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The Bridge

Posted: Wed Mar 12, 2014 10:36 pm
by dkightley
A simple name......but its the most appropriate name for my next layout. That is if you can call it a "layout"!

My next project is to create an exhibition display of the Uk's (if not the world's) best known railway bridge...the Forth crossing. The layout will be somewhere around 25 foot long and only 2 feet deep. The track plan is simply a long...very long dog-bone loop..with a switchable dead section at either end and separate controllers for the Northbound and Southbound legs.

The bridge is going to be totally 3D printed in as close to scale realism as I can get within the feasibility of construction. So far, I've made some progress in 3D modelling some of the many components need to create the structure. Here's an assembled centre tower with the discrete components all in different colours:
Bridge3DC.jpg (45.14 KiB) Viewed 28339 times
The north and south towers are not as long, but are similar to each other, and each of the six cantilever sections are the same. So, once I;ve cracked one whole section, its simply a matter of reprinting. Did I say "simply"??

And here's a partial assembly of some of the parts I've printed so far. The red parts are final or close to final; the white parts are the initial sample print. First one side:
IMG_0955_red.JPG (50.12 KiB) Viewed 28339 times
One of the feet atop its caisson:
IMG_0956_red.JPG (30.68 KiB) Viewed 28339 times
And finally, the lower cross lattice girder:
IMG_0957_red.JPG (32.15 KiB) Viewed 28339 times

Re: The Bridge

Posted: Thu Mar 13, 2014 12:39 am
by peterg
Wish i was clever! Great project Doug......guess you live in a long narrow house to manage a 25 foot layout :lol:

Re: The Bridge

Posted: Thu Mar 13, 2014 12:55 am
by dkightley!

In fact I don't have anywhere inside that I'll be able to set the layout up!

I'll have to rely on the weather forecast!

Re: The Bridge

Posted: Thu Mar 13, 2014 1:33 am
by martink
That's impressive... And I was impressed by the 1.5m trestle bridge on Orbost!

Re: The Bridge

Posted: Thu Mar 13, 2014 1:40 am
by mattd10
Couldn't you have gone for something smaller to at least give others a chance of outdoing you ;)
I may have to do a scale replica of the channel tunnel (all out of sight of course) just the portals :D

But seriously, this looks bloomin amazing and cannot wait to see it take shape!

Sent from mobile device

Re: The Bridge

Posted: Fri Mar 14, 2014 1:45 am
by dkightley
There are two reasons for choosing the Forth bridge as my number two layout....

Firstly, I wanted something that would challenge my skills in using the latest technology in modelmaking. I don't like doing easy things!! So far I've had about a 50% failure rate when printing most of what I've done so far. And I'm talking about single prints taking up to 8 hours!!

And secondly, I wanted to do something with a "Wow" factor that would get the scale noticed. Most who have seen T gauge have seen it as a novelty. I want to change that..and make the sceptics think twice before dismissing it. Most think of the novelty factor...the track around the rim of a hat, inside a toilet seat or a briefcase. I want them to talk about modelling railways in T...and the capabilities of such a small scale. The Forth bridge is impracticable in all other scales....but not in T!

I'm anticipating the build to take many months. I have the overall layout sketched out in memory...and on scraps of paper. The bridge itself is something like 18 feet long overall...and I'm planning loops behind angled scenic backdrops at either end...and a painted backdrop to try and give some feel of depth. I already have a set of folding tables that line up to give an 8 metre long and 600mm wide platform to assemble the sections on...which will probably be 1 metre lengths to match the table sizes.

As yet, I've not decided which way to orientate the bridge. Do I place it facing West with the road bridge in the background....or facing east with the estuary as the backdrop?? The latter may win the day so the bridge is not obviously I can run almost anything across it. The only non-realistic thing will be that the bridge will have no scaffolding screening any part of it. It'll be between coats of paint!!

I'll post updates and photos as often as there's something new to show.....

Re: The Bridge

Posted: Fri Mar 14, 2014 11:24 am
by peterg
Sounds like it will certainly WOW the sceptics when it's done Doug!
Your determination to quiet these people is great....still being new to the game i have no axe to grind as such but i do hate the dyed in the wool tendency where change and product evolution is concerned. Remember when computers were the size of the front room. Mobile phones have far more computing power than took men to the moon. Carry on the good work.

How will you join the various sections on a regular basis for exhibitions and the like ??


Re: The Bridge

Posted: Fri Mar 14, 2014 6:45 pm
by dkightley
I haven't thought that deep into the design yet.....but I'll probably use dowels for location and either "turnbuckle" fasteners or bolts/wingnuts to secure sections of the board.

The bridge will be pre-assembled in sections and the caissons will locate loosely on supports fixed to the layout board...and current thoughts are for the track to be connected with flexi-joiners and the bridge sections held together with discreetly located nuts/bolts.

And I'm open to thoughts on how to get acres and acres of water surface with the right amount of waves!! :shock:

Re: The Bridge

Posted: Fri Mar 14, 2014 7:48 pm
by peterg
Hope this doesn't sound too way out but ;

Supposing you had a relatively high speed fan playing on the water fluid from the moment it was poured until the point that it sets....would that make waves or shall i just go back to sleep ;)

PS: Or just tell people that it's a calm day.

Re: The Bridge

Posted: Thu Mar 27, 2014 6:29 pm
by dkightley
Here's a first version of one of the fifteen viaduct girder sections. Printed in two pieces; the road bed and the girderwork:
Img_0968_red.jpg (38.13 KiB) Viewed 28126 times
Img_0967_red.jpg (41.02 KiB) Viewed 28126 times
Flexi-track slides neatly into the two slots on the top of the road bed section with the rail head flush with the top surface. With each section slightly over 4 1/2 inches long, the viaduct one end is just under 23 inches long...and the other between 45 and 46 inches long. Yikes...I'll need to build in space for a track joint part way down the Queensferry viaduct! :shock:

Its incredible to think that when they built the bridge, these 168 ft long sections were assembled on partly built columns...and then jacked up bit by bit to allow the column to be built up underneath. Victorian engineering at its best!!

