a freely ventilated, rain-proof, but un-heated shed for about 25 years, so we’re exposed to ever-changing atmospheric conditions, eventually becoming a sort of multi-storey hotel for over-wintering field mice, and did they warp? Not one bit. They went to recycling in perfect order when my daughter decided to get rid of all my old junk from what had in the mean time become her shed.

[peterfgf]

6mm marine ply ought to be good.  You mentioned cross braces (presumably in the 14" direction), but nothing about longitudinal stiffening in the 5' longer direction.  As suggested by a previous poster,  I used 100mm deep transverse and longitudinal of 9mm birch ply and found they gave adequate stiffness without any warping in two years.  They were glued and screwed to a 9mm top. 

I left the offcuts of ply in my dampish shed and they have started to warp. 
I think the trick is to get good strength/stiffness (not the same thing) in the vertical direction to support the top and prevent warping.  The addition of diagonal horizontal braces would be even better at resisting warping (something I didn't do). I have reservations about the effectiveness of adding a second skin as a "guitar construction" to deal with warping. You can always drill out some large diameter holes if you are worried about weight (and to get the wiring through the transverse stiffeners). 
As another previous poster said, warping can be difficult to remove, but I had some success with an experiment with a steam iron on one of the pieces in the shed and managed to reduce the warp.  I attached stiffeners before it tried to revert to the bent state.

Peterfgf

[Harlequin]

3 hours ago, Lacathedrale said:

I have a board made from 6mm marine ply and softwood braces in each corner. There are cross-braces of the same 6mm ply and softwood every 18" or so. Generally it seems stable, but I have noticed a shallow twist in the boards. Is there anything that can be done to save this, or am I stuffed? I was thinking a bottom panel and/or diagonals - but I've not tried to save a board like this, only rid myself of it!

 

Thank you!

Diagonal bracing will prevent a box frame like this from twisting if designed in from the word go.

 

So you could try installing some now. Clamp the board so that the twist is removed and then glue in some 6mm ply diagonal pieces (with holes where needed) that are the full depth of the frame, firmly from corner to corner of every division. Leave clamped up for at least 24 hours then cross your fingers, release and see what you've got.

 

If it doesn't work, no great loss.

 

Edited October 29, 2022 by Harlequin

[Lacathedrale]

The height of the sides/braces is full depth - 100mm as discussed. I see what you mean about getting it flat and THEN adding diagonals or a bottom skin - makes alot of sense. I'll get some pictures up so we can see what we're talking about.

 

The strips were cut with a table saw, and the PSE was cut with a chop saw and stop so I'm fairly confident they're all the correct size - I just noticed a see-saw rock.

 

Thank you!

[Nearholmer]

7 hours ago, peterfgf said:

have reservations about the effectiveness of adding a second skin as a "guitar construction" to deal with warping.

The body of a guitar (or an aeroplane wing) is a box, which is how/why that construction is stable. It’s surprising how much you can cut out , provided you choose carefully where to do it, while retaining stability.

Edited October 29, 2022 by Nearholmer

[RobinofLoxley]

This is a shape that would be likely to warp. You have a long frame  -forget the top - it has to be made perfectly square like cabinet making square. The cross braces can help if they are exact fits in the frame. If the starting frame isn't square it can't be corrected later.

 

If you start by fixing sides using the base as reference specifically for this board shape you are at a disadvantage.

 

If the warp is too much you may have to start again. 

[DCB]

18 hours ago, RobinofLoxley said:

This is a shape that would be likely to warp. You have a long frame  -forget the top - it has to be made perfectly square like cabinet making square. The cross braces can help if they are exact fits in the frame. If the starting frame isn't square it can't be corrected later.

 

If you start by fixing sides using the base as reference specifically for this board shape you are at a disadvantage.

 

If the warp is too much you may have to start again. 

It probably was straight when built.  I avoid new timber because it always seems to warp, even if you pick the best specimens Wickes or B&Q  have they still warp.  I Raid a skip,l  Old structural timber, inner framing of interior doors etc.  I True it up with a  table saw or plane. 

In this case as the frame has warped is it possible to clamp or screw the ends in some substantial timbers and twist it forcibly back the other way, over centre and keep it there or a few hours or days? That way hopefully it settles back level.   Personally I never use anything so solid as 6mm ply as a wide baseboard top indoors preferring fiber board or sundela board so I don't get this particular issue but it does sag and when it does I pack the track up level through the dips.   Outside I have some thick ply baseboard top, it warped/ sagged so I built up the track base like big ballast on the less bad bit and cut out the bad bit and spliced in a new chunk with a substantial "Doubler" under the join screwed to both new and old sections with a lot of countersunk screws.    The thing is the built up track looks a lot better than the laid flat on the board version especially as I left the non running lines sagging.... 

Edited October 31, 2022 by DCB

[AndyID]

Is it really stable or do you think it's going to twist even more? If it's stable don't worry about it. I know it's a bit of a pain but it's best not to rely on a baseboard being true and level the track as you lay it like they do on the real thing. BTW, sidings are typically a good bit lower than main-line tracks as they are much more heavily ballasted.

[Lacathedrale]

It's been built now for about six months and not been subject to lots of moisture/etc. I think in retrospect I should have painted it as soon as it was done.

 

It's pretty heavy for its size (compared to the Grainge and Hodder boards I have) so I'm reluctant to put a bottom skin on, even with cutouts - but I'll see what I can do. I haven't made it into the garage yet but when I do I'll double check the flatness and take some pictures - thank you for the help!