L-Girder Construction

This article first appeared in the January/February 1993 issue of AMRA's 'Journal'.
By Steve J Chapman.

The normal method of baseboard construction involves building one or more frames with cross members at appropriate distances and attaching them together to form a complete frame for the layout. This layout frame then has legs attached to it to lift it to an appropriate height. Finally the baseboard top is fitted either covering the entire frame (solid top) or just where the tracks are to go (open top). If gradients are to be included then a section of the baseboard top is fitted to the top of risers attached to the crossmembers. This method of baseboard construction can be used for any style of layout (permanent, portable, or anything in between). The major disadvantages are the quantity of timber required for its construction and the limitations that it places on baseboard shape.

If a permanent open top layout is to be built then an alternative baseboard construction method is possible which not only reduces the amount of timber required but also allows a layout of almost any size and shape to be produced. This method also has the advantage of avoiding the need to screw into end-grain timber without the need to use fancy joints. The method is called L-Girder construction because the main support consists of L-Girders rather than rectangular frames.

 

An L girder is so called because it is shaped like the letter L. An L girder has an advantage over an ordinary length of timber of the same thickness. Where an ordinary length of timber bends relatively easily in the direction of its short side an L girder is more rigid in both directions. The L girder also has an advantage over a piece of solid timber of the same overall dimensions because the thickness of the timber that you have to screw through in order to attach it to the rest of the layout is much less. The L shape can be obtained from ordinary timber by one of two methods.

The first method involves taking a piece of timber having a quite substantial cross section (say 3" x 2") and cutting a smaller section from the side of it (say 2" x 1") to leave an L shaped piece of timber. This is a fairly involved process and involves making two rather long straight saw cuts of even depth.

A much simpler method is to simply take two pieces of timber (say 2" x 1") and screw and glue them together so that the short side of one edge buts up against one edge of the long side of the other (see figure one). L girder cross section This gives an L girder of the same size and strength much more quickly and easily.

 

A small layout can be built on one conventional baseboard frame while a medium to large layout requires the use of several frames joined together. Using L girder construction a small to medium layout can be built using two L girders and additional L girders can be added as the layout grows. Whereas the conventional frames are attached directly to one another to build the layout, the L girders are attached via cross-members and do not come into direct contact.

Normally a layout would have one L girder toward the front edge of the baseboard and the second near the back edge. An L shaped layout might have a third L girder across the short end of the L.

 

The next step once the L girders have been constructed is to set them at an appropriate height from the floor. This height should be no higher than the lowest level of the scenery in the vicinity of the L girders and might be an inch or two lower. There are two methods of fixing the L girders at an appropriate height.

Since an L girder layout frame ends up all in one piece and cannot be separated up into sections the way that a conventional layout can an L girder layout is normally a permanent fixture. If the layout runs along a wall then the rear L girder can be attached to the wall directly without requiring any type of legs (figure two). L girder attached to a wall All that is required is to screw through the thickness of the long side of the L girder directly into the wall. If a backscene board is to be fitted then this should be attached to the L girder before the L girder is fixed to the wall, otherwise the backscene will need to be attached to the wall separately.

For the front L girder (or both if the layout is to be free standing) then legs can be attached to the outside of the long side of the L (figure three). L girder attached to a leg These legs will not need to be anywhere near as close together as with a conventional frame layout because the L girder can support itself over much longer distances than the conventional frame can. This is one instance of where the L girder construction uses less timber. As with screwing the L girder directly to the wall the screws should be put in through the width of the long side of the L girder.

 

At this stage you will notice that whereas a conventional frame with four legs attached is free standing, the L girders will still not stand upright by themselves. In order for the construction to stand upright we must now attach the first few crossmembers.

