The making of a viaduct..

[dkightley]

With the now almost normal view of 3D printers being the salvation of all. Buy a printer, unpack it....and print whatever you want! Not quite!!

To give an idea of what's involved in the process, I thought I'd detail the design and printing of a medium sized model. The Forth bridge is a bit on the big side...and is taking a long time to do, so I need something smaller.

When barneyadi (aka Dave) announced that he was going to build a layout featuring the Ribblehead viaduct, i offered to help by designing and printing an accurate and detailed model of the viaduct..which he accepted. A perfect example to run through the processes involved....so here goes!

Firstly, for those who are not familiar with Ribblehead, hers' a photo I lifted from the web:

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The viaduct is 400m long and 32m high at its highest, and consists of 24 almost identical arches each of length 14m. The arches are grouped into four sets of six arches, and the intersection between each set of six having a thicker column. Reasonably straight forward....but not quite. The viaduct is curved! So the first stage in the design was to consult Google Earth to find out the curvature....

Here's a satelite view:

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Using this image, I decided to make an assumption....the viaduct is a constant radius, so I worked out the radius of the "curve" and it's angle. I've lost the actual figures...and can't remember the radius (it was huge!!), but the angle of the curve for the whole viaduct is 16 degrees.

From all of the above data, I made a very rough mock-up of the viaduct in my 3D package so I could get an idea if the figures I had were good......and to send an image to Dave so he could see what he'd let himself in for! Here's the mock-up:

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As I was designing this remotely, and the fact I had some gash printing filament going spare, I printed off a low resolution ( print layer thickness of 0,25mm) copy of the viaduct and sent it to Dave so he could check it wasn't going to be the wrong size, etc for the layout he had in mind. I didn't take any photos so can't post one.

[dkightley]

Once Dave had given me the OK to proceed, I started work on the detail of the design.....

I decided to go for a road deck printed in four pieces that would form the curve. The four sections will fit securely together and have slots to hold twin track flexitrack. Each arch will be printed separately and will fit to the road deck and to the adjacent arch section. Several blobs of superglue should hold all the pieces together!! The arches are separate so that I can keep the amount of design work down. One standard arch; two lead-in sections, and a thin section to sit between two arches to make up the thicker columns!

I've designed it this way also because of the physical restraints in the manufacturing process. I intend to print the arches standing up so as to get the greatest surface detail on the sides...and so I can dial in support to ensure the arches print correctly. The road deck is in four sections due to the available build volume in my printer....but I'll be able to print the deck also the right way up....again with some support to ensure accurate printing

So, on with the CAD work. Here's a shot of the single arch with a single portion of the road deck:

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The deck is keyed into the arch, the top of which is shallowed out so the edges meet flush. The slots for the flexitrack can be clearly seen...cribbed from the Forth bridge! I've not yet put any keying to locate the arch sections together, but have started the stonework detail.

Here's a progress shot of the stone detail:

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This is one aspect where the design process has to take into account not only the size of the end product, but also the technology being used to produce it. Once my printer has had chance to approximate the surface, all of those triangular faces in the surface will be softened out and it'll look spot on! The only problem ....is the number of sticky out bits!! There's hundreds!! And each one is different to give a sense of randomness.

Just to give an idea of the proportion....each of the stone courses will be 1mm high!

[mattd10]

Fantastic thread and great to see the processes behind creating something for home printing! Look forward to seeing more and photos of the viaduct!

[dkightley]

Thanks for the comment, Matt.

I've reached a notable point....all the stonework texturing done on the arch section. And here's a shot of two sections of the viaduct placed next to each other to give an idea of how the final viaduct will look:

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The next step is to add the keying that will align the columns at the bottom, and the skewing of the end faces by 0.33 degrees to form the curve....and then I'll be ready for a test print. That is once I get my printer back together....

[Nutter]

How big is that going to be?

[dkightley]

Each arch section is 34mm long x 24mm wide x 70mm high...and the overall viaduct length is approx 850mm

[dkightley]

I've not forgotten this project.

I now have my printer back in action......but I'm far too involved in the organising and running of a WW2 event at the Tramway Museum at the moment to be able to do very much towards it.

Once the event is over (after the 10th August) and I've had time to recover, I'll be able to get some printing done.....

[dkightley]

Now I've got some of my energy back after a totally exhausting but amazing week of wartime event management, I'm back on the case.

I've done a test print of the road deck for one arch's worth. Here it is still on the printer plate with it's raft and support:

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And here's it once removed and with the raft and support removed:

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First impressions are that the stonework pattern on some of the coarses needs randomising a bit...which I've done.

To form the road deck for a quarter of the viaduct, I then angled off both of the ends so the formed a slightly wedged section...then mirrored the shape four times to get a deck section eight arches long:

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The section at each end (with surfaces marked in red) will be shortened to form either the end of the viaduct, or the extra length at the joins.

