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Discussion Starter · #1 ·
I am just after an opion please on plywood beams for baseboard construction.
Do we think that two strips of 4mm ply say 4" wide by 8 to 10 feet long with 2" by 1"
spacers inbetween would be strong enough to be self supporting and not sag over that length.
In actual fact it would be supported but only in the middle section and I did not wish the ends
to move towards the floor.
Thanks
 

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Not too sure about ply but I would ,and have,used L girders to span 10 ft without any support in the middle ,so I would expect vice versa with the ends .Those girders are very strong indeed though heavy .Others will know far more about ply ,though to me it sounds feasible .
martin
 

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I am a great fan of having 2 foot (60cm) square holes under my layout as a maximium with out bracing.

Over 10 foot I would put bracing every 2 foot.

It is better to be safe than sorry.
 

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Hi Smokeyone and welcome to the MRF.

Personally I think that 4mm ply is far too thin for a beam of that length as it is likely to twist and distort. I would use 12mm ply and, as Rossi has said, construct a 'T' shaped girder. You could use 9mm ply as the top of the girder but I think 4mm would be too thin to provide sufficient strength to stop the 12mm 'I' part of the beam from sagging.

If you are determined to use 4mm ply then the only way to make up a beam of that length would be to build a 'box' structure with internal bracings at say every foot.
 

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***See attached.

I have no idea about weight you want to support but given an average layout I comment as follows:

The 4mm ply will be OK but it really needs a structural core between them.

The attached is my guess at a totally rigid 8 foot by 4" beam with 2x1 used for top and bottom with verticals each 2 feet and diagonals in compression to stop any chance of sag.

actually 2 x 1/2" or nearest metric would be heavy enough if you make like this AND have accurate joints for the diagonals - you could stand on it with no sagging.

If it was mine I'd do it this way but would probably opt for perhaps a little more ply depth (125mm~150mm?) as I like my layouts really strong.

Good clean accurate carpentry and screws about every 12" top and bottom + Glue on every edge is important. Diagonals should butt to the verticals not the top and bottom plate as they will be in compression so need a direct end support. Verticals should be screwed and glued to top and bottom plate.

Richard
 

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*** (Phew.... <wipes Brow>).

I remembered you were an engineer moments after posting, and was hoping I'd got it right. To be totally honest I wasn't 100% sure whether or not each second diagonal should maybe be the other way to balance pressure on the vertical bits?

Richard
 

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Discussion Starter · #10 ·
Thanks all for the help.
It does not have to be 4mm ply, that's just info I picked up after googling and using the rest of the sheet for elevated track but I would like to keep the weight down a bit.
So if I have the details correct 4mm ply for the sides but 6mm would be better ---
say 5" plus wide..so far so good!
Space it out two inches with 2" by 1" top and bottom followed by diagonals & verticals also made of 2" by 1"

Different subject - how was the drawing made!

Thanks again
 

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*** I'm glad it helped.

The drawing is nothing special really - it was made on a very old bit of software which is quick and easy for diagrammes - an early version of pagemaker (it has no direct export ability so I then print as a PDF then resave the PDF as a JPG). However drawing tools in excel, word and many other easily available programmes are easily used for such non-scaled drawings.

regards

Richard
 

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Discussion Starter · #12 ·
Thanks again for the help and the drawing. I was curious about the drawing and assumed it took only a short while to do ( not a high tech CAD programme) otherwise it would have taken a while.
Cheers for the beam suggestion, that'll be brilliant for what I have in mind. Two beams supported in the middle
side by side and then mount the layout modules on top across the beams.
The modules will be a bit long - say 5.5 feet but only a couple of feet wide.
I am using the module idea because even though the layout is likely to be permant it may have to be moved someday!
Would guess the modules could be made out of the 6mm ply as well -
Would I get away with 3" deep ply with one inch thick spacers for the modules.......or is there a better way......
 

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Hi smokeyone.

I wouldn't reduce the depth of the beam as that is what provides the strength under load. Width can be whatever you need but the old football addage of "strength in depth" is definitely the one to bear in mind.
 
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