9mm or 12mm Birch Plywood Baseboards

[alangdance]

Just started to think about some new base boards> Not sure what to go with. Should I go with 9mm or 12mm Birch Ply.

This is for the framework and Tops.

Any help would be most grateful.

 

Alan

[gismorail]

I have always used the 9mm size and as long as the boards are carefully constructed there's plenty of strength with this size. 

[Pete the Elaner]

How big are your boards?

I used 12mm ply with 3'x18" boards with a softwood frame & longitudinal brace, again made from softwood. They stayed nice & flat but I felt these were over-engineered & therefore heavier than they needed to be.

I used 9mm ply with 6mm ply frames on the following layout, but the boards were a lot bigger: 3'6"x 2'6" with a diagonal brace. I felt the tops were ok but I think I went too much for lightness with the frames.

I also varnished the boards to help keep any dampness out. Even though both of these 2 were intended to stay in the spare room, water is still used for ballasting & scenery.

Edited December 31, 2018 by Pete the Elaner

[brossard]

I used 12mm (1/2") birch ply for ends since it's very stable.  For sides I use lowest quality because it only has to space the ends and support the top.  It's also light.  For tops I used VG one side 3/8" ply.  1/2" is too heavy and 1/4" is too wimbly.

 

I got the lumber yard to cut my ply sheets into 4" strips.  A friend helped me cut the tops to shape.

 

I use steel dowels to position the boards.

 

Birch ply is dense and heavy so I'm thinking of ways to optimise strength, stability and weight.  Important for a layout that has to be moved around.  Not that the layout in the link will ever do that.

 

See the link below.

 

John

Edited December 31, 2018 by brossard

[HLT 0109]

Alan,

 

It will depend to some extent on what gauge you are working in.  I have just completed a four-element baseboard totalling 2m x 1m using 6mm birch ply for the top, using the remainder for sandwich sides until I ran out - then I used cheaper offcuts that were lying around in the garage.  The layout is N gauge and I am very pleased with the results.  The birch ply was great to work with - very resistent to splintering - but I think there may be some drumming when trains are running.  I hope to overcome this by using cork underlay to the track.  The cheaper stuff was much less pleasing to work with and would not, in my view, be suitable for the top.  Each element of my board is a different shape and size so the bracing has been difficult but the largest spacing is about 600mm x 300mm.

 

This is my way of suggesting that 12mm is unnecessary unless you have to limit the number of braces or are working in a larger scale, and also to suggest that you consider 6mm for lightness.

 

Harold.

[Robin2]

9mm ply is for structures that a person will be standing on. 

 

3mm ply (or 4mm) will be perfectly strong enough for railway modelling. Even then it should have lots of holes for lightness.

 

...R

[DaveArkley]

Just started to think about some new base boards> Not sure what to go with. Should I go with 9mm or 12mm Birch Ply.

This is for the framework and Tops.

 

Any help would be most grateful.

 

Alan

 

 

I use 9mm ply for surface and 6mm for the frame on 1220mm * 600mm baseboards. As Robin2 says above they are strong enough to walk on, I've tried it.

 

I can't agree with him that 3 or 4mm will be strong enough, I rejected 6mm for my boards because I could flex the baseboard, frame and all.

 

Cheers

Dave

[justin1985]

9mm ply is for structures that a person will be standing on.

 

3mm ply (or 4mm) will be perfectly strong enough for railway modelling. Even then it should have lots of holes for lightness.

 

...R

Agreed - 4mm and perhaps 6mm used strategically have been absolutely fine in my experience, including on large club exhibition layouts. The strength should be in the structure, not the thickness of the material.

 

Think Mosquito!

 

J

[CloggyDog]

9mm or 12mm is overkill for most baseboards, more so if they are supposed to be portable!

 

4-6mm will be sufficient and will also be lightweight.

[Phil Bullock]

Agreed - 4mm and perhaps 6mm used strategically have been absolutely fine in my experience, including on large club exhibition layouts. The strength should be in the structure, not the thickness of the material.

 

Think Mosquito!

 

J

 

Ply - balsa - ply laminate then? But we wont be travelling at 400 mph plus....

 

Phil

[justin1985]

Ply - balsa - ply laminate then? But we wont be travelling at 400 mph plus....

 

Phil

Thinking logically, balsa would probably work well sandwiched and glued as a spacer in a traditional ply girder design! (I.e. as spacer blocks between two strips of ply to make a beam).

