Garden Railway Forum

Posted: **Wed Apr 08, 2026 4:21 am**

I have been using 3D builder to repair downloaded stls before printing and it keeps trying to save in .3MF format.
My curiosity got the better of me so I googled the difference and its AI said that cura can handle it.
digging deeper I asked for more details and this is the answer.

In UltiMaker Cura, a 3MF Project File is like a "snapshot" of your entire 3D printing session. While a standard file only saves the 3D shape, a project file saves everything you see on your screen so you can come back exactly where you left off.
What exactly is inside?
When you use File > Save Project, Cura bundles these four things into one single file:

The Models: Every 3D object on your build plate, including exactly where you moved, rotated, or scaled them.
The Printer Profile: The specific printer you were using (e.g., an Ender 3 or an UltiMaker S5) and its hardware settings like nozzle size.
Material Settings: The type of filament (PLA, PETG, etc.) and specific temperatures or flow rates you adjusted.
Slicing Parameters: All those settings in the side panel—layer height, infill percentage, support structures, and even advanced "hidden" settings.

Why this is a "Superpower" for Beginners

No More Guesswork: If you print something perfectly today and want to print it again in six months, you won't have to remember which settings you used. Opening the project file restores them all instantly.
Safe Experimenting: You can save "Version A" of a project with one set of settings, then try a "Version B" without losing your original work.
Easy Troubleshooting: If you're stuck, you can send your .3mf project file to a more experienced friend. They can open it and see exactly what settings might be causing your print to fail.

How to use it correctly

Saving: Always use File > Save Project... (or Ctrl+S).
Warning: Do not use "File > Export". This often saves just the model and throws away all your settings.
Opening: When you open a .3mf file, Cura will ask: "Open as project" or "Import models".
Choose Open as project to load all the settings.
Choose Import models if you just want the 3D shape and want to use your current, different settings.

Pro Tip: Look for the UltiMaker Support guide if you want to learn about "Universal Cura Projects," which are special project files designed to be shared with people who have different printers than yours.
A links it suggested for information;
https://support.ultimaker.com/s/article/000002979

Haven't had a chance to peruse it but it could be interesting no more changing settings for each model

Posted: **Wed Apr 08, 2026 5:51 am**

Thanks for that Graeme, I've always thought that 3MF was a something a bit exotic and never bothered to investigate. I rarely use Cura/FDM these days, preferring resin prints but now I'll have to investigate how Chitubox and Anycubic Workshop interact with it.

Posted: **Wed Apr 08, 2026 7:49 am**

GAP wrote: ↑Wed Apr 08, 2026 4:21 am Easy Troubleshooting: If you're stuck, you can send your .3mf project file to a more experienced friend. They can open it and see exactly what settings might be causing your print to fail.

I wonder if an AI tool would be able to analyse it

Rik

Posted: **Wed Apr 08, 2026 8:58 am**

ge_rik wrote: ↑Wed Apr 08, 2026 7:49 am
GAP wrote: ↑Wed Apr 08, 2026 4:21 am Easy Troubleshooting: If you're stuck, you can send your .3mf project file to a more experienced friend. They can open it and see exactly what settings might be causing your print to fail.
I wonder if an AI tool would be able to analyse it

Not wishing to derail this thread, but I'd be wary of using AI in that context. Whilst mentally doodling recently, I asked Gemini to design me a fairly simple circuit, which it did and which on the face of it with my limited electronic knowledge seemed reasonable. It said it couldn't provide an actual circuit diagram but it did give me the hole coordinates to use for each component, so then I then asked it to use appropriate images and to place the items on the piece of stripboard using the hole coordinates that it specified, which it did. However when I enlarged it and looked closely, it had used a12 pin image for an 8-pin 555 timer( but with the correct label on it!) and had turned another component through 90 degrees to fit it on the board, with no relevance to the hole positions! When I asked it to check the image it said everything was fine and complimented me on my soldering!