Re: The Bridge

Posted: Sat Mar 29, 2014 10:46 am
by tjejojyj
Hi Doug

What source material did you use as the basis of you CAD model?
Do you find there is a maximum or optimal size and thickness of components you print?

I'm thinking that 3D printing would be a good way to make a version of the Landwasser Viaduct and Langwieser Viaduct for the Rhatishe Bahn layout I'm planning. It would be nice to make them to scale.

I'll add my 2 cents to say I eagerly look forward to seeing images of your completed layout. It sounds wonderful.

Re: The Bridge

Posted: Mon Mar 31, 2014 8:48 pm
by dkightley
What source material did you use as the basis of you CAD model?
Everything I have so far has either been downloadable images from the internet...downloaded on the basis of "personal non-commercial use only", and three books on the subject of the bridge that I have purchased. Fortunately, lots of people have posted photos of the bridge...and a good "engineer's eye" can get a lot of information from a few pictures!!
Do you find there is a maximum or optimal size and thickness of components you print?
This is a simple which I wish there was a simple answer! Alas, there isn't. The differing 3D printing technologies and systems have totally different printing capabilities.

Take a look at the design criteria for the differing materials available from Shapeways for example. The minimum wall thickness and detail tolerances differ wildly between the materials. And the minimum dimensions for the hot extrusion method that the Makerbot printer I have ( and all other similar printers) are actually different in each of the x-y-z axes. For instance, extruding through a 0.4mm diameter nozzle give an extruded bead of 0.4mm wide, so its impossible to have a vertical wall thickness of less than 0.4mm, whereas its perfectly possible to extrude a layer that is 0.2 mm thick! You have to be quite inventive on how to utilise the printing process! ;)

Perhaps forum members may be willing to pass on their experiences of 3D printing in the so-named forum section.

Gosh! What a subtle hint that was! :shock: :shock: ;)

Re: The Bridge

Posted: Wed Apr 02, 2014 11:38 pm
by dkightley
Another component drafted out. Needs detailing, hollowing out and a mounting insert designing...but we're getting there!
IMG_0975_red.JPG (48.8 KiB) Viewed 14507 times
Let me see....I'll need thirteen of them. 8-)

Re: The Bridge

Posted: Sat Apr 05, 2014 12:32 am
by dkightley
After many hours of 3D detailing work, I finally have some textures on the viaduct supports. Here's the before and after...and the after version took a whopping three hours to print!!
IMG_0977_red.JPG (62.67 KiB) Viewed 14947 times

Re: The Bridge

Posted: Sat Apr 05, 2014 9:23 am
by Slarge
Woah! :shock: you modelled all that texture? How?
Seriously how? Are they truncated pyramids or something?
Bricks are things we would never even consider modelling at this scale when making architectural models 3D viz, 3D for Printing or the Old school scalpel scored cardboard.
You just pushed the boundaries of modeling at this scale yet again!

Re: The Bridge

Posted: Sat Apr 05, 2014 10:44 pm
by dkightley
Basically, I found out quite quickly that at this scale we have to design not for the detail....but for how the printer prints.

To illustrate this, here's what the model looks likes in my 3D package:
TextureDetail.jpg (60.75 KiB) Viewed 14922 times
Compare the 3D model with the finished article. They're similar...but to get the end result, I have to exaggerate some of the surface shaping. And the rest is down to sheer trial and error!

And getting that level of detail for brickwork took hours and hours of repetitive dividing lines up and joining the dots! And then every sticking out node (forming the centres of the bricks) was moved out individually!

Re: The Bridge

Posted: Sun Apr 06, 2014 9:21 am
by tjejojyj
That looks really good. From the first photo it looks like you have copied a 'block' pattern about ten times up the column.

(I was just thinking about asking whether such surface texture was possible at this scale as it is a facet of the Landwasser Viaduct.)

Re: The Bridge

Posted: Sun Apr 06, 2014 10:53 am
by martink
What you are doing is very, very impressive. While 3D is pretty much essential for the complex ironwork, have you considered using more traditional modelling techniques for simple bits like the pillars? The old trick of sticking suitably embossed plasticard onto wooden piers springs to mind.

Re: The Bridge

Posted: Sun Apr 06, 2014 4:19 pm
by dkightley
With wanting to get as near to true scale as possible, I only thought of using 3D modelling to get the level of results I was looking for. And it also allows me to produce pre-production parts so I can make absolutely sure things fit together exactly how I want.

For example, with the tower "hot off the press", here's an example of all pre-production parts assembled together for the first time! And with the HST placed almost in the right place, it gives an ides of the scale of the structure.
IMG_0983_red.JPG (54.66 KiB) Viewed 14898 times
There's four separate parts here...all of which are not in their final form, but knowing they fit together, I can press on with the time consuming detailing.

btw This tower is actually the largest single component volume-wise in the whole bridge! And it happens to be a key component in the design, as I now know exactly how high the track bed will be above the I can now work on the roadway sections for the centre tower, which I have partly produced.

I had doubts as to whether I would be able to pull this project off. I'm starting to feel slightly confident that I might just succeed!

Re: The Bridge

Posted: Sun Apr 06, 2014 8:16 pm
by peterg
Seeing the parts together...with the train, just confirms how great this will be.
I think we will be seeing you in a magazine with this one at some point!!