Pont y Gelli - A composite printed bridge

[Trevor Thompson]

The second path crossing for the current extension on the "Railway in the Valley of the Mill" was inspired by the drawings and photos in "The Little Train to Llan Ffestiniog" by Chris Jones. The Real bridge wasn't actually on the Ffestiniog Railway - but was on what should have been an extension to it.

It was a wooden trellis bridge built on stone piers, with three spans each 80 feet long. I will only need to model one span, or a shortened version of it to span the 1 meter gap.

The 3 D model to show you what it will look like:

It is to be a composite structure, the strength being provided by an alloy sub structure which will be encased in a filament printed skin. The alloy substructure and the gap it is to fill:

The alloy is 20mm x 60mm angle 2mm thick, fixed 45 mm apart using 4 stainless tube spacers and nuts and M6 bolts. The track will be mounted on a printed planked deck, with longitudinal sleepers printed into place. I think I will print the chairs on at the same time. ( I am currently extending the track using ABS printed chairs. The trick is to wash the chairs with acetone which reinforces the inter layer bonds. )

I am omitting the wooden supports under the bridge which were added to strengthen the original inadequate structure - you just wouldn't believe it in a model. The ballasting on the wooden decking will also be omitted.

The first sections are printing.

Trevor

[philipy]

That is a lovely bit of drawing and the print should be equally impressive. Looking forward to seeing it in due course.

[ge_rik]

Another masterpiece in the making!

Rik

[SimonWood]

Instantly recognisable!

My first book on the Welsh narrow gauge was Prideaux's pictorial history. There's a superb double page spread of a photos of a passenger train posed in front of the viaduct with the rows of cottages behind. Very memorable.

[Trevor Thompson]

Instantly recognisable!

My first book on the Welsh narrow gauge was Prideaux's pictorial history. There's a superb double page spread of a photos of a passenger train posed in front of the viaduct with the rows of cottages behind. Very memorable.

Yes that is on the cover of the book I quoted. That is what inspired me.

Trevor

[StuartJ]

An ingenious design with the alloy substructure - very interested to see how this develops.

[GAP]

I will be watching the progress of this with great interest.

[Trevor Thompson]

The trelliswork cover for one side of the bridge is now printed and bonded onto the aluminium frame:

That was printed in 8 sections, 2 at a time flat on the bed of the printer. I used the "tree like" supports which enabled the true shapes of trelliswork to be printed. 4 sections of the trelliswork for the other side has been printed. Later in the week the decking should be in the printer.

I used gorilla glue to attach the trelliswork to the alloy, and acetone to bond the sections together.

Trevor

[ge_rik]

Looking good - as always

Rik

[Phil.P]

Looking good..

I am *still* concerned about the longevity of 3D printed items, especially in the garden. - I know printing yourself, you know the type of filament you have used, but we mere-mortals, buying a kit with 3D printed components, I wonder what they will be like in 5, 10, 20 years?

Will also be interested to see how the bonding of print to aluminium, holds up..
Especially after a few heat-cold cycles?


The modelling is brilliant, it is the resistance to the elements, that concerns me.

Phil.P

[philipy]

Phil.

3D printed components, I wonder what they will be like in 5, 10, 20 years?

The modelling is brilliant, it is the resistance to the elements, that concerns me.

I detailed my build of this station and all the ancilliary items, back in April 2018. The platform face, platform lamp, bench, windows, doors, fences, gate, fire buckets, gutters, downpipes, drain grille, 'way out', etc, are all printed in PLA ( Trevor uses ABS which should be even more durable):

...and here it is in my gallery entry, as of a couple of weeks ago:

It has all been out in wind, rain and shine, summer and winter, 24/7/365 for 5 years. The lamp post is drunk because it got kicked by a rampaging dog. The platform is growing a nice crop of moss and everything is a bit splashed, of course, but those are the only sign of defects.
Come back in another 15 years for the answer to the third part of your question!

[philipy]

Trevor,
That bridge side looks superb. Keep going ( I know you will, of course!).

[Peter Butler]

Will also be interested to see how the bonding of print to aluminium, holds up..
Especially after a few heat-cold cycles?


The modelling is brilliant, it is the resistance to the elements, that concerns me.

Phil.P

I have concerns about that to.... my only experience with Gorilla glue is when separating parts of a kit which someone else had built using it (foamy residue is a clue). It snapped apart with little resistance! How it works on two Gorillas bonded together is something I haven't yet tried.

[GAP]

Looking good..

I am *still* concerned about the longevity of 3D printed items, especially in the garden. - I know printing yourself, you know the type of filament you have used, but we mere-mortals, buying a kit with 3D printed components, I wonder what they will be like in 5, 10, 20 years?

Will also be interested to see how the bonding of print to aluminium, holds up..
Especially after a few heat-cold cycles?


The modelling is brilliant, it is the resistance to the elements, that concerns me.

