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Boxed Pony (Howe) Truss Overpass

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  • Boxed Pony (Howe) Truss Overpass

    The Boston & Maine used wood for many bridges into the 1920s. The Historic American Engineering Record documented a couple: This one still stands AFAIK:

    This one was replaced in 1995, but it's a better example to follow for the Chipman St. overpass west of Bexley Depot on my B&M Eastern Route layout:

  • #2
    The Sinnott Rd. (Meetinghouse) bridge from railroad west:

    The signal bridge stands but is unused - I should photograph it this summer. The end of one of the enclosed trusses:

    One of the angle braces keeping the skewed trusses from folding up and collapsing:

    I wish I'd known where this was 25 years ago; when I cross its replacement I'm about 5 minutes from Seashore Trolley Museum.

    I'd started this project last decade: I made a sketch with dimensions and bought the wood I'd need to build it. The model will be right at the edge of the layout, so it has to be durable. I decided not to do the hidden trusses as my bridge will be fairly well-maintained. Instead, I made formers for the truss enclosures out of hardboard.

    I planed an angle on the top edge; the tin roof covering the truss had to shed rain. I painted them black and then my attention shifted to something else.

    When the challenge was launched, I thought I'd join with a signal scratchbuild. But the materials were slow to arrive and I want a couple more photos before I start. So I restarted this today: Here one of the formers is ready to be sheathed with Northeastern 1/32" thick 1/16" scribed basswood.


    • #3
      Looks like a fun project, James!

      I do hope you'll make it in good repair to showcase the proud part of Minuteman life, and not the run-down stuff in some of the photos....

      Looking forward to more!


      in Michigan


      • #4

        Very interesting prototype. Particularly being skewed with the additional braces.


        Not everything that is faced can be changed, but nothing can be changed until it is faced. James Baldwin


        • #5
          Thanks, Pete and Mike. Here's glue drying on the first side subassembly's second lamination:

          A little scary when it first curled, but it came back overnight. The second (longer) side is waiting to be straight enough for its 2nd lamination. This morning I went to Michaels for flooring material - I was looking for 1/16" plywood, but they had 1/8 and 1/32, so I'll laminate two 1/32 strips together, with their from-the-factory curls opposing.


          • #6
            Great idea, different from the usual bridge overpass builds. Nice use of materials, looking forward to the end result.

            Louis L&R Western Railroad
            Pacific Northwest Logging in the East Coast


            • #7
              What a neat bridge James. I'm glad you have the prototype picture a modeler could end up skewed for building it as it was. Not on this board though. Those who hang out here know better.
              It's only make-believe


              • #8
                Thanks, Louis and Robert. Besides the HAER, the last few B&M boxed pony truss bridges were written up in Mainline Modeler (4/92), Trains (2/94) and Railpace (4/98). When I was a teenager, two spanned Newburyport's City RR branch, and two more were nearby (Salisbury and Newbury, MA). Space didn't allow me to model any of the prototypes, but putting this one in Bexley will help with the feel. Even though I don't have any photo evidence of multi-span boxed pony truss bridges; I expect they existed, but perhaps didn't last past the '30s.

                At any rate, I got the floor lamination done last night:

                And that really wasn't enough clamps. I probably should have weighted it on a flat metal or glass surface.

                Here's the test fit. Over breakfast I'll consider: Glue it together as-is, with the main floor beams the only floor components modeled. Or I model the whole floor system, which makes a Merit Award a possibility but might make it more fragile.

                Prototypes with heavy traffic used two layers of deck boards instead of the one sketched. Chipman St. will model two layers with asphalt applied on top.


                • #9
                  James, what a unique bridge! This will make a great addition and conversation piece on your layout.



                  • #10
                    Thanks, Dave. Browsing RR-Line while glue is drying on the first stage of the flooring system:

                    I drew the floor plank joints in pencil, rather than add a layer of scribed sheetwood to the lamination. The 0.7mm lead I used didn't make much of a depression in the plywood, so putting the base color and weathering on this will be tricky. And I wish I'd used six stringers rather than five.


                    • #11
                      A lot of the bridge plans I've studied have two stringers under the rail (with a small space between for drainage). You could add more stringers, this looks a bit "light" to me.

                      Modeling 1890s (because the voices in my head told me to)


                      • #12
                        Dave, this bridge is road-only. If I ever put trolley tracks in Bexley, the line down to the harbor will pass over the B&M at the tunnel farther east.

                        Last night I finished installing the floor beams, including the outriggers that will carry the truss braces. This morning I'm fitting the trusses to the floor:

                        The floor beams that are square to the sides are hung from the bottom of the trusses. Those at an angle (and the cutoff ends of others above the piers) will bear on cribbing atop the masonry bridge piers and abutments.

                        I didn't get the same projection on all the floor beams, so filing is required to make the floor/truss joint stand up to handling. But I won't glue them together till everything is stained/painted. First, I'll get the wood bearing pieces and cribbing atop the piers worked out.


                        • #13
                          Nice! Glad to see that the cutting mat is coming in handy too.


                          • #14
                            Looking good!


                            • #15
                              Interesting bridge, James. I really like these types of unique structures. Looking forward to seeing the completed model!