New deck for an Atlas girder bridge


#1

Things still seem too slow on the forums, so I’ll start another discussion topic. The General category is usually the best place for friends to show off what you’ve been working on, unless you are showing construction at the A&O. So if you feel comfortable showing off your recent project, please speak up here!

I’m on the hook for two bridges to complete the A&O mainline. I recently revisited an Atlas deck girder bridge, weathered a long time ago as an object lesson for a weathering clinic given to the local modeling club (there were far more talented folks in the club who do weathering, but I received a tap on the shoulder because “You take photos.”

The colors may seem a bit bright, but they do closely match a prototype photo I used. I won’t post that photo because the copyright is owned by someone else, and I do not have permission to post it.

Where installed there will be little light on the face of the girder and that further mutes the vibrancy of colors. Most of this work was done with gouache, supplemented by acrylics sprayed on the bottom and inside, and also overall acrylic flat. It seemed OK for a first round with gouache. :neutral_face:

The problem with the Atlas bridge to my eye is the plastic injection-molded deck. It looks like plastic and far oversize, with unrealistic looking ties, and it is set up for included brass code 148 rail. The mold maker engraved tie grain detail into the mold, instead of removing all but the grain. So the grain became an “outie” instead of an “innie.” Ugh! :disappointed: Sorry but I don’t buy it.

New ties and guard timbers were ripped from Midwest basswood sheets. I made the ties a prototypical 8" wide and 11" high for 12 inch centers, and 10 feet long. It is common in modern practice for bridge ties to be taller than wide as that greatly increases their stiffness. Here I wanted to add extra vertical clearance so that when spiking code 125 rail with tie plates there would be a lessened chance of a spike hitting the girder. If two did that, on opposite girders, there would be a short circuit. And a short that probably wouldn’t express itself until a most important operating session held for very distinguished guests. :open_mouth:

The guard timbers started at 8" wide by 6" tall. About 0.020", or approximately one scale inch, was removed during dapping on the mill.

I cut all the bridge wood on a Byrnes precision miniature table saw. In this photo we see cutting ties to length using a simple table saw sled I made at home. Fellow club member and friend Jack Heier gave me the inspiration and demonstrated a sled he made out of acrylic for use on one of his home-made table saws. Jack is a modeler whom I greatly admire and whose skills I doubt I will never equal.

The sled increases safety for fingers in crosscuts and improves precision from cut to cut. I did not take a photo of ripping the ties stock to dimension. With my digital caliper the tie stock varied about +0/-0.003" in width. The blade was a Thurston slitting saw, if I recall it was 0.020" wide, and slightly hollow ground to minimize binding. I really do not mean to brag, but the Byrnes saw is really that good!


#2

Hey! You didn’t gimm’ie enough info. This looks interesting. Thanks for the posting.


#3

You’re right, Jeff. I was pretty tired yesterday and didn’t post everything I intended to.

Here’s the original Atlas deck that I retired. It has simulated nuts on the guard “timber” metal straps, but no J bolt heads.

On the new deck, for a little more strength and to make aligning the ties easier, I dapped the guard timbers. That was a common prototype practice which involved cutting dados on the bottom of the guard timber where it made a lap joint on a tie. I dapped both timbers at the same time in my mill. Wrapping the timbers with masking tape eliminated tear-out of wood at the edges. 8" W x 11" H x 10’ L ties were spaced every foot. Anticipating that the wood would swell a bit when stained, the slots were cut a bit wide.

Assembly began on a piece of Micore, which holds T pins very nicely. You may notice that the scale of the plan underneath is wrong; my laser printer shrank the length. Since the timbers were dapped, I could ignore the plan and still get everything in place. I lightened the photo quite a bit so the dapping can be seen.

Longer walkway ties went in last.

The Atlas girder and still-separate new deck went to the A&O for planning. Here David marks where to cut out the subroadbed. At this point, I haven’t trimmed the guard timbers to length, nor added the walkway and NBWs. Those will wait until David lays the curved rails and tie plates.