Posted: **Wed Apr 08, 2026 9:14 am**

I don't use Cura but in Bambu Studio a .3mf file can save multiple plates of models, again this can be handy for keeping everything together while allowing you to print bits separately (i.e. one plate at a time). I imagine Cura can do something similar.

Posted: **Wed Apr 08, 2026 11:51 pm**

ge_rik wrote: ↑Wed Apr 08, 2026 7:49 am
GAP wrote: ↑Wed Apr 08, 2026 4:21 am Easy Troubleshooting: If you're stuck, you can send your .3mf project file to a more experienced friend. They can open it and see exactly what settings might be causing your print to fail.
I wonder if an AI tool would be able to analyse it

Rik

I asked my new little playmate Claude if it could analyse iy and this is the reply

Yes, I can analyse .3MF files! They're actually easier to work with than STLs in some ways.
What's in a .3MF file
A .3MF file is essentially a ZIP archive containing XML data. Unlike STL (which is just raw triangle mesh data), .3MF files contain richer information:
FeatureSTL.3MFGeometry (triangles)

Color / materials

Multiple objects

(one mesh)

Object names

Scale / units

(always mm)Thumbnail

(often)Print settings

(sometimes)
What I can analyse from a .3MF

Mesh geometry — triangle count, vertex count, bounding box, dimensions
Object structure — named components, how many bodies
Materials & colors — if embedded
Print settings — if a slicer wrote them in (e.g. Bambu, PrusaSlicer)
Manifold/watertight check — same as STL analysis
Volume & surface area — calculated from the mesh

Posted: **Wed Apr 08, 2026 11:57 pm**

philipy wrote: ↑Wed Apr 08, 2026 8:58 am
ge_rik wrote: ↑Wed Apr 08, 2026 7:49 am
GAP wrote: ↑Wed Apr 08, 2026 4:21 am Easy Troubleshooting: If you're stuck, you can send your .3mf project file to a more experienced friend. They can open it and see exactly what settings might be causing your print to fail.
I wonder if an AI tool would be able to analyse it
Not wishing to derail this thread, but I'd be wary of using AI in that context. Whilst mentally doodling recently, I asked Gemini to design me a fairly simple circuit, which it did and which on the face of it with my limited electronic knowledge seemed reasonable. It said it couldn't provide an actual circuit diagram but it did give me the hole coordinates to use for each component, so then I then asked it to use appropriate images and to place the items on the piece of stripboard using the hole coordinates that it specified, which it did. However when I enlarged it and looked closely, it had used a12 pin image for an 8-pin 555 timer( but with the correct label on it!) and had turned another component through 90 degrees to fit it on the board, with no relevance to the hole positions! When I asked it to check the image it said everything was fine and complimented me on my soldering!

I wouldn't trust AI with circuit design as far as I could throw it!!
Anything that comes with this warning "Claude is AI and can make mistakes. Please double-check responses." i will not rely on.
It can do a reasonable job on schematics but I treble check them.
Whatever you do do not get it to layout a veroboard for you or you will end up with a mess guaranteed to blow up in your face.
Having said that it is handy for writing and debugging computer code (the code it has written) of my projects and asking general questions about things Like getting ideas on how big a power supply I would need to run a number of servos.

