Ply frames? Why? What for?

[Derekstuart]

Sorry this is related to a previous thread but with a more specific question.

 

Can anyone please tell me what advantage ply frames- with double skins and then a soft wood spacer- are supposed to have? I've just built one today. All wood nicely cut on a table saw and so far I can see lots of disadvantages compared to 2*1 timber. Namely that the amount of joins between ply and softwood spacers is far more than the 6 or so that I would have for purely soft wood frames.

 

I suppose the obvious answer is that if soft wood timber works for me then go for it, but when many well respected people are using ply I have to ask what I've missed.

 

I can see the advantage of contouring- building the track above the terrain or the other way around, but I can achieve the same by screwing soft wood spacers above the main framing.

 

I'm going to build a traditional timber version tomorrow to compare the weight, but so far I can't tell it's any lighter.

 

Any thoughts please?

[asmay2002]

Sorry this is related to a previous thread but with a more specific question.

 

Can anyone please tell me what advantage ply frames- with double skins and then a soft wood spacer- are supposed to have? I've just built one today. All wood nicely cut on a table saw and so far I can see lots of disadvantages compared to 2*1 timber. Namely that the amount of joins between ply and softwood spacers is far more than the 6 or so that I would have for purely soft wood frames.

 

I suppose the obvious answer is that if soft wood timber works for me then go for it, but when many well respected people are using ply I have to ask what I've missed.

 

I can see the advantage of contouring- building the track above the terrain or the other way around, but I can achieve the same by screwing soft wood spacers above the main framing.

 

I'm going to build a traditional timber version tomorrow to compare the weight, but so far I can't tell it's any lighter.

 

Any thoughts please?

In theory ply should be less likely to warp and ought to be stronger.

[Derekstuart]

That is proving to be the case vertically- quite strong, but the "sandwich" (I think that's what people call them) is bending. I haven't put any diagonal supports in. I will try that next.

 

This is a 4ft by 2ft and I have a mid "sandwich" effectively 2 times 2ft by 2ft boxes. Is that enough or do I need more "sandwiches" in it?

In theory ply should be less likely to warp and ought to be stronger.

[melmerby]

My baseboards are 10mm ply with 10mm ply vertical edges 100mm deep - no softwood at all apart from the legs.

Most are braced down the middle with another 100mm vertical

 

Each is 4' x 3' and I can stand on them.

A piece of ply on edge is extremely rigid.

 

Can't understand this idea of "bracing" ply with 2 x 1. All you are doing is bracing the 2 x1 with the ply!

 

Keith

[Happy Hippo]

One of the big advantages of the twin skin system is being able to make base board frames which are curved.

 

A thin piece of ply will curve quite easily. Put in the blocks then glue and pin another pice of thin ply to the blocks and you get a very rigid structure.

 

It is also very light.

 

I've used this system on a curved bridge on my garden line, and it makes a very rigid structure.

 

It also works well if you need strength in making an open base board.

 

By all means use 2 x 1 with 4 x 2 tops, but you are just another member of the  flat earth club.

 

Have a look at Barry Norman's book on Layout design to get a better idea of how effective this system is.

[PaulRhB]

Ply double skin frames don't warp like a lot of kiln dried softwood frames can and is lighter while taking up no more room. It does need cross braces but becomes very strong once the board is finished. It's a lot of work but worth it for big boards or ones that will be exposed to a range of temp and humidity.

[BG John]

I built traditional 2x1 softwood with half inch chipboard top boards for my first EM layout 40 years ago. It soon started sagging in the middle, and only became rigid when I attached the ply backscene and front decorative edging. It didn't move after that.

 

I built several ply sandwich type boards from 4mm ply with a 4mm ply top over 30 years ago. The layout they were for didn't get built, so they spent years in two different lofts. Then they spent several years as an exhibition stand for the company I half owned, and after that one board was cut down to make two small boards for the original version of "Small, Broad and Totally Pointless". The other boards were scrapped about 10 years ago, and were still as flat and rigid as the day I built them. The SB&TP bits have now been rebuilt into a bigger board and are still fine. I doubt if I could have done the same successfully with a chipboard and 2x1 board.

[chaz]

Sorry this is related to a previous thread but with a more specific question.

 

Can anyone please tell me what advantage ply frames- with double skins and then a soft wood spacer- are supposed to have? I've just built one today. All wood nicely cut on a table saw and so far I can see lots of disadvantages compared to 2*1 timber. Namely that the amount of joins between ply and softwood spacers is far more than the 6 or so that I would have for purely soft wood frames.

 

I suppose the obvious answer is that if soft wood timber works for me then go for it, but when many well respected people are using ply I have to ask what I've missed.

 

I can see the advantage of contouring- building the track above the terrain or the other way around, but I can achieve the same by screwing soft wood spacers above the main framing.

