Wooden Coasters – 101

Wooden coasters (woodies) have the following basic characteristics

Track and Wheel arangements:

Initially early coasters used methods inherited from the railroads. which was adequate for these early ‘Scenic Railways” or “Switchback Railways”. These early coasters were relatively slow, had gentle up and down slopes, and easy curves. As the speed increased the flat curves of these coasters could not be negotiated at anything but a relatively low speed. Hence the following 3 basic types of wood track evolved, and were used on what we now consider classic woodies. These track types are presented here in order of evolution.

Side Friction:
This is the side friction arrangement which was one of the earliest methods for track construction. As you can see this was basically dependent on gravity to keep the car on the track. Needless to say coasters on these tracks had gentle hills, so the cars would not skip track (come out, or derail).

Flanged Wheel


The flanged wheel arrangement was a significant improvement over the side friction. Because the car was basically held into the track allowing for some negative-g’s (where the running wheels come off the running rails, and the car is still retained to the track ). These allowed for tracks with steeper hill crests. The drawback was that the retention of the car to the track during a negative-g segment caused friction, slowing the cars down and causing heavy wear on both the underfriction bar and the underfriction rail in the area where they came in contact.

Standard:


The Standard method, as it became, was an evolution of the other designs. This kept the cars captive, and by using an underfriction wheel, reduced wear and tear on both the track and the cars. This was an important development in track design, and now designers had the freedom to make rides with lots of negative-g’s (air-time). This is the type of rail system that you can see on most modern coasters. Many of the older coasters using the other methods were converted to use this method, not only to increase safety, but also to allow tracks to be modified to give a more thrilling ride and increase rider ‘air-time’ (negative-g’s).

All the tacks were typically made from oak for its strength and longevity, but because of the high cost and quantities needed for most modern track work douglas fir is used for its ability to withstand the pounding of cars and its ability to accept pressure preservation treatments.
Typical tracks are made up of multiple laminations of lumber, typically 7 to 9 layers. The thickness and number of layers vary from designer to designer and ride to ride depending on the designers specification. Occasionally you may find additional layers in areas where the g-forces are very high, like in the dips, or valleys between the hills.

The track is built up piece by piece and carefully bolted clamped and bent to conform to the desired section whether straight or curved up or down, depending on the rides profile. This is a very time consuming process as the boards (typically 12 ft) have to be nailed in place foot by foot and bent using large C-Clamps. This process then is repeated for each of the layers in the track. The track itself is attached to the horizontal ledgers of the support bents, and numerous ‘gaging’ ties are interspersed under the track and in between the ledgers in order to insure the rails are and stay at the specified distance.

The finishing of the rail generally includes attaching a ‘riding’ surface of half inch thick flat iron bar stock, typically 6 in wide. These are attached with countersunk bolts into the top laminations of the rails. Additional bar stock is also added to the inside friction guides (that keep the car centered on the track), and on the underside of the lip for the underfriction wheels of the cars. These iron surfaces not only give a good surface for the wheels to ride on they also protect the wood track from undue wear.

Surprisingly to most people, the track is not rigidly attached to the supporting structure, except in areas of high stress. Due to the tight construction of the rails, and their forming, they hold their shape and position very well all by themselves. Think of it this way, because the tracks are effectively a continuous piece (ok 2 pieces of rail), and are built and formed to fit the layout, they can literally rest (or float) on the support structure, with only the ties maintaining the spacing between the rails. This is actually desired, because it allows for expansion and contraction of the rails, and allows the coaster to flex of give a bit. The flexing is desired in the structure (see below) to absorb the high forces exerted by a passing train. This flexing actually making the whole coaster stronger. This is much the same as why you can snap a candy stick (or cane) fairly easily, while it is much harder to snap a twizzler, it will give a lot but snapping it off very difficult (similarly a pvc pipe and a rubber hose).

Structural:

The whole track structure of the coaster is supported by a series ‘bents’, These bents are usually made from pairs of 4 x 6′s spaced about 9 feet apart (wide), and attached with a series of cross braces and chords to give them strength. They are then attached to concrete footers, and then each other with more braces and chords. There are a lot of these on any coaster, each one of a specific height with ledgers at specific angles. The bents are each made individually for the particular section they are needed for. So, on say a ride with approximately 3000 feet of track, you should expect to see at least 334 individual bents, perhaps more depending on the particular layout.

On the corner sections the bents are further reinforced from the lateral forces of a passing car with batter braces. These allow the forces to be counteracted or spread out, in the direction that the weight of the passing car would exert further adding to the stability of the support structure.

Mechanical Components:

Lift Hill

Car ‘dogs’

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