Pont y Gelli - A composite printed bridge

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Trevor Thompson
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Re: Pont y Gelli - A composite printed bridge

Post by Trevor Thompson » Wed Mar 08, 2023 9:46 am

philipy wrote:
Tue Mar 07, 2023 1:18 pm
Phil.
Phil.P wrote:
Tue Mar 07, 2023 12:48 pm
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! :lol:
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!

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Re: Pont y Gelli - A composite printed bridge

Post by SimonWood » Wed Mar 08, 2023 12:57 pm

Looking great Trevor.
Trevor Thompson wrote:
Tue Mar 07, 2023 11:04 am
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?

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Re: Pont y Gelli - A composite printed bridge

Post by Trevor Thompson » Wed Mar 08, 2023 3:20 pm

SimonWood wrote:
Wed Mar 08, 2023 12:57 pm
Looking great Trevor.
Trevor Thompson wrote:
Tue Mar 07, 2023 11:04 am
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!

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Re: Pont y Gelli - A composite printed bridge

Post by philipy » Wed Mar 08, 2023 3:58 pm

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!

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Re: Pont y Gelli - A composite printed bridge

Post by Trevor Thompson » Thu Mar 09, 2023 12:04 pm

philipy wrote:
Wed Mar 08, 2023 3:58 pm
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!

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Re: Pont y Gelli - A composite printed bridge

Post by Trevor Thompson » Thu Mar 09, 2023 12:11 pm

Both sides are covered in the lattice work. I have some deck printed. The rail fits in the chairs and it the deck fits in place. Rolling stock flanges miss the chairs as well:
IMG_2824.JPG
IMG_2825.JPG
However. The gauge is a bit tight. 31.25mm instead of 32mm. I think the deck would be better if it were a bit thicker as well. So I have modified the design and will start printing again. It will take a while as each piece of deck takes 8 hours to print. I think I will wait until I have 4 lengths ready before fixing it into position.

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Re: Pont y Gelli - A composite printed bridge

Post by philipy » Thu Mar 09, 2023 1:28 pm

Trevor Thompson wrote:
Thu Mar 09, 2023 12:04 pm
Oh matching screw threads - how did you do that?
I was doing some work for an acquaintance, just printing project boxes for him. Part of his work involves a small lens focussing onto a photodiode on a pcb and he asked if it would be possible to print some sort of screw focusing mechanism. I said I'm sure it's possible but no idea how to actually draw a screw thread, let alone how printable it would be.
Anyway, a quick search came up with this Youtube link:
https://www.youtube.com/watch?v=k8AC5LNMo-g

...and to my amazement, not only is the video really easy to follow but it actually works! Took me several goes to work through it and get the steps into my poor brain but the result is perfect for what I needed.

Basically I needed a 22mm ID tube with a screw thread on the outside face, and a 3mm thick plate with a matching internal threaded hole, and to get 2 or 3 threads on the inside of the plate hole.

I followed the video to get a solid screwed rod and then used the scale tool to push and pull it until I had the threads deep enough to get 3 in the 3mm plate i.e 1mm pitch. Then I drew a 22mm diam circle on the end and pushed it through to get the hollow cylinder.

I duplicated that and saved one copy, out of the way to avoid accidents.
I then constructed a box to completely enclose the hollow threaded cylinder and checked to ensure yhat the top and bottom faces were all coplaner ( had to use "intersect faces" to be sure). Then I deleted all the internal geometry and that left me with an internally threaded hole in a block. This thread of course exactly matches the original one so there is no way they would slide inside each other, so I scaled the block slightly in the horizontal plane to make it approx half the thread depth larger diameter.... hey presto!

Screw thread as constructed - compressed to the right pitch - matched threaded block
Screenshot 2023-03-09 13.15.28.png
And this is the end result ( ignore the gap, I made this one too tight and had to cut it off :oops: ):
P1010019.jpg

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Re: Pont y Gelli - A composite printed bridge

Post by SimonWood » Thu Mar 09, 2023 3:13 pm

Trevor Thompson wrote:
Thu Mar 09, 2023 12:11 pm
I have some deck printed.
That really looks the part!

Deck, sleepers and chairs all printed together?

It has inspired me to think that I could upgrade the look of my bridges, not to anything as impressive as you are printing, but with a deck and handrails it would be a big improvement in appearance.