Before we start attaching crossmembers we need to realise a few differences between L girder crossmembers and the crossmembers in a conventional frame. The crossmembers in a conventional frame are contained within the frame and their length is determined by the size of the frame also the crossmembers at the end of each frame is duplicated by another crossmember on the next frame so as to provide some means for attaching the frames together. An L girder crossmember sits on top of the frame and except in the case of an L girder attached to a wall projects some distance (6" - 10") beyond the L girder. Not all L girder crossmembers need to be the same length and you can easily obtain a curved baseboard edge by fixing crossmembers of appropriate lengths. Crossmembers when attached can be slightly longer than intended as it is a simple matter to cut them shorter at a later stage in the baseboard construction. Also as there are no frames to be joined together there will not be any need for any duplicated crossmembers. This is another instance where less timber is required.

Crossmembers are attached by placing the member with its shortest side flat against the top (short side) of the L girder and screwing up through the L girder into the cross member (figure four). The front L girder should always be attached with the inverted L facing outward. A freestanding rear L girder will face away from the front L girder so that they are both facing outward. A wall fixed L girder will face the 'wrong' way due to the method by which it is attached to the wall however this doesn't matter as in this case the wall adds additional strength.

cross member attached to two L girders

To make the baseboard free standing will require the last crossmember at each end to be fitted first followed (for very long layouts) by one or two of the crossmembers toward the middle. The other crossmembers can then be fitted.

 

A solid top could now be fitted on top of the crossmembers provided that all of the L girders have been built to the same height. This would complete the baseboard construction if this was done however this loses many of the advantages of the L girder method.

The L girder system works better with an open top approach. Using this method of construction almost any landscaping features can be easily incorporated into the layout.

The next stage of construction is to fit the risers and lay the trackbed. It is probably best to cut a section of trackbed before making the risers to support it so that the risers can be made to fit. It is probably not a good idea to cut the pieces of trackbed exactly to length yet since if they are to be fitted on a grade then a slightly longer length will be required.

The risers to go under the piece of trackbed can then be built. The first thing to do is to cut the riser somewhat longer than the actual height required. Then a piece of timber the same length as the track bed width is screwed across one end of it. This end will be the top. If two pieces of trackbed are to join over a riser then it might be advisable to fit a second piece of timber across the other side at the top for the second trackbed to be fastened to.

The completed riser is then attached to the appropriate place on the crossmember. Since the riser max need to have its height adjusted slightly when the trackbed is fitted, it should not be permanently fixed to start with. Two alternative ways to initially attach it are 1) cut a slot down the centre and put a single screw through the slot to attach it (the height can then be adjusted by loosening the screw slightly) and 2) clamping the riser in place.

riser attached to cross member trackbed attached to riser

Once a number of risers have been positioned then the trackbed can be laid temporarily in place and the risers adjusted to give proper support. The risers can then be properly attached to the crossmember (figure five) and the trackbed fixed in place (figure six). If the bottom of the riser projects too far below the crossmember it can now be trimmed off.

 

The final step in constructing an L girder baseboard is to finish off the edges. This can be done immediately after the trackbed is laid in order to get the baseboard construction finished or it can be left until after the track is laid (or even wired).

Landscape contours should be cut from hardboard or thin ply. This is then bent to fit against the ends of the crossmembers. The ends of the crossmembers can be trimmed slightly, if necessary, to allow for an even curve. The contours can the be attached to the crossmembers either by screwing into end grain which is not so important here since this is only supporting a thin edging strip (figure seven), or by attaching a scrap of timber to the top or bottom of the crossmember at the end and attaching the contour to that (figure eight).

landscape contour landscape contour attached via support block

The various contour pieces can then be joined where their ends butt together by attaching scraps of timber across them on the side nearest the L girder. This can occur anywhere provided that the edge is relatively straight but can have problems when the edge is curved. With curved edges it is probably best to position the joins in the contour next to a crossmember end and use the second method of attaching the two contour ends to the crossmember.

 

The L girder baseboard is now complete (figure nine). All of the subsequent stages of layout construction will be no different from what would normally be required with a conventional open top baseboard except that you already have the contour strip fitted to the edge.

complete L girder frame

L girder construction is a practical alternative to conventional baseboard frames when a permanent layout is required. It provides a strong support for your layout using less timber than a conventional frame having the same strength.

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Copyright Stephen Chapman