 

I'm going to build a traditional timber version tomorrow to compare the weight, but so far I can't tell it's any lighter.

 

Any thoughts please?

 

 

The number of joins between ply and softwood spacers doesn't matter at all. They are all glue and pin joins and require no special skills - you certainly don't need to cut halving joints etc. You say lots of disadvantages - maybe you could list a few?

 

Sandwich type frames built from good quality birch ply' (not the far eastern rubbish) are stable, frames built from kiln-dried pine are anything but.

 

Of course you are free to make your baseboards however you like, using whatever materials you want but my preference is for the ply' sandwich.

 

Dock Green (link below) has four baseboards made that way and coupled together top and bottom and on either side with adapted hinges. It has been to at least a dozen shows, manhandled in and out of vans, carried between two blokes, wheeled on sack trucks etc. The frames appear totally stable with the plywood top surfaces staying flat and level.

 

Chaz

[Derekstuart]

Thanks for the further info chaps.

 

Chaz, yes of course I can and will make them the way that works best for me. The reason I haven't dismissed the ply method is because there are so many people who I respect who have used this system.

 

On that basis I shall continue trying it. I have previously built timber frames. I will have a go next at a single skin ply- 1 of each of the three methods and see which will work best for me.

 

Thanks again.

[MPR]

Thanks for the further info chaps.

 

Chaz, yes of course I can and will make them the way that works best for me. The reason I haven't dismissed the ply method is because there are so many people who I respect who have used this system.

 

On that basis I shall continue trying it. I have previously built timber frames. I will have a go next at a single skin ply- 1 of each of the three methods and see which will work best for me.

 

Thanks again.

I would also emphasise the importance of diagonal bracing, it makes a huge difference to the torsional rigidity of any baseboard.

[Bernard Lamb]

I would also emphasise the importance of diagonal bracing, it makes a huge difference to the torsional rigidity of any baseboard.

Any diagonal bracing will make a huge difference, but if it is designed correctly the amount of material can be reduced to a minimum while the rigidity can be maintained at a high level. 

It is basically about changing the node points in relation to the length that gives the desired effect.

Simple view of the idea here.

http://www.structuremag.org/?p=8715

I used to design them, but the examples I worked on were mostly for use in an upright position.

Bernard

[chaz]

I would also emphasise the importance of diagonal bracing, it makes a huge difference to the torsional rigidity of any baseboard.

 

I must admit I haven't bothered. It's quite true that if you don't add diagonal bracing the frame will twist, but I make sure that baseboards are supported at all four corners. In fact more than that; for the FVRR the legs are screwed to the floor - no twisting is possible. That strategy is only possible with a fixed layout - exhibition managers would get a bit overheated if you started drilling the floor....

[PatB]

That strategy is only possible with a fixed layout - exhibition managers would get a bit overheated if you started drilling the floor....

 

That's why we have curtains to conceal the under-baseboard area. You can get away with anything under there .

[Guest]

Sorry this is related to a previous thread but with a more specific question.

 

Can anyone please tell me what advantage ply frames- with double skins and then a soft wood spacer- are supposed to have? I've just built one today. All wood nicely cut on a table saw and so far I can see lots of disadvantages compared to 2*1 timber. Namely that the amount of joins between ply and softwood spacers is far more than the 6 or so that I would have for purely soft wood frames.

 

I suppose the obvious answer is that if soft wood timber works for me then go for it, but when many well respected people are using ply I have to ask what I've missed.

 

I can see the advantage of contouring- building the track above the terrain or the other way around, but I can achieve the same by screwing soft wood spacers above the main framing.

 

I'm going to build a traditional timber version tomorrow to compare the weight, but so far I can't tell it's any lighter.

 

Any thoughts please?

 

Derek... I asked something similar a week or two ago. That may even have been the "previous thread" you mention.

I did actually make up a small 2ft x 2ft "box" using 3mm ply and softwood packers. No diagonal bracing, admittedly. I then made up an identical one using 3" x1" softwood (or 69mm x 21mm PSE in modern-speak). Preferred the softwood one, if I'm honest. The ply and packer board was lighter but somehow felt rather flimsy. Also, too much pfaffing about using the ply and packer option, especially for a larger layout. Having had a chance to suck-it-and-see, I shall revert to dinosaur mode and stick with ply-topped softwood for layout boards. A nice experiment for sure but I was hoping for a "Wow - that's so much better" reaction to the ply and packer board. It just didn't happen.

[jcm@gwr]

I must admit I haven't bothered. It's quite true that if you don't add diagonal bracing the frame will twist, but I make sure that baseboards are supported at all four corners. In fact more than that; for the FVRR the legs are screwed to the floor - no twisting is possible. That strategy is only possible with a fixed layout - exhibition managers would get a bit overheated if you started drilling the floor....

