This is a stupid Question MOH {My Other Half} is helping me to ask:
Does anyone know if {and who makes and who has for sale/order} a curved bridge {of any type, steel girder, truss plate, wood whatever} that will fit an HO 18"R curve?
MOH, who is “in charge” of the under-the-table-top-Xmas-tree-layout, wants to see a curved bridge on the HO 18"R loop {mini oval with a 2" straight away piece}.
I know there are lots of “curved bridges” available, but what Radius are they?
MOH has found Walther’s # 528-21350 Noch 7x2.25" bridge and thinks it would be perfect. But that is the length and width…what is the radius?
Does anyone know what radius this bridge is?
How about Walther’s # 272-120476 curved bridge with a 43.7 cm radius? {WE are NOT good at converting Cm’s to inches I’m affraid} Although now that I think about it, 2.54 cm per inch- 43.7 cm/2.54cm =17.204 inches…so maybe for an 18R"??? so close? Or Not?
Wow! You’re usually answering questions rather than asking them.
The conversion from in to cm is 2.54. so your Faller bridge piece with the 43.7cm radius works out to about 17.2"; not quite 18, but since it’s fairly wide, you may be able to get away with a little judicious work with a file or Dremel tool. It may not even be necessary, since it’s designed for track with molded on roadbed.
Kibri has a curved stone bridge kit (Walthers #405-8723) which is 415-425mm, otherwise 42.5 cm, which is also about 17" and might work as well.
JV Models has a curved wooden trestle (Walthers #345-2016) craftsman kit which, according to their website, can be built in any radius or configuration.
The other thing you might consider is that, even though the rails themselves are curved, many prototypical bridges are built of short, straight sections supporting the curved rails.
One question–how DEEP of a dip in the layout do you want the bridge to cover? Because I think with an 18" radius, your best bet is to go with a trestle-type curved bridge. Walthers makes a fairly shallow ‘wooden’ trestle kit (up to about 4" deep, IIRC) that can be utilized by clipping the deck-braces to an 18" radius curve, and then attaching the bents to the cross-braces. A solid curved deck bridge seems pretty unprototypical to me–even if Noch makes one–so I’d definitely go with a relatively shallow curved trestle design. Curved wooden trestles or steel viaducts are common on US railroads–I have a large curved viaduct on my own Yuba River Sub constructed from two Micro-Engineering Tall Steel Viaduct kits–but a curved deck bridge just sounds like an engineering nightmare.
The Noch bridge is tighter than 18"r if one I remember correctly. I was able to use it with flex track and cheated the curve as much as possible though running an 89’ passenger car over it didn’t work. The other bridge is closer to what you want but they look quite strange in real life. I had a set of these on a previous layout and didn’t much like the way they look. They will however clear an 89’ car and any of the longer 3axel truck locomotives. Hope that helps. J.R.
A quick engineering lesson. Nearly all the weight a bridge can carry is transmitted to the bottom horizontal member in tension and the top horizontal member in compression. A real railroad rarely used curved bridge members as it makes the calculations much more difficult then straight lines. A real railroad would build two straight sides or multiple straight sides that the curving rails could ride on. The PRR had a truss bridge the track went thought where the sides were at least twice as wiide as a straight track bridge. Other bridges have been.built as deck bridges with the bridge portion under the railroad. a truss bridge or plate girder turned upside down so the track could curve with no interference. That’s how I would do it.
Campbell has had kits for a long time for curved wood trestles. The builder chooses the radius. They are not hard to make based on my experience with them.
I too was looking for a curved bridge to fit an 18" radius and was having trouble finding one at the LHS or online. LHS had the Noch bridge but I thought it was too European. They also had a small Pile trestle that could be built straight or curved but it was only 6" long and it wasn’t tall enough for me.
The solution I chose… Design one myself! I liked the Pile trestle design the best and figured designing my own would be fun and a good use of my 3D Design software I use at work. Long story short, I ended up creating a flexible design that takes several custom parameters that I input and will instantly morph into a custom sized bridge. For example, I set the radius to 18" and a 30 degree curve that was 1.625" high. and this is what I get.
If I enter a taller height (deeper gorge), more bents and 45 degrees, I get this.
The design of these are really pretty simple and can be made from off the shelf bass wood. I also think building it would make for a nice project even if it’s your first scratch built model. I
I realize real RR’s avoided curved brides like the plague, but there isn’t room for a 9" or even cut down straight bridge unless it’s only 2" long, and puts it NOT in the place MOH {My Othr Half} sees it.
It isn’t to be very deep, thats why a girder or truss bridge would be perfect.
We have N scale running on this layout and MOH would like to see the Nscale as the HO passes by from MOH’s vantage point, which I have asssured MOH, that using left over 3% and 4% Woodland Scenics foam inclines that were no good opposite ends to opposite ends will make perfect Risers instead upon which to perch the N scale higher than the HO, but the bridge idea is sticking in MOH’s head.
You would think as popular as 18"R is, someone would make one.
I may have to resort to making a trestle of my own or trying to curve on 18"R styrene to build one myself.
I made an 18R curved bridge from Atlas track that comes with the roadbed. (True Track I think)
I took the track off of the plastic roadbed and turned the roadbed sections up-side-down. I added pieces of styrene to build up the sides on the top and bottom, then added steel beam sections also to the bottom. The track was glued in it on the bottom, which is now the top. This made a cast concrete type of bridge. And of course, the track was ballasted when done.