Just past the intermediate signals will be an Overland pin-connected truss, also with a new deck.


#4

Love it Bob great work. I used Mt Albert Scale Lumber on my decking. Are you going to actually do the J bolts underneath?



#5

No J bolts below. If I catch anyone looking for them… who knows what could happen! :open_mouth:

On this bridge, to functionally serve in place of real J bolts, I plan to cut a few short lengths of tie stock and glue them under selected ties as lateral locating pins. Then at David’s suggestion the ties will receive Pliobond and be dropped onto the girders. Since the deck is open and the normal viewing angle is from above, I’ll also add a bit of rust to the tops of the girders before glue-up. Because it will be dark between the ties, I’ll probably use a much lighter than normal rust color along with splotches of “spilled coal” black.

Pre-weathering of the pin connected truss will be “interesting.” It also needs an appointment with Mr. Resistance Soldering Iron.


#6

I need to touch up things on the Pin Connected bridge. What do you think about the gray? Should it be silver in your opinion? Rust stains around the pins and moving areas the rest dust. My era is 1940’s 50’s so it’s only 20 years old. Good luck on the repair. On those J Bolts me too. I promise I will not peek under. :wink:


#7

My recollection is that most bridges were painted silver or black, before they turned to rust. That said, it is tough to tell the difference between gray and silver in most photographs. Most shots I’ve collected of the Clinchfield’s Pool Point bridge do seem to suggest a gray instead of silver.

http://www.railpictures.net/photo/254634/

Either silver or gray would show off the detail better than black. Personally, if my Overland bridge was gray I’d probably airbrush it silver before weathering.

Whatever you do, the two bridges should probably match in color.


#8

So I said that they should match in color? That might be expected, given that a RR might normally paint back-to-back bridges a consistent color.

Well, I revisited a photo I made of the UP bridge in LaSalle, CO. Some of the girders are silver, but others black. Go figure!

A cool detail on the east side of the bridge is the collection of several sets of weathered timber bents along with trees caught on the timbers. Rust weathering on the rightmost pier seems to have been interrupted by human removal of something, perhaps offensive graffiti.

There is a small UP girder bridge in Fort Collins under which similar but less weathered timbers can be seen.


#9

Bob, thank you very much for the exceptional reference photos. Per your advice the St Vrain River bridge shall be silver. Weathered too. :slight_smile:
This is my conceptual drawing for the exhibit showing the old right of way.


#10

Replacements? Seems like I once read something about why silver paint but it has been too many years.


#11

Still trying to find the time to get back the project. Here’s a fun piece I did showing some continued progress.


#12

Back on A&O bridge projects, I’m on the hook for two. First is another view of the Atlas deck girder bridge after delivery to the A&O B&B department. I’ll add NBWs and a walkway after it is installed since they are not physically required for trains to operate.

In the distance is a suspected Overland pin connected truss. It may have been damaged in shipment to Overland and sold on the gray market because it came in the usual green box but without a genuine Overland label on the end. The deck and walkway substructure was badly bent on both ends, and frankly it looked like metal instead of wood.

Caliper measurements revealed there should be 25 ties in each of the 6 “runs” between pairs of floor beams. But the beams were not uniform in spacing. After pondering a while, I decided to mill a plexiglass fixture to space the ties.

Ties were then laid in the slots and guard timbers glued on top. Everything was held in alignment using machinists’ angles and 1-2-3 blocks.

The end result is a two-piece deck that needs to be precisely lap joined in the middle.

The deck will be attached from below with hidden phosphor bronze spring clips that rotate into place. After splicing the two deck halves, it will be time to lay rails and lightly weather the superstructure with a light black sludge wash to pop details and some light rust chalks.


#13

David test fits the location for the pin connected truss. Interior structural elements for the piers have been glued and screwed. Bob has not yet finished the deck assembly. There are more tie plates to spike, guard rails to lay, then install J bolts and 304 NBW castings for the guard timbers.


#14

Looks very wonderful David. A masterpiece in the making.