Model railroad, simple bridge

by wolverineboat, published

Model railroad, simple bridge by wolverineboat Mar 1, 2014



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This is a simple model of a steel bridge for model railroads. This design is based on pictures on the internet and does not model a specific bridge. I couldn't find a name for this type of bridge on the internet. Compared to a truss bridge, this design will not be very strong in the center. So it may not be a good example of a railroad bridge. I will be releasing a model of a truss bridge in a little while.

.stl files are provided for O (can be used for S), HO and N/Z. Because of the design, it should print very well and without any problems.


This is a simple model of a steel bridge for model railroads. I took some liberties in the design to make printing easier.

Three versions are provided: one for O or S, one for HO, and one for N or Z. The models were scaled in OpenSCAD so that the i-beams were more appropriate for the scale. You can further scale these models to meet your needs.

The dimensions of the O design are

  • track width = 60 mm
  • overall bridge width = 90 mm
  • length = 200 mm
  • overall height = 49.3 mm

The dimensions of the HO design are

  • track width = 36 mm
  • overall bridge width = 54 mm
  • length = 150 mm
  • overall height = 31.8 mm

The dimensions of the N design (also for Z) are

  • track width = 21 mm
  • overall bridge width = 31.5 mm
  • length = 100 mm
  • overall height = 21.6 mm

Parts list: None.

Assembly instructions: None.

Printing Instructions: The bridge tends to warp lengthwise. Adhesion to the build plate is very important. The i-beams were designed for printing. There really shouldn't be much cleanup of the bridges. If you are using blue tape, small holes in it won't affect the printing because it will be on the bottom of the bridge.

Bridges were printed on a Makerbot Replicator2

  • PLA (Makerbot filament)
  • Printed: Low(faster) resolution, 8% infill, 2 shells, 0.30 mm layer height, 230C
  • the longer bridges warped a little lengthwise. i carefully used a heat gun to warm the plastic enough to bend them straight.

Some best practices for printing:

  • optimize print parameters for your printer, filament, etc (only you can determine the best parameters)
  • use good filament
  • level your build plate prior to printing complex parts. it's worth the few minutes it takes. always level after removing tape, or if pulling hard to remove a part.
  • make sure the build plate is clean.
  • if using blue tape, stretch it tight when applying it to the build plate.
  • if you have small holes in the blue tape, the bridge should still print without any problems.
  • pre-feed the filament 30 to 60-s before printing (i.e., run load for 30-60s)
  • do not print several complicated parts in one build (do complex parts by themselves)
  • I find that printing faster is better (probably so the filament can't ball up in one spot)
  • when the filament spool gets low, the filament can be tightly wound on the spool and the filament may not feed properly... take special care...
  • when a new spool is used, it is easy for the filament to jump outside the spool and then it will bind up later around the spool holder ruining your build
  • make sure it is easy for the filament to enter the filament feed tube. others have designed spools, mounts, etc. for that purpose. i use a small rope that forces the filament away from the spool before entering the filament feed tube.
  • if you hear clicking when printing, that may be a result of the filament wrapped around the spool and not feeding
  • make sure that there aren't any obstructions on the spool, such as some filament used to hold it in place during shipping
  • for the replicaor2, look at the blob a filament in the left front part of the build plate and then the trail of filament to the biuild location. there should be a glob, and the line of filament should be continuous and smooth
  • one way to remove parts when using blue tape is to use a very thin spatula bought in craft-art stores (advice from youtube). get one with a wide, blunt front end (not long and thin). mine is 11 mils thick (0.011") and 20-mm wide at the front. a painting spatula/scraper in hardware stores won't work and may damage the build plate. (I use blue tape so I don't have any best practices for bare plates, heated plates or for other tapes like mylar)
  • perform regular maintenance (grease, etc).
  • when I continued to have problems printing even after performing maintenance, following troublshooting instructions, changing filaments, cleaning gears, cleaning everything, optimizing print parameters, changing temperatures, etc., I bought a new extruder assembly from Makerbot and it solved all of my problems.

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, LGPL version 2.1, or (at your option) any later version of the GPL. see http://www.gnu.org/licenses/gpl-2.0.html

Woverine Boat LLC is providing this document and its contents on an "as is" basis and makes no representations or warranties of any kind with respect to this communication or its contents. Woverine Boat LLC disclaims all such representations and warranties, including for example warranties of merchantability and fitness for a particular purpose.

Version number 3.A (first distributed version)
Author : Wolverine Boat, LCC - [email protected]
Copyright © 2014 by Wolverine Boat, LCC
Created March 1, 2014
March 1, 2014 ... original version
Special instructions:
User feedback:
Designed with OpenSCAD 2013.06

Model train info (approximate values and may depend on manufacturer (1" equals 25.4 mm)

O27 scale 1:48, track ~50.0-mm W x 10.3-mm H, typical car ~54.8-mm W x 79.3-mm H, car+track ~ 89.6 mm H, 1-ft = 6.4 mm

S scale 1:64, track ~47.0-mm W x 13.6-mm H, typical box car 51.2-mm W x 67.8-mm H, car+track ~ 81.4-mm H, 1 ft=4.8 mm

HO 1:87, track ~28.5-mm W x 4.6-mm H, typical box car 36.0-mm W x 55.8-mm H, car+track ~60.4-mm H, 1 ft=3.6 mm

N 1:160, track ~16.0-mm W x 3.8-mm H, typical box car 20.3-mm W x 31.5-mm H, car+track ~ 35.3-mm H, 1 ft=1.9 mm

Z 1:220, track ~16.0-mm W x 4.7-mm H, typical box car 15.6-mm W x 21.9-mm H, car+track ~ 26.6-mm H, 1 ft=1.4 mm

(Lionel O track is 4.4-mm higher than O27 track). I have not listed G scale because it's too big for my designed parts.

Disclaimer: This bridge was not based on a specific prototype and there isn't a true scale for this bridge. The design is based loosely on Google images of various bridges around the world. Features and dimensions of real bridges were altered for the simplicity of the design and to make the bridge printable.

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