 

They key point is that an L or I girder is strong way beyond the sum of its parts. Just look at a metal girder compared to a rod of the same cross section - there's a reason structural metal is always girders rather than thick solid beams.

 

But of course, go ahead and use 12mm ply with a flat top baseboard - if you're particularly fond of hernias. What is speed for a Mosquito is portability and manageability for you.

 

J

[Steven B]

I've used 6mm Birch ply boards without any problems other than having to find very short screws for fitting point motors etc.

[Keith Addenbrooke]

As some of the contributors have already noted, the answer depends on many factors.  Twenty years ago I bought a set of standard 4' x 2' (nominal) 12mm ply boards from a well-known DIY store, which I braced with nothing more than 2" x 1" softwood underneath the four edges (ie: no intermediate cross-bracing). 

 

On the plus side, they have survived 7 house moves, been stored loosely upright for nearly all that time (mainly in garages) and remain true and flat to this day.  I have on occasions briefly put my weight onto them without harm (to me or the boards).  So, in that sense, they've proved durable if that's a priority in your plans.

 

On the down side, they turned out to be much heavier than I thought they would.  They're also not nearly as portable as I'd hoped: the 4' x 2' size is bulkier than I'd imagined it would be - the warehouse wasn't a good reference point for the rooms in my house, so the convenience I experienced when making a quick purchase one lunchtime has come at a cost down the line.  I can't comment on the effects of adding scenery (both weight and liquid) as I've never got that far, I'm afraid.

 

Just some things to bear in mind I wish I'd known at the time.  Hope it helps.

[NIK]

Hi,

 

As has been said it depends on the application.

 

A OO finescale club exhibition layout I help with has 6.5mm birch ply tops but they are supported at least every foot in X and Y by 6 inch deep 5.5mm ordinary ply uprights. The upright ends of the boards have two layers of 9mm birch ply to provide a strong and stable interface to the next board and keep the tracks and scenery aligned. The joints were accurately made otherwise the layout would rely entirely on the glue joints. The layout is ten years old now with no sign of warping even though some boards are 4' x 3'.

 

I don't know of any hard and fast rules for determining the thickness of birch ply baseboard tops. Assuming very good support from very deep ordinary ply 9mm birch top may be good for 2mm finescale layouts for a 10 year plus layout lifetime.

 

For O gauge and above the locos may become heavier than scenery of the same size but the degree of deflection in the baseboard top that can be tolerated may go up a bit.

However the locos are less likely to be removed from a layout unless its only used at exhibitions so the stress may be applied for much longer.

If the buildings on an O gauge layout can be made part of the structure then the baseboard top takes less of the stress.

 

I've done computer simulations of 10mm birch ply tops with 10mm birch ply uprights and they showed great stiffness even when large round holes were added in the uprights to lighten the structure and allow cables to pass through.

 

I haven't found any engineering data for ordinary ply so I haven't been able to simulate that.

 

Using three ply rather than 5ply or 7ply or 9 (the number of layers) may be going away from using an engineering material.

 

Also if the ply isn't sealed and the room its in gets too cold and moist then self warping might get bad.

 

 

Regards

 

Nick

 

 

[AlunKimber]

I used 6 mm ply in a monocoque design, so structure rather than material thickness giving the strength. So far, so good...............

Cheers

Alun

[DCB]

Even 9mm sounds very thick and heavy if used as a large sheet, not too bad used as track beds on L girders  but ply is a nightmare to stick track pins in and very noisy.   I would use some form of fibre board, Sundela if you are a multi millionaire, or some insulation board like we used.

[jim.snowdon]

Hi,

 

As has been said it depends on the application.

 

A OO finescale club exhibition layout I help with has 6.5mm birch ply tops but they are supported at least every foot in X and Y by 6 inch deep 5.5mm ordinary ply uprights. The upright ends of the boards have two layers of 9mm birch ply to provide a strong and stable interface to the next board and keep the tracks and scenery aligned. The joints were accurately made otherwise the layout would rely entirely on the glue joints. The layout is ten years old now with no sign of warping even though some boards are 4' x 3'.

 

I don't know of any hard and fast rules for determining the thickness of birch ply baseboard tops. Assuming very good support from very deep ordinary ply 9mm birch top may be good for 2mm finescale layouts for a 10 year plus layout lifetime.

 

For O gauge and above the locos may become heavier than scenery of the same size but the degree of deflection in the baseboard top that can be tolerated may go up a bit.

However the locos are less likely to be removed from a layout unless its only used at exhibitions so the stress may be applied for much longer.