 

 

That's why we have curtains to conceal the under-baseboard area. You can get away with anything under there .

 

An idea just popped into my head (I'll have to have a lie-down in a minute!)

as a lot of shows are in sports halls or schools, which quite often have very

smooth (even polished) wooden floors, would it not be possible to use some

form of suction fixing to hold the legs securely?

I'm thinking of the type that holds your sat-nav/dash-cam/smart-phone to the

windscreen, or even those glass handling thingies.

[The Stationmaster]

That is proving to be the case vertically- quite strong, but the "sandwich" (I think that's what people call them) is bending. I haven't put any diagonal supports in. I will try that next.

 

This is a 4ft by 2ft and I have a mid "sandwich" effectively 2 times 2ft by 2ft boxes. Is that enough or do I need more "sandwiches" in it?

 

Is the 'sandwich' bending before or after assembly into the baseboard unit?   The first time I put some of these together I found that for some reason some of the side beams came out slightly curved after I'd put them together but all was corrected when I added crossbraces and put the top on. 

[PatB]

An idea just popped into my head (I'll have to have a lie-down in a minute!)

as a lot of shows are in sports halls or schools, which quite often have very

smooth (even polished) wooden floors, would it not be possible to use some

form of suction fixing to hold the legs securely?

I'm thinking of the type that holds your sat-nav/dash-cam/smart-phone to the

windscreen, or even those glass handling thingies.

 

I can see this working on at least some floors. You might get into trouble if your suckers lift any of the little blocks out of someone's parquet .

[chaz]

Is the 'sandwich' bending before or after assembly into the baseboard unit?   The first time I put some of these together I found that for some reason some of the side beams came out slightly curved after I'd put them together but all was corrected when I added crossbraces and put the top on. 

 

A couple of points. When I am making frame members I check the ply' strips. If they are slightly curved (they often are) I oppose the curves - glueing and pinning them so that initially they curve outwards in the middle. The two curves will tend to cancel out.

 

Your are quite right about adding the top - should a long side be slightly out of line it can be pushed or pulled straight whilst the top is screwed down. I find the ends tend not to curve much by virtue of being that much shorter and proportionally more of their length fixed to spacer blocks.

 

I cut all my ply' strips by hand with a panel saw - I no longer have access to a good, bench mounted circular saw and I don't consider jig-saws to be accurate enough. When I assemble my frames I do it upside down on a flat surface. I want the top edge to be flat - some unevenness of the bottom edge will not matter too much.

 

Chaz

[Derekstuart]

Hello Pete

I did read your thread in depth and came to no obvious conclusions. People seemed to prefer the ply method but didn't really explain why. I know Croydon NS was built flat, as would be expected for the area and I can't see how timber could be beaten for that. Where I thought ply would give me an advantage is that I have a 1:140 track gradient following a 1:80 general terrain (so that the track is on an embankment at one end and in a cutting at the other) and also it slides to the side around 1:200.

 

I could use standard timber to give me the lowest point (the bottom of the embankment on the North end) and build up the track height by screwing "extension" pieces onto the timber. When I was a lad I had a 4*2 board which was supported on 2*1 timber and it stayed perfectly true for many years- despite being stored on its end (trackless) it never warped and was only thrown out due to damp. (actually some of the timber was saved and now lives on another layout- not mine). I think I might be joining you in the 'flat earth society'...

 

EDIT: I have just tried to bend a piece of 3*1 timber and gave up. I did manage to bend the ply sandwich though.

 

Derek... I asked something similar a week or two ago. That may even have been the "previous thread" you mention.

I did actually make up a small 2ft x 2ft "box" using 3mm ply and softwood packers. No diagonal bracing, admittedly. I then made up an identical one using 3" x1" softwood (or 69mm x 21mm PSE in modern-speak). Preferred the softwood one, if I'm honest. The ply and packer board was lighter but somehow felt rather flimsy. Also, too much pfaffing about using the ply and packer option, especially for a larger layout. Having had a chance to suck-it-and-see, I shall revert to dinosaur mode and stick with ply-topped softwood for layout boards. A nice experiment for sure but I was hoping for a "Wow - that's so much better" reaction to the ply and packer board. It just didn't happen.

 

 

Hello Mike, it's after assembly. I built the 2 longitudinal 'sandwiches' at 4ft, with 3 transverse 'sandwiches' built to just under 22 inches, so that they fit inside the longitudinal frames (others have suggested the outer ends should be full width and that the long frames shortened to maintain 4 by 2).

 

My best option so far seems to be some longitudinal soft wood beams to hold each sandwich true to its neighbour, but that seems to defeat the whole point.