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Re: Pont y Gelli - A composite printed bridge

Post by Trevor Thompson » Thu Mar 09, 2023 3:18 pm

SimonWood wrote:
Thu Mar 09, 2023 3:13 pm
Trevor Thompson wrote:
Thu Mar 09, 2023 12:11 pm
I have some deck printed.
That really looks the part!

Deck, sleepers and chairs all printed together?

It has inspired me to think that I could upgrade the look of my bridges, not to anything as impressive as you are printing, but with a deck and handrails it would be a big improvement in appearance.
Yes printed in one piece. Had a bit of a problem with the printer - messed up the slicer settings and made the layer height too high, so the layers were not bonded properly on one section. The other section parted from the bed - part of the same problem. All sorted now. So starting the deck again wasn't really a problem. If you want the stl file for the chairs I can add it to the forum.

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Re: Pont y Gelli - A composite printed bridge

Post by Trevor Thompson » Wed Mar 15, 2023 5:47 pm

The deck is now printed and assembled with the rails inserted:
IMG_2851.JPG
Excuse the different colours that I have used to print the deck, I wanted to use up what I had in stock before ordering more filament. It just needs the handrail added, and the first section of that is in place.

As an aside it is interesting what a difference the colour makes to the way the filament prints. The white filament seems to require a slightly higher temperature to print properly. I get consistent issues printing white - such as the sides of the chairs fall off readily and there are more stray bits of filament lying around when the print is finished.

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Re: Pont y Gelli - A composite printed bridge

Post by Trevor Thompson » Thu Mar 16, 2023 9:24 am

philipy wrote:
Thu Mar 09, 2023 1:28 pm
Trevor Thompson wrote:
Thu Mar 09, 2023 12:04 pm
Oh matching screw threads - how did you do that?
I was doing some work for an acquaintance, just printing project boxes for him. Part of his work involves a small lens focussing onto a photodiode on a pcb and he asked if it would be possible to print some sort of screw focusing mechanism. I said I'm sure it's possible but no idea how to actually draw a screw thread, let alone how printable it would be.
Anyway, a quick search came up with this Youtube link:
https://www.youtube.com/watch?v=k8AC5LNMo-g

...and to my amazement, not only is the video really easy to follow but it actually works! Took me several goes to work through it and get the steps into my poor brain but the result is perfect for what I needed.

Basically I needed a 22mm ID tube with a screw thread on the outside face, and a 3mm thick plate with a matching internal threaded hole, and to get 2 or 3 threads on the inside of the plate hole.

I followed the video to get a solid screwed rod and then used the scale tool to push and pull it until I had the threads deep enough to get 3 in the 3mm plate i.e 1mm pitch. Then I drew a 22mm diam circle on the end and pushed it through to get the hollow cylinder.

I duplicated that and saved one copy, out of the way to avoid accidents.
I then constructed a box to completely enclose the hollow threaded cylinder and checked to ensure yhat the top and bottom faces were all coplaner ( had to use "intersect faces" to be sure). Then I deleted all the internal geometry and that left me with an internally threaded hole in a block. This thread of course exactly matches the original one so there is no way they would slide inside each other, so I scaled the block slightly in the horizontal plane to make it approx half the thread depth larger diameter.... hey presto!

Screw thread as constructed - compressed to the right pitch - matched threaded block
Screenshot 2023-03-09 13.15.28.png

And this is the end result ( ignore the gap, I made this one too tight and had to cut it off :oops: ):
P1010019.jpg
Impressive and stored away for future use.

Trevor

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Re: Pont y Gelli - A composite printed bridge

Post by Trevor Thompson » Wed Mar 22, 2023 1:28 pm

The bridge is now complete, apart from painting:
IMG_2860.JPG
So I can put it aside until the trackbed catches up!

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Re: Pont y Gelli - A composite printed bridge

Post by Peter Butler » Wed Mar 22, 2023 1:47 pm

It does look to be a magnificent structure Trevor, a complicated item to build by any other means.
The best things in life are free.... so why am I doing this?

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Re: Pont y Gelli - A composite printed bridge

Post by SimonWood » Wed Mar 22, 2023 6:32 pm

Superb! Looks wonderful with Linda giving a sense of scale.

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