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Tom Fassett's Trestle Jig building Instructions
   How to make a jig for building model trestle supports
Tom Fassett

This is a set of instructions for building a jig which will allow you to quickly produce the upright supports for model railroad trestles.  The jig presented here is modeled to HO scale but can be easily modified for any scale.  I employ a "build as you go" method meaning I use the jig to build a support which helps build the jig.  By this I mean I begin building the first support before the jig is completed and use it as a template for placing some of the guides which assist in building more units.  I have found that the jigs usually take a couple hours to build but save an enormous amount of time when you have to make identical, repetitive pieces. You can also design your jig to use any scale of wood.  Mine uses 1/4" balsa for the horizontal beams and 3/8" balsa for the vertical supports.   I also designed this jig to allow the builder to make different sizes of supports without having to make multiple jigs.  This comes in handy when a trestle must conform to the slope of a mountain (like most real trestles do).   I have included a picture of each step so you can see what I am talking about in the instructions.  So, good luck and start building!

To begin, cut a sheet of styrene big enough to hold the trestle support you want to build, leaving a little on each side.  Mine is about 4 1/2" wide and 5 1/2" tall.  I used a thin piece of styrene and glued it onto a a piece of foam board.  This is much cheaper than buying a 1/4" thick sheet of styrene, and makes cutting the styrene possible with a hobby knife.  Buff the surface of the styrene with fine grit sandpaper (400 grit or higher) or use a "green scrub" pad.  This cleans any oils off the surface and creates tiny crevices for the adhesive.  The picture at the right shows the styrene back ready for marking.
Draw horizontal lines at even intervals to provide a guide for placing the base of the various heights of support.  I drew mine at approximately 1" apart.  When you draw the bottom line, be sure to leave enough room to glue the styrene base guide on (see figure 7).  The exact distance between my lines is actually based on the closest HO measurement, but you can use any division you want.  The distance I settled on was just shy of an inch, or 7 scale feet (for HO).  This makes my largest support 35 scale feet tall or about 4 13/16".
Next I determined how wide the top and bottom pieces would be.  I drew these lines vertically below the bottom line and above the top line.  Take a look at figure 2 and you can see the bottom lines already drawn in.  Then I connect the lines together forming an angled line between the under side of the top brace and the top of the bottom brace.  For this jig, the base is a scale 28 feet wide, or about 3 7/8".  The top cross piece is 20 scale feet or about 2 3/4".
I then used the square and a ruler to pinpoint the actual intersection of the angled and horizontal lines.  This makes sure that the next steps are properly centered.
The next step is to draw in the guides for the vertical supports.  I chose to have five vertical supports, but you can use however many you want.  I also build a lot of 4 beam trestles (especially if the width is smaller).  The easiest way to get these lines is to measure between the two outer lines.  Place a mark at the exact center between the outer lines and use a square to draw the center line.  This line should be exactly 90 degrees from the base line.  The center should always be straight up and down when you have an odd number of uprights.  After you have this line, measure between the center and outer lines and make a mark at the center of these two lines.  You need to do this for the top and the bottom as this line is not straight up and down.  Do this on both sides.  Then draw a line between your marks for the two remaining uprights.  My jig has about 4 1/2 scale feet (5/8") between uprights at the top and 6 1/2 scale feet (7/8+") at the bottom.  You should now have a jig that looks like the figure at the right.
Next, measure out from the "intersections" where the outer lines and the horizontal lines come together and draw a guide line.  These are the width of the base on shorter supports as well as the width of the braces on larger supports.  I make mine 1 scale foot  beyond the outer line or just under 5/16".
Now it is time to start gluing the styrene guides on.  Cut a piece the maximum width of the bottom base piece.  My base is 28 scale feet wide or about 3 7/8".  Glue this piece on just below the base line.  Use a square to make sure it is exactly 90 degrees to the vertical lines.  Do this for the top as well, gluing just above the top line.  My top piece is 20 scale feet or 2 3/4".
Next glue small guides on the ends of the long pieces.  These are your width guides for the top and bottom main brace.  They also help hold the top and bottom piece in place while you are installing the other pieces.  Be sure these are at a 90 degree angle to the top and bottom guide.
Here is where I begin to build the jig and the first trestle support together.  I could just measure everything and glue on all the guides but this is much faster and a whole lot easier.  Cut the top and bottom brace and sand the ends to fit in between the outer guides of the top and bottom of the jig.  They should be slightly snug but not too tight or you will have trouble removing the finished support from the jig.