Is the 'sandwich' bending before or after assembly into the baseboard unit?   The first time I put some of these together I found that for some reason some of the side beams came out slightly curved after I'd put them together but all was corrected when I added crossbraces and put the top on. 

 

Thanks again for the info chaps. It is really interesting to see the varied way people tackle such challenges... Now where is that number for the professional board building company??

[durham light infantry]

Seemed to work ok for the Mosquito...

 

 

Mike

[Andy Hayter]

Derekstuart

 

I have used over the years a whole host of baseboard methods.

 

2 x 1 with solid (various materials) top  - flat earth

9mm ply front (8cm) and back 25cm minimum. Softwood ends and 6mm top - flat earth

sandwich 9mm ply from back and sides - with and without back scene board.  Top 6 or 9mm ply - can be open frame, but must not be.  If open frame you really need 9mm plus ply for the base.

 

and currently

9mm outer frame all round.  Extruded PS block base - flat earth but could probably be also open frame.  work  in progress so I will say no more at this stage.

 

From the others I have been most please with the 9mm front and back scene, with softwood ends and 6mm ply top for flat earth layouts.  However for open frame where the landscape falls below as well as above the track level, the sandwich method wins hands down - and that is its real benefit.  Some extra work certainly, but it gives a flexibility that the flat earth (track at ground zero and all scenery has to be built up) cannot do. 

 

So horses for courses.  Both are very stable if well constructed and braced.  Weight differences are not that big.  Both able to be dragged around the world - exhibitions or just house moves.  The sandwich method takes a little more construction time but gives you opportunities that would be more difficult with a simple flat ply top. 

 

Edited to add:

 

If you need legs on your boards, then they are easy as pie with the sandwich method.  Use softwood of the same thickness as the separators in the sandwich and they just slot in.  Add a stop, to prevent the baseboard from sliding to the bottom of the leg.  a simple cross brace between legs holds them stable.  Ply tops need something a little more substantial

[Derekstuart]

Andy,

 

thanks for that description. Added to the other comments above I have a good bit of info.

 

To avoid doubt are you saying the sandwich skin should be made of 9mm or is that for single skin? I imagine a double skin of 9mm would be incredibly strong. Also is that to 80mm depth for single or double?

 

 

Mike/D.L.I.

That's a damned good example. I knew a Mosquito pilot. He showed me a photo of one of his 'kites' after Jerry had used it for target practice. I suppose if it can stand the Luftwaffe it can stand a model railway.

[Ian J.]

I've used ply on boards for a layout that is currently frozen (stuck in storage awaiting me having a home). However I didn't use the double-skin system. As they are 'flat earth' the frame was assembled at least in part by gluing it to the top of the board, and with the cross beams and diagonals the whole board unit cannot be twisted. But I've used a very light construction without much in the way of joint bracing, so in one or two places the glue hasn't been enough to hold an end in place and then the twisting can start to happen. Once I get the boards out of storage all loose ends will be glued back into place and hopefully will hold. I do make sure I handle them with care though. They wouldn't survive the rough handling I've seen at some exhibition set ups.

[hayfield]

I think along with lightness the ply frames also win out on cost. With a local DIY chain able to offer a free cutting service buying an 8' x 4' sheet is not much dearer than a 2' x 4' they sell

 

With kiln dries wood warping now at alarming rates once taken home, I would even consider MDF boards duly painted with silk emulsion as a second choice as I had a set which was kept in our old un-heated club house for 3 years without any issues

[Andy Hayter]

Andy,

 

thanks for that description. Added to the other comments above I have a good bit of info.

 

To avoid doubt are you saying the sandwich skin should be made of 9mm or is that for single skin? I imagine a double skin of 9mm would be incredibly strong. Also is that to 80mm depth for single or double?

 

 

Mike/D.L.I.

That's a damned good example. I knew a Mosquito pilot. He showed me a photo of one of his 'kites' after Jerry had used it for target practice. I suppose if it can stand the Luftwaffe it can stand a model railway.

 

 

 

I used 9mm for both the single and sandwich construction for the simple reason that at the time our then local timber merchant could offer a good quality 9mm ply at an attractive price - pence per sq foot more expensive than a poorer quality 6mm ply.    The 6mm ply had a tendency to splinter when cut - even on his professional  cutting beds.  The 9mm cut cleanly at home as well as on his kit.

 

I see no reason why 6mm could not be used but probably the bits of wood making up centre of the sandwich would need to be closer together.  With 9mm ply the wood blocks were spaced at around 1 per 12 to 15 inches.  With 6mm I think I would be inclined to put the blocks in at about 9inch intervals.   

 

For single skin I would not go much lower than 9mm ply for the sides.  Certainly 6mm is not rigid enough - another failed experiment.