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 How to Build a Tunnel Portal by Kaykam
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Posted - 05/04/2005 :  10:01:44 AM  Show Profile
Moderator's Note: The following tutorial on scratchbuilding wooden tunnel portals was posted by Kaykam in the Construction Forum. A copy of the tutorial has been moved here for safekeeping. The original thread is still open for questions and comments:

As a new model railroader, the RR-L forums have provided me with invaluable information. In return, I would like to share my experience in building wooden tunnel portals and retaining walls that will be used on my layout. Hopefully someone can get something out of my process as much as I have gotten from other posts.

Why make my own you ask? I felt it was a project that I could do as a novice scratch builder. Plus it allowed me the flexibility to design my own portals and retaining wall sizes.

The first picture shows a completed portal with retaining wall. Since I needed several of the portals for my layout, I built a prototype and then copied the rest from it. They took me about three hours to complete each one – certainly a good rainy night project.

The next picture shows some of the tools used plus the base. I cut the base from 1/4" birch plywood using my cross cut saw where possible and finishing the cuts with a scroll saw. I also cut some 1/2" supports out of the plywood also. Note that you want to get the base portal cuts as square as possible as the final boards will go on easier. Also shown is the 1/16 x 4" x 24" Basswood that I used for the lumber. This came from a local craft store for around $2.50.

Next step was to cut the lumber. I guessed that at a minimum, 12x12's lumber was used to build the real portals. That is something like 5/64's in HO scale, so I made the lumber 3/16's to make it a little easier to measure. I used a straight edge and Exacto knife to cut to width. You want to keep the knife as straight as possible. Although not shown, all the 3/16 lumber was beveled on the edges using coarse sand paper before gluing to the base. This provided some additional depth to the lumber strips.

This picture shows the strip lumber and the ˝” supports glued to the back of the base. I used a small hobby saw to cut the small angled supports. They are used to attach the inside lumber plus provide an attachment point for the tunnel liner.

This picture shows some of the lumber glued to the front of the base. Note the pencil lines applied with a small square running across the front. These are used for reference to keep the lumber straight as you apply it to the front. I started by applying the first lumber strip right above the opening in the base and then worked up.

A comment about gluing: After gluing a section, I would turn the piece face down and clamp it for a few minutes to allow the glue to set. Sometimes I would get to much glue applied and it would seep up through the boards. Before the glue got hard I would run my utility knife blade point along the grove to clean out any excess glue. (I found out from the prototype that wood glue does not take the acrylic washes the same way raw wood does….)

Once I had applied the top boards, I worked down from the center board leaving the boards longer on the angled portion. Once they were dried, I clamped down to flat surface and used the utility knife to trim off the excess from the back.

This is a picture with all the front boards applied. You will notice that the lumber on the outside edges was not straight. I used the method described above to trim all the edges from the back side. When cutting the lumber from my 3/16" strips, I found it easier to use the wire cutter portion of my pliers. This left some pieces a little longer than others but trimmed easily as described above.

Next step is to cut and apply the side boards. You want to make sure that they do not extend beyond the front boards so that the trim boards can be applied evenly.

Finally the trim boards can be added. Note how they hide the front edges of the side boards.

Here is a picture of the completed back with a tunnel liner. Note how the ˝” supports are used for the side boards as well as for attaching the tunnel liner. Note that the retainer walls were made in the same fashion but allowing for overlap on the trim boards.

I finished the wood by first applying a diluted acrylic burnt umber wash followed by a diluted black wash.

Here is finished portal..

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