If the buildings on an O gauge layout can be made part of the structure then the baseboard top takes less of the stress.

 

I've done computer simulations of 10mm birch ply tops with 10mm birch ply uprights and they showed great stiffness even when large round holes were added in the uprights to lighten the structure and allow cables to pass through.

 

I haven't found any engineering data for ordinary ply so I haven't been able to simulate that.

 

Using three ply rather than 5ply or 7ply or 9 (the number of layers) may be going away from using an engineering material.

 

Also if the ply isn't sealed and the room its in gets too cold and moist then self warping might get bad.

 

 

Regards

 

Nick

Even in 0 gauge, 6mm birch ply supported every 150mm along the general line of the track by 6mm ply webs 100-150mm deep, even with lightening holes cut in them, is more than robust enough to both support the track and survive being manhandled in and out of storage and round the exhibition circuit for many years. Our previous club layout, East Dean, was built that way, with every joint glued only, and is still doing the rounds with its current owners.

Our current layout still uses 6mm birch ply for the tops, but has the transverse webs more widely spaced to give better access underneath. To maintain support under the track, a longitudinal web is provided, 50mm deep.

 

There is no reason that I can see to prevent an intelligently designed baseboard to be built from even 3 or 4mm ply - provided it is adequately braced and supported for the loads it will handle, which are generally lower than people imagine.

 

Jim

[teaky]

Even in 0 gauge, 6mm birch ply supported every 150mm along the general line of the track by 6mm ply webs 100-150mm deep, even with lightening holes cut in them, is more than robust enough to both support the track and survive being manhandled in and out of storage and round the exhibition circuit for many years. Our previous club layout, East Dean, was built that way, with every joint glued only, and is still doing the rounds with its current owners.

Our current layout still uses 6mm birch ply for the tops, but has the transverse webs more widely spaced to give better access underneath. To maintain support under the track, a longitudinal web is provided, 50mm deep.

 

There is no reason that I can see to prevent an intelligently designed baseboard to be built from even 3 or 4mm ply - provided it is adequately braced and supported for the loads it will handle, which are generally lower than people imagine.

 

Jim

That's helpful.  I've been pondering this very thing over the last few days, Jim.  What form did the joints take?  Just ply to ply at right angles or with a (softwood) fillet on the inside angle?  Any particular adhesive?  Clamped until set and that's it?  Conventional wisdom always seems to point towards a softwood fillet and screws, with or without glue but I have not managed to find any explanation for this other than avoiding screwing into end grain.

[Robin2]

I have found the Everbuild 502 Wood Adhesive to be very good. AFAIK it is just PVA but it has reasonable grab and the joints can be handled after about 20 minutes.

 

I built a baseboard about 2000 x 350 mm by about 50 to 100mm deep (it varied) using cheap 4mm ply. The vertical webs at the ends and internally were 10mm softwood. All the joints were glued along the edges of the ply and IIRC I had some fillets here and there. Certainly NOT along the full length of each joint. A fillet of glue along the edge(s) of a joint hugely increases the strength of the joint.

 

I have no doubt the webs could have been made with 4mm ply, but cutting them accurately would have been tedious.

 

The strength came from the fact that it had a bottom as well as a top. However most of the bottom was cut away to allow access to the innards. IIRC everything was cut away except a width of about 50mm where it contacted the vertical webs. I think I had two internal webs for the 2000mm length - making bays about 500m wide. Certainly there were not more than 3 webs.

 

As usual I never finished the layout and eventually I broke up the baseboard. Before doing that I tested it by standing on it when it was supported at each end. It did not break.

 

...R

 

PS ... my latest attempt at a layout is using a baseboard made from 25mm Celotex and no timber at all.

Edited January 4, 2019 by Robin2

[doilum]

18mm for the ends with steel pattern makers dowels.

Everything else: 6mm is more than adequate especially if the backscene is integral. This the conclusion of 40 years of my own and club layouts.

What I don't understand is the current trend to solid top boards braced by thick sides. It took us long enough to persuade the previous generation to abandon 3/4" chipboard on 4x1 framing in favour of open plan ply construction and curved boards.

The key is to have the joints between boards true, hence my preference for the thicker ply. Using a thin ply for the sides allows a depth of 6" or more. This avoids the risk of flexing. Where geography demands that you cut into the sides localised bracing restores the strength.

The join between the sides and cross braces needs a filet of shaped scrap wood. Whilst PVA has always been my first choice adhesive, Evosticks foaming urethane

[doilum]

Glue fills even moderate gaps and is incredibly strong onc hard.