Posted: **Thu Apr 09, 2026 12:23 am**

GAP wrote: ↑Wed Apr 08, 2026 11:57 pm
philipy wrote: ↑Wed Apr 08, 2026 8:58 am
ge_rik wrote: ↑Wed Apr 08, 2026 7:49 am
GAP wrote: ↑Wed Apr 08, 2026 4:21 am Easy Troubleshooting: If you're stuck, you can send your .3mf project file to a more experienced friend. They can open it and see exactly what settings might be causing your print to fail.
I wonder if an AI tool would be able to analyse it
Not wishing to derail this thread, but I'd be wary of using AI in that context. Whilst mentally doodling recently, I asked Gemini to design me a fairly simple circuit, which it did and which on the face of it with my limited electronic knowledge seemed reasonable. It said it couldn't provide an actual circuit diagram but it did give me the hole coordinates to use for each component, so then I then asked it to use appropriate images and to place the items on the piece of stripboard using the hole coordinates that it specified, which it did. However when I enlarged it and looked closely, it had used a12 pin image for an 8-pin 555 timer( but with the correct label on it!) and had turned another component through 90 degrees to fit it on the board, with no relevance to the hole positions! When I asked it to check the image it said everything was fine and complimented me on my soldering!
I wouldn't trust AI with circuit design as far as I could throw it!!
Anything that comes with this warning "Claude is AI and can make mistakes. Please double-check responses." i will not rely on.
It can do a reasonable job on schematics but I treble check them.
Whatever you do do not get it to layout a veroboard for you or you will end up with a mess guaranteed to blow up in your face.
Having said that it is handy for writing and debugging computer code (the code it has written) of my projects and asking general questions about things like getting ideas on how big a power supply I would need to run a number of servos.

Posted: **Thu Apr 09, 2026 9:31 am**

I think the .3mf format is most useful for saving prints rather than models. As it can save all the printer settings it's easy to return and duplicate a print. However I always save the model in STL or STEP as well as that is just the model data and is likely to be more widely compatible in the longer term if you want to print in a different set up or make further changes to the deign.

I can't understand why 3D Builder defaults to this because it's not saving any printing settings, just annoying behaviour.

GAP wrote: ↑Wed Apr 08, 2026 11:57 pm I wouldn't trust AI with circuit design as far as I could throw it!!
Anything that comes with this warning "Claude is AI and can make mistakes. Please double-check responses." i will not rely on.

If you want pictorial circuit design, I'd agree there are a lot of issues. However the fundament data on what to connect to what is usually sound.
AI coding is probably one of the biggest uses of AI in the world now and widely relied on.
I used ChapGPT & Claude last year a lot to create coding for Arduino type microcontrollers. Particularly code for a r/c loco controller which uses a WiFi hotspot to log into via a phone and be able to drive the loco from a phone. It took something like 1100 lines of code and lot of revisions, but the end results works well. There's no chance with my limited coding experience that I could have written myself, but with AI it was possible.

Posted: **Thu Apr 09, 2026 10:51 pm**

Paul_in_Ricky wrote: ↑Thu Apr 09, 2026 9:31 am I think the .3mf format is most useful for saving prints rather than models. As it can save all the printer settings it's easy to return and duplicate a print. However I always save the model in STL or STEP as well as that is just the model data and is likely to be more widely compatible in the longer term if you want to print in a different set up or make further changes to the deign.

I can't understand why 3D Builder defaults to this because it's not saving any printing settings, just annoying behaviour.

GAP wrote: ↑Wed Apr 08, 2026 11:57 pm I wouldn't trust AI with circuit design as far as I could throw it!!
Anything that comes with this warning "Claude is AI and can make mistakes. Please double-check responses." i will not rely on.
If you want pictorial circuit design, I'd agree there are a lot of issues. However the fundament data on what to connect to what is usually sound.
AI coding is probably one of the biggest uses of AI in the world now and widely relied on.
I used ChapGPT & Claude last year a lot to create coding for Arduino type microcontrollers. Particularly code for a r/c loco controller which uses a WiFi hotspot to log into via a phone and be able to drive the loco from a phone. It took something like 1100 lines of code and lot of revisions, but the end results works well. There's no chance with my limited coding experience that I could have written myself, but with AI it was possible.

"There's no chance with my limited coding experience that I could have written myself, but with AI it was possible." Exactly how I operate
I used Claude and Chat GPT to design a display that shows my point settings. As my points are remote from the display controller (raspberry pi) I am using wifi. I reconfigured an old router/modem as an access point and everything connects to the network. The display is a python program that I can edit the lines on as well as add and delete points,signals and sensors if the layout changes. I now have a display repeater on an old laptop that I use as a radio so I can see the point settings from across the room, I can add as many as I want so long as the device can log into the train network.
With AI the things I can do code wise appears to be limited by how good my imagination is.

Garden Railway Forum

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