26/06/2026
Technical update….
We use a few less common technologies in our models but by far the most evident is the extensive use for 3D prints so I thought we would have a short update on our experiences in this hot weather!
Firstly, we use resin (SLA) prints not FDM for our locos. This is because resin prints produce smoother more detailed parts. We still love FDM equally! and use this technology in RC aircraft and boats. That’s not to say some of our parts couldn’t be printed on an FDM machine!
Over the last couple of days, we have seen ambient temperatures of 32-33degreesC These temperatures are no issue to our resin prints however, most of our parts are dull, matt grey in colour so absorb radiation increasing the temperature of the part. We measured the surface temperature of an old design roof panel at 58degreesC going beyond the glass transition temperature (Tg) of the material. At about 40degreesC our prints will be softer to the touch. The yellow cab ends rarely get above ambient temperature because the brighter colour is better at reflecting radiation.
We hear about 3D prints collapsing in to a heap when exposed to sunlight so let’s look at the facts...
Will my resin print melt in hot weather?
No, resin prints don’t melt, they get soft (which we will talk about later) and then burn if exposed to enough heat (lots!)
Will they deform?
It depends! Once the temperature of the material goes beyond the Tg the material will deform easier when exposed to some external force including its own mass (gravity!). The higher the temperature the softer is gets. If the part is designed well and has some supporting structure then it will sit quite happily in our summer sun without changing shape. If a load (like my finger) is applied to the part when it is soft then yes it will deform. It may spring back as shown in our photo. If it is allowed to cool with the load still applied then it will adopt its new shape.
Can it be fixed?
It depends! Heating the part to just above its Tg often returns the part to its original shape, infact this process is used to correct warped parts when they are new and fresh off the printer.
How long will the parts last?
It depends! we have parts (without paint) out permanently in the sun for over 12months with no changes to shape or cracks or spontaneous combustion (equate that to taking a model out for only a few hours per week) I`m sure the mechanical properties will have degraded but were concentrating on non-load bearings scale parts (for now!).
How do we look after our 3D printed model?
Keep your 3D prints out of the sun or cover with a reflective material when not in use. We made a cover using a silver reflective material. A technique used extensively with composite RC aircraft, yes sunlight effects epoxy resins also. If the model is driving the cool breeze will rapidly lower the temperature of the parts and the problem goes away. If the part is permanently sited outdoors in the sun then paint with brighter more reflective colours.
FDM prints typically have a higher Tg even PLA compared to resin prints so this is less of an issue. We often read about 3D printed model aircraft deforming when left in a hot car but the difference here is that these models have very thin walls, tend to use light weight PLA and therefore collapse even under their own mass.
So in conclusion, don’t be scared to take your 3D prints out in the sun, just follow the rules and maybe avoid the 2 days a year the temperatures goes above 30degrees!
There is some interesting stuff on our website and you will read about acrylic paints, these paints are great for not absorbing UV radiation which helps to protect our 3D prints as UV radiation degrades material properties over time. It just so happens that the best paints we have used so far (Railmatch Acrylics) is acrylic!
