I borrowed a concept from the N-Trackers in my area to build a hinged "geezer gate" module that has been very successful in NCT layouts over the years. The hinged end has the hinge axis just above the rail tops (this is crucial). The free end has a trapezoidal "tooth" that fits into a socket. With the appropriate hold down device(s), the tooth locks into the socket and the two halves of the 48" module become solid. The bridge deck is 3/4" Birch ply with 1/4" sides. This module uses tinplate track. To keep the track ends aligned at the hinge and deck break, the track ends rest on wide wooden ties glued to the base deck and the track is secured with nails (1/2" or 3/4") driven through holes drilled into the rail flange. (The nails are working loose after years of use and I'll replace them with screws). I find that a 1/16" gap in the rails is no problem. Rails ends at the break need to be trimmed (the flange is slightly recessed) to prevent snagging when opening or closing. Rough rolling over the bridge is mostly caused by operators failing to firmly press the deck/tooth into the socket and the rail ends are at different heights.
The NCT has built additional geezer gates that have been more problematic in operation than mine. Modular layouts introduce a number of issues not present in a fixed layout. Small errors such as member's modules not assembling perfectly square or corners not precisely 90 degrees can build an alignment error that manifests itself at the geezer gate. The precision of the tooth lock into the socket can overcome some misalignment. Again, the tooth lock depends on the tooth being pressed firmly into the socket and I'll be trying out hold down levers on the NCT gates to see if closing the gate can be made more precise.
In summary, the success of a hinged bridge is dependent on a means to precisely align the free end of the bridge once closed. Achieving good alignment on a fixed layout bridge will be much easier than a modular layout and gravity may be sufficient for alignment.
I'll follow this post with photos and drawings.
John
