Building a 1:100 Scale Bailey Bridge : 13 Steps (with Pictures)

The kit referenced here has now been released to Thingiverse and limited copies are available for sale on eBay.

This instructable describes the assembly of a 3D Printed kit for a 1:100 scale replica of the famous Bailey Bridge of World War 2.

From Wikipedia:

The Bailey bridge is a type of portable, pre-fabricated, truss bridge. It was developed by the British during World War II for military use and saw extensive use by British, Canadian and the American military engineering units.
A Bailey bridge had the advantages of requiring no special tools or heavy equipment to assemble. The wood and steel bridge elements were small and light enough to be carried in trucks and lifted into place by hand, without requiring the use of a crane. The bridges were strong enough to carry tanks.
Bailey bridges continue to be extensively used in civil engineering construction projects and to provide temporary crossings for foot and vehicle traffic.

The design for this kit was done in Sketchup from images of plans found on the Internet. The goal was to be as accurate as possible in terms of following the famous design, but obviously having to make allowances for the scale such that it be assemble-able, for the fact that the kit will be 3D Printed, and finally to minimize print time as much as possible.

There are currently four variants of the Bailey Bridge that can be built with this kit though only the Double-Single version is for sale on eBay. The bridge can also be printed with a road that is 55mm wide to support Flames of War game play. The kits for sale on eBay include this as an option.

Step 1: Inventory Your Parts

We are building a two section bridge of the Double-Single variety (Double Panels, Single Level). The parts for this model are:

One Road Bed with built-in Transoms
Four Panels
Eight Rakers (vertical bracing)
Six Bracing Frames (horizontal bracing)
Two Foot Walks
Four Double Base Plates
Two Ramps (Optional)
Two Ramp Supports (Optional)
Two Walk Way Ramps (Optional)
One Section Joiner (Optional)

Note that part #6 has been altered as you can see in the second image above. This Instructable will be updated prior to release of the model files to reflect any build testing changes.

Step 2: Collect Some Tools and Supplies

This is not a particularly easy model to build but it is not that hard either. I suspect that anyone choosing to build it is probably an experienced model builder and will have their own tools and way of doing things. If not and you want to know what tools to have handy here you are (counter clockwise from the bottom right):

Tweezers! There are some fiddly little parts.
Small screw driver
Craft knife
Something that you can use as a square
Super glue
Palette and "pen" for precise glueing (I printed these but you can devise your own if you so desire).

Step 3: Clean the Parts

Support Material:

The road bed MAY have been 3D Printed with an option called support material which, in effect, helps the printer to print in thin air as plastic is extruded on top of the support material which is then removed. In some cases this is not needed and in others it helps to produce a much cleaner print than without it. I still debate, on an almost print to print basis, whether the extra time and material is really worth it in the case of this bridge.

In any case, if you have it, It is easy to remove. You can use a small needle nose pliers and/or a small screwdriver or craft knife. The part should end up completely clean as shown above.

Stray Extrusion:

Some of the parts may have whiskers of stray extrusion, particularly from the first layer. These should be carefully cleaned off. Very little effort should be required as the whiskers will be very small if they exist at all. Some of the small whiskers may come off by simply rubbing the part.

Step 4: Join Road Beds (if Applicable)

Skip this step if you are only building a single kit.

As with the full scale version the 1:100 Bailey Bridge can be extended section by section as far as one would like.

In the full scale world (see above illustration) you would use a Single-Single for the shortest (unsupported) spans and then moving up through the Double-Single, to a Triple-Double and even beyond. Apparently there were tables that showed you exactly what parts would be needed down to the brass tacks.

In my 1:100 world I make a single, double, and triple section bridges in one unit for ease of assembly. With each section being 30.47mm long this corresponds to a full scale bridge length of 10, 20, and 30 feet. It was suggested to me that the latter two lengths are the most appropriate for an FoW game. The 10 foot version is there to pad out an odd size bridge longer than three sections.

In the example shown on this page a single section is being joined with a double section to create a three section bridge. This is extra effort since a three section version is available with the road bed, panels, and walk ways all printed the appropriate length!

If you do need to join two road beds then do so as shown above using the provided joiner. It is very important to make sure the sections line up and that they stay this way when your adhesive sets! This is aided by the use of some weights as shown above. The weight will also help the road bed stay flat.

Step 5: Install Inner Panels

Carefully slide an inner panels on to each side of the road bed. They need to be snug against the road bed and the road bed needs to be firmly pressed down to seat the panel. You can, and should, press down pretty firmly! You can glue somewhat generously from the bottom and probably not worry about the top.

Note that the panel is printed with the outer frame being thicker than the inner cross bars. This mirrors the full scale version and provides depth to the model. Given that these parts are 3D Printed, however, one side will be flat and shiny and the other side will show the variation (see picture above). This is the case for the panels and for the Bracing Frame used later. In both cases try to position the part to hide the shiny flat surface and to display the other side.

In the case of the inner panel you should position the flat shiny side to the outside and the nicer side facing the road.

Step 6: Install Panel Braces

The panel braces should be attached as shown above. Like most of this model they are held only with the glue...there are no slots given the scale. No need to worry about the good or bad side on these pieces but I would suggest that the inner support diagonals all run the same way and that be preferably from the top of the inner to the bottom of the outer.

Step 7: Install Outer Panels

Please read the next step before proceeding as you may want to combine it with this step.

The outer panels should now be installed and secured tightly against the braces and the road bed pushed down to seat the panels (push down hard). The nice side of the panel should face out.

Step 8: Install Base Plates

This step has changed since the Instructable was written.

In the full scale version of the Bailey Bridge the base plates would have rested on a prepared bed on either shore and been quite a bit smaller than in the 1:100 version. I am imagining that my base plates include some of that prepared bed/foundation!

Note that I originally had four individual base plates while above shows two connected into one piece. That connection helps to ensure that your bridge has "reasonably" straight panels as well as making the part easier to handle. The connecting bar should be cut away once the adhesive has set.

Step 9: Install Brace Frame

There should now be a flat platform on which to secure the Brace Frames. One on either end of each side and one over where the joints would be between sections of the bridge.

Step 10: Install Foot Walk

The Foot Walk should lay down neatly on the protruding ends of the transoms. Be careful of the hand rail as it is quite delicate!

Step 11: Install Ramps (if Desired)

If you want to install ramps, which in this case I do not, you can do so as shown. The example of a bridge with ramps is the second bridge ever built from this kit.