Liftout Bridge and Mill Pond
The liftout bridge and mill pond has replaced a duckunder and town-center area in the NPF Railway. The duckunder had already become a big issue, and a knee injury in 2007 made this project a much more desirable solution.
Lift-out bridge over the lower pond. That water's so calm, it's like a sheet of glass!
With the bridge lifted out, the lower pond pushes back under the upper pond. Now it's easy to reach the back of the lyout including all the back (North) switches.
The upper pond also lifts out ...
... and the lower pond pushes all the way back, to allow complete access for an 8-foot span of the layout back, in about 10 seconds - without ever ducking under! Pulling the lower pond forward, placing the upper pond, and re-attaching the bridge takes under a minute - and that's really taking it easy.
Lift-Out Section
The first task was creating the lift-out section. Once this was accomplished, the underside of the layut was reinforced; wires were re-routed around the opening; the track was re-installed using a temporary knife-switch style connection on one end, and still using the old track pins on the other end.
The liftout section after trackbed addjustments and new track laid.
The usual track pins replaced with flat strips of metal. I used Gargraves track connectors, pressed flat, with the spring-clip part snipped off.
The Gargraves track section presses down over these tabs in an easy but reasonably snug fit.
Bracing the lift-out plywood section at just the right height is critical. Using a 1x2 allowed for a semi-adjustable brace.
Lift-Out Bridge
Next came construction of the bridge, using a pony truss kit from Black Bear Construction. After working with several different solutions and trying a couple different track types, I changed my mind about a hinged lift-up and went instead with a slightly better version of the same knife-switch style solution I'd used before. This has worked very well and is fairly easy to use.
With the bridge built, both tracks are secured to the bridge deck. That means six of the little knife-switch connections go in all at once. The Gargraves track with its wide openings really helps here.
The other end comes out just as easily, once the pins are ground down a little. These pin connections have to be pretty loose to keep from causing any of the 4 track sections involved from shifting. Note the basswood beam screwed down to the 1x2: this is shimmed underneath and then screwed into position to get the bridge deck height to line up just right to the track.
Putting the bridge back in starts with the pins on one sied, lined up and fidgeted into place one or two at a time. You can see a larger black screw set up as a guide for the bridge line-up; it's heavy enough to serve as a guard as well, so a big push on the bridge won't dislodge the track. The "scenicking" in the lower pond at this time is an Eastside Trains shirt.
Mill Pond
The mill pond is 2 sections: the upper pond lifts out and the lower pond slides back on home-made drawer glides. Each section is essentially a shallow box with a sliding glass top to allow scenicking under the "water" surface. So far the upper pond is scenicked under the glass (still need to put some weeds and stain on the glass itself) and the lower pond is not.
The lower mill pond is a shallow drawer made as thin as possible to preserve clearance under the layout.
Dadoes on 3 sides to keep the glass snug: on the upper pond, the glass is actually holding the pond in place, and these dadoed slots are what the pond base is supported by.
The drawer glides are smooth cedar strips sized just right for some aluminum U-channel. The bottom is 1/8" plywood to conserve drawer depth. The glass bottom clears the top of the drawer front by about 1/32" so the underside can take a light stain wash as the last bit of scenicking.
The drawer channels run 5 feet to the back of the layout. Screw holes are bent in & countersunk to keep from catching the drawer as it slides.
The glides need to be well-fitted laterally, but it's ok if they are not a complete fit top to bottom within the channel... the glides only ride on the channel bottom anyway, since the drawer is usually pushed back not pulled forward. Note the washers used as shims to get the channel height just right for a smooth but minimal clearance above the drawer.
Here is the upper pond with its pond-bottom scenery in place. The box is notched at the 4 corners to allow the glass to sit on top of the layout plywood in these spots. The glass rests on the plywood, the dadoes trap the glass, and the pond box sits suspended in its hole, held up by the glass itself. Using tripl-thickness tempered glass with smoothed edges and corners, we're not worried about the weight or the glass breaking.