Lift up flap and plywood expansion problem

Hi all,

Another of my little posts.

I have a hinged lift up flap on my baseboard build.

Now its giving trouble, Having used a good dense 9mm ply.

The ply has expanded, and said flap has become a right pain.

Would medite or similar be a better material to use for this vital back saver?

I am getting too old for clambering under baseboards!

regards,

Derek

Hi Derek,

I'm surprised the ply has shifted, did you seal

it when it was first made? That should have

kept it under control.

Also, is it subject to extremes of temperature

and humidity? If it is, I would be more worried

about the whole layout!

Either make a new flap (from ply) or trim back

the original, then give it a few coats of seal,

(matt varnish, floor seal, even diluted PVA)

Good luck, Jeff

Thanks Jeff,
My layout is in unheated rooms upstairs.
Temperatures the past couple of nights have dropped a lot.
Its marine ply on the flap unsealed I am ashamed to admit.
I will take your advice, Also install a heat source to keep humidity or damp at bay.

regards,

Derek

Derek,
The heater will control the temperature (obviously!)
But if you have a damp/humidity problem then you need
better ventilation.
You can get humidity controlled extractor fans, not cheap, but worth it considering the value of your layout.
Jeff

I have used 12mm MDF sealed with varnish together with 3 longitudinal braces of 1" aluminium C channel screwed underneath. While this stops most expansion, as my lift up is right next to the outside door, it does expand a bit so I have sanded back the un-hinged end for clearance purposes.

Thanks again Jeff for your advice.
I will take a look at those humidity jobs.

Also Ron thats a good tip with sanding hinge end and useing aluminium braces.

I will let you know how I get on.

regards,

Derek

I have a hinged flap on my 20ft long layout in my workshop. The lifting end of the flap butts up against one end, at right-angles, of the fiddle yard. That end of the fiddle yard has a flexible movement of about 6mm back, and forth against the lifting flap, it accomodates expansion sufficiently.

When installing a hinged flap, what kind of gap do you need between the rail joints on the hinged side to stop them from jarring when you lift the flap ?

Toto

Hi Toto,
The gap doesn't have to be big, couple of mm tops.
What is more important is to have the end of the flap not
cut at 90*, this is so it clears as it lifts.
After all, the longest dimension on the flap is from the hinge pivot to the bottom of the lifting end, if that makes sense!
Jeff

The pivot part of the hinge must be equal to or higher than the rails and I just use a Dremel to cut the rail gaps.

Model Railroading on a Budget

Beat me to it, Sol, herewith a digram of what I think you mean? To ensure that the rail ends don't snag with hinge wear an angled cut is useful.






I too am surprised that the ply has moved/swollen, more likely the  [presumably] softwood framing has moved as is probably of greater length.

A slightly higher tech solution for layouts in areas of variable humidity would be to align the lifting end on magnetic handbag catches and to fit undersized hinge pins allowing lengthwise expansion whilst lateral alignment would be preserved by the hinge cheeks.

(Click to enlarge)

Doug

Thanks for clarifying that. The diagram helps as well.

Cheers

Toto

The problem of expansion is limited to providing room for the wood to move as the expansion coefficient of nickel silver rail is sweet FA per mega length over a very large temperature range.
I measured 0.3mm per 150mm over a 50 deg C range (i.e. freezer to outside my Cyprus house in the summer). That if my maths is correct (unlikely) is around 0.009% per Deg C.

Depends what you mean by sweet FA Rob.

I may be working this out wrongly, but I think the temperature range in my garage of about 18⁰C (9⁰ - 26⁰C) means a 1 meter length of Peco flexitrack will expand by about 0.8mm.

So two lengths together will expand over the range by about 1.5mm, which may explain why I had to take up a piece yesterday which I laid in March as it had become unstuck and slightly raised.

Of course, it could be just my naff track laying


Ed

(PS OK, I know, I know, Peco flexitrack is still sold in good old yards, 914mm)

For a lift up or a piece of track that MUST stay exactly the same length, solder each end to copper clad, and cut and join in the middle with fishplates leaving a small expansion gap.

Personally I would be more worried about the sub base expanding/contrcting with humidity changes.

Doug

Hi Derek,

Ply top and softwood frame - different expansion coefficients. All that glue in  the ply effectively seals the inner layers. Make the frame out of ply, a lot lighter, stronger, and the same coefficient. Is this construction grade ply (5 layers) or furniture grade (9 or more?). Big difference in 'warpability". Dropping the bridge, rather than elevating it, makes life a lot easier as well.

Nigel