Phil.P

I have had 2 pieces of PLA glued together with "plastic magic" lying out on my layout in the Australian sun for 12-18 months now with no sign of deterioration as of yet.

[Trevor Thompson]

Will also be interested to see how the bonding of print to aluminium, holds up..
Especially after a few heat-cold cycles?


The modelling is brilliant, it is the resistance to the elements, that concerns me.

Phil.P

I have concerns about that to.... my only experience with Gorilla glue is when separating parts of a kit which someone else had built using it (foamy residue is a clue). It snapped apart with little resistance! How it works on two Gorillas bonded together is something I haven't yet tried.

Firstly let me comment on the gorilla glue.

This glue has a long history as a boat building adhesive. The original version was a patented glue called "Balcaton" - which I used about 30 years ago to make a cold moulded dinghy. It is still in my garage. It isn't a "structural" adhesive in the way that epoxy glues are but it is still a useful adhesive. When the patent ran out (time expired) it became a generic glue that anyone could copy. So it arrived as this version of gorilla glue. It is a foaming polyurethane glue, moisture cured, and totally waterproof. So I have no qualms about using it - but sensibly. For example I bond the track to the concrete trackbed with it and use bricks to weight it down while it foams. I can prise it up it the alignment is wrong but otherwise it stays put - even if the ballasting is delayed for 6 months. I don't think it is suitable for assembling a plastic kit, not because it lack strength - but because as it foams it is going to go everywhere and be difficult to get off.

Now let me comment on the use on the bridge. In many ways this is just temporary, as the build progresses you will see that the top flange of the alloy angle is going to get encased in the ABS components. IF it does let go, the components are not going to be able to go anywhere. The ABS components will be welded together and may be able to slide along the length of the bridge as a unit, but they won't be able to move apart. At the risk of repetition - the ability to weld ABS with acetone is the main reason I use ABS. For me, that ability counteracts all of the difficulties in printing in ABS.

I have no doubt that the structures I am making will stand up well in the outdoors. You have seen how many complex and large structures I have made - I am very confident that I haven't wasted my time or my money!

Trevor

[Trevor Thompson]

Phil.

3D printed components, I wonder what they will be like in 5, 10, 20 years?

The modelling is brilliant, it is the resistance to the elements, that concerns me.

I detailed my build of this station and all the ancilliary items, back in April 2018. The platform face, platform lamp, bench, windows, doors, fences, gate, fire buckets, gutters, downpipes, drain grille, 'way out', etc, are all printed in PLA ( Trevor uses ABS which should be even more durable):

DSC_0021 small.jpg

...and here it is in my gallery entry, as of a couple of weeks ago:

DSC_0001[1]s.jpg

It has all been out in wind, rain and shine, summer and winter, 24/7/365 for 5 years. The lamp post is drunk because it got kicked by a rampaging dog. The platform is growing a nice crop of moss and everything is a bit splashed, of course, but those are the only sign of defects.
Come back in another 15 years for the answer to the third part of your question!

That station looks brilliant and (having followed your posts) is one of the things which has inspired me. I am not there with the detail yet - but I have added guttering to my latest models!

Trevor

[SimonWood]

Looking great Trevor.

That was printed in 8 sections, 2 at a time flat on the bed of the printer. I used the "tree like" supports which enabled the true shapes of trelliswork to be printed.

What do you mean by 'true shapes' here? Is that in the sense that you could have fudged things and drawn the nearer planks double thickness and just had them intersect with the layer below to avoid having to support while printing?

[Trevor Thompson]

Looking great Trevor.

That was printed in 8 sections, 2 at a time flat on the bed of the printer. I used the "tree like" supports which enabled the true shapes of trelliswork to be printed.

What do you mean by 'true shapes' here? Is that in the sense that you could have fudged things and drawn the nearer planks double thickness and just had them intersect with the layer below to avoid having to support while printing?

Yes that is exactly what I was trying to describe!

Trevor

[philipy]

Thats very interesting. I've never used tree supports so far. Mainly because I wasn't really sure what they did or what use they would be over 'normal' supports and i've never had the need to investigate, but perhaps I will now.
So many things to learn, all the time. Like, this past weekend I've learned how to do a pair of matching screw threads in Sketchup. No idea what thread they are but since they are a pair it doesn't matter!

[Trevor Thompson]

Thats very interesting. I've never used tree supports so far. Mainly because I wasn't really sure what they did or what use they would be over 'normal' supports and i've never had the need to investigate, but perhaps I will now.
So many things to learn, all the time. Like, this past weekend I've learned how to do a pair of matching screw threads in Sketchup. No idea what thread they are but since they are a pair it doesn't matter!

Oh matching screw threads - how did you do that?

Don't know what I would use them for - but until you know you never need to use them! That is a pleasure of this printing business - there is always something new to learn!

Trevor