I'm currently printing a test arch and will post a picture tomorrow...

[JBModels]

Looks lovely Doug..... with a bit of painting and weathering it's going to be a wonderful piece!

[dkightley]

A day late (I don't like making a promise and not keeping it!) , but here's the first archway print:

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I actually had issues with the stability of the support as it was printing...and I must have disturbed the print plate as I was trying to add bits of blue-tac to steady things. Notice the horizontal stripes on the back of the right-hand column..twas me moving the bed around whilst it was printing!! And I'd noticed an issue with the extrusion rate causing stringy bits on the surface. Both issues resolved as I've done a partial print since.

Also, since taking the photo I've actually broken the arch into two so I could place the two halves back to back to check the proportions of the column. I've also started making the wider section for the column for arch 6/7, 12/13 and 18/19, and for the lead-in and lead-out. No photo yet to make the explanation clearer...

[dkightley]

I've reached the point of readiness for printing.

I'll need four six arch sections:

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Four six arch road sections:

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Stonework and a short road sections for one end:

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And stonework and a short road section for the other end:

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And here's the whole viaduct in all it's glory:

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It'll take a while to print....I'll have to schedule the printing very carefully. Each six arch section will take over 20 hours to print!!

[JBModels]

It looks well..... 20 hours!! A pretty long time.

[dkightley]

Here's one reason why 3D printing is not actually a "breakthrough" for mass-production.....but an asset for prototyping.

For example a Lego brick that takes 15 seconds to make (along with half a dozen other similar bricks) by injection moulding (where 14 of those seconds is cooling time!) can take as long as 15 minutes to make on a typical FFF 3D printer. The big difference that does matter is the cost. To injection mould one sample new brick would cost in excess of £10,000 in tooling and labour costs.....but less than £20 in labour costs to 3D print, and it can be re-designed and re-printed many, many times in the same time it woukd take to produce one set of moulding tools..

Coming back to the subject in hand, yes, 20 hours is a long time. But in terms of what the printing process is, we're looking at a lot of work the printer has to do....and it doesn't really matter how long it does take providing the end product is good quality and unique!

I'm actually setting up to print the stonework sections from files I'll be writing and copying to a SD card reader in the printer....so I don't need to have my PC connected and running during the print process.

[Nutter]

Very interesting regarding print times, however it will look good when finished , when will you get back to updates on the bridge.

[JBModels]

There's also the option of making 1 or 2 master prints and then making moulds for resin cast stuff too. The good thing is that with multiple moulds you can cast multiple objects and speed up the process in case you want to sell stuff like this.

I'd prefer the 3D printing method also no matter what the time is.

[dkightley]

...when will you get back to updates on the bridge

I've had a rather busy and exhausting time over the past few weeks; preparing for and running a 7 day WW2 event at the Museum, clearing up afterwards, and manning a 3D printing demonstration at a models event at the museum over last weekend. Today I've just about managed to get the house straight ( ) so I can now start concentrating again on The Bridge again. With something like 10 months to it's first booked outing, I need to crack on with it!

[dkightley]

Managed to get a bit of print time in for this project...

Here's the two small end rail deck sections and one of the viaduct end sections:

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And here's one of the rail deck sections in place on top of the end section:

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Most of this will be buried under the ground surface...this bit is the very end of the viaduct and the viaduct proper will go off to the right

[dkightley]

First of the rail deck sections fresh off the printer:

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This wasn't actually the first one to be printed...it's the third! The first two suffered one of the big problems with fff printing - separation from the bed!

What happens is that as the plastic cools, it wants to contract, and this contraction sets up terrific stresses in the plastic that can "curl" the extremities away from the bed.....resulting in a print that can be best described as "banana shaped". One cure...as you can see I have used here....is to add "mouse ears" (the name coined from Mickey Mouse, btw!!) to the corners to increase the surface area in contact with the bed to stop the curling. Because I have been using a raft, I simply had to add the mouse ears to the raft by dropping in small discs. Where a raft is not used, the ears would have to be attached to the part being printed.

All I need to do to finish this section is carefully prise off the raft and the support structure underneath....and remove the support inside the track grooves. And not forgetting, print the other three.....

[barneyadi]

Looking great Doug, keep up the good work.

[dkightley]

After a marathon of just under 15 hours printing, hot off the press is the first of four six-arch sections:

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It's still stuck to the build plate and has all its supports underneath the arches.

After several light taps with a chisel handle, the section released from the build plate....and the support came away nice and easily. And less than 5 minutes after the above shot, here's the section roughly assembled with it's rail deck...and the viaduct end section:

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Three arch sections and t'ther end to go!....having got all four of the rail deck sections printed.