Making a log trestle bridge.
                                                                                                            
I got my inspiration for making this kind of Log Bridge from an actual photograph Taken by Darius Kinsey in his magnificent book "The Locomotive Portraits" The photograph was of the Sound Timber Companies fine log bridge over the Sauk River. The idea of building this kind of bridge was --- " Minimum expense" Logs were hauled to the area and some used as piles driven into the ground to form the piers. Big logs were used above and below the ties, which formed the spans. After which, the track was then laid.
I am sure that there are a number of modellers who model the American scene who would dearly love to have a trestle bridge on their layout, but have not the courage to start to build one. I know that you can buy a variety of trestle bridges, but to have one that's scratchbuilt for the desired location is always nice to see when its completed and in place.
Most modellers tend to make the traditional timber trestle using many bents made from a jig. Oh yes, I have made this kind on many an occasion on various layouts but decided that this time I would try my hand at this fascinating log trestle. So, here's how I made my log trestle bridge.
For the lower log trestle I used I used 1/2" balsa dowel for the main logs above and 3/4" balsa dowel below the ties. The ties themselves were 1/4" square. The first task on my agenda was to remove all the ties (For the gap needed across the gorge) from a length of 0-16.5 Peco track. 1/4" square hardwood was cut to the length needed to accommodate the logs above and also wide enough for the locos to pass along. These were cut to 3-3/4" wide then stained with a Dark Oak, when dry they were spaced at 3/8" intervals along the rail. Photos#1 &2 

The next step was to cut to length the 2 - 3/4" dowels and the 2 - 1/2" dowels. Once cut they were scribed with a rasp to give a bark effect - Photo#3 & 4 

Then stained with once again with" Dark Oak" Photo#5 

When dry, they were dry brushed with grey and browns. The same procedure was taken with the ties.

Once all the logs were done in this way the fun of putting it all together could be started. 
I needed two of this kind of Log Bridge to span the gorge below. One was in fact 4" higher than the other so I planned on making the one above different in looks to the one below, but keeping the log idea for both. The top one as will be seen in photo#6

is more on the lines of a simple trestle with braces forming the main strength of the bridge. 
With all the logs now stained and ready to be made up, I started by placing the main large (3/4") log underneath the 1/4" ties. Photo#7

next I placed on top the 1/2" log - photo#8.

When the glue for these logs was fully dried, I inlaid the 1/8" stripwood between the rails. Photo#9 

the next part of the operation was to use rope to lash the top and bottom logs together. I used "Billings Boats" rope, which comes in 50-meter lengths. This rope is used normally for rigging ships with. Photo#10 

shows the rope in place.
For the main uprights which hold the trestle, I needed to make a half-moon trim on the top to match the 3/4" log profile it was going into - Photo#11. 

Once this was completed and the logs glued together, I then applied the outer log stays. Photo#12 
that were also lashed with rope Photo#13
. I also placed further logs lower down as stays for added support. Here is the completed log bridge end. Photo#14.

Photo #'s 15 & 16

show the completed bridges. Photo#17

shows log decking.

The traditional timber trestle
Photo#18 shows a trestle I made using this kind of jig

As I stated earlier the traditional trestle is made using some sort of paper template, which is very time consuming. I devised a method, which is quick and easy way to construct as many of the risers that you may require. You still have to draw out the plan on card (not paper) but only once will you need to draw it out. The beauty of it is you could make hundreds of trestle bridges using the one card. - Here's how to make it. 
Get hold of some 1/16th card approximately 8" wide by the height you want to make the trestle (You will need four pieces) and mark out the size of the main riser you require, draw it out as if you were going to use it to pin the wood to it. Once this has been achieved, glue one of the other three pieces underneath the drawing and carefully cut out with a craft knife the outline of the trestle, both pieces. (See photo#19 top left)

You only need to cut out the five straight pieces. Now glue the other two pieces of card together and place them underneath the card you have just cut out and glue or staple the four pieces together. (Photo#19 top right) Now you will need some 1/4" balsa or hard wood and make up the pieces about 1/2" long and glue these to the card as shown in fig 1 top left (In red) all that remains for you to do now is to try out your jig. Using 1/4" square timber cut off five pieces the length you require and inlay them into the jig. (photo#19 -bottom) now cut off the cross members and using a very small amount of glue, place them across the timber and onto the 1/4" blocks.(RED - photo#19) before going onto the next pieces use some track pins (PECO 1/2"and pin through the pieces of wood at the glue joints just lightly tap them in with a small hammer, don't go all the way into the card just enough to hold it in place. Now do the same all the way down to the bottom. When all is complete, (It takes me about 5 min. for each one) gently lifting it out of the jig.
Now here's why you didn't knock those track pins all the way home, you need to cut off the tops and bottoms of the overlap first, then glue and place the other five pieces opposite the first five, but this part is even easier. Remember, a small amount of glue on each piece then place it underneath and when all is square, lightly tap the track pins to secure the pieces together. When you have completed all pieces in the same way. Drill a small hole in a piece wood (Off cut) and place the track pins over the hole and lightly tap them all the way home, turn it over and cut off the remaining track pin not required, and you are ready to start another one. I tend to leave the diagonal pieces until I have completed the amount of trestle bents that are required.
Tall or short - Thin or fat any trestle bridge can be made this way. A 9' curved trestle.

Here's a 9' curved trestle made using this kind of jig.

Happy Modelling.
Paul Templar.