Large Scale Central

GS gondola

Modeling Technical Modeling
#1

Hi guys,
I have a technical problem I have not been able to figure out, so I am hoping some of the more seasoned 3D hands can give me some guidance or assistance.
About fifteen years ago I got an AutoCAD file for one of these gondolas. The model looks like this in AutoCAD:

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I’ve been using AutoCAD since 1985 but have little experience with 3D. I have Sketchup, AutoCAD 2022 and Autodesk Fusion 360 available to me.
Here’s how the model looks in Chitubox:
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What I’d like to do is produce these in 1:29 scale. Unfortunately it would have to be done in three equal pieces to fit my 3D printer’s build space. Do any of you now how to break up solid models into smaller pieces? Do you know how to get the parts scaled up to the correct size for my scale?
Thanks in advance,
Matt

#2

To cut the model into 3 pieces you can use the slice command in AutoCAD. This video makes it look pretty simple. How to Cut a 3D Object in AutoCAD using Slice Command - YouTube
Assuming the model is HO scale you will need to scale it up by 300.3% for 1:29 scale.

#3

I hope you figure this out soon, I need a few.

#4

http://thomas-messmer.com/index.php/20-free-knowledge/howtos/3d-printing/69-split-3d-objects

I use meshlab for this sort of thing (if I correctly understand your issue)

#5

Thanks Dan, I will give that a shot.

#6

Thanks Steve! I will try that if I can’t figure it out in AutoCAD.

#7

For scaling Cura has an option to scale the input file before you generate the G-code file.
It doesn’t do the math for you so you need to do some calculation to get it to a percentage (IMS).

#8

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Not sure what scale you are starting with. But here is a cheat sheet I devised for me to go from scale to scale on my various designs. If your design is say 1:1 and you want 1:29 then reduce the design TO (not by) 3.4%.

I use the program “MatterControl” for all my resizing or breaking apart designs into smaller units. What I don’t think it does though is split bodies. I haven’t figured it out if it does.

#9

Devon,

thanx for the cheat-sheet!

If I remember correctly, meshlab can split bodies along planes, or even shapes.

#10

Easy to scale in Chitubox.

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#11

With cura:

cura-scale-100
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cura-scale-50
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#12

Cura is a decent program for slicing FDM. However, He has indicated that he already has Chitubox and so likely intends to print in Resin.

#13

Understood, just adding info to the discussion, as this will be found by
someone a year or two from now while doing a search on the general concept.

ps:
perhaps the topic title should be modified along those lines. This isn’t
so much a discussion of a “GS gondola”, as it is the techniques for slicing
up an existing .stl model.

#14

So Dan and others,

What’s better to import into a 3d slicer program? A full 1:1 CAD or something scaled? I’m guessing that a full 1:1 would even “fit” per say in the slicer program?

I’m just learning about slicer programs now that I’m finally setting up my resin printer.

#15

It’s certainly preferable to have your files already scaled before bringing them into the slicer. This is so you know the final tolerances of the print. If you load a 1:1 model into a slicer and rescale it you may find details too thin to print or maybe a coupler pocket or bolster ends up not correct for a commercial part you would like to use.
Using a slicer is more of a “quick and dirty” method to use when you just want to print something in a different scale and you are confident no editing is required to achieve a good print. In the pic I posted, I’m rescaling a 28mm figure that is known to print successfully. Since I’m scaling up, I know he will print fine when I print in 1:29. Also, If all you have is the STL then using a slicer to scale is easier.

#16

Yep that totally makes sense. I’ve actually set up my designs to have a minimum tolerance/thickness that I can easily adjust. I started with the Shapeways min. as a base point and I’m sure I’ll figure out that i can tweak that as I learn my printer.

#17

You got it Craig. It comes with experience. I model 1:29 so I draw in 1:29 and I’ve been doing this for quite a few years now so I’ve memorized many of the conversions (like 4in is 3.5mm) and just know what needs to be adjusted for the right balance of prototypical look vs durability. Also, many of my designs are to enhance Aristo and USA Trains models which are not exactly 1:29 so I need to consider that as well.

#18

Hi guys,
Thanks so much for the input and suggestions. I’m used to the AutoCAD world where everything is drawn to real world size and then printed to the appropriate scale.
Tonight I decided to test print a portion of the car body on my Elegoo Mars 3 printer. My printer is only large enough to do two panels at a time, so I will have to do this in a bunch of pieces. I used water washable resin for this build. It came out decent for a first try:

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The inside wall didn’t bond correctly, and I broke a portion of the frame removing the part from the build plate:
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And the leading edges aren’t great:
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But still, I’m satisfied that these cars will likely become a reality. Stay tuned!

Cheers,
Matt

#19

Matt, It looks like you didn’t add any supports? May I suggest printing with the top edge flat on the build plate and add supports to the cross bracing? You can probably get away with auto supports.
Like this

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#20

Hi Dan,
You’re right, I didn’t use any supports. The other problem is that rotated in the way of your example and sized to 1:29, it won’t fit the build area:

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Unless I have something set wrong in the settings…

Thanks,
Matt