Wibbly wobbly roof

[ge_rik]

I have now made three models of an early version of the Southwold Railway Cleminson coaches. The first one is now a couple of years old. Its roof was made from five 3D printed sections glued together. After fixing the passengers inside, I decided to glue down the roof using prototypical arched battens underneath for alignment. The other two coaches have unglued roofs at present.

When I came to use the first coach today, I noticed its roof now has a somewhat serpentine appearance.

IMG_20240330_113536_513.jpg (8.08 MiB) Viewed 294 times

It has been stored in my conservatory over winter but we've had the poly carbonate roof replaced with insulated opaque sheeting to conserve heat in the winter and make it habitable in the summer, so the variations in heat haven't been too extreme. It certainly hasn't been hot!

For now, the other two coach roofs haven't repeated this phenomenon, though they have both bowed up slightly at the ends. Just trying to decide whether to leave the other roofs unglued (though the bowed up ends will be very obvious) or whether just to glue them down at the ends.

Rik

[Peter Butler]

Rather than possibly repeating the failure I would strip all the roof section off the coaches and replace with either thin ply or HIP. I certainly couldn't live with that appearance after all the detailed work in the coaches themselves.

[philipy]

I'm afraid to say that I agree with Peter. I think you know yourself that you won't be happy with either of your suggested solutions, longer term.

On a broader note, I think that the long thin sections that we tend to use are susceptable to warping generally.

[ge_rik]

Thanks chaps. Yes, I've decided to replace all the roofs with plasticard. I can see the other roofs ending up like this eventually.

Rik

[drewzero1]

Rik, I've had the same issue with some of my cardboard roofs but hadn't expected it to happen with a 3D printed roof. I have an OpenSCAD model somewhere for roof battens with an interlocking spine; I use it for cardboard roofs but it might be usable as a form for thin ply or plastic.

Screenshot_20240330-102427__01.jpg (359.03 KiB) Viewed 272 times

If you're interested at all I can dig up the code and dust it off, or generate an STL for your dimensions.

[Trevor Thompson]

I have not had problems with coach roofs distorting - but the canopy on one of my station buildings buckles in strong sunlight and then flattens when it gets cold. I think the difference is in the thickness of the roof. I tend to make my coach roofs as thick as I can being nearly flat inside. The canopy was a thin layer on top of a framework.


Trevor

[GAP]

I have now made three models of an early version of the Southwold Railway Cleminson coaches. The first one is now a couple of years old. Its roof was made from five 3D printed sections glued together. After fixing the passengers inside, I decided to glue down the roof using prototypical arched battens underneath for alignment. The other two coaches have unglued roofs at present.

When I came to use the first coach today, I noticed its roof now has a somewhat serpentine appearance.
IMG_20240330_113536_513.jpg


It has been stored in my conservatory over winter but we've had the poly carbonate roof replaced with insulated opaque sheeting to conserve heat in the winter and make it habitable in the summer, so the variations in heat haven't been too extreme. It certainly hasn't been hot!

For now, the other two coach roofs haven't repeated this phenomenon, though they have both bowed up slightly at the ends. Just trying to decide whether to leave the other roofs unglued (though the bowed up ends will be very obvious) or whether just to glue them down at the ends.

Rik

Rik,
Even though the temp outside hasn't been that hot inside a shed the temp could be up to or greater than twice the outside temp.
I had a opaque polycarbonate patio roof at a previous house and the temp under was far hotter than the air temp and it was open on 3 sides.
Cars internal temp here can reach in excess of 60C and my sheds have reached temps of over 40C over summer with the outside only being 30C.
I would either make the prints thicker or use HIP as you have said or store the coaches on a lower shelf.

[ge_rik]

Rik,
Even though the temp outside hasn't been that hot inside a shed the temp could be up to or greater than twice the outside temp.
I had a opaque polycarbonate patio roof at a previous house and the temp under was far hotter than the air temp and it was open on 3 sides.
Cars internal temp here can reach in excess of 60C and my sheds have reached temps of over 40C over summer with the outside only being 30C.
I would either make the prints thicker or use HIP as you have said or store the coaches on a lower shelf.

Thanks Graeme
I'm going to try a plasticard (HIPS) replacement and will put longitudinal bracing in addition to the transverse battens. The other two roofs are ok for now. They've been stored in my workshop. I've realised now that the shelf on which I stored the affected coach is above a radiator. I can only assume there was sufficient heat from that to cause the distortion - even though the overall ambient temperature in the conservatory has stayed low through the winter.

Curious stuff this PLA

Rik

[GTB]

Curious stuff this PLA

PLA was developed as a biodegradable plastic for making cheap biodegradable shopping bags. That idea fell flat on it's face when it was found that the bags didn't degrade when buried in a landfill........

If you look it up PLA has a very low Tg compared to the engineering polymers such as ABS. Tg is the temperature where a polymer starts to soften and distort. For ABS it is about 105 C, for acrylic and polystyrene it is about 100 C and for PLA it is about 60 C. The properties that make PLA easy to print, make it less heat tolerant than other common polymers.

FWIW, my models are stored in the train room which is part of the house, with insulation in the roof and walls and sun blocking curtains. The temperature in the house over the last few years has varied between 7 C on a winter morning to 32 C on a summer afternoon. I have a little electronic thermo-hygrograph that isn't a full data logger, but does keep track of the min. and max. readings (until the battery goes flat).

My laminated polystyrene sheet rolling stock roofs have been dimensionally stable for over a decade now. The method including the former is shown in this old post. https://gardenrails.org/viewtopic.php?p=84700. The framing under the roof is shown in a different post from about the same time. https://gardenrails.org/viewtopic.php?p=65794


Regards,
Graeme