Next, transfer your measurements for the uprights (your vertical lines drawn earlier) to the top and bottom brace (note the pencil marks in the figure at the right).  Cut your vertical pieces and sand them to fit with the pencil mark in the exact center of each upright piece.  Note that all but the center upright must have an angle where it attaches to the top and bottom brace.  These can be made by laying the piece of wood on the jig and drawing a line (on the piece to be cut) using the wood brace below.  Cut these pieces at the angle of the line, but be sure they are a slight bit long.  Then they can be sanded to fit perfectly by trial and error.  Be sure not to sand too much off as these need to be snug--especially on the first support made as it also acts as a template for the other guides.  Glue these pieces to the braces and allow these joints to dry.
If you look at figure 10, you might notice that there appears to be a couple "extra" lines at the top and bottom.  These are brass wire used to center the uprights on the thicker top and bottom brace.  The wire lifts the uprights off the jig so that they are attached in the horizontal center of the top and bottom brace.  I went with this method as it allows me to use different sizes of wood for various pieces of the support.  I use a different thickness of wire depending on the width of the wood (both the top and bottom, and uprights).  This also allows the jig to do "double duty" by making different sizes and heights of support.  If I glued a "shim" piece in to raise the uprights off the jig it would interfere when I was trying to make a shorter trestle.  The wire is easily moved and solves this problem.
Now it is time to glue on all the little styrene guides.  This is the point where you top off the coffee cup and put on your favorite CD...  For my jig I needed 50 little styrene pieces for the upright guides.  The length of these pieces is not critical, nor is the angle cut.  Mine are all about 1/4" long.  Notice on the figure at the right that I placed a scrap of wood on the 2nd baseline as a reference (the little red piece).  This is to make sure that I leave enough room to place a brace in the jig when I make shorter supports.  Remember that each horizontal line is the bottom of a base or the bottom of a horizontal brace.  Be sure you do not glue any guides where they will be in the way of other pieces.  You will see how the various braces are placed later on.  Put a drop of cement on a styrene guide and place it up against the upright as shown.  I use plastic weld so I can place the piece first, get it into position and hold it with a dentist's probe and then dip the brush in the plastic weld and touch the place where the guide and the base come together.  The plastic weld will run under the guide and does not stick to the wood.
After you have glued all the upright guides on, your jig should look like the figure at the right.  Notice that there is a set of guides between each horizontal line.  This is to hold the uprights in proper alignment when making shorter supports.
Here is the jig with the wood removed.  Note how the vertical lines run between the guides and the guides are centered between the horizontal lines so they do not interfere with the braces.
Now it is time to start adding the guides for the base pieces of the shorter uprights.  Remember the lines I drew 5/16" to the outside of the intersection between the vertical and horizontal lines?  This is where the base for the shorter supports will rest.  Glue two small guides to the outside of the lines beyond the outer vertical line.  The vertical placement of these guides is not critical, just the horizontal placement.  Also, use a square to make sure they are at a 90 degree angle from the vertical center of the jig.  They should also be the exact same distance from the center line.  Cut a piece of wood to fit exactly between these two guides.
The next step is to glue the base guides on the bottom brace (of the shorter supports).  Line your piece of wood up with the the corresponding line (with the line at the bottom of the wood).  Use a square to be sure the wood is at a 90 degree angle to the center line.  Next, place the bottom guides against the wood and cement in to place.  Be sure the guides are centered between the vertical lines so they do not interfere with the upright supports.  See the figure at the right for proper placement of these guides.  Do this for each horizontal line, cutting the proper sized piece of wood for each size of support brace.
Here is what the completed jig should look like.  Note the addition of the outer guides and base guides for the horizontal lines.
Here is a full sized support cut and placed in the jig and ready for gluing.
Here is the next size down ready for gluing.  Note how the horizontal guides hold the shorter pieces just like the full size template.
And the next size down ready for glue...
And an even smaller upright...
And the smallest upright.

These instructions are for building the upright supports only.  It is hard to design a template for all parts of a trestle as there is no set length or shape.  These supports can be used for a trestle of any length, as well as a curved trestle, etc. I am working on some designs for adding the remaining pieces to complete a trestle and will post the instructions as soon as I get them done.  In the meantime, you can build uprights to your hearts content...

Tom Fassett