Basic wood movement

Great article for a common need for many of us.

Forgive me, but I’d like to add a little information about wood movement to help others considering a project like this.  My other hobby is woodworking and while I don’t consider myself an expect here is some basic information about wood movement.  

A piece of wood will not expand and contract the same amount in each axis of the board.  The major contraction will be across the grain.  Put another way, looking at a piece of wood you see the “lines” or growth rings.  The expansion will be the ring lines moving apart.  For practical purposes the ring lines don’t get longer.

All wood is not cut the same way from the tree which can also affect expansion and contraction.  The most common cut is flat sawn or plain saw.  This is the least expensive wood, think of your common 2x4.  Wood can also be quarter sawn, a more expensive cut.  Some people use quarter sawn for large flat surfaces such as table tops because it won’t expanded and contract as much as flat sawn.  Quarter sawn would not be economically feasible for 99% of model railroaders building benchwork, but should be considered in applications like a liftout.

Plywood also has different properties then solid wood.  While it can move, it is much more stable then solid wood.  When looking at plywood count the number of plys (layers).  Generally the more plys the more stable and expensive the plywood.  The number of plys can be 5 to 9 or more.  Baltic birch or Russian birch will be your most expensive plywood and have the most plys and no voids between them.

I’m using cabinet grade plywood for all my bench work which I rip into strips for all my structural members including my legs.  This way I minimize the movement issues of solid wood.  If I needed to build a gate, liftout, duckunder I would use the Baltic birch to minimize any wood movement, but that is just my opinion.

I’ve just touch the surface about wood as there are many other things to consider, but don’t let the issue of wood movement scare you off from building a gate/liftout because as this article shows it can be done very successfully with a little advance planning and knowledge of what you are building with.

aluminum rather than wood

I utilized simple 3/4" alum pieces as one would find on home deck and stair railings.

Made a box structure of them to support 3 bridges across the entrance-way door to my train shed,....early construction,... https://forum.mrhmag.com/post/layout-room-entrance-swingdown-bridges-3-of-them-in-combo-12210684

lifts